Up-Regulation of SIRT1 Reduces Endoplasmic Reticulum Stress and Renal Fibrosis.

BACKGROUND: Endoplasmic reticulum (ER) stress is emerging as an important factor in the development of organ fibrosis. Therefore, modulation of ER stress may serve as one of the possible therapeutic approaches to renal fibrosis. SIRT1, a class III histone deacetylase, has been found to exert beneficial effects in kidney diseases. However, it is largely unknown whether and how SIRT1 suppresses the ER stress. We postulated that upregulation of SIRT1 would suppress the ER stress through induction of heme oxygenase-1 (HO-1) and thioredoxin.

METHODS: HK-2 tubular cells, experimental mouse models of tunicamycin (TM)-induced ER stress and unilateral ureteral obstruction (UUO) were used. Expression of ER stress-induced protein was measured by Western blot analysis and immunohistochemical staining. ER stress was induced by chemical ER stress inducers [TM [,]thapsigargin (TG)] and non-chemical inducers such as angiotensin II, aldosterone, high glucose and albumin.

RESULTS: SIRT1 activator (SRT1720) induced SIRT1 expression in a time- and dose-dependent manner in HK-2 cells. SRT1720 suppressed the TM- or TG-induced ER stress, as shown by inhibition of TM- or TG-induced upregulation of glucose-related protein 78 (GRP78), phosphor-specific eukaryotic translation initiation factor-2α and C/EBP homologous protein through HO-1 and thioredoxin, which were abolished by pretreatment with SIRT1 inhibitor (sirtinol). SRT1720 also suppressed the ER stress induced by angiotensin II, aldosterone, high glucose and albumin. In animal studies, treatment with SRT1720 reduced the tubular expression of GRP78 and increased the expression of HO-1 and thioredoxin. SRT1720 also reduced the UUO-induced renal fibrosis.

CONCLUSION: SIRT1 may serve as a promising therapeutic target by reducing ER stress and fibrosis.