Normotensive metabolic syndrome in mice deleted of the gene, Type 1 transient receptor potential canonical channel.

Metabolic syndrome has become a global epidemic, affecting all developed countries/communities with growing economies. Worldwide, increasing efforts have been directed at curbing this growing problem. Mice deleted of the gene encoding Type 1 Transient Receptor Potential Canonical Channel (Trpc1) were found to weigh heavier than controls. They had fasting hyperglycemia and impaired glucose tolerance vs. wild type controls. Beyond 1 year of age, plasma triglyceride level in null mice was elevated. Plasma cholesterol tended to be higher than controls. Livers in null mice were heavier, richer in triglyceride, and more echogenic vs. controls on ultrasound evaluation. Hematocrit was lower in null mice of both genders beginning at 2nd/3rd month of age in the absence of bleeding/ hemolysis. Measured by indirect tail-cuff method or by the direct arterial cannulation, blood pressures in null mice were lower than controls. We conclude that Trpc1 gene regulates body metabolism and that except for hypertension, phenotypes of mice after deletion of the Trpc1 gene resemble the metabolic syndrome, suggesting that this could be a good experimental model for future investigation on the pathogenesis and management of this disorder.

Control of PTH secretion by the TRPC1 ion channel.

Familial hypocalciuric hypercalcemia (FHH) is a genetic condition associated with hypocalciuria, hypercalcemia, and, in some cases, inappropriately high levels of circulating parathyroid hormone (PTH). FHH is associated with inactivating mutations in the gene encoding the Ca2+-sensing receptor (CaSR), a GPCR, and GNA11 encoding G protein subunit α 11 (Gα11), implicating defective GPCR signaling as the root pathophysiology for FHH. However, the downstream mechanism by which CaSR activation inhibits PTH production/secretion is incompletely understood. Here, we show that mice lacking the transient receptor potential canonical channel 1 (TRPC1) develop chronic hypercalcemia, hypocalciuria, and elevated PTH levels, mimicking human FHH. Ex vivo and in vitro studies revealed that TRPC1 serves a necessary and sufficient mediator to suppress PTH secretion from parathyroid glands (PTGs) downstream of CaSR in response to high extracellular Ca2+ concentration. Gα11 physically interacted with both the N- and C-termini of TRPC1 and enhanced CaSR-induced TRPC1 activity in transfected cells. These data identify TRPC1-mediated Ca2+ signaling as an essential component of the cellular apparatus controlling PTH secretion in the PTG downstream of CaSR.

Pigment epithelium-derived factor, a noninhibitory serine protease inhibitor, is renoprotective by inhibiting the Wnt pathway.

Pigment epithelium-derived factor (PEDF) expression is downregulated in the kidneys of diabetic rats, and delivery of PEDF suppressed renal fibrotic factors in these animals. PEDF has multiple functions including anti-angiogenic, anti-inflammatory and antifibrotic activities. Since the mechanism underlying its antifibrotic effect remains unclear, we studied this in several murine models of renal disease. Renal PEDF levels were significantly reduced in genetic models of type 1 and type 2 diabetes (Akita and db/db, respectively), negatively correlating with Wnt signaling activity in the kidneys. In unilateral ureteral obstruction, an acute renal injury model, there were significant decreases of renal PEDF levels. The kidneys of PEDF knockout mice with ureteral obstruction displayed exacerbated expression of fibrotic and inflammatory factors, oxidative stress, tubulointerstitial fibrosis, and tubule epithelial cell apoptosis, compared to the kidneys of wild-type mice with obstruction. PEDF knockout enhanced Wnt signaling activation induced by obstruction, while PEDF inhibited the Wnt pathway-mediated fibrosis in primary renal proximal tubule epithelial cells. Additionally, oxidative stress was aggravated in renal proximal tubule epithelial cells isolated from knockout mice and suppressed by PEDF treatment of renal proximal tubule epithelial cells. PEDF also reduced oxidation-induced apoptosis in renal proximal tubule epithelial cells. Thus, the renoprotective effects of PEDF are mediated, at least partially, by inhibition of the Wnt pathway. Hence, restoration of renal PEDF levels may have therapeutic potential for renal fibrosis.

