Angiotensin II Type 2 Receptor (AT2R) in Glomerulogenesis

Epidemiologic data indicate that maternal diabetes significantly associates with congenital anomalies of the kidney and urinary tract (CAKUT), which implies an increased chance of CAKUT in the offspring of mothers with diabetes compared to the general population. The causes of CAKUT are multifactorial, involving genetic and environmental factors. The angiotensin II receptor type 2 (AT2R) is one of the candidate genes to be implicated in both human and murine CAKUT. Although numerous studies support the influence of genetic and environmental factors on kidney development and the pathogenesis of CAKUT, the impacts of the AT2R gene and hyperglycemic milieu in utero on kidney development and long-term outcomes in the offspring of diabetic mothers remain unclear. This thesis aims to investigate the influence of each factor individually, as well as their interaction. Firstly, we investigated whether AT2R deficiency (AT2R knock-out (KO)) impairs glomerulogenesis via podocytes formation, maturation and integrity. We observed that glomerulogenesis is decreased in AT2RKO embryos at embryonic day 15 (E15), but actual nephron numbers are no different between AT2RKO and wild-type newborn mice. AT2RKO mice exhibited renal dysplasia with lower glomerular tuft volume and reduced podocyte numbers at the age of three weeks. Our studies demonstrated that loss of AT2R via NADPH oxidase 4 (Nox4)-derived reactive oxygen species (ROS) generation stimulates ectopic hedgehog interacting protein (Hhip) expression, which further triggers either podocyte apoptosis by the activation of the caspase-3 and p53 pathways or podocyte epithelial–to– mesenchymal transition (EMT) by the activation of TGFβ1–Smad2/3 signaling. Glomerular Hhip mRNA is upregulated in kidney biopsies of patients with focal segmental glomerulosclerosis (FSGS). The results suggest that AT2R deficiency is associated with podocyte loss/dysfunction and is mediated, at least in part, via increased ectopic Hhip expression in podocytes. Secondly, we aimed to establish the underlying mechanisms by which a hyperglycemic milieu in utero and a post-weaning high-fat diet (HFD) accelerate the perinatal programming of kidney injury. We observed that the offspring of dams with severe maternal diabetes have an intrauterine growth restriction (IUGR) phenotype and develop mild hypertension and evidence of kidney injury in adulthood. Moreover, those offspring fed with a post-weaning HFD result in rapid catch-up growth and subsequent profound kidney injury associated with the augmentation of renal TGFβ1 and collagen type IV expression, increased production of ROS, and accumulation of renal lipids, but not systemic hypertension. In vitro studies demonstrated that HFD or free fatty acids accelerate the process of perinatal programming of kidney injury, via increased CD36 and fatty acid-binding protein 4 (Fabp4) expression, which targets ROS, nuclear factor-kappa B and TGFβ1 signaling. These results indicate that early postnatal exposure to HFD in IUGR offspring of diabetic dams increases the risk of later developing kidney injury, but not hypertension. In summary, AT2R plays an essential role in glomerulogenesis and influences the podocyte integrity and function via alterations of Hhip expression. In addition, the offspring of diabetic mothers have an increased risk of hypertension and kidney injury; postnatal overnutrition further accelerates kidney injury in those offspring. Although both AT2R and hyperglycemic milieu in utero have an impact on kidney development and later kidney diseases, the interaction between these two factors still needs further studies.

Keyphrases: CAKUT, maternal diabetes, AT2R deficiency, glomerulogenesis, podocytes, Hhip, postnatal overnutrition, perinatal programming, reactive oxygen species