Toll-like receptor 4 mutation protects the kidney from Ang-II-induced hypertensive injury

Cellular autophagy is a protective mechanism where cells degrade damaged organelles to maintain intracellular homeostasis. Apoptosis, on the other hand, is considered as programmed cell death. Interestingly, autophagy inhibits apoptosis by degrading apoptosis regulators. In hypertension, an imbalance of autophagy and apoptosis regulators can lead to renal injury and dysfunction. Previously, we have reported that toll-like receptor 4 (TLR4) mutant mice are protective against renal damage, in part, due to reduced oxidative stress and inflammation. However, the detailed mechanism remained elusive. In this study, we tested the hypothesis of whether TLR4 mutation reduces Ang-II-induced renal injury by inciting autophagy and suppressing apoptosis in the hypertensive kidney. Male mice with normal TLR4 expression (TLR4N, C3H/HeOuJ) and mutant TLR4 (TLR4M, C3H/HeJ^Lps-d) aged 10-12 weeks were infused with Ang-II (1000 ng/kg/d) for 4 weeks to create hypertension. Saline infused appropriate control were used. Blood pressure was increased along with increased TLR4 expression in TLR4N mice receiving Ang-II compared to TLR4N control. Autophagy was downregulated, and apoptosis was upregulated in TLR4N mice treated with Ang-II. Also, kidney injury markers plasma lipocalin-2 (LCN2) and kidney injury molecule 1 (KIM-1) were upregulated in TLR4N mice treated with Ang-II. Besides, increased nuclear translocation and activity of NF-kB were measured in Ang-II-treated TLR4N mice. TLR4M mice remained protected against all these insults in hypertension. Together, these results suggest that Ang-II-induced TLR4 activation suppresses autophagy, induces apoptosis and kidney injury through in part by activating NF-kB signaling, and TLR4 mutation protects the kidney from Ang-II-induced hypertensive injury.