Multi-scale cortical bone traits vary in females and males from two mouse models of genetic diversity

Understanding the genetic basis of cortical bone traits can allow for the discovery of novel genes or biological pathways regulating bone health. Mice are the most widely used mammalian model for skeletal biology and allow for the quantification of traits that cannot easily be evaluated in humans, such as osteocyte lacunar morphology. The goal of our study was to investigate the effect of genetic diversity on multi-scale cortical bone traits of 3 long bones in skeletally-mature mice. We measured bone morphology, mechanical properties, material properties, lacunar morphology, and mineral composition of mouse bones from 2 populations of genetic diversity. Additionally, we compared how intrabone relationships varied in the 2 populations. Our first population of genetic diversity included 72 females and 72 males from the 8 inbred founder strains used to create the Diversity Outbred (DO) population. These 8 strains together span almost 90% of the genetic diversity found in mice (Mus musculus). Our second population of genetic diversity included 25 genetically unique, outbred females and 25 males from the DO population. We show that multi-scale cortical bone traits vary significantly with genetic background; heritability values range from 21% to 99% indicating genetic control of bone traits across length scales. We show for the first time that lacunar shape and number are highly heritable. Comparing the 2 populations of genetic diversity, we show that each DO mouse does not resemble a single inbred founder, but instead the outbred mice display hybrid phenotypes with the elimination of extreme values. Additionally, intrabone relationships (eg, ultimate force vs. cortical area) were mainly conserved in our 2 populations. Overall, this work supports future use of these genetically diverse populations to discover novel genes contributing to cortical bone traits, especially at the lacunar length scale.

Genetic variation influences the skeletal response to hindlimb unloading in the eight founder strains of the diversity outbred mouse population

During disuse, mechanical unloading causes extensive bone loss, decreasing bone volume and strength. Variations in bone mass and risk of osteoporosis are influenced by genetics; however, it remains unclear how genetic variation affects the skeletal response to unloading. We previously found that genetic variation affects the musculoskeletal response to 3 weeks of immobilization in the 8 Jackson Laboratory J:DO founder strains: C57Bl/6J, A/J, 129S1/SvImJ, NOD/ShiLtJ, NZO/HlLtJ, CAST/EiJ, PWK/PhJ, and WSB/EiJ. Hindlimb unloading (HLU) is the best model for simulating local and systemic contributors of disuse and therefore may have a greater impact on bones than immobilization. We hypothesized that genetic variation would affect the response to HLU across the eight founder strains. Mice of each founder strain were placed in HLU for 3 weeks, and the femurs and tibias were analyzed. There were significant HLU and mouse strain interactions on body weight, femur trabecular BV/TV, and femur ultimate force. This indicates that unloading only caused significant catabolic effects in some mouse strains. C57BL/6 J mice were most affected by unloading while other strains were more protected. There were significant HLU and mouse strain interactions on gene expression of genes encoding bone metabolism genes in the tibia. This indicates that unloading only caused significant effects on bone metabolism genes in some mouse strains. Different mouse strains respond to HLU differently, and this can be explained by genetic differences. These results suggest the outbred J:DO mice will be a powerful model for examining the effects of genetics on the skeletal response to HLU.

Systems genetics approaches for understanding complex traits with relevance for human disease

Quantitative traits are often complex because of the contribution of many loci, with further complexity added by environmental factors. In medical research, systems genetics is a powerful approach for the study of complex traits, as it integrates intermediate phenotypes, such as RNA, protein, and metabolite levels, to understand molecular and physiological phenotypes linking discrete DNA sequence variation to complex clinical and physiological traits. The primary purpose of this review is to describe some of the resources and tools of systems genetics in humans and rodent models, so that researchers in many areas of biology and medicine can make use of the data.

Single-Cell Transcriptomics of Bone Marrow Stromal Cells in Diversity Outbred Mice: A Model for Population-Level scRNA-Seq Studies

Genome-wide association studies (GWASs) have advanced our understanding of the genetics of osteoporosis; however, the challenge has been converting associations to causal genes. Studies have utilized transcriptomics data to link disease-associated variants to genes, but few population transcriptomics data sets have been generated on bone at the single-cell level. To address this challenge, we profiled the transcriptomes of bone marrow-derived stromal cells (BMSCs) cultured under osteogenic conditions from five diversity outbred (DO) mice using single-cell RNA-seq (scRNA-seq). The goal of the study was to determine if BMSCs could serve as a model to generate cell type-specific transcriptomic profiles of mesenchymal lineage cells from large populations of mice to inform genetic studies. By enriching for mesenchymal lineage cells in vitro, coupled with pooling of multiple samples and downstream genotype deconvolution, we demonstrate the scalability of this model for population-level studies. We demonstrate that dissociation of BMSCs from a heavily mineralized matrix had little effect on viability or their transcriptomic signatures. Furthermore, we show that BMSCs cultured under osteogenic conditions are diverse and consist of cells with characteristics of mesenchymal progenitors, marrow adipogenic lineage precursors (MALPs), osteoblasts, osteocyte-like cells, and immune cells. Importantly, all cells were similar from a transcriptomic perspective to cells isolated in vivo. We employed scRNA-seq analytical tools to confirm the biological identity of profiled cell types. SCENIC was used to reconstruct gene regulatory networks (GRNs), and we observed that cell types show GRNs expected of osteogenic and pre-adipogenic lineage cells. Further, CELLECT analysis showed that osteoblasts, osteocyte-like cells, and MALPs captured a significant component of bone mineral density (BMD) heritability. Together, these data suggest that BMSCs cultured under osteogenic conditions coupled with scRNA-seq can be used as a scalable and biologically informative model to generate cell type-specific transcriptomic profiles of mesenchymal lineage cells in large populations. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Multi-Scale Cortical Bone Traits Vary in Two Mouse Models of Genetic Diversity

Understanding the genetic basis of cortical bone traits can allow for the discovery of novel genes or biological pathways regulating bone health. Mice are the most widely used mammalian model for skeletal biology and allow for the quantification of traits that can't easily be evaluated in humans, such as osteocyte lacunar morphology. The goal of our study was to investigate the effect of genetic diversity on multi-scale cortical bone traits of three long bones in skeletally-mature mice. We measured bone morphology, mechanical properties, material properties, lacunar morphology, and mineral composition of mouse bones from two populations of genetic diversity. Additionally, we compared how intra-bone relationships varied in the two populations. Our first population of genetic diversity included 72 females and 72 males from the eight Inbred Founder strains used to create the Diversity Outbred (DO) population. These eight strains together span almost 90% of the genetic diversity found in mice (Mus musculus). Our second population of genetic diversity included 25 genetically unique, outbred females and 25 males from the DO population. We show that multi-scale cortical bone traits vary significantly with genetic background; heritability values range from 21% to 99% indicating genetic control of bone traits across length scales. We show for the first time that lacunar shape and number are highly heritable. Comparing the two populations of genetic diversity, we show each DO mouse does not resemble a single Inbred Founder but instead the outbred mice display hybrid phenotypes with the elimination of extreme values. Additionally, intra-bone relationships (e.g., ultimate force vs. cortical area) were mainly conserved in our two populations. Overall, this work supports future use of these genetically diverse populations to discover novel genes contributing to cortical bone traits, especially at the lacunar length scale.

Long-read proteogenomics to connect disease-associated sQTLs to the protein isoform effectors of disease

A major fraction of loci identified by genome-wide association studies (GWASs) lead to alterations in alternative splicing, but interpretation of how such alterations impact proteins is hindered by the technical limitations of short-read RNA-seq, which cannot directly link splicing events to full-length transcript or protein isoforms. Long-read RNA-seq represents a powerful tool to define and quantify transcript isoforms, and recently, infer protein isoform existence. Here we present a novel approach that integrates information from GWAS, splicing QTL (sQTL), and PacBio long-read RNA-seq in a disease-relevant model to infer the effects of sQTLs on the ultimate protein isoform products they encode. We demonstrate the utility of our approach using bone mineral density (BMD) GWAS data. We identified 1,863 sQTLs from the Genotype-Tissue Expression (GTEx) project in 732 protein-coding genes which colocalized with BMD associations (H 4 PP ≥ 0.75). We generated deep coverage PacBio long-read RNA-seq data (N=∼22 million full-length reads) on human osteoblasts, identifying 68,326 protein-coding isoforms, of which 17,375 (25%) were novel. By casting the colocalized sQTLs directly onto protein isoforms, we connected 809 sQTLs to 2,029 protein isoforms from 441 genes expressed in osteoblasts. Using these data, we created one of the first proteome-scale resources defining full-length isoforms impacted by colocalized sQTLs. Overall, we found that 74 sQTLs influenced isoforms likely impacted by nonsense mediated decay (NMD) and 190 that potentially resulted in the expression of new protein isoforms. Finally, we identified colocalizing sQTLs in TPM2 for splice junctions between two mutually exclusive exons, and two different transcript termination sites, making it impossible to interpret without long-read RNA-seq data. siRNA mediated knockdown in osteoblasts showed two TPM2 isoforms with opposing effects on mineralization. We expect our approach to be widely generalizable across diverse clinical traits and accelerate system-scale analyses of protein isoform activities modulated by GWAS loci.

Infertility and treatments used have minimal effects on first-trimester placental DNA methylation and gene expression

OBJECTIVE

To determine whether deoxyribonucleic acid (DNA) methylation alterations exist in the first-trimester human placenta between conceptions using fertility treatments and those that do not and, if so, whether they are the result of underlying infertility or fertility treatments. We also assessed whether significant alterations led to changes in gene expression.

