Toll-Like Receptor 4 Activation Contributes to Diabetic Bladder Dysfunction in a Murine Model of Type 1 Diabetes

Abstract

Diabetic bladder dysfunction (DBD) is a common urological complication of diabetes. Innate immune system activation via Toll-like receptor 4 (TLR4) leads to inflammation and oxidative stress and was implicated in diabetes pathophysiology. We hypothesized that bladder hypertrophy and hypercontractility in DBD is mediated by TLR4 activation. Wild-type (WT) and TLR4 knockout (TLR4KO) mice were made diabetic by streptozotocin (STZ) treatment, and bladder contractile function and TLR4 pathway expression were evaluated. Immunohistochemistry confirmed the expression of TLR4 in human and mouse bladder. Recombinant high-mobility group box protein 1 (HMGB1) increased bladder TLR4 and MyD88 expression and enhanced contractile response to electrical field stimulation. Bladder expression of TLR4 and MyD88 and serum expression of HMGB1 were increased in STZ compared with control mice. Carbachol (CCh)-mediated contraction was increased in bladders from STZ mice, and TLR4 inhibitor CLI-095 attenuated this increase. Induction of diabetes by STZ in WT mice increased bladder weight and contractile responses to CCh and to electrical field stimulation. TLR4KO mice were not protected from STZ-induced diabetes; however, despite levels of hyperglycemia similar to those of WT STZ mice, TLR4KO STZ mice were protected from diabetes-induced bladder hypertrophy and hypercontractility. These data suggest that TLR4 activation during diabetes mediates DBD-associated bladder hypertrophy and hypercontractility.

A systematic review of urinary bladder hypertrophy in experimental diabetes: Part 2. Comparison of animal models and functional consequences

“…STZ injection has also been used in mice to induce diabetes. Two studies largely confirm findings in STZ‐injected rats, that is, an increased contraction in response to EFS, muscarinic, and purinergic agonists and KCl accompanied by an increased mRNA expression of M 3 muscarinic receptors but not M 2 or P2X 1 receptors . However, two interesting additional observations were made.…”

“…Two studies largely confirm findings in STZinjected rats, that is, an increased contraction in response to EFS, muscarinic, and purinergic agonists and KCl accompanied by an increased mRNA expression of M 3 muscarinic receptors but not M 2 or P2X 1 receptors. 8,53,86 However, two interesting additional observations were made. First, the Ca 2+ -channel blocker nifedipine and the rho kinase inhibitor Y-27,635 had considerably greater inhibitory effects in diabetic as compared to control mice, which was accompanied by an up-regulation of L-type Ca 2+ -channel mRNA, 53 suggesting that not only an increase in receptor but also in ion channel expression may be involved in the enhanced agonist responses.…”

“…Second, in vitro addition of the toll-like receptor four antagonist CLI-95 normalized the enhanced carbacholinduced contraction; moreover, the diabetes-associated increase in contractile responses to EFS and carbachol was largely abolished in knock-out mice lacking the toll-like receptor 4. 8 Finally, one of these studies suggested that enhancements may not be detectable at early time points (2 weeks after STZ injection) but only at later ones (8-9 or 22-24 weeks), which contrasts the time course of hypertrophy development 4 ; moreover, enhancements disappeared when contractions were normalized to those elicited by KCl, but interpretation of this finding is difficult as the KCl responses were not reported. 86 A second report based on the same animals described a reduced contraction to EFS in M 2 receptor knock-out but not wild-type mice, which similarly involved the muscarinic and the purinergic component of contraction, 87 pointing to possible compensatory changes in the contributions of M 2 and M 3 receptors.…”

“…First, the Ca 2+ ‐channel blocker nifedipine and the rho kinase inhibitor Y‐27,635 had considerably greater inhibitory effects in diabetic as compared to control mice, which was accompanied by an up‐regulation of L‐type Ca 2+ ‐channel mRNA, suggesting that not only an increase in receptor but also in ion channel expression may be involved in the enhanced agonist responses. Second, in vitro addition of the toll‐like receptor four antagonist CLI‐95 normalized the enhanced carbachol‐induced contraction; moreover, the diabetes‐associated increase in contractile responses to EFS and carbachol was largely abolished in knock‐out mice lacking the toll‐like receptor 4 . Finally, one of these studies suggested that enhancements may not be detectable at early time points (2 weeks after STZ injection) but only at later ones (8‐9 or 22‐24 weeks), which contrasts the time course of hypertrophy development; moreover, enhancements disappeared when contractions were normalized to those elicited by KCl, but interpretation of this finding is difficult as the KCl responses were not reported .…”

Toll-Like Receptors and Targeted Therapy in Diabetes Mellitus

“…6 There are accumulating evidence that TLRs signaling may participate in DM complications and progression. [7][8][9] Linagliptin, an antiglycemic therapeutic agent, has been shown to exert its beneficial effects on blood cerebrovascular circulation partly through the inhibition of TLR-2 activity. 10 In addition, it has been noted that insulin exerts its effects in part by inhibition of TLR-4 derived signaling pathways.…”