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Published on: January 23, 2018
Rap1b GTPase ameliorates glucose-induced mitochondrial dysfunction
1Department of Pathology, Northwestern University, Chicago, Illinois 60611, USA.
Abstract:
The role of tubular injury in diabetic nephropathy is relatively unknown, despite that apoptosis of tubular epithelial cells is commonly observed in human renal biopsies. The GTPase Ras-proximate-1 (Rap1b) is upregulated in the hyperglycemic state and is known to increase B-Raf, an antiapoptotic effector protein. In this study, the effects of high glucose on renal tubular apoptosis and the potential ability for Rap1b to ameliorate these effects were investigated. In the kidneys of diabetic mice, apoptotic tubular cells and dysmorphic mitochondria were observed, Bcl-2 expression was decreased, and Bax expression was increased. Total Rap1b expression was slightly increased, but its associated GTPase activity was significantly decreased. In vitro, high extracellular glucose led to decreased Bcl-2 expression, reduced Rap1b GTPase activity, and increased levels of both Bax and GTPase activating protein in a proximal tubular cell line (HK-2). These changes were accompanied by increased DNA fragmentation, decreased high molecular weight mitochondrial DNA, altered mitochondrial morphology and function, disrupted Bcl-2-Bax and Bcl-2-Rap1b interactions, and reduced cell survival. Overexpression of Rap1b partially prevents these abnormalities. Furthermore, the BH4 domain of Bcl-2 was found to be required for successful protein-protein interaction between Bcl-2 and Rap1b. In summary, these data suggest that Rap1b ameliorates glucose-induced mitochondrial dysfunction in renal tubular cells.
Insights
High glucose induces kidney tubular cell apoptosis by disrupting mitochondrial function. Ras-proximate-1 (Rap1b) protein may protect against this damage, suggesting a therapeutic target for diabetic nephropathy.
Area of Science:
- Nephrology
- Molecular Biology
- Cell Biology
Background:
- Diabetic nephropathy is characterized by tubular injury, but the underlying mechanisms are not fully understood.
- Apoptosis of renal tubular epithelial cells is a common feature in diabetic kidney disease.
- The GTPase Ras-proximate-1 (Rap1b) is linked to hyperglycemia and may influence cell survival pathways.
Purpose of the Study:
- To investigate the impact of high glucose on renal tubular cell apoptosis.
- To explore the protective role of Rap1b against high glucose-induced cellular damage.
- To elucidate the molecular mechanisms involving Rap1b, Bcl-2, and mitochondrial function.
Main Methods:
- Analysis of diabetic mouse kidneys for apoptosis, mitochondrial morphology, and protein expression (Bcl-2, Bax, Rap1b).
- In vitro studies using a proximal tubular cell line (HK-2) exposed to high glucose.
- Assessment of DNA fragmentation, mitochondrial DNA, mitochondrial function, and protein-protein interactions (Bcl-2, Bax, Rap1b).
- Overexpression of Rap1b to evaluate its protective effects.
Main Results:
- Diabetic kidneys and high glucose-treated cells showed increased tubular apoptosis, altered mitochondrial structure, decreased Bcl-2, and increased Bax.
- High glucose reduced Rap1b GTPase activity and disrupted Bcl-2 interactions with Bax and Rap1b.
- Rap1b overexpression partially rescued cells from high glucose-induced damage.
- The BH4 domain of Bcl-2 is crucial for its interaction with Rap1b.
Conclusions:
- High glucose induces renal tubular cell apoptosis and mitochondrial dysfunction.
- Rap1b plays a protective role by ameliorating glucose-induced mitochondrial damage.
- Rap1b's interaction with Bcl-2, mediated by the BH4 domain, is important for cell survival in hyperglycemia.
