Protective effects of low-dose carbon monoxide against renal fibrosis induced by unilateral ureteral obstruction

Abstract

Tubulointerstitial fibrosis is a hallmark of chronic progressive kidney disease leading to end-stage renal failure. An endogenous product of heme oxygenase activity, carbon monoxide (CO), has been shown to exert cytoprotection against tissue injury. Here, we explored the effects of exogenous administration of low-dose CO in an in vivo model of renal fibrosis induced by unilateral ureteral obstruction (UUO) and examined whether CO can protect against kidney injury. UUO in mice leads to increased extracellular matrix (ECM) deposition and tubulointerstitial fibrosis within 4 to 7 days. Kidneys of mice exposed to low-dose CO, however, had markedly reduced ECM deposition after UUO. Moreover, low-dose CO treatment inhibited the induction of α-smooth muscle actin (α-SMA) and major ECM proteins, type 1 collagen and fibronectin, in kidneys after UUO. In contrast, these anti-fibrotic effects of CO treatment were abrogated in mice carrying null mutation of Mkk3, suggesting involvement of the MKK3 signaling pathway in mediating the CO effects. Additionally, in vitro CO exposure markedly inhibited TGF-β1-induced expression of α-SMA, collagen, and fibronectin in renal proximal tubular epithelial cells. Our findings suggest that low-dose CO exerts protective effects, via the MKK3 pathway, to inhibit development of renal fibrosis in obstructive nephropathy.

Autophagy Promotes Intracellular Degradation of Type I Collagen Induced by Transforming Growth Factor (TGF)-β1

“…We have previously reported that exposure to low-dose CO (250 ppm) markedly reduced collagen deposition in the kidneys after UUO in mice (34). Moreover, low-dose CO treatment inhibited the induction of ␣-smooth muscle actin and major ECM proteins, Col-I and fibronectin, in the mouse kidneys after UUO.…”

“…CO is an endogenous product of heme oxygenase activity that has been shown to exert potent cytoprotection against tissue injury including kidney fibrosis (34), and recently CO has been shown to induce autophagy (48). Lowdose CO (250 ppm) increased the expression and activation of the autophagic protein LC3 in the mouse lung, and in cultured human alveolar (A549) or bronchial epithelial cells in a timedependent manner (48).…”

“…Western Blot Analysis-Immunoblotting was carried out as described previously (33,34). To evaluate for aggregate formation of Col-I, a centrifugal fractionation assay followed by immunoblotting was performed as described by to Ishida et al (9).…”

“…CO Exposures-For low-dose CO exposure, cells were incubated with 250 ppm concentration of exogenous CO along with 5% CO 2 in humidified modular chambers maintained at 37°C, and CO levels in the chambers were monitored as described previously (34). In CO donor experiments, MMC were incubated in media containing 0.5% FBS for 24 h with various concentrations of CORM-2 (0 to 20 mM).…”

“…In the present study, we examined the functional role of autophagy in the regulation of Col-I induced by TGF-␤1. We also explored the role of autophagy in reducing Col-I expression by treatment with low-dose carbon monoxide (CO) which we have previously shown to exert anti-fibrotic effects in a model of kidney fibrosis induced by unilateral ureteral obstruction (UUO) (34). We hypothesized that the induction of autophagy promotes intracellular degradation of Col-I and that the autophagic process may serve as a cytoprotective mechanism to maintain cellular homeostasis.…”