Improvement of cardiac functions by chronic metformin treatment is associated with enhanced cardiac autophagy in diabetic OVE26 mice.

OBJECTIVE: Autophagy is a critical cellular system for removal of aggregated proteins and damaged organelles. Although dysregulated autophagy is implicated in the development of heart failure, the role of autophagy in the development of diabetic cardiomyopathy has not been studied. We investigated whether chronic activation of the AMP-activated protein kinase (AMPK) by metformin restores cardiac function and cardiomyocyte autophagy in OVE26 diabetic mice. RESEARCH DESIGN AND METHODS: OVE26 mice and cardiac-specific AMPK dominant negative transgenic (DN)-AMPK diabetic mice were treated with metformin or vehicle for 4 months, and cardiac autophagy, cardiac functions, and cardiomyocyte apoptosis were monitored. RESULTS: Compared with control mice, diabetic OVE26 mice exhibited a significant reduction of AMPK activity in parallel with reduced cardiomyocyte autophagy and cardiac dysfunction in vivo and in isolated hearts. Furthermore, diabetic OVE26 mouse hearts exhibited aggregation of chaotically distributed mitochondria between poorly organized myofibrils and increased polyubiquitinated protein and apoptosis. Inhibition of AMPK by overexpression of a cardiac-specific DN-AMPK gene reduced cardiomyocyte autophagy, exacerbated cardiac dysfunctions, and increased mortality in diabetic mice. Finally, chronic metformin therapy significantly enhanced autophagic activity and preserved cardiac functions in diabetic OVE26 mice but not in DN-AMPK diabetic mice. CONCLUSIONS: Decreased AMPK activity and subsequent reduction in cardiac autophagy are important events in the development of diabetic cardiomyopathy. Chronic AMPK activation by metformin prevents cardiomyopathy by upregulating autophagy activity in diabetic OVE26 mice. Thus, stimulation of AMPK may represent a novel approach to treat diabetic cardiomyopathy.

Deletion of the receptor for advanced glycation end products reduces glomerulosclerosis and preserves renal function in the diabetic OVE26 mouse.

OBJECTIVE: Previous studies showed that genetic deletion or pharmacological blockade of the receptor for advanced glycation end products (RAGE) prevents the early structural changes in the glomerulus associated with diabetic nephropathy. To overcome limitations of mouse models that lack the progressive glomerulosclerosis observed in humans, we studied the contribution of RAGE to diabetic nephropathy in the OVE26 type 1 mouse, a model of progressive glomerulosclerosis and decline of renal function. RESEARCH DESIGN AND METHODS: We bred OVE26 mice with homozygous RAGE knockout (RKO) mice and examined structural changes associated with diabetic nephropathy and used inulin clearance studies and albumin:creatinine measurements to assess renal function. Transcriptional changes in the Tgf-beta1 and plasminogen activator inhibitor 1 gene products were measured to investigate mechanisms underlying accumulation of mesangial matrix in OVE26 mice. RESULTS: Deletion of RAGE in OVE26 mice reduced nephromegaly, mesangial sclerosis, cast formation, glomerular basement membrane thickening, podocyte effacement, and albuminuria. The significant 29% reduction in glomerular filtration rate observed in OVE26 mice was completely prevented by deletion of RAGE. Increased transcription of the genes for plasminogen activator inhibitor 1, Tgf-beta1, Tgf-beta-induced, and alpha1-(IV) collagen observed in OVE26 renal cortex was significantly reduced in OVE26 RKO kidney cortex. ROCK1 activity was significantly lower in OVE26 RKO compared with OVE26 kidney cortex. CONCLUSIONS: These data provide compelling evidence for critical roles for RAGE in the pathogenesis of diabetic nephropathy and suggest that strategies targeting RAGE in long-term diabetes may prevent loss of renal function.