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Regulation of inositol 1,4,5-trisphosphate receptors by transforming growth factor-beta: implications for vascular
1Department of Medicine, Thomas Jefferson University, Philadelphia, PA 19107, USA.
Abstract:
Diabetes in its early stages is associated with enhanced glomerular blood flow and systemic vasodilation. Possible consequences of enhanced glomerular blood flow are glomerular hypertrophy, increased shear stress, and subsequent glomerulosclerosis. The prosclerotic cytokine, transforming growth factor-beta (TGF-beta), has been well established to play a key role in mesangial matrix accumulation in diabetes; however, its role in regulating vascular tone has not been studied in depth. Earlier studies have demonstrated that vascular smooth muscle cells and mesangial cells pretreated with TGF-beta have impaired calcium mobilization to inositol 1,4,5-trisphosphate (IP3) generating agonists, such as platelet-derived growth factor (PDGF) and Angiotensin I1 (Ang II). We postulated that this action of TGF-beta may be caused by regulation of the key intracellular calcium channel, the inositol 1,4,5-trisphosphate receptor (IP3R). Mesangial and smooth muscle cells primarily contain the types I IP3R and III IP3R isoforms. Short-term exposure of mesangial cells to TGF-beta (15-60 min) leads to phosphorylation of the type I IP3R at specific serine residues. Long-term exposure of mesangial cells to TGF-beta (24 hours) leads to down-regulation of protein levels of both types I and III IP3Rs as assessed by Western blot and confocal analysis. Permeabilization of cells and exposure to IP3 leads to impaired calcium mobilization if cells are pretreated with TGF-beta. As an in vivo correlation, we found that streptozotocin-induced diabetic rats and mice have reduced renal type I IP3R expression. By immunostaining, we found reduction of type I IP3R in glomerular cells and arteriolar smooth muscle cells of the diabetic rat kidney. Treatment of diabetic mice with a neutralizing anti-TGF-beta antibody completely prevents diabetic glomerular hypertrophy. We conclude that the vascular dysfunction of diabetes leading to glomerular hypertrophy is mediated, in part, by TGF-beta-induced regulation of IP3Rs.
Insights
Transforming growth factor-beta (TGF-beta) impairs calcium signaling in diabetes by altering inositol 1,4,5-trisphosphate receptors (IP3Rs). This vascular dysfunction contributes to diabetic kidney disease, specifically glomerular hypertrophy.
Area of Science:
- Nephrology
- Molecular Biology
- Cardiovascular Physiology
Background:
- Early diabetes involves increased glomerular blood flow and vasodilation, potentially causing kidney damage.
- Transforming growth factor-beta (TGF-beta) is a known factor in diabetic kidney matrix accumulation.
- TGF-beta's role in regulating vascular tone and calcium signaling in diabetes requires deeper investigation.
Purpose of the Study:
- To investigate the role of TGF-beta in regulating vascular tone and calcium mobilization in diabetic nephropathy.
- To determine if TGF-beta affects inositol 1,4,5-trisphosphate receptors (IP3Rs), key calcium channels, in mesangial and smooth muscle cells.
- To correlate in vitro findings with in vivo observations in diabetic animal models.
Main Methods:
- Treatment of mesangial cells with TGF-beta and assessment of IP3R phosphorylation and protein levels via Western blot and confocal microscopy.
- Cell permeabilization assays to measure calcium mobilization in response to IP3.
- Analysis of renal IP3R expression in streptozotocin-induced diabetic rats and mice using immunostaining.
- In vivo study involving treatment of diabetic mice with anti-TGF-beta antibodies.
Main Results:
- Short-term TGF-beta exposure induced type I IP3R phosphorylation; long-term exposure reduced both type I and III IP3R protein levels in mesangial cells.
- TGF-beta pretreatment impaired calcium release from intracellular stores upon IP3 stimulation.
- Diabetic rats and mice showed reduced renal type I IP3R expression, particularly in glomerular and arteriolar smooth muscle cells.
- Anti-TGF-beta antibody treatment prevented glomerular hypertrophy in diabetic mice.
Conclusions:
- TGF-beta regulates IP3R expression and function, contributing to impaired calcium signaling in vascular cells.
- TGF-beta-induced IP3R modulation is a significant mechanism underlying vascular dysfunction and glomerular hypertrophy in diabetic nephropathy.
- Targeting TGF-beta signaling may offer a therapeutic strategy for preventing diabetic kidney complications.