Obesity-associated family with sequence similarity 13, member A (FAM13A) is dispensable for adipose development and insulin sensitivity

Breathing new life into the study of COPD with genes identified from genome-wide association studies

COPD is a major cause of morbidity and mortality globally. While the significance of environmental exposures in disease pathogenesis is well established, the functional contribution of genetic factors has only in recent years drawn attention. Notably, many genes associated with COPD risk are also linked with lung function. Because reduced lung function precedes COPD onset, this association is consistent with the possibility that derangements leading to COPD could arise during lung development. In this review, we summarise the role of leading genes (HHIP, FAM13A, DSP, AGER and TGFB2) identified by genome-wide association studies in lung development and COPD. Because many COPD genome-wide association study genes are enriched in lung epithelial cells, we focus on the role of these genes in the lung epithelium in development, homeostasis and injury.

Comprehensive genetic study of the insulin resistance marker TG:HDL-C in the UK Biobank

Insulin resistance (IR) is a well-established risk factor for metabolic disease. The ratio of triglycerides to high-density lipoprotein cholesterol (TG:HDL-C) is a surrogate marker of IR. We conducted a genome-wide association study of the TG:HDL-C ratio in 402,398 Europeans within the UK Biobank. We identified 369 independent SNPs, of which 114 had a false discovery rate-adjusted P value < 0.05 in other genome-wide studies of IR making them high-confidence IR-associated loci. Seventy-two of these 114 loci have not been previously associated with IR. These 114 loci cluster into five groups upon phenome-wide analysis and are enriched for candidate genes important in insulin signaling, adipocyte physiology and protein metabolism. We created a polygenic-risk score from the high-confidence IR-associated loci using 51,550 European individuals in the Michigan Genomics Initiative. We identified associations with diabetes, hyperglyceridemia, hypertension, nonalcoholic fatty liver disease and ischemic heart disease. Collectively, this study provides insight into the genes, pathways, tissues and subtypes critical in IR.

The impact of SNP density on quantitative genetic analyses of body size traits in a wild population of Soay sheep

Understanding the genetic architecture underpinning quantitative traits in wild populations is pivotal to understanding the processes behind trait evolution. The 'animal model' is a popular method for estimating quantitative genetic parameters such as heritability and genetic correlation and involves fitting an estimate of relatedness between individuals in the study population. Genotypes at genome-wide markers can be used to estimate relatedness; however, relatedness estimates vary with marker density, potentially affecting results. Increasing density of markers is also expected to increase the power to detect quantitative trait loci (QTL). In order to understand how the density of genetic markers affects the results of quantitative genetic analyses, we estimated heritability and performed genome-wide association studies (GWAS) on five body size traits in an unmanaged population of Soay sheep using two different SNP densities: a dataset of 37,037 genotyped SNPs and an imputed dataset of 417,373 SNPs. Heritability estimates did not differ between the two SNP densities, but the high-density imputed SNP dataset revealed four new SNP-trait associations that were not found with the lower density dataset, as well as confirming all previously-found QTL. We also demonstrated that fitting fixed and random effects in the same step as performing GWAS is a more powerful approach than pre-correcting for covariates in a separate model.

Epigenomic and Transcriptomic Prioritization of Candidate Obesity-Risk Regulatory GWAS SNPs

Concern about rising rates of obesity has prompted searches for obesity-related single nucleotide polymorphisms (SNPs) in genome-wide association studies (GWAS). Identifying plausible regulatory SNPs is very difficult partially because of linkage disequilibrium. We used an unusual epigenomic and transcriptomic analysis of obesity GWAS-derived SNPs in adipose versus heterologous tissues. From 50 GWAS and 121,064 expanded SNPs, we prioritized 47 potential causal regulatory SNPs (Tier-1 SNPs) for 14 gene loci. A detailed examination of seven loci revealed that four (CABLES1, PC, PEMT, and FAM13A) had Tier-1 SNPs positioned so that they could regulate use of alternative transcription start sites, resulting in different polypeptides being generated or different amounts of an intronic microRNA gene being expressed. HOXA11 and long noncoding RNA gene RP11-392O17.1 had Tier-1 SNPs in their 3' or promoter region, respectively, and strong preferences for expression in subcutaneous versus visceral adipose tissue. ZBED3-AS1 had two intragenic Tier-1 SNPs, each of which could contribute to mediating obesity risk through modulating long-distance chromatin interactions. Our approach not only revealed especially credible novel regulatory SNPs, but also helped evaluate previously highlighted obesity GWAS SNPs that were candidates for transcription regulation.