DESIGN

We compared DNA methylation of the first-trimester placenta from singleton pregnancies that resulted in live births from unassisted, in vitro fertilization (IVF), and non-IVF fertility treatment (NIFT) conceptions using the Infinium MethylationEPIC BeadChip array. Significant CpG sites were compared with corresponding ribonucleic acid sequencing analysis in similar cohorts to determine whether methylation alterations lead to differences in gene expression.

SETTING

Academic medical center.

PATIENT(S)

A total of 138 singleton pregnancies undergoing chorionic villus sampling resulting in a live birth were recruited for methylation analysis (56 unassisted, 38 NIFT, and 44 IVF conceptions). Ribonucleic acid-sequencing data consisted of 141 subjects (74 unassisted, 33 NIFT, and 34 IVF conceptions) of which 116 overlapped with the methylation cohort.

INTERVENTION(S)

In vitro fertilization-conceived pregnancy or pregnancy conceived via NIFT, such as ovulation induction and intrauterine insemination.

MAIN OUTCOME MEASURE(S)

Significant methylation changes at CpG sites after adjustment for multiple comparisons. The secondary outcome was gene expression changes of significant CpG sites.

RESULT(S)

Of the 741,145 probes analyzed in the placenta, few were significant at Bonferroni <0.05: 185 CpG sites (0.025%) significant in pregnancies conceived with the fertility treatments (NIFT + IVF) vs. unassisted conceptions; 28 in NIFT vs. unassisted; 195 in IVF vs. unassisted; and only 13 (0.0018%) in IVF vs. NIFT conceptions. Of all significant CpG sites combined, 10% (35) were located in genes with suggestive gene expression changes, but none were significant after adjustment for multiple comparisons (ribonucleic acid sequencing false discovery rate <0.05). None of the 13 differentially methylated probes in the IVF vs. NIFT placenta were located in genes with suggestive IVF vs. NIFT gene expression differences.

CONCLUSION(S)

Underlying infertility is the most significant contributor to the minimal differences in first-trimester placental methylation, and not the specific fertility treatment used, such as IVF.

Intramembranous bone regeneration in diversity outbred mice is heritable

There are over one million cases of failed bone repair in the U.S. annually, resulting in substantial patient morbidity and societal costs. Multiple candidate genes affecting bone traits such as bone mineral density have been identified in human subjects and animal models using genome-wide association studies (GWAS). This approach for understanding the genetic factors affecting bone repair is impractical in human subjects but could be performed in a model organism if there is sufficient variability and heritability in the bone regeneration response. Diversity Outbred (DO) mice, which have significant genetic diversity and have been used to examine multiple intact bone traits, would be an excellent possibility. Thus, we sought to evaluate the phenotypic distribution of bone regeneration, sex effects and heritability of intramembranous bone regeneration on day 7 following femoral marrow ablation in 47 12-week old DO mice (23 males, 24 females). Compared to a previous study using 4 inbred mouse strains, we found similar levels of variability in the amount of regenerated bone (coefficient of variation of 86 % v. 88 %) with approximately the same degree of heritability (0.42 v. 0.49). There was a trend toward more bone regeneration in males than females. The amount of regenerated bone was either weakly or not correlated with bone mass at intact sites, suggesting that the genetic factors responsible for bone regeneration and intact bone phenotypes are at least partially independent. In conclusion, we demonstrate that DO mice exhibit variation and heritability of intramembranous bone regeneration that will be suitable for future GWAS.

Bridging the splicing gap in human genetics with long-read RNA sequencing: finding the protein isoform drivers of disease

Aberrant splicing underlies many human diseases, including cancer, cardiovascular diseases and neurological disorders. Genome-wide mapping of splicing quantitative trait loci (sQTLs) has shown that genetic regulation of alternative splicing is widespread. However, identification of the corresponding isoform or protein products associated with disease-associated sQTLs is challenging with short-read RNA-seq, which cannot precisely characterize full-length transcript isoforms. Furthermore, contemporary sQTL interpretation often relies on reference transcript annotations, which are incomplete. Solutions to these issues may be found through integration of newly emerging long-read sequencing technologies. Long-read sequencing offers the capability to sequence full-length mRNA transcripts and, in some cases, to link sQTLs to transcript isoforms containing disease-relevant protein alterations. Here, we provide an overview of sQTL mapping approaches, the use of long-read sequencing to characterize sQTL effects on isoforms, the linkage of RNA isoforms to protein-level functions and comment on future directions in the field. Based on recent progress, long-read RNA sequencing promises to be part of the human disease genetics toolkit to discover and treat protein isoforms causing rare and complex diseases.

Identification of Known and Novel Long Noncoding RNAs Potentially Responsible for the Effects of Bone Mineral Density (BMD) Genomewide Association Study (GWAS) Loci

Osteoporosis, characterized by low bone mineral density (BMD), is the most common complex disease affecting bone and constitutes a major societal health problem. Genome-wide association studies (GWASs) have identified over 1100 associations influencing BMD. It has been shown that perturbations to long noncoding RNAs (lncRNAs) influence BMD and the activities of bone cells; however, the extent to which lncRNAs are involved in the genetic regulation of BMD is unknown. Here, we combined the analysis of allelic imbalance (AI) in human acetabular bone fragments with a transcriptome-wide association study (TWAS) and expression quantitative trait loci (eQTL) colocalization analysis using data from the Genotype-Tissue Expression (GTEx) project to identify lncRNAs potentially responsible for GWAS associations. We identified 27 lncRNAs in bone that are located in proximity to a BMD GWAS association and harbor single-nucleotide polymorphisms (SNPs) demonstrating AI. Using GTEx data we identified an additional 31 lncRNAs whose expression was associated (false discovery rate [FDR] correction < 0.05) with BMD through TWAS and had a colocalizing eQTL (regional colocalization probability [RCP] > 0.1). The 58 lncRNAs are located in 43 BMD associations. To further support a causal role for the identified lncRNAs, we show that 23 of the 58 lncRNAs are differentially expressed as a function of osteoblast differentiation. Our approach identifies lncRNAs that are potentially responsible for BMD GWAS associations and suggest that lncRNAs play a role in the genetics of osteoporosis. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Transcriptome-wide association study and eQTL colocalization identify potentially causal genes responsible for human bone mineral density GWAS associations

Genome-wide association studies (GWASs) for bone mineral density (BMD) in humans have identified over 1100 associations to date. However, identifying causal genes implicated by such studies has been challenging. Recent advances in the development of transcriptome reference datasets and computational approaches such as transcriptome-wide association studies (TWASs) and expression quantitative trait loci (eQTL) colocalization have proven to be informative in identifying putatively causal genes underlying GWAS associations. Here, we used TWAS/eQTL colocalization in conjunction with transcriptomic data from the Genotype-Tissue Expression (GTEx) project to identify potentially causal genes for the largest BMD GWAS performed to date. Using this approach, we identified 512 genes as significant using both TWAS and eQTL colocalization. This set of genes was enriched for regulators of BMD and members of bone relevant biological processes. To investigate the significance of our findings, we selected PPP6R3, the gene with the strongest support from our analysis which was not previously implicated in the regulation of BMD, for further investigation. We observed that Ppp6r3 deletion in mice decreased BMD. In this work, we provide an updated resource of putatively causal BMD genes and demonstrate that PPP6R3 is a putatively causal BMD GWAS gene. These data increase our understanding of the genetics of BMD and provide further evidence for the utility of combined TWAS/colocalization approaches in untangling the genetics of complex traits.

Fentanyl-induced acute and conditioned behaviors in two inbred mouse lines: Potential role for Glyoxalase

An increase in opioid-overdose deaths was evident before the COVID-19 pandemic, and has escalated since its onset. Fentanyl, a highly potent synthetic opioid, is the primary driver of these recent trends. The current study used two inbred mouse strains, C57BL/6 J and A/J, to investigate the genetics of behavioral responses to fentanyl. Mice were tested for conditioned place preference and fentanyl-induced locomotor activity. C57BL/6J mice formed a conditioned place preference to fentanyl injections and fentanyl increased their activity. Neither effect was noted in A/J mice. We conducted RNA-sequencing on the nucleus accumbens of mice used for fentanyl-induced locomotor activity. Surprisingly, we noted few differentially expressed genes using treatment as the main factor. However many genes differed between strains. We validated differences in two genes: suppressor APC domain containing 1 (Sapcd1) and Glyoxalase 1 (Glo1), with quantitative PCR on RNA from the nucleus accumbens and prefrontal cortex (). In both regions A/J mice had significantly higher expression of both genes than did C57BL/6 J. In prefrontal cortex, fentanyl treatment decreased Glo1 mRNA. Glyoxalase 1 catalyzes the detoxification of reactive alpha-oxoaldehydes such as glyoxal and methylglyoxal, is associated with anxiety and activity levels, and its inhibition reduces alcohol intake. We suggest that future studies assess the ability of Glo1 and related metabolites to modify opioid intake.

Dynamic changes in immune gene co-expression networks predict development of type 1 diabetes

Significant progress has been made in elucidating genetic risk factors influencing Type 1 diabetes (T1D); however, features other than genetic variants that initiate and/or accelerate islet autoimmunity that lead to the development of clinical T1D remain largely unknown. We hypothesized that genetic and environmental risk factors can both contribute to T1D through dynamic alterations of molecular interactions in physiologic networks. To test this hypothesis, we utilized longitudinal blood transcriptomic profiles in The Environmental Determinants of Diabetes in the Young (TEDDY) study to generate gene co-expression networks. In network modules that contain immune response genes associated with T1D, we observed highly dynamic differences in module connectivity in the 600 days (~ 2 years) preceding clinical diagnosis of T1D. Our results suggest that gene co-expression is highly plastic and that connectivity differences in T1D-associated immune system genes influence the timing and development of clinical disease.

