Association between congenital defects in papillary outgrowth and functional obstruction in Crim1 mutant mice

Skeletal muscle transcriptome in healthy aging

Age-associated changes in gene expression in skeletal muscle of healthy individuals reflect accumulation of damage and compensatory adaptations to preserve tissue integrity. To characterize these changes, RNA was extracted and sequenced from muscle biopsies collected from 53 healthy individuals (22-83 years old) of the GESTALT study of the National Institute on Aging-NIH. Expression levels of 57,205 protein-coding and non-coding RNAs were studied as a function of aging by linear and negative binomial regression models. From both models, 1134 RNAs changed significantly with age. The most differentially abundant mRNAs encoded proteins implicated in several age-related processes, including cellular senescence, insulin signaling, and myogenesis. Specific mRNA isoforms that changed significantly with age in skeletal muscle were enriched for proteins involved in oxidative phosphorylation and adipogenesis. Our study establishes a detailed framework of the global transcriptome and mRNA isoforms that govern muscle damage and homeostasis with age.

New Genetic Loci Associated With Chronic Kidney Disease in an Indigenous Australian Population

The common occurrence of renal disease in Australian Aboriginal populations such as Tiwi Islanders may be determined by environmental and genetic factors. To explore genetic contributions, we performed a genome-wide association study (GWAS) of urinary albumin creatinine ratio (ACR) in a sample of 249 Tiwi individuals with genotype data from a 370K Affymetrix single nucleotide polymorphism (SNP) array. A principal component analysis (PCA) of the 249 individual Tiwi cohort and samples from 11 populations included in phase III of the HapMap Project indicated that Tiwi Islanders are a relatively distinct and unique population with no close genetic relationships to the other ethnic groups. After adjusting for age and sex, the proportion of ACR variance explained by the 370K SNPs was estimated to be 37% (using the software GCTA.31; likelihood ratio = 8.06, p-value = 0.002). The GWAS identified eight SNPs that were nominally significantly associated with ACR (p < 0.0005). A replication study of these SNPs was performed in an independent cohort of 497 individuals on the eight SNPs. Four of these SNPs were significantly associated with ACR in the replication sample (p < 0.05), rs4016189 located near the CRIM1 gene (p = 0.000751), rs443816 located in the gene encoding UGT2B11 (p = 0.022), rs6461901 located near the NFE2L3 gene, and rs1535656 located in the RAB14 gene. The SNP rs4016189 was still significant after adjusting for multiple testing. A structural equation model (SEM) demonstrated that the rs4016189 SNP was not associated with other phenotypes such as estimated glomerular filtration rate (eGFR), diabetes, and blood pressure.

Prolonged prenatal hypoxia selectively disrupts collecting duct patterning and postnatal function in male mouse offspring

KEY POINTS

In the present study, we investigated whether hypoxia during late pregnancy impairs kidney development in mouse offspring, and also whether this has long-lasting consequences affecting kidney function in adulthood. Hypoxia disrupted growth of the kidney, particularly the collecting duct network, in juvenile male offspring. By mid-late adulthood, these mice developed early signs of kidney disease, notably a compromised response to water deprivation. Female offspring showed no obvious signs of impaired kidney development and did not develop kidney disease, suggesting an underlying protection mechanism from the hypoxia insult. These results help us better understand the long-lasting impact of gestational hypoxia on kidney development and the increased risk of chronic kidney disease.

ABSTRACT

Prenatal hypoxia is a common perturbation to arise during pregnancy, and can lead to adverse health outcomes in later life. The long-lasting impact of prenatal hypoxia on postnatal kidney development and maturation of the renal tubules, particularly the collecting duct system, is relatively unknown. In the present study, we used a model of moderate chronic maternal hypoxia throughout late gestation (12% O₂ exposure from embryonic day 14.5 until birth). Histological analyses revealed marked changes in the tubular architecture of male hypoxia-exposed neonates as early as postnatal day 7, with disrupted medullary development and altered expression of Ctnnb1 and Crabp2 (encoding a retinoic acid binding protein). Kidneys of the RARElacZ line offspring exposed to hypoxia showed reduced β-galactosidase activity, indicating reduced retinoic acid-directed transcriptional activation. Wild-type male mice exposed to hypoxia had an early decline in urine concentrating capacity, evident at 4 months of age. At 12 months of age, hypoxia-exposed male mice displayed a compromised response to a water deprivation challenge, which was was correlated with an altered cellular composition of the collecting duct and diminished expression of aquaporin 2. There were no differences in the tubular structures or urine concentrating capacity between the control and hypoxia-exposed female offspring at any age. The findings of the present study suggest that prenatal hypoxia selectively disrupts collecting duct patterning through altered Wnt/β-catenin and retinoic acid signalling and this results in impaired function in male mouse offspring in later life.