Adipocyte Biology from the Perspective of In Vivo Research: Review of Key Transcription Factors

Obesity and type 2 diabetes are both significant contributors to the contemporary pandemic of non-communicable diseases. Both disorders are interconnected and associated with the disruption of normal homeostasis in adipose tissue. Consequently, exploring adipose tissue differentiation and homeostasis is important for the treatment and prevention of metabolic disorders. The aim of this work is to review the consecutive steps in the postnatal development of adipocytes, with a special emphasis on in vivo studies. We gave particular attention to well-known transcription factors that had been thoroughly described in vitro, and showed that the in vivo research of adipogenic differentiation can lead to surprising findings.

miR‑30a‑5p induces the adipogenic differentiation of bone marrow mesenchymal stem cells by targeting FAM13A/Wnt/β‑catenin signaling in aplastic anemia

Aplastic anemia (AA) is a bone marrow failure syndrome with high morbidity and mortality. Bone marrow (BM)-mesenchymal stem cells (MSCs) are the main components of the BM microenvironment, and dysregulation of BM-MSC adipogenic differentiation is a pathologic hallmark of AA. MicroRNAs (miRNAs/miRs) are crucial regulators of multiple pathological processes such as AA. However, the role of miR-30a-5p in the modulation of BM-MSC adipogenic differentiation in AA remains unclear. The present study aimed to explore the effect of miR-30a-5p on AA BM-MSC adipogenic differentiation and the underlying mechanism. The levels of miR-30a-5p expression and family with sequence similarity 13, member A (FAM13A) mRNA expression in BM-MSCs were quantified using reverse transcription-quantitative (RT-q) PCR. The mRNA expression levels of adipogenesis-associated factors [fatty acid-binding protein 4 (FABP4), lipoprotein lipase (LPL), perilipin-1 (PLIN1), peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT/enhancer binding protein α (C/EBPα)] were analyzed using RT-qPCR. Lipid droplet accumulation was evaluated using Oil Red O staining in BM-MSCs. The interaction between miR-30a-5p and the FAM13A 3′-untranslated region was identified by TargetScan, and a dual-luciferase reporter assay was used to confirm the interaction. The expression levels of FAM13A and Wnt/β-catenin pathway-related proteins were examined via western blotting. The results showed that miR-30a-5p expression levels were significantly elevated in BM-MSCs from patients with AA compared with those in control subjects (iron deficiency anemia). miR-30a-5p expression levels were also significantly increased in adipose-induced BM-MSCs in a time-dependent manner. miR-30a-5p significantly promoted AA BM-MSC adipogenic differentiation, and significantly enhanced the mRNA expression levels of FABP4, LPL, PLIN1, PPARγ and C/EBPα as well as lipid droplet accumulation. miR-30a-5p was also demonstrated to target FAM13A in AA BM-MSCs. FAM13A significantly reduced BM-MSC adipogenic differentiation by activating the Wnt/β-catenin signaling pathway. In conclusion, miR-30a-5p was demonstrated to serve a role in AA BM-MSC adipogenic differentiation by targeting the FAM13A/Wnt/β-catenin signaling pathway. These findings suggest that miR-30a-5p may be a therapeutic target for AA.

Dysmetabolic adipose tissue in obesity: morphological and functional characteristics of adipose stem cells and mature adipocytes in healthy and unhealthy obese subjects

The way by which subcutaneous adipose tissue (SAT) expands and undergoes remodeling by storing excess lipids through expansion of adipocytes (hypertrophy) or recruitment of new precursor cells (hyperplasia) impacts the risk of developing cardiometabolic and respiratory diseases. In unhealthy obese subjects, insulin resistance, type 2 diabetes, hypertension, and obstructive sleep apnoea are typically associated with pathologic SAT remodeling characterized by adipocyte hypertrophy, as well as chronic inflammation, hypoxia, increased visceral adipose tissue (VAT), and fatty liver. In contrast, metabolically healthy obese individuals are generally associated with SAT development characterized by the presence of smaller and numerous mature adipocytes, and a lower degree of VAT inflammation and ectopic fat accumulation. The remodeling of SAT and VAT is under genetic regulation and influenced by inherent depot-specific differences of adipose tissue-derived stem cells (ASCs). ASCs have multiple functions such as cell renewal, adipogenic capacity, and angiogenic properties, and secrete a variety of bioactive molecules involved in vascular and extracellular matrix remodeling. Understanding the mechanisms regulating the proliferative and adipogenic capacity of ASCs from SAT and VAT in response to excess calorie intake has become a focus of interest over recent decades. Here, we summarize current knowledge about the biological mechanisms able to foster or impair the recruitment and adipogenic differentiation of ASCs during SAT and VAT development, which regulate body fat distribution and favorable or unfavorable metabolic responses.