Current evidence on potential of adipose derived stem cells to enhance bone regeneration and future projection

Injuries to the postnatal skeleton are naturally repaired through successive steps involving specific cell types in a process collectively termed “bone regeneration”. Although complex, bone regeneration occurs through a series of well-orchestrated stages wherein endogenous bone stem cells play a central role. In most situations, bone regeneration is successful; however, there are instances when it fails and creates non-healing injuries or fracture nonunion requiring surgical or therapeutic interventions. Transplantation of adult or mesenchymal stem cells (MSCs) defined by the International Society for Cell and Gene Therapy (ISCT) as CD105+CD90+CD73+CD45-CD34-CD14orCD11b-CD79αorCD19-HLA-DR- is being investigated as an attractive therapy for bone regeneration throughout the world. MSCs isolated from adipose tissue, adipose-derived stem cells (ADSCs), are gaining increasing attention since this is the most abundant source of adult stem cells and the isolation process for ADSCs is straightforward. Currently, there is not a single Food and Drug Administration (FDA) approved ADSCs product for bone regeneration. Although the safety of ADSCs is established from their usage in numerous clinical trials, the bone-forming potential of ADSCs and MSCs, in general, is highly controversial. Growing evidence suggests that the ISCT defined phenotype may not represent bona fide osteoprogenitors. Transplantation of both ADSCs and the CD105^- sub-population of ADSCs has been reported to induce bone regeneration. Most notably, cells expressing other markers such as CD146, AlphaV, CD200, PDPN, CD164, CXCR4, and PDGFRα have been shown to represent osteogenic sub-population within ADSCs. Amongst other strategies to improve the bone-forming ability of ADSCs, modulation of VEGF, TGF-β1 and BMP signaling pathways of ADSCs has shown promising results. The U.S. FDA reveals that 73% of Investigational New Drug applications for stem cell-based products rely on CD105 expression as the “positive” marker for adult stem cells. A concerted effort involving the scientific community, clinicians, industries, and regulatory bodies to redefine ADSCs using powerful selection markers and strategies to modulate signaling pathways of ADSCs will speed up the therapeutic use of ADSCs for bone regeneration.

A computational approach for identification of core modules from a co-expression network and GWAS data

This protocol describes the application of the "omnigenic" model of the genetic architecture of complex traits to identify novel "core" genes influencing a disease-associated phenotype. Core genes are hypothesized to directly regulate disease and may serve as therapeutic targets. This protocol leverages GWAS data, a co-expression network, and publicly available data, including the GTEx database and the International Mouse Phenotyping Consortium Database, to identify modules enriched for genes with "core-like" characteristics. For complete details on the use and execution of this protocol, please refer to Sabik et al. (2020).

Using "-omics" Data to Inform Genome-wide Association Studies (GWASs) in the Osteoporosis Field

PURPOSE OF REVIEW

Osteoporosis constitutes a major societal health problem. Genome-wide association studies (GWASs) have identified over 1100 loci influencing bone mineral density (BMD); however, few of the causal genes have been identified. Here, we review approaches that use "-omics" data and genetic- and systems genetics-based analytical strategies to facilitate causal gene discovery.

RECENT FINDINGS

The bone field is beginning to adopt approaches that are commonplace in other disease disciplines. The slower progress has been due in part to the lack of large-scale "omics" data on bone and bone cells. This is however changing, and approaches such as eQTL colocalization, transcriptome-wide association studies (TWASs), network, and integrative approaches are beginning to provide significant insight into the genes responsible for BMD GWAS associations. The use of "-omics" data to inform BMD GWASs has increased in recent years, leading to the identification of novel regulators of BMD in humans. The ultimate goal will be to use this information to develop more effective therapies to treat and ultimately prevent osteoporosis.

Osteoblasts Generate Testosterone From DHEA and Activate Androgen Signaling in Prostate Cancer Cells

Bone metastasis is a complication of prostate cancer in up to 90% of men afflicted with advanced disease. Therapies that reduce androgen exposure remain at the forefront of treatment. However, most prostate cancers transition to a state whereby reducing testicular androgen action becomes ineffective. A common mechanism of this transition is intratumoral production of testosterone (T) using the adrenal androgen precursor dehydroepiandrosterone (DHEA) through enzymatic conversion by 3β- and 17β-hydroxysteroid dehydrogenases (3βHSD and 17βHSD). Given the ability of prostate cancer to form blastic metastases in bone, we hypothesized that osteoblasts might be a source of androgen synthesis. RNA expression analyses of murine osteoblasts and human bone confirmed that at least one 3βHSD and 17βHSD enzyme isoform was expressed, suggesting that osteoblasts are capable of generating androgens from adrenal DHEA. Murine osteoblasts were treated with 100 nM and 1 μM DHEA or vehicle control. Conditioned media from these osteoblasts were assayed for intermediate and active androgens by liquid chromatography-tandem mass spectrometry. As DHEA was consumed, the androgen intermediates androstenediol and androstenedione were generated and subsequently converted to T. Conditioned media of DHEA-treated osteoblasts increased androgen receptor (AR) signaling, prostate-specific antigen (PSA) production, and cell numbers of the androgen-sensitive prostate cancer cell lines C4-2B and LNCaP. DHEA did not induce AR signaling in osteoblasts despite AR expression in this cell type. We describe an unreported function of osteoblasts as a source of T that is especially relevant during androgen-responsive metastatic prostate cancer invasion into bone. © 2021 American Society for Bone and Mineral Research (ASBMR). This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Identification of a Core Module for Bone Mineral Density through the Integration of a Co-expression Network and GWAS Data

The "omnigenic" model of the genetic architecture of complex traits proposed two categories of causal genes: core and peripheral. Core genes are hypothesized to directly regulate disease and may serve as therapeutic targets. Using a cell-type- and time-point-specific gene co-expression network for mineralizing osteoblasts, we identify a co-expression module enriched for genes implicated by bone mineral density (BMD) genome-wide association studies (GWASs), correlated with in vitro osteoblast mineralization and associated with skeletal phenotypes in human monogenic disease and mouse knockouts. Four genes from this module (B4GALNT3, CADM1, DOCK9, and GPR133) are located within the BMD GWAS loci with colocalizing expression quantitative trait loci (eQTL) and exhibit altered BMD in mouse knockouts, suggesting that they are causal genetic drivers of BMD in humans. Our network-based approach identifies a "core" module for BMD and provides a resource for expanding our understanding of the genetics of bone mass.

Genomic variants within chromosome 14q32.32 regulate bone mass through MARK3 signaling in osteoblasts

Bone mineral density (BMD) is a highly heritable predictor of osteoporotic fracture. GWAS have identified hundreds of loci influencing BMD, but few have been functionally analyzed. In this study, we show that SNPs within a BMD locus on chromosome 14q32.32 alter splicing and expression of PAR-1a/microtubule affinity regulating kinase 3 (MARK3), a conserved serine/threonine kinase known to regulate bioenergetics, cell division, and polarity. Mice lacking Mark3 either globally or selectively in osteoblasts have increased bone mass at maturity. RNA profiling from Mark3-deficient osteoblasts suggested changes in the expression of components of the Notch signaling pathway. Mark3-deficient osteoblasts exhibited greater matrix mineralization compared with controls that was accompanied by reduced Jag1/Hes1 expression and diminished downstream JNK signaling. Overexpression of Jag1 in Mark3-deficient osteoblasts both in vitro and in vivo normalized mineralization capacity and bone mass, respectively. Together, these findings reveal a mechanism whereby genetically regulated alterations in Mark3 expression perturb cell signaling in osteoblasts to influence bone mass.

Genetic variability affects the response of skeletal muscle to disuse

OBJECTIVE

To examine whether genetic variability plays a role in skeletal muscle response to disuse.

METHODS

We examined skeletal muscle response to disuse in five different strains of mice: CAST/EiJ, NOD/ShiLtJ, NZO/HILtJ, 129S1/SvImJ and A/J. Mice had one limb immobilized by a cast for three weeks.

RESULTS

Response to immobilization was dependent on the strain of mice. Skeletal muscle mass/body weight was decreased by immobilization in all strains except 1291/SvImJ. Immobilization decreased absolute skeletal muscle mass in quadriceps and gastrocnemius in NOD/ShiltJ and NZO/HILtJ mice. Three weeks of immobilization resulted in an increase in quadriceps levels of atrogenes in CAST/EiJ. Immobilization resulted in an increase in quadriceps and gastrocnemius levels of Myh4 in CAST/EiJ. A similar trend was observed for Myh7 in gastrocnemius muscle. Immobilization resulted in a decrease of the p-p70S6K1/total p706SK1 ratio in quadriceps of NOD/ShiLtJ mice and the gastrocnemius of A/J mice. Immobilization did not affect the p-4EBP1/total 4EBP1 ratio in quadriceps of any of the strains examined. However, the p-4EBP1/total 4EBP1 ratio in gastrocnemius was greater in immobilized, relative to control, limbs in CAST/EiJ mice.

CONCLUSION

Genetic variability affects the response of skeletal muscle to disuse.

