Abstract
Background and Aims
Rhabdomyolysis is characterized by the breakdown of the skeletal muscle and the subsequent myoglobin (Mb) release into the bloodstream. A common complication of this syndrome is acute renal injury (AKI). Once filtered by the kidney, Mb causes oxidative stress, inflammation and tubular cell death. There is no specific treatment for rhabdomyolysis-AKI, so it is crucial a better understanding of this syndrome to identify new therapeutic targets. Klotho is an anti-aging protein mostly expressed by the kidney. In addition to its functions in the regulation of mineral metabolism, Klotho protects from AKI-harmful effects. However, no previous studies analyzed the role of Klotho in rhabdomyolysis.
Method
We performed a pre-clinical model of rhabdomyolysis in C57BL/6J mice (male, 12 weeks old, n=30) by intramuscular injection of 10 ml/kg of 50% glycerol (≥99.5% m/v). Mice were sacrificed 3 and 6 hours or 1, 3, 7 and 30 days after glycerol administration. To evaluate to beneficial effect of Klotho in rhabdomyolysis, C57BL/6J mice were injected intraperitoneally with 0.1 mg/kg recombinant mouse Klotho (1819-KL, R&D Systems), or vehicle (PBS) 30 minutes before and 1, 3 and 5 days after glycerol injection. Blood, urine and renal samples were collected to analyze renal function, Klotho/FGF23 levels, oxidative stress, inflammation, fibrosis and cell death, all of them pathological processes affecting Klotho expression. In addition, we carried out studies in murine tubular cells (MCTs) to study the molecular mechanisms involved in Klotho regulation.
Results
Our results indicate that rhabdomyolysis induces an early decrease in Klotho renal mRNA and protein expression as well as Klotho serum levels. Klotho levels decreased in line with augmentation of creatinine concentration, kidney inflammation (CCL2 and IL-6 mRNA expression) and tubular injury marker NGAL. Moreover, patients with rhabdomyolysis-AKI also showed lower plasma Klotho levels and increased FGF23 plasma concentration than age-matched healthy individuals. Renal klotho protein expression remained reduced one month after rhabdomyolysis-induction, in line with long term renal fibrosis and pro-inflammatory macrophage accumulation (F4/80+ cells). Exogenous recombinant Klotho administration ameliorated renal function and reduced rhabdomyolysis-mediated tubular cell death oxidative stress (4-HNE staining) and tubular injury 24h after glycerol injection. In the same line, Klotho administration during AKI development reduced long term renal fibrosis and macrophage infiltration one month later. Antioxidant therapies with N-acetylcysteine (NAC) and sulforaphane, a potent Nuclear factor erythroid-2-related factor 2 (Nrf2) inducer, reduced Mb-mediated Klotho decrease in cultured tubular cells. Inhibition of TNF-α and IL-6 with infliximab and tocilizumab, respectively, also reverted Mb-mediated Klotho decrease. Inhibition of the inflammatory NFkB and p38 pathways also prevented Mb-mediated Klotho reduction.
Conclusion
Our findings are the first to demonstrate decreased renal and soluble Klotho levels not only in the early phases of rhabdomyolysis-induced AKI, but also when renal function was recovered, indicating that long-term consequences of AKI, such as inflammation and fibrosis, are also involved in Klotho downregulation. In addition, our results also indicate that Klotho administration may be a potential strategy to decrease rhabdomyolysis- long term negative effects.
TNF Superfamily: A Growing Saga of Kidney Injury Modulators