Loss of family with sequence similarity 107, member A (FAM107A) induces browning in 3T3-L1 adipocytes

Induction of white fat browning (beiging) and activation of brown fat has been considered a promising strategy to treat obesity and associated metabolic complications. However, the molecular mechanisms regulating brown and beige fat-mediated thermogenesis remains unclear. Our study aimed to identify genes with a hitherto unknown mechanism in the metabolic functions of adipocytes and identified family with sequence similarity 107, member A (FAM107A) as a factor that interferes with fat browning in white adipocytes. We explored physiological roles of FAM107A in cultured 3T3-L1 white adipocytes and HIB1B brown adipocytes by using FAM107A-deficient adipocytes. Significant loss in FAM107A gene functionality induced fat browning was evidenced by evaluating the gene and protein expression level of brown fat-associated markers through real-time qRT-PCR and immunoblot analysis, respectively. Deficiency of FAM107A promoted mitochondrial biogenesis and significantly upregulated core fat-browning marker proteins (PGC-1α, PRDM16, and UCP1) and beige-specific genes (Cd137, Cited1, Tbx1, and Tmem26). Furthermore, FAM107A increased adipogenesis and negatively regulated lipid metabolism in 3T3-L1 adipocytes. In addition, in-silico analysis revealed a strong interaction between FAM107A and β3-AR based on their energy binding score. Next, mechanistic study revealed that specific knockdown of FAM107A induces browning in white adipocytes via activation of β3-AR, AMPK and p38 MAPK-dependent signaling pathways. Our data unveiled a previously unknown mechanism of FAM107A in the regulation of lipid metabolism and identified its significant role in metabolic homeostasis. This highlighted the potential of FAM107A as a pharmacotherapeutic target in treating obesity and related metabolic disorders.

Photoacoustic molecular imaging-escorted adipose photodynamic-browning synergy for fighting obesity with virus-like complexes

Photodynamic therapy and adipose browning induction are two promising approaches to reverse obesity. The former strategy acts rapidly and locally, whereas the latter has a more gradual and widespread effect. Despite their complementarity, they have rarely been combined and imaged non-invasively in vivo. Here we introduce an adipose-targeting hepatitis B core protein complex that contains a traceable photosensitizer (ZnPcS₄ (zinc phthalocyanine tetrasulfonate)) and a browning agent (rosiglitazone) that allows simultaneous photodynamic and browning treatments, with photoacoustic molecular imaging. After intravenous injection in obese mice, the complex binds specifically to white adipose tissues, especially those rich in blood supply, and drives adipose reduction thanks to the synergy of ZnPcS₄ photodynamics and rosiglitazone browning. Using photoacoustic molecular imaging, we could monitor the changes induced by the treatment, which included complex activity, lipid catabolism and angiogenesis. Our findings demonstrate the anti-obesity potential of our feedback-based synergic regimen orchestrated by the targeted hepatitis B core complex.

FAM13A Represses AMPK Activity and Regulates Hepatic Glucose and Lipid Metabolism

Obesity commonly co-exists with fatty liver disease with increasing health burden worldwide. Family with Sequence Similarity 13, Member A (FAM13A) has been associated with lipid levels and fat mass by genome-wide association studies (GWAS). However, the function of FAM13A in maintaining metabolic homeostasis in vivo remains unclear. Here, we demonstrated that rs2276936 in this locus has allelic-enhancer activity in massively parallel reporter assays (MPRA) and reporter assay. The DNA region containing rs2276936 regulates expression of endogenous FAM13A in HepG2 cells. In vivo, Fam13a-/- mice are protected from high-fat diet (HFD)-induced fatty liver accompanied by increased insulin sensitivity and reduced glucose production in liver. Mechanistically, loss of Fam13a led to the activation of AMP-activated protein kinase (AMPK) and increased mitochondrial respiration in primary hepatocytes. These findings demonstrate that FAM13A mediates obesity-related dysregulation of lipid and glucose homeostasis. Targeting FAM13A might be a promising treatment of obesity and fatty liver disease.

FAM13A affects body fat distribution and adipocyte function

Genetic variation in the FAM13A (Family with Sequence Similarity 13 Member A) locus has been associated with several glycemic and metabolic traits in genome-wide association studies (GWAS). Here, we demonstrate that in humans, FAM13A alleles are associated with increased FAM13A expression in subcutaneous adipose tissue (SAT) and an insulin resistance-related phenotype (e.g. higher waist-to-hip ratio and fasting insulin levels, but lower body fat). In human adipocyte models, knockdown of FAM13A in preadipocytes accelerates adipocyte differentiation. In mice, Fam13a knockout (KO) have a lower visceral to subcutaneous fat (VAT/SAT) ratio after high-fat diet challenge, in comparison to their wild-type counterparts. Subcutaneous adipocytes in KO mice show a size distribution shift toward an increased number of smaller adipocytes, along with an improved adipogenic potential. Our results indicate that GWAS-associated variants within the FAM13A locus alter adipose FAM13A expression, which in turn, regulates adipocyte differentiation and contribute to changes in body fat distribution.