Exercise during pregnancy mitigates negative effects of parental obesity on metabolic function in adult mouse offspring

Parental health influences embryonic development and susceptibility to disease in the offspring. We investigated whether maternal voluntary running during gestation could protect the offspring from the adverse effects of maternal or paternal high-fat diet (HF) in mice. We performed transcriptomic and whole-genome DNA methylation analyses in female offspring skeletal muscle and targeted DNA methylation analysis of the peroxisome proliferator-activated receptor-γ coactivator-1α (Pgc-1α) promoter in both male and female adult offspring. Maternal HF resulted in impaired metabolic homeostasis in male offspring at 9 mo of age, whereas both male and female offspring were negatively impacted by paternal HF. Maternal exercise during gestation completely mitigated these metabolic impairments. Female adult offspring from obese male or female parent had skeletal muscle transcriptional profiles enriched in genes regulating inflammation and immune responses, whereas maternal exercise resulted in a transcriptional profile similar to offspring from normal chow (NC)-fed parents. Maternal HF, but not paternal HF, resulted in hypermethylation of the Pgc-1α promoter at CpG-260, which was abolished by maternal exercise. These findings demonstrate the negative consequences of maternal and paternal HF for the offspring's metabolic outcomes later in life possibly through different epigenetic mechanisms, and maternal exercise during gestation mitigates the negative consequences.NEW & NOTEWORTHY Maternal or paternal obesity causes metabolic impairment in adult offspring in mice. Maternal exercise during gestation can completely mitigate metabolic impairment. Maternal obesity, but not paternal obesity, results in hypermethylation of the Pgc-1α promoter at CpG-260, which can be abolished by maternal exercise.

Sexually Dimorphic Crosstalk at the Maternal-Fetal Interface

CONTEXT

Crosstalk through receptor ligand interactions at the maternal-fetal interface is impacted by fetal sex. This affects placentation in the first trimester and differences in outcomes. Sexually dimorphic signaling at early stages of placentation are not defined.

OBJECTIVE

Investigate the impact of fetal sex on maternal-fetal crosstalk.

DESIGN

Receptors/ligands at the maternal-fetal surface were identified from sexually dimorphic genes between fetal sexes in the first trimester placenta and defined in each cell type using single-cell RNA-Sequencing (scRNA-Seq).

SETTING

Academic institution.

SAMPLES

Late first trimester (~10-13 weeks) placenta (fetal) and decidua (maternal) from uncomplicated ongoing pregnancies.

MAIN OUTCOME MEASURES

Transcriptomic profiling at tissue and single-cell level; immunohistochemistry of select proteins.

RESULTS

We identified 91 sexually dimorphic receptor-ligand pairs across the maternal-fetal interface. We examined fetal sex differences in 5 major cell types (trophoblasts, stromal cells, Hofbauer cells, antigen-presenting cells, and endothelial cells). Ligands from the CC family chemokine ligand (CCL) family were most highly representative in females, with their receptors present on the maternal surface. Sexually dimorphic trophoblast transcripts, Mucin-15 (MUC15) and notum, palmitoleoyl-protein carboxylesterase (NOTUM) were also most highly expressed in syncytiotrophoblasts and extra-villous trophoblasts respectively. Gene Ontology (GO) analysis using sexually dimorphic genes in individual cell types identified cytokine mediated signaling pathways to be most representative in female trophoblasts. Upstream analysis demonstrated TGFB1 and estradiol to affect all cell types, but dihydrotestosterone, produced by the male fetus, was an upstream regulator most significant for the trophoblast population.

CONCLUSIONS

Maternal-fetal crosstalk exhibits sexual dimorphism during placentation early in gestation.

Old Mice Have Less Transcriptional Activation But Similar Periosteal Cell Proliferation Compared to Young-Adult Mice in Response to in vivo Mechanical Loading

Mechanical loading is a potent strategy to induce bone formation, but with aging, the bone formation response to the same mechanical stimulus diminishes. Our main objectives were to (i) discover the potential transcriptional differences and (ii) compare the periosteal cell proliferation between tibias of young-adult and old mice in response to strain-matched mechanical loading. First, to discover potential age-related transcriptional differences, we performed RNA sequencing (RNA-seq) to compare the loading responses between tibias of young-adult (5-month) and old (22-month) C57BL/6N female mice following 1, 3, or 5 days of axial loading (loaded versus non-loaded). Compared to young-adult mice, old mice had less transcriptional activation following loading at each time point, as measured by the number of differentially expressed genes (DEGs) and the fold-changes of the DEGs. Old mice engaged fewer pathways and gene ontology (GO) processes, showing less activation of processes related to proliferation and differentiation. In tibias of young-adult mice, we observed prominent Wnt signaling, extracellular matrix (ECM), and neuronal responses, which were diminished with aging. Additionally, we identified several targets that may be effective in restoring the mechanoresponsiveness of aged bone, including nerve growth factor (NGF), Notum, prostaglandin signaling, Nell-1, and the AP-1 family. Second, to directly test the extent to which periosteal cell proliferation was diminished in old mice, we used bromodeoxyuridine (BrdU) in a separate cohort of mice to label cells that divided during the 5-day loading interval. Young-adult and old mice had an average of 15.5 and 16.7 BrdU+ surface cells/mm, respectively, suggesting that impaired proliferation in the first 5 days of loading does not explain the diminished bone formation response with aging. We conclude that old mice have diminished transcriptional activation following mechanical loading, but periosteal proliferation in the first 5 days of loading does not differ between tibias of young-adult and old mice. © 2020 American Society for Bone and Mineral Research.

Genetic analysis of osteoblast activity identifies Zbtb40 as a regulator of osteoblast activity and bone mass

Osteoporosis is a genetic disease characterized by progressive reductions in bone mineral density (BMD) leading to an increased risk of fracture. Over the last decade, genome-wide association studies (GWASs) have identified over 1000 associations for BMD. However, as a phenotype BMD is challenging as bone is a multicellular tissue affected by both local and systemic physiology. Here, we focused on a single component of BMD, osteoblast-mediated bone formation in mice, and identified associations influencing osteoblast activity on mouse Chromosomes (Chrs) 1, 4, and 17. The locus on Chr. 4 was in an intergenic region between Wnt4 and Zbtb40, homologous to a locus for BMD in humans. We tested both Wnt4 and Zbtb40 for a role in osteoblast activity and BMD. Knockdown of Zbtb40, but not Wnt4, in osteoblasts drastically reduced mineralization. Additionally, loss-of-function mouse models for both genes exhibited reduced BMD. Our results highlight that investigating the genetic basis of in vitro osteoblast mineralization can be used to identify genes impacting bone formation and BMD.

SUN-361 Cultured Murine Osteoblasts Convert DHEA to Testosterone

Androgens have complex effects on the skeleton. Besides gonadal testosterone (T), the adrenal produces the androgen precursor dehydroepiandrosterone (DHEA), using 3β- and 17β-hydroxysteroid dehydrogenases (3βHSD & 17βHSD) to convert to T in target tissues. Microarray analyses of murine calvarial osteoblasts, RT-PCR of long bone osteoblasts, and RNA-Seq of human bone biopsies confirmed that each of the enzyme families is expressed in osteoblasts, suggesting osteoblasts can generate androgens from the adrenal-derived androgen precursor DHEA. Activation of osteoblast androgen receptor (AR) signaling by DHEA was detected using an AR reporter construct, providing evidence that active androgens are generated. To understand how DHEA is converted to T, we treated murine primary osteoblasts with 100 nM and 1 μM DHEA, or vehicle control. Conditioned media were collected 1, 2, and 3 days after DHEA treatment and assayed for intermediate and active androgens by tandem mass spectrometry with two-dimensional chromatography. As DHEA was consumed, the androgen intermediates androstenediol (A5) and androstenedione (A4) were generated and subsequently converted to T. The peak concentrations of T generated by DHEA 100 nM and 1 μM were 22 and 101 pg/ml, respectively. The equilibrium dissociation constant of the AR for T is ~0.2 nM (57.7 pg/ml), indicating sufficient T production to activate AR in androgen-sensitive osteoblasts. Cultured osteoblasts preferentially converted DHEA to A5, via 17βHSD, rather than to A4, signifying that in the conversion of DHEA to T, 3βHSD is the rate-limiting step. Of the 13 17βHSD isoforms, 7 were expressed in these samples. In contrast, only a single gene isoform of Hsd3b—Hsd3b7—was abundantly expressed in mouse osteoblasts and human bone. We investigated the effects of 3βHSD7 in osteoblasts. An Hsd3b7 shRNA knocked-down mRNA and protein expression by >85%, and caused an osteoblast growth defect compared to an shRNA control. 3βHSD7 has known functions in bile acid synthesis, converting 7α-hydroxycholesterol to 7α-hydroxycholestenone (7HC). Treatment of Hsd3b7 knockdown osteoblasts with 7HC rescued the growth defect suggesting that osteoblasts might generate 7HC or a subsequent metabolite as a trophic factor. We now report an unreported function of bone as a source of T, by conversion of the adrenal androgen precursor DHEA, using 3βHSD7 as a common enzyme for androgen and bile acid synthesis, and leading to the activation of osteoblast AR signaling. These data suggest that the skeleton has evolved protective mechanisms against hypogonadal bone loss that exploits the continued production of adrenal DHEA. This concept is especially important in men with prostate cancer bone metastasis undergoing testicular-targeted therapies whereby adrenal DHEA may continue to fuel cancer growth, and in bone maturation during adrenarche before the pubertal rise in gonadal androgens.

