Effect of Mycophenolate and Rapamycin on Cellular Senescence in Lupus Nephritis

Background: Lupus nephritis (LN) is an important cause of acute kidney injury (AKI) and chronic kidney disease (CKD). Cellular senescence has been implicated in AKI and CKD progression and precedes kidney fibrosis. We previously reported that mycophenolic acid (MPA) and rapamycin possess anti-fibrotic properties in resident renal cells. Rapamycin has been shown to inhibit cellular senescence in endothelial cells but the effect of mycophenolate (MMF) on cellular senescence remains obscure. This study compared the effect of MMF and rapamycin on cellular senescent markers in LN. Methods: NZB/W F1 mice with active LN were treated with vehicle, MMF or rapamycin for 8 weeks, and kidneys were harvested to assess the expression of cellular senescence and fibrosis markers. Cellular senescence was induced in HK-2 cells by gamma irradiation (10Gy) in the presence or absence of MPA (5mg/ml) or rapamycin (5ng/ml) for 48h. Expression of p16, p21, collagen I and fibronectin was assessed by qPCR and Western blot analysis. Cell morphology and size was assessed by phase contrast microscopy and quantified by ImageJ. Results: Using NephroSeq datasets, tp53, cdkn1a and cdkn2a expression were significantly increased in LN patients compared to healthy subjects or patients with minimal change disease, and correlated with proteinuria, serum creatinine level and interstitial fibrosis, and inversely correlation with GFR. Increased expression of cdkn1a, cdkn2a, fn1, col1a1 and col3a1 expression was observed in NZB/W F1 mice with active disease compared to pre-disease mice. MMF or rapamycin treatment both significantly reduced mediators of cellular senescence and fibrosis. Gamma irradiation increased cell size by 2.87-fold and was accompanied by increased p16 and p21 expression compared to non-irradiated cells. Incubation of gamma irradiated cells with MPA or rapamycin led to preserved cell morphology and reduced cell size towards that of non-irradiated cells. MPA reduced p16 and p21 at both gene and protein levels, whereas rapamycin had no effect. Conclusion: Therapies that target cellular senescence may delay AKI and CKD. Our findings suggest that MMF and rapamycin have distinct senolytic properties. Further studies are warranted to delineate their mechanism of action. Funding: Government Support – Non-U.S.