AB293. SPR-20 Temporal changes of detrusor muscle function in a high fat diet and low dose streptozotocin diabetic model: the compensated and decompensated states

Objective: Bladder smooth muscle (detrusor muscle) undergoes temporal changes in response to diabetes resulting in diabetic bladder dysfunction (DBD). Type I DBD induces an early compensated state of bladder function exhibiting detrusor muscle remodeling and a hypercontractile phenotype progressing into a late decompensated state of bladder function and a hypocontractile phenotype. While the majority of DBD studies have been performed in type I diabetes, relatively few have been performed in type II diabetes, which accounts for ~90% of all diabetic cases. In a type II model, we aimed to establish a timeline of DBD. We hypothesized that force to exogenous stimulation would be (I) increased in the compensated state and positively correlated with myosin light chain (MLC) and phosphorylation calcium sensitization proteins [17 kDa protein-kinase C potentiated protein phosphatase 1 inhibitor (CPI-17) and myosin phosphatase targeting regulatory subunit (MYPT1)]; (II) decreased in the decompensated state and negatively correlated with MLC and phosphorylation calcium sensitization proteins (CPI-17 and MYPT1).

Methods: Type II diabetes was induced by utilizing a high fat diet (HFD; 45% fat), to induce insulin resistance and two low doses of streptozotocin (STZ; 30 mg/kg), to induce hyperglycemia and compromised pancreatic β-cell function. Functional studies were performed in urothelium denuded bladder strips in the presence of carbachol and ATP. Tissues were frozen at peak force in response to exogenous stimulation and used for western blot analysis of contractile proteins.

Results: The HFD/STZ model developed the compensated state at 1 week post-STZ and the decompensated state at 4 months post-STZ administration. Diabetic bladders were hypertrophied compared to control in both DBD states. The compensated state was characterized by increased volume per void and increased detrusor muscle contractility to exogenous addition of carbachol and ATP. The enhanced detrusor contractility to carbachol was not due to increased levels of myosin light chain (MLC) phosphorylation. The decompensated state was characterized by increased volume per void, number of voids, and contractility to ATP but not carbachol. This suggests that progression from the compensated to decompensated states involves decreased contractility to muscarinic stimulation. In addition, proteins involved with calcium sensitization and MLC demonstrated decreased phosphorylation levels.

Conclusions: In the HFD/STZ model, the compensated state was not mediated by changes in MLC phosphorylation. The decompensated state exhibited reduced force from 3 month post-STZ to 6 month post-STZ, which can be attributed to decreased phosphorylation of MLC and calcium sensitization proteins, CPI-17 and MYPT1.

Funding Source(s): Diabetic Complications Program/NIDDK; NIH grant DK85734

Keywords: Diabetes; high fat diet; bladder; urothelium; in vitro contractility; western blot