OR24-07 Fetal Sex Impacts First Trimester Maternal-Fetal Communication in Humans

The placenta serves as a regulator of fetal growth throughout pregnancy. Signaling at the maternal-fetal interface is critical during placentation and lays the groundwork for placenta function, affecting pregnancy outcomes. Fetal growth is impacted by fetal sex, with males larger than females, and maternal gestational diabetes and obesity independently increase the risk of macrosomia in male fetuses only. We previously demonstrated differentially expressed genes (DEGs) among sexes involves ancient canonical pathways and metabolic functions in placenta tissue. As these are likely impacted by signaling at the maternal-fetal interface, our aim here was to identify sex differences in signaling at the maternal-fetal interface and among individual cell types within the placenta to explain these differences. RNA-sequencing of first trimester placenta and maternal decidua as well as single cell RNA-sequencing in first trimester placenta was performed in ongoing pregnancies. We identified 91 sexually dimorphic receptor-ligand pairs across the maternal-fetal interface. From these, 35 of 115 receptors and/or ligand genes were also found to be upstream regulators of pathways critical in sexually dimorphic placentation which may define regulation. Single cell analysis identified five major cell types (trophoblasts, stromal cells, hofbauer cells, antigen presenting cells, and endothelial cells), and all had sexually dimorphic genes. Among individual cell types, ligands from the CC-family of cytokines were most highly representative in females, with their corresponding receptors present on the maternal surface. Furthermore, upstream regulator analysis of sexually dimorphic genes demonstrated TGFβ1 and estradiol to significantly affect all cell types. Dihydrotestosterone, which is produced by the male fetus, was an upstream regulator that was most significant for the trophoblast population. In addition, gene ontology enrichment analysis identified distinctive enriched functions between male and female trophoblasts, with cytokine mediated signaling pathways most representative. MUC15 and NOTUM were the most highly expressed sexually dimorphic autosomal genes found in distinct cell types of the trophoblast population, cell types critical for placentation and nutrient exchange. Thus, differences in hormone and immune signaling pathways may account for differential gene expression and differences in trophoblast function during placentation, which may in turn explain developmental differences, including fetal size, well-being, and overall outcomes.

RNA-sequencing analysis of differential gene expression associated with arterial stiffness

OBJECTIVES

Arterial stiffness is recognized as an important predictor of cardiovascular disease morbidity and mortality, independent of traditional cardiovascular disease risk factors. Given that arterial tissue is not easily accessible, most gene expression studies on arterial stiffness have been conducted on animals or on patients who have undergone by-pass surgeries. In order to obtain a deeper understanding of early changes of arterial stiffness, this study compared transcriptome profiles between healthy adults with higher and lower arterial stiffness.

METHODS

The sample included 20 healthy female adults without cardiovascular disease. Arterial stiffness was measured by carotid-femoral pulse wave velocity, the "gold-standard" measure of central arterial stiffness. Peripheral blood samples collected to PAXgene™ RNA tubes were used for RNA sequencing (RNA-seq). The potential confounding effects of age, body mass index, and mean arterial pressure were controlled for in RNA-seq analysis. To validate RNA-seq results, quantitative real-time PCR (qRT-PCR) was performed for six selected genes.

RESULTS

The findings demonstrated that genes including CAPN9, IL32, ERAP2, RAB6B, MYBPH, and miRNA626 were down-regulated, and that MOCS1 gene was up-regulated among the people with higher arterial stiffness. Real-time PCR showed that the changes of CAPN9, IL32, ERAP2, and RAB6B were in concordance with RNA-seq data, and confirmed the validity of the gene expression profiles obtained by RNA-seq analysis.

CONCLUSIONS

Previous studies have suggested the potential roles of CAPN9, IL32, and ERAP2 in structural changes of the arterial wall through up-regulation of metalloproteinases. However, the current study showed that CAPN9, IL32, and ERAP2 were down-regulated in the individuals with higher arterial stiffness, compared with those with lower arterial stiffness. The unexpected directions of expression of these genes may indicate an effort to maintain vascular homeostasis during increased arterial stiffness among healthy individuals. Further studies are guaranteed to investigate the roles of CAPN9, IL32, and ERAP2 in regulating arterial stiffness in people with and without cardiovascular disease.

A novel voluntary weightlifting model in mice promotes muscle adaptation and insulin sensitivity with simultaneous enhancement of autophagy and mTOR pathway

Our understanding of the molecular mechanisms underlying adaptations to resistance exercise remains elusive despite the significant biological and clinical relevance. We developed a novel voluntary mouse weightlifting model, which elicits squat-like activities against adjustable load during feeding, to investigate the resistance exercise-induced contractile and metabolic adaptations. RNAseq analysis revealed that a single bout of weightlifting induced significant transcriptome responses of genes that function in posttranslational modification, metabolism, and muscle differentiation in recruited skeletal muscles, which were confirmed by increased expression of fibroblast growth factor-inducible 14 (Fn14), Down syndrome critical region 1 (Dscr1) and Nuclear receptor subfamily 4, group A, member 3 (Nr4a3) genes. Long-term (8 weeks) voluntary weightlifting training resulted in significantly increases of muscle mass, protein synthesis (puromycin incorporation in SUnSET assay) and mTOR pathway protein expression (raptor, 4e-bp-1, and p70S6K proteins) along with enhanced muscle power (specific torque and contraction speed), but not endurance capacity, mitochondrial biogenesis, and fiber type transformation. Importantly, weightlifting training profound improved whole-body glucose clearance and skeletal muscle insulin sensitivity along with enhanced autophagy (increased LC3 and LC3-II/I ratio, and decreased p62/Sqstm1). These data suggest that resistance training in mice promotes muscle adaptation and insulin sensitivity with simultaneous enhancement of autophagy and mTOR pathway.

Genetic Dissection of Femoral and Tibial Microarchitecture

Our understanding of the genetic control of bone strength has relied mainly on estimates of bone mineral density. Here we have mapped genetic factors that influence femoral and tibial microarchitecture using high‐resolution x‐ray computed tomography (8‐μm isotropic voxels) across a family of 61 BXD strains of mice, roughly 10 isogenic cases per strain and balanced by sex. We computed heritabilities for 25 cortical and trabecular traits. Males and females have well‐matched heritabilities, ranging from 0.25 to 0.75. We mapped 16 genetic loci most of which were detected only in females. There is also a bias in favor of loci that control cortical rather than trabecular bone. To evaluate candidate genes, we combined well‐established gene ontologies with bone transcriptome data to compute bone‐enrichment scores for all protein‐coding genes. We aligned candidates with those of human genome‐wide association studies. A subset of 50 strong candidates fell into three categories: (1) experimentally validated genes already known to modulate bone function (Adamts4, Ddr2, Darc, Adam12, Fkbp10, E2f6, Adam17, Grem2, Ifi204); (2) candidates without any experimentally validated function in bone (eg, Greb1, Ifi202b), but linked to skeletal phenotypes in human cohorts; and (3) candidates that have high bone‐enrichment scores, but for which there is not yet any functional link to bone biology or skeletal system disease (including Ifi202b, Ly9, Ifi205, Mgmt, F2rl1, Iqgap2). Our results highlight contrasting genetic architecture between sexes and among major bone compartments. The alignment of murine and human data facilitates function analysis and should prove of value for preclinical testing of molecular control of bone structure. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Antiangiogenic VEGF165b Regulates Macrophage Polarization via S100A8/S100A9 in Peripheral Artery Disease

BACKGROUND

Atherosclerotic occlusions decrease blood flow to the lower limbs, causing ischemia and tissue loss in patients with peripheral artery disease (PAD). No effective medical therapies are currently available to induce angiogenesis and promote perfusion recovery in patients with severe PAD. Clinical trials aimed at inducing vascular endothelial growth factor (VEGF)-A levels, a potent proangiogenic growth factor to induce angiogenesis, and perfusion recovery were not successful. Alternate splicing in the exon-8 of VEGF-A results in the formation of VEGFxxxa (VEGF₁₆₅a) and VEGFxxxb (VEGF₁₆₅b) isoforms with existing literature focusing on VEGF₁₆₅b's role in inhibiting vascular endothelial growth factor receptor 2-dependent angiogenesis. However, we have recently shown that VEGF₁₆₅b blocks VEGF-A-induced endothelial vascular endothelial growth factor receptor 1 (VEGFR1) activation in ischemic muscle to impair perfusion recovery. Because macrophage-secreted VEGF₁₆₅b has been shown to decrease angiogenesis in peripheral artery disease, and macrophages were well known to play important roles in regulating ischemic muscle vascular remodeling, we examined the role of VEGF₁₆₅b in regulating macrophage function in PAD.

METHODS

Femoral artery ligation and resection were used as an in vivo preclinical PAD model, and hypoxia serum starvation was used as an in vitro model for PAD. Experiments including laser-Doppler perfusion imaging, adoptive cell transfer to ischemic muscle, immunoblot analysis, ELISAs, immunostainings, flow cytometry, quantitative polymerase chain reaction analysis, and RNA sequencing were performed to determine a role of VEGF₁₆₅b in regulating macrophage phenotype and function in PAD.

RESULTS

First, we found increased VEGF₁₆₅b expression with increased M1-like macrophages in PAD versus non-PAD (controls) muscle biopsies. Next, using in vitro hypoxia serum starvation, in vivo pre clinical PAD models, and adoptive transfer of VEGF₁₆₅b-expressing bone marrow-derived macrophages or VEGFR1^+/- bone marrow-derived macrophages (M1-like phenotype), we demonstrate that VEGF₁₆₅b inhibits VEGFR1 activation to induce an M1-like phenotype that impairs ischemic muscle neovascularization. Subsequently, we found S100A8/S100A9 as VEGFR1 downstream regulators of macrophage polarization by RNA-Seq analysis of hypoxia serum starvation-VEGFR1^+/+ versus hypoxia serum starvation-VEGFR1^+/- bone marrow-derived macrophages.

CONCLUSIONS

In our current study, we demonstrate that increased VEGF₁₆₅b expression in macrophages induces an antiangiogenic M1-like phenotype that directly impairs angiogenesis. VEGFR1 inhibition by VEGF₁₆₅b results in S100A8/S100A9-mediated calcium influx to induce an M1-like phenotype that impairs ischemic muscle revascularization and perfusion recovery.

