Abstract
We investigated whether renal hedgehog interacting protein (Hhip) expression contributes to the progression of diabetic nephropathy (DN) and studied its related mechanism(s) in vivo and in vitro. Here, we show that Hhip expression is highly elevated in glomerular endothelial cells of adult type 1 diabetic (T1D) Akita and T2D db/db mouse kidneys as compared to non-diabetic control littermates. Hyperglycemia enhances reactive oxygen species (ROS) generation via NADPH oxidase 4 (Nox4) activation and stimulates renal Hhip gene expression, and that elevated renal Hhip gene expression subsequently activates the TGFβ1- Smad2/3 cascade and promotes endothelial to mesenchymal transition associated with endothelial cell fibrosis/apoptosis in vivo and in vitro. Furthermore, kidneys of low-dose streptozotocin-induced diabetic heterozygous Hhip deficient (Hhip+/−) mice displayed a normal albumin/creatinine ratio with fewer features of DN (glomerulosclerosis/fibrosis and podocyte apoptosis/loss) and less evidence of renal compensation (glomerular hypertrophy and hyperfiltration) as compared to diabetic wild type controls (Hhip+/+). Thus, our studies demonstrated that renal Hhip expression is associated with nephropathy development in diabetes and that hyperglycemia-induced renal Hhip expression may mediate glomerular endothelial fibrosis and apoptosis in diabetes, a novel finding.
Highlights
Hedgehog interacting protein (Hhip), a signaling molecule in the hedgehog (Hh) pathway, was originally discovered as a putative antagonist of all 3 secreted Hh ligands, i.e., Sonic (Shh), Indian (Ihh), and Desert (Dhh)[5,6,7,8,9,10]
We demonstrated that Hhip expression is significantly increased in diabetic GECs and that kidney injury is ameliorated in diabetic Hhip+/− mice
While GEC injury is the hallmark of early renal injury in diabetic nephropathy (DN), there is a pressing need to identify novel insights into causal processes that contribute to the onset of diabetes-related glomerular endothelial injury or its progression that may help to identify potential therapeutic targets[1,2,3]
Summary
Hedgehog interacting protein (Hhip), a signaling molecule in the hedgehog (Hh) pathway, was originally discovered as a putative antagonist of all 3 secreted Hh ligands, i.e., Sonic (Shh), Indian (Ihh), and Desert (Dhh)[5,6,7,8,9,10]. Hhip regulates cell function via either canonical- or non-canonical hedgehog pathways[5,6,7,8,9,10,12,13]. We recently discovered that Hhip gene expression is differentially up-regulated in the kidneys of the offspring in our murine model of maternal diabetes, impairing nephrogenesis[20]. We hypothesized that hyperglycemia regulates Hhip gene expression and that elevated renal Hhip gene expression contributes to DN development and progression. We determined the mechanisms of hyperglycemia-induced renal Hhip gene expression that result in apoptosis of GECs and endothelial to mesenchymal transition (EndoMT)-related renal fibrosis
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