Neonatal vascularization and oxygen tension regulate appropriate perinatal renal medulla/papilla maturation

Congenital medullary dysplasia with obstructive nephropathy is a common congenital disorder observed in paediatric patients and represents the foremost cause of renal failure. However, the molecular processes regulating normal papillary outgrowth during the postnatal period are unclear. In this study, transcriptional profiling of the renal medulla across postnatal development revealed enrichment of non-canonical Wnt signalling, vascular development, and planar cell polarity genes, all of which may contribute to perinatal medulla/papilla maturation. These pathways were investigated in a model of papillary hypoplasia with functional obstruction, the Crim1(KST264/KST264) transgenic mouse. Postnatal elongation of the renal papilla via convergent extension was unaffected in the Crim1(KST264/KST264) hypoplastic renal papilla. In contrast, these mice displayed a disorganized papillary vascular network, tissue hypoxia, and elevated Vegfa expression. In addition, we demonstrate the involvement of accompanying systemic hypoxia arising from placental insufficiency, in appropriate papillary maturation. In conclusion, this study highlights the requirement for normal vascular development in collecting duct patterning, development of appropriate nephron architecture, and perinatal papillary maturation, such that disturbances contribute to obstructive nephropathy.

Improving our resolution of kidney morphogenesis across time and space

As with many mammalian organs, size and cellular complexity represent considerable challenges to the comprehensive analysis of kidney organogenesis. Traditional analyses in the mouse have revealed early patterning events and spatial cellular relationships. However, an understanding of later events is lacking. The generation of a comprehensive temporospatial atlas of gene expression during kidney development has facilitated advances in lineage definition, as well as selective compartment ablation. Advances in quantitative and dynamic imaging have allowed comprehensive analyses at the level of organ, component tissue and cell across kidney organogenesis. Such approaches will enhance our understanding of the links between kidney development and final postnatal organ function. The final frontier will be translating this understanding to outcomes for renal disease in humans.

Collecting duct-derived cells display mesenchymal stem cell properties and retain selective in vitro and in vivo epithelial capacity

We previously described a mesenchymal stem cell (MSC)-like population within the adult mouse kidney that displays long-term colony-forming efficiency, clonogenicity, immunosuppression, and panmesodermal potential. Although phenotypically similar to bone marrow (BM)-MSCs, kidney MSC-like cells display a distinct expression profile. FACS sorting from Hoxb7/enhanced green fluorescent protein (GFP) mice identified the collecting duct as a source of kidney MSC-like cells, with these cells undergoing an epithelial-to-mesenchymal transition to form clonogenic, long-term, self-renewing MSC-like cells. Notably, after extensive passage, kidney MSC-like cells selectively integrated into the aquaporin 2-positive medullary collecting duct when microinjected into the kidneys of neonatal mice. No epithelial integration was observed after injection of BM-MSCs. Indeed, kidney MSC-like cells retained a capacity to form epithelial structures in vitro and in vivo, and conditioned media from these cells supported epithelial repair in vitro. To investigate the origin of kidney MSC-like cells, we further examined Hoxb7(+) fractions within the kidney across postnatal development, identifying a neonatal interstitial GFP(lo) (Hoxb7(lo)) population displaying an expression profile intermediate between epithelium and interstitium. Temporal analyses with Wnt4(GCE/+):R26(tdTomato/+) mice revealed evidence for the intercalation of a Wnt4-expressing interstitial population into the neonatal collecting duct, suggesting that such intercalation may represent a normal developmental mechanism giving rise to a distinct collecting duct subpopulation. These results extend previous observations of papillary stem cell activity and collecting duct plasticity and imply a role for such cells in collecting duct formation and, possibly, repair.