The State of Systems Genetics in 2017

Cell Systems invited 16 experts to share their views on the field of systems genetics. In questions repeated in the headings, we asked them to define systems genetics, highlight its relevance to researchers outside the field, discuss what makes a strong systems genetics paper, and paint a picture of where the field is heading in the coming years. Their responses, ordered by the journal but otherwise unedited, make it clear that deciphering genotype to phenotype relationships is a central challenge of systems genetics and will require understanding how networks and higher-order properties of biological systems underlie complex traits. In addition, our experts illuminate the applications and relevance of systems genetics to human disease, the gut microbiome, development of tools that connect the global research community, sustainability, drug discovery, patient-specific disease and network models, and personalized treatments. Finally, a table of suggested reading provides a sample of influential work in the field.

Mouse genome-wide association and systems genetics identifies Lhfp as a regulator of bone mass

Bone mineral density (BMD) is a strong predictor of osteoporotic fracture. It is also one of the most heritable disease-associated quantitative traits. As a result, there has been considerable effort focused on dissecting its genetic basis. Here, we performed a genome-wide association study (GWAS) in a panel of inbred strains to identify associations influencing BMD. This analysis identified a significant (P = 3.1 x 10⁻¹²) BMD locus on Chromosome 3@52.5 Mbp that replicated in two separate inbred strain panels and overlapped a BMD quantitative trait locus (QTL) previously identified in a F2 intercross. The association mapped to a 300 Kbp region containing four genes; Gm2447, Gm20750, Cog6, and Lhfp. Further analysis found that Lipoma HMGIC Fusion Partner (Lhfp) was highly expressed in bone and osteoblasts. Furthermore, its expression was regulated by a local expression QTL (eQTL), which overlapped the BMD association. A co-expression network analysis revealed that Lhfp was strongly connected to genes involved in osteoblast differentiation. To directly evaluate its role in bone, Lhfp deficient mice (Lhfp^-/-) were created using CRISPR/Cas9. Consistent with genetic and network predictions, bone marrow stromal cells (BMSCs) from Lhfp^-/- mice displayed increased osteogenic differentiation. Lhfp^-/- mice also had elevated BMD due to increased cortical bone mass. Lastly, we identified SNPs in human LHFP that were associated (P = 1.2 x 10⁻⁵) with heel BMD. In conclusion, we used GWAS and systems genetics to identify Lhfp as a regulator of osteoblast activity and bone mass.

Osteoporosis is a common, chronic disease characterized by low bone mineral density (BMD) that puts millions of Americans at high risk of fracture. Variation in BMD in the general population is, in large part, determined by genetic factors. To identify novel genes influencing BMD, we performed a genome-wide association study in a panel of inbred mouse strains. We identified a locus on Chromosome 3 strongly associated with BMD. Using a combination of systems genetics approaches, we connected the expression of the Lhfp gene with BMD-associated genetic variants and predicted it influenced BMD by altering the activity of bone-forming osteoblasts. Using mice deficient in Lhfp, we demonstrated that Lhfp negatively regulates bone formation and BMD. These data suggest that inhibiting Lhfp may represent a novel therapeutic strategy to increase BMD and decrease the risk of fracture.

Differences in First-Trimester Maternal Metabolomic Profiles in Pregnancies Conceived From Fertility Treatments

CONTEXT

Maternal metabolic status reflects underlying physiological changes in the maternal-placental-fetal unit that may help identify contributors to adverse pregnancy outcomes associated with infertility and treatments used.

OBJECTIVE

To determine if maternal metabolomic profiles differ between spontaneous pregnancies and pregnancies conceived with fertility treatments that may explain the differences in pregnancy outcomes.

DESIGN

Metabolon metabolomic analysis and ELISAs for 17-β-estradiol and progesterone were performed during the late first trimester of pregnancy.

SETTING

Academic institution.

SUBJECTS

Women in the Spontaneous/Medically Assisted/Assisted Reproductive Technology cohort (N = 409), 208 of whom conceived spontaneously and 201 with infertility [non in vitro fertilization treatments (NIFT), n=90; in vitro fertilization (IVF), n=111].

INTERVENTION

Mode of conception.

MAIN OUTCOME MEASURES

Levels of of 806 metabolites within eight superpathways, 17-β-estradiol, and progesterone in maternal plasma in the late first trimester.

RESULTS

Metabolomic differences in the lipid superpathway (i.e., steroid metabolites, lipids with docosahexaenoyl acyl chains, acyl cholines), and xanthine and benzoate metabolites (P < 0.05) were significant among the spontaneous and two infertility groups, with greatest differences between the spontaneous and IVF groups. 17-β-estradiol and progesterone levels were significantly elevated in the infertility groups, with greatest differences between the spontaneous and IVF groups.

CONCLUSION

Metabolomic profiles differ between spontaneous and infertility pregnancies, likely driven by IVF. Higher levels of steroids and their metabolites are likely due to increased hormone production from placenta reprogrammed from fertility treatments, which may contribute to adverse outcomes associated with infertility and the treatments used.

Differential gene expression during placentation in pregnancies conceived with different fertility treatments compared with spontaneous pregnancies

OBJECTIVE

To identify differences in the transcriptomic profiles during placentation from pregnancies conceived spontaneously vs. those with infertility using non-in vitro fertilization (IVF) fertility treatment (NIFT) or IVF.

DESIGN

Cohort study.

SETTING

Academic medical center.

PATIENT(S)

Women undergoing chorionic villus sampling at gestational age 11-13 weeks (n = 141), with pregnancies that were conceived spontaneously (n = 74), with NIFT (n = 33), or with IVF (n = 34), resulting in the delivery of viable offspring.

INTERVENTION(S)

Collection of chorionic villus samples from women who conceived spontaneously, with NIFT, or with IVF for gene expression analysis using RNA sequencing.

MAIN OUTCOME MEASURE(S)

Baseline maternal, paternal, and fetal demographics, maternal medical conditions, pregnancy complications, and outcomes. Differential gene expression of first-trimester placenta.

RESULT(S)

There were few differences in the transcriptome of first-trimester placenta from NIFT, IVF, and spontaneous pregnancies. There was one protein-coding differentially expressed gene (DEG) between the spontaneous and infertility groups, CACNA1I, one protein-coding DEG between the spontaneous and IVF groups, CACNA1I, and five protein-coding DEGs between the NIFT and IVF groups, SLC18A2, CCL21, FXYD2, PAEP, and DNER.

CONCLUSION(S)

This is the first and largest study looking at transcriptomic profiles of first-trimester placenta demonstrating similar transcriptomic profiles in pregnancies conceived using NIFT or IVF and spontaneous conceptions. Gene expression differences found to be highest in the NIFT group suggest that the underlying infertility, in addition to treatment-related factors, may contribute to the observed gene expression profiles.

Single limb immobilization model for bone loss from unloading

Hindlimb suspension is the most used model for inducing bone loss from unloading but requires a separate ground control group. This control group cannot be used for genetic studies involving outbred mice. In this study, we evaluated a single limb immobilization (SLI) model for inducing bone loss from unloading, with the contralateral limb from the same animal used as a control. Male 10-week old C57Bl/6J mice had one limb immobilized for one, two, or three weeks. Subsequently, an additional group of male 16-week old C57Bl/6J mice had one limb immobilized for three weeks. SLI resulted in decreased tibial trabecular BV/TV, Tb Th, and Tb N compared to contralateral limbs in young mice. Femoral trabecular BV/TV, Tb Th, Tb N, and femoral cortical area fraction were also decreased. Mechanical properties were not affected after three weeks. In adult mice, femoral trabecular BV/TV, Tb Th, and Tb N were decreased. Femoral stiffness, ultimate stress, and Young's modulus were decreased. Bone properties decreased by SLI were also decreased by hindlimb suspension previously. The results suggest SLI can be an effective model for inducing bone loss in growing and adult mice after three weeks of immobilization.

Dissecting the Genetics of Osteoporosis using Systems Approaches

Osteoporosis is a condition characterized by low bone mineral density (BMD) and an increased risk of fracture. Traits contributing to osteoporotic fracture are highly heritable, indicating that a comprehensive understanding of bone requires a thorough understanding of the genetic basis of bone traits. Towards this goal, genome-wide association studies (GWASs) have identified over 500 loci associated with bone traits. However, few of the responsible genes have been identified, and little is known of how these genes work together to influence systems-level bone function. In this review, we describe how systems genetics approaches can be used to fill these knowledge gaps.

Sex differences in the late first trimester human placenta transcriptome

Background

Development of the placenta during the late first trimester is critical to ensure normal growth and development of the fetus. Developmental differences in this window such as sex-specific variation are implicated in later placental disease states, yet gene expression at this time is poorly understood.

Methods

RNA-sequencing was performed to characterize the transcriptome of 39 first trimester human placentas using chorionic villi following genetic testing (17 females, 22 males). Gene enrichment analysis was performed to find enriched canonical pathways and gene ontologies in the first trimester. DESeq2 was used to find sexually dimorphic gene expression. Patient demographics were analyzed for sex differences in fetal weight at time of chorionic villus sampling and birth.

Results

RNA-sequencing analyses detected 14,250 expressed genes, with chromosome 19 contributing the greatest proportion (973/2852, 34.1% of chromosome 19 genes) and Y chromosome contributing the least (16/568, 2.8%). Several placenta-enriched genes as well as histone-coding genes were identified to be unique to the first trimester and common to both sexes. Further, we identified 58 genes with significantly different expression between males and females: 25 X-linked, 15 Y-linked, and 18 autosomal genes. Genes that escape X inactivation were highly represented (59.1%) among X-linked genes upregulated in females. Many genes differentially expressed by sex consisted of X/Y gene pairs, suggesting that dosage compensation plays a role in sex differences. These X/Y pairs had roles in parallel, ancient canonical pathways important for eukaryotic cell growth and survival: chromatin modification, transcription, splicing, and translation.

Conclusions

This study is the first characterization of the late first trimester placenta transcriptome, highlighting similarities and differences among the sexes in ongoing human pregnancies resulting in live births. Sexual dimorphism may contribute to pregnancy outcomes, including fetal growth and birth weight, which was seen in our cohort, with males significantly heavier than females at birth. This transcriptome provides a basis for development of early diagnostic tests of placental function that can indicate overall pregnancy heath, fetal-maternal health, and long-term adult health.

Electronic supplementary material

The online version of this article (10.1186/s13293-018-0165-y) contains supplementary material, which is available to authorized users.

A MicroRNA93-Interferon Regulatory Factor-9-Immunoresponsive Gene-1-Itaconic Acid Pathway Modulates M2-Like Macrophage Polarization to Revascularize Ischemic Muscle

BACKGROUND

Currently, no therapies exist for treating and improving outcomes in patients with severe peripheral artery disease (PAD). MicroRNA93 (miR93) has been shown to favorably modulate angiogenesis and to reduce tissue loss in genetic PAD models. However, the cell-specific function, downstream mechanisms, or signaling involved in miR93-mediated ischemic muscle neovascularization is not clear. Macrophages were best known to modulate arteriogenic response in PAD, and the extent of arteriogenic response induced by macrophages is dependent on greater M2 to M1 activation/polarization state. In the present study, we identified a novel mechanism by which miR93 regulates macrophage polarization to promote angiogenesis and arteriogenesis to revascularize ischemic muscle in experimental PAD.

METHODS

In vitro (macrophages, endothelial cells, skeletal muscle cells under normal and hypoxia serum starvation conditions) and in vivo experiments in preclinical PAD models (unilateral femoral artery ligation and resection) were conducted to examine the role of miR93-interferon regulatory factor-9-immunoresponsive gene-1 (IRG1)-itaconic acid pathway in macrophage polarization, angiogenesis, arteriogenesis, and perfusion recovery.

RESULTS

In vivo, compared with wild-type controls, miR106b-93-25 cluster-deficient mice (miR106b-93-25^-/-) showed decreased angiogenesis and arteriogenesis correlating with increased M1-like macrophages after experimental PAD. Intramuscular delivery of miR93 in miR106b-93-25^-/- PAD mice increased angiogenesis, arteriogenesis, and the extent of perfusion, which correlated with more M2-like macrophages in the proximal and distal hind-limb muscles. In vitro, miR93 promotes and sustains M2-like polarization even under M1-like polarizing conditions (hypoxia serum starvation). Delivery of bone marrow-derived macrophages from miR106b-93-25^-/- to wild-type ischemic muscle decreased angiogenesis, arteriogenesis, and perfusion, whereas transfer of wild-type macrophages to miR106b-93-25^-/- had the opposite effect. Systematic analysis of top differentially upregulated genes from RNA sequencing between miR106b-93-25^-/- and wild-type ischemic muscle showed that miR93 regulates IRG1 function to modulate itaconic acid production and macrophage polarization. The 3' untranslated region luciferase assays performed to determine whether IRG1 is a direct target of miR93 revealed that IRG1 is not an miR93 target but that interferon regulatory factor-9, which can regulate IRG1 expression, is an miR93 target. In vitro, increased expression of interferon regulatory factor-9 and IRG1 and itaconic acid treatment significantly decreased endothelial angiogenic potential.

CONCLUSIONS

miR93 inhibits interferon regulatory factor-9 to decrease IRG1-itaconic acid production to induce M2-like polarization in ischemic muscle to enhance angiogenesis, arteriogenesis, and perfusion recovery in experimental PAD.

Using GWAS to identify novel therapeutic targets for osteoporosis

Osteoporosis is a common, increasingly prevalent, global health burden characterized by low bone mineral density (BMD) and increased risk of fracture. Despite its significant impact on human health, there is currently a lack of highly effective treatments free of side effects for osteoporosis. Therefore, a major goal in the field is to identify new drug targets. Genetic discovery has been shown to be effective in the unbiased identification of novel drug targets and genome-wide association studies (GWASs) have begun to provide insight into genetic basis of osteoporosis. Over the last decade, GWASs have led to the identification of ∼100 loci associated with BMD and other bone traits related to risk of fracture. However, there have been limited efforts to identify the causal genes underlying the GWAS loci or the mechanisms by which GWAS loci alter bone physiology. In this review, we summarize the current state of the field and discuss strategies for causal gene discovery and the evidence that the novel genes underlying GWAS loci are likely to be a new source of drug targets.

Integrating GWAS and Co-expression Network Data Identifies Bone Mineral Density Genes SPTBN1 and MARK3 and an Osteoblast Functional Module

Bone mineral density (BMD) is a highly heritable predictor of osteoporotic fracture. Genome-wide association studies (GWAS) for BMD have identified dozens of associations; yet, the genes responsible for most associations remain elusive. Here, we used a bone co-expression network to predict causal genes at BMD GWAS loci based on the premise that genes underlying a disease are often functionally related and functionally related genes are often co-expressed. By mapping genes implicated by BMD GWAS onto a bone co-expression network, we predicted and inferred the function of causal genes for 30 of 64 GWAS loci. We experimentally confirmed that two of the genes predicted to be causal, SPTBN1 and MARK3, are potentially responsible for the effects of GWAS loci on chromosomes 2p16.2 and 14q32.32, respectively. This approach provides a roadmap for the dissection of additional BMD GWAS associations. Furthermore, it should be applicable to GWAS data for a wide range of diseases.

Optimization of techniques for multiple platform testing in small, precious samples such as human chorionic villus sampling

BACKGROUND

Multiple testing to understand global changes in gene expression based on genetic and epigenetic modifications is evolving. Chorionic villi, obtained for prenatal testing, is limited, but can be used to understand ongoing human pregnancies. However, optimal storage, processing and utilization of CVS for multiple platform testing have not been established.

RESULTS

Leftover CVS samples were flash-frozen or preserved in RNAlater. Modifications to standard isolation kits were performed to isolate quality DNA and RNA from samples as small as 2-5 mg. RNAlater samples had significantly higher RNA yields and quality and were successfully used in microarray and RNA-sequencing (RNA-seq). RNA-seq libraries generated using 200 versus 800-ng RNA showed similar biological coefficients of variation. RNAlater samples had lower DNA yields and quality, which improved by heating the elution buffer to 70 °C. Purification of DNA was not necessary for bisulfite-conversion and genome-wide methylation profiling. CVS cells were propagated and continue to express genes found in freshly isolated chorionic villi.

CONCLUSIONS

CVS samples preserved in RNAlater are superior. Our optimized techniques provide specimens for genetic, epigenetic and gene expression studies from a single small sample which can be used to develop diagnostics and treatments using a systems biology approach in the prenatal period. © 2016 John Wiley & Sons, Ltd.

The Hybrid Mouse Diversity Panel: a resource for systems genetics analyses of metabolic and cardiovascular traits

The Hybrid Mouse Diversity Panel (HMDP) is a collection of approximately 100 well-characterized inbred strains of mice that can be used to analyze the genetic and environmental factors underlying complex traits. While not nearly as powerful for mapping genetic loci contributing to the traits as human genome-wide association studies, it has some important advantages. First, environmental factors can be controlled. Second, relevant tissues are accessible for global molecular phenotyping. Finally, because inbred strains are renewable, results from separate studies can be integrated. Thus far, the HMDP has been studied for traits relevant to obesity, diabetes, atherosclerosis, osteoporosis, heart failure, immune regulation, fatty liver disease, and host-gut microbiota interactions. High-throughput technologies have been used to examine the genomes, epigenomes, transcriptomes, proteomes, metabolomes, and microbiomes of the mice under various environmental conditions. All of the published data are available and can be readily used to formulate hypotheses about genes, pathways and interactions.

Genomic Modifiers of Natural Killer Cells, Immune Responsiveness and Lymphoid Tissue Remodeling Together Increase Host Resistance to Viral Infection

The MHC class I D^k molecule supplies vital host resistance during murine cytomegalovirus (MCMV) infection. Natural killer (NK) cells expressing the Ly49G2 inhibitory receptor, which specifically binds D^k, are required to control viral spread. The extent of D^k-dependent host resistance, however, differs significantly amongst related strains of mice, C57L and MA/My. As a result, we predicted that relatively small-effect modifier genetic loci might together shape immune cell features, NK cell reactivity, and the host immune response to MCMV. A robust D^k-dependent genetic effect, however, has so far hindered attempts to identify additional host resistance factors. Thus, we applied genomic mapping strategies and multicolor flow cytometric analysis of immune cells in naive and virus-infected hosts to identify genetic modifiers of the host immune response to MCMV. We discovered and validated many quantitative trait loci (QTL); these were mapped to at least 19 positions on 16 chromosomes. Intriguingly, one newly discovered non-MHC locus (Cmv5) controlled splenic NK cell accrual, secondary lymphoid organ structure, and lymphoid follicle development during MCMV infection. We infer that Cmv5 aids host resistance to MCMV infection by expanding NK cells needed to preserve and protect essential tissue structural elements, to enhance lymphoid remodeling and to increase viral clearance in spleen.

Uncovering the genetic basis of resistance to viral infection and disease is critical to learning about how immune defenses might be adjusted, how to design better vaccines, and how to elicit effectual immune protection in human populations. Prior studies have shown that both MHC and non-MHC genes support host defenses, or endow specialized immune cells with efficient sensing or responsiveness to infection. Many additional resistance genes remain to be identified, including difficult to detect smaller-effect alleles, which might add to or interact with other genetic factors. Our grasp of the complex interaction involving these genetic elements is thus inadequate. We combined genomic and multiparameter phenotypic analyses to map and identify host genes that control immune cells or sensitivity to viral infection. We reasoned that some might also affect viral clearance. Thus we enumerated a range of immune cell traits in mice before and after infection, which permitted genomic analysis of viral immunity, and mapping of genetic modifiers for each trait. Our study demonstrates that distinct loci collectively regulate both NK cells and host resistance, which provides a framework to understand the genetic interactions, and a variety of potential novel targets to adjust NK cell functionality and host resistance to infection.

ADAM12: a genetic modifier of preclinical peripheral arterial disease

In prior studies from multiple groups, outcomes following experimental peripheral arterial disease (PAD) differed considerably across inbred mouse strains. Similarly, in humans with PAD, disease outcomes differ, even when there are similarities in risk factors, disease anatomy, arteriosclerotic burden, and hemodynamic measures. Previously, we identified a locus on mouse chromosome 7, limb salvage-associated quantitative trait locus 1 (LSq-1), which was sufficient to modify outcomes following experimental PAD. We compared expression of genes within LSq-1 in Balb/c mice, which normally show poor outcomes following experimental PAD, with that in C57Bl/6 mice, which normally show favorable outcomes, and found that a disintegrin and metalloproteinase gene 12 (ADAM12) had the most differential expression. Augmentation of ADAM12 expression in vivo improved outcomes following experimental PAD in Balb/c mice, whereas knockdown of ADAM12 made outcomes worse in C57Bl/6 mice. In vitro, ADAM12 expression modulates endothelial cell proliferation, survival, and angiogenesis in ischemia, and this appeared to be dependent on tyrosine kinase with Ig-like and EGF-like domain 2 (Tie2) activation. ADAM12 is sufficient to modify PAD severity in mice, and this likely occurs through regulation of Tie2.

Overlapping mouse subcongenic strains successfully separate two linked body fat QTL on distal MMU 2

BACKGROUND

Mouse chromosome 2 is linked to growth and body fat phenotypes in many mouse crosses. With the goal to identify the underlying genes regulating growth and body fat on mouse chromosome 2, we developed five overlapping subcongenic strains that contained CAST/EiJ donor regions in a C57BL/6J (hg/hg) background (hg is a spontaneous deletion of 500 Kb on mouse chromosome 10). To fine map QTL on distal mouse chromosome 2 a total of 1,712 F2 mice from the five subcongenic strains, plus 278 F2 mice from the HG2D founder congenic strain were phenotyped and analyzed. Interval mapping (IM) and composite IM (CIM) were performed on body weight and body fat traits on a combination of SNP and microsatellite markers, which generated a high-density genotyping panel.

RESULTS

Phenotypic analysis and interval mapping of total fat mass identified two QTL on distal mouse chromosome 2. One QTL between 150 and 161 Mb, Fatq2a, and the second between 173.3 and 175.6 Mb, Fatq2b. The two QTL reside in different congenic strains with significant total fat differences between homozygous cast/cast and b6/b6 littermates. Both of these QTL were previously identified only as a single QTL affecting body fat, Fatq2. Furthermore, through a novel approach referred here as replicated CIM, Fatq2b was mapped to the Gnas imprinted locus.

CONCLUSIONS

The integration of subcongenic strains, high-density genotyping, and CIM succesfully partitioned two previously linked QTL 20 Mb apart, and the strongest QTL, Fatq2b, was fine mapped to a ~2.3 Mb region interval encompassing the Gnas imprinted locus.

A novel IFITM5 mutation in severe atypical osteogenesis imperfecta type VI impairs osteoblast production of pigment epithelium-derived factor

Osteogenesis imperfecta (OI) types V and VI are caused, respectively, by a unique dominant mutation in IFITM5, encoding BRIL, a transmembrane ifitm-like protein most strongly expressed in the skeletal system, and recessive null mutations in SERPINF1, encoding pigment epithelium-derived factor (PEDF). We identified a 25-year-old woman with severe OI whose dermal fibroblasts and cultured osteoblasts displayed minimal secretion of PEDF, but whose serum PEDF level was in the normal range. SERPINF1 sequences were normal despite bone histomorphometry consistent with type VI OI and elevated childhood serum alkaline phosphatase. We performed exome sequencing on the proband, both parents, and an unaffected sibling. IFITM5 emerged as the candidate gene from bioinformatics analysis, and was corroborated by membership in a murine bone co-expression network module containing all currently known OI genes. The de novo IFITM5 mutation was confirmed in one allele of the proband, resulting in a p.S40L substitution in the intracellular domain of BRIL but was absent in unaffected family members. IFITM5 expression was normal in proband fibroblasts and osteoblasts, and BRIL protein level was similar to control in differentiated proband osteoblasts on Western blot and in permeabilized mutant osteoblasts by microscopy. In contrast, SERPINF1 expression was decreased in proband osteoblasts; PEDF was barely detectable in conditioned media of proband cells. Expression and secretion of type I collagen was similarly decreased in proband osteoblasts; the expression pattern of several osteoblast markers largely overlapped reported values from cells with a primary PEDF defect. In contrast, osteoblasts from a typical case of type V OI, with an activating mutation at the 5'-terminus of BRIL, have increased SERPINF1 expression and PEDF secretion during osteoblast differentiation. Together, these data suggest that BRIL and PEDF have a relationship that connects the genes for types V and VI OI and their roles in bone mineralization.

Bioenergetics during calvarial osteoblast differentiation reflect strain differences in bone mass

Osteoblastogenesis is the process by which mesenchymal stem cells differentiate into osteoblasts that synthesize collagen and mineralize matrix. The pace and magnitude of this process are determined by multiple genetic and environmental factors. Two inbred strains of mice, C3H/HeJ and C57BL/6J, exhibit differences in peak bone mass and bone formation. Although all the heritable factors that differ between these strains have not been elucidated, a recent F1 hybrid expression panel (C3H × B6) revealed major genotypic differences in osteoblastic genes related to cellular respiration and oxidative phosphorylation. Thus, we hypothesized that the metabolic rate of energy utilization by osteoblasts differed by strain and would ultimately contribute to differences in bone formation. In order to study the bioenergetic profile of osteoblasts, we measured oxygen consumption rates (OCR) and extracellular acidification rates (ECAR) first in a preosteoblastic cell line MC3T3-E1C4 and subsequently in primary calvarial osteoblasts from C3H and B6 mice at days 7, 14, and 21 of differentiation. During osteoblast differentiation in media containing ascorbic acid and β-glycerophosphate, all 3 cell types increased their oxygen consumption and extracellular acidification rates compared with the same cells grown in regular media. These increases are sustained throughout differentiation. Importantly, C3H calvarial osteoblasts had greater oxygen consumption rates than B6 consistent with their in vivo phenotype of higher bone formation. Interestingly, osteoblasts utilized both oxidative phosphorylation and glycolysis during the differentiation process although mature osteoblasts were more dependent on glycolysis at the 21-day time point than oxidative phosphorylation. Thus, determinants of oxygen consumption reflect strain differences in bone mass and provide the first evidence that during collagen synthesis osteoblasts use both glycolysis and oxidative phosphorylation to synthesize and mineralize matrix.

Bicc1 is a genetic determinant of osteoblastogenesis and bone mineral density

Patient bone mineral density (BMD) predicts the likelihood of osteoporotic fracture. While substantial progress has been made toward elucidating the genetic determinants of BMD, our understanding of the factors involved remains incomplete. Here, using a systems genetics approach in the mouse, we predicted that bicaudal C homolog 1 (Bicc1), which encodes an RNA-binding protein, is responsible for a BMD quantitative trait locus (QTL) located on murine chromosome 10. Consistent with this prediction, mice heterozygous for a null allele of Bicc1 had low BMD. We used a coexpression network-based approach to determine how Bicc1 influences BMD. Based on this analysis, we inferred that Bicc1 was involved in osteoblast differentiation and that polycystic kidney disease 2 (Pkd2) was a downstream target of Bicc1. Knock down of Bicc1 and Pkd2 impaired osteoblastogenesis, and Bicc1 deficiency-dependent osteoblast defects were rescued by Pkd2 overexpression. Last, in 2 human BMD genome-wide association (GWAS) meta-analyses, we identified SNPs in BICC1 and PKD2 that were associated with BMD. These results, in both mice and humans, identify Bicc1 as a genetic determinant of osteoblastogenesis and BMD and suggest that it does so by regulating Pkd2 transcript levels.

Glucagon regulates hepatic kisspeptin to impair insulin secretion

Early in the pathogenesis of type 2 diabetes mellitus (T2DM), dysregulated glucagon secretion from pancreatic α cells occurs prior to impaired glucose-stimulated insulin secretion (GSIS) from β cells. However, whether hyperglucagonemia is causally linked to β cell dysfunction remains unclear. Here we show that glucagon stimulates via cAMP-PKA-CREB signaling hepatic production of the neuropeptide kisspeptin1, which acts on β cells to suppress GSIS. Synthetic kisspeptin suppresses GSIS in vivo in mice and from isolated islets in a kisspeptin1 receptor-dependent manner. Kisspeptin1 is increased in livers and in serum from humans with T2DM and from mouse models of diabetes mellitus. Importantly, liver Kiss1 knockdown in hyperglucagonemic, glucose-intolerant, high-fat-diet fed, and Lepr(db/db) mice augments GSIS and improves glucose tolerance. These observations indicate a hormonal circuit between the liver and the endocrine pancreas in glycemia regulation and suggest in T2DM a sequential link between hyperglucagonemia via hepatic kisspeptin1 to impaired insulin secretion.