Drp1-mediated mitochondrial fission promotes renal fibroblast activation and fibrogenesis

Yating Wang,Xueqing Yu,Huiyan Li,Zhong Zhong,Yihan Wang,Jinjin Fan,Wei Chen,Yi Zhou,Liping Xiong,Haiping Mao,Fengxian Huang,Miaoqing Lu,Xuan Peng

doi:10.1038/s41419-019-2218-5

Abstract

Excessive mitochondrial fission acts as a pro-proliferative marker in some cancers and organ fibrosis; its potential role in renal fibroblast activation and fibrogenesis has never been investigated. Here, we showed more pronounced fragmented mitochondria in fibrotic than in non-fibrotic renal fibroblast in humans and mice. In a mouse model of obstructive nephropathy, phosphorylation of Drp1 at serine 616 (p-Drp1S616) and acetylation of H3K27(H3K27ac) was increased in fibrotic kidneys; pharmacological inhibition of mitochondrial fission by mdivi-1 substantially reduced H3K27ac levels, fibroblasts accumulation, and interstitial fibrosis. Moreover, mdivi-1 treatment was able to attenuate the established renal fibrosis. In cultured renal interstitial fibroblasts, targeting Drp1 using pharmacological inhibitor or siRNA suppressed TGF-β1-elicited cell activation and proliferation, as evidenced by inhibiting expression of α-smooth muscle actin (α-SMA) and collagen I, as well as by reducing DNA synthesis. In contrast, Drp1 deletion enhanced cell apoptosis, along with decreased mitochondrial fragmentation, mtROS elevation, and glycolytic shift upon TGF-β1 stimulation. In Drp1 deletion fibroblasts, re-expression of wild-type Drp1 rather than Drp1S616A mutant restores the reduction of TGF-β-induced-Drp1 phosphorylation, H3K27ac, and cell activation. Moreover, TGF-β1 treatment increased the enrichment of H3K27ac at the promoters of α-SMA and PCNA, which was reversed in Drp1-knockdown fibroblasts co-transfected with empty vector or Drp1S616A, but not wild-type Drp1. Collectively, our results imply that inhibiting p-Drp1S616-mediated mitochondrial fission attenuates fibroblast activation and proliferation in renal fibrosis through epigenetic regulation of fibrosis-related genes transcription and may serve as a therapeutic target for retarding progression of chronic kidney disease.

Highlights

In response to various chronic insults, renal interstitial resident fibroblasts undergo morphological and functional alteration to transdifferentiate into myofibroblasts, which express α-smooth muscle actin (α-SMA) and produce abundance of extracellular matrix components[1,2]
These results indicate that impaired mitochondrial dynamics in fibroblasts may be involved in the pathogenesis of renal fibrosis
Immunofluorescence staining results showed that the expression of α-SMA was barely expressed and p-Drp1S616 was not detectable in shamoperated kidneys, whereas increased expression of p-Drp1S616 and α-SMA positive myofibroblasts accumulation was observed in ureteral obstruction (UUO)-induced fibrotic kidneys (Fig. 1g)

Summary

Introduction

In response to various chronic insults, renal interstitial resident fibroblasts undergo morphological and functional alteration to transdifferentiate into myofibroblasts, which express α-SMA and produce abundance of extracellular matrix components[1,2]. The mechanisms underlying the Mitochondria are extremely dynamic organelles, constantly undergoing antagonistic processes of fission and fusion. Mitofusin-1 (Mfn1), Mitofusin-2 (Mfn2), and optic atrophy 1 (OPA1) proteins mediate fusion, whereas dynamin-related protein 1 (Drp1) executes fission by recruiting to the mitochondrial outer membrane to drive scission[5,6,7]. Phosphorylation of Drp[1] at serine 616 (p-Drp1S616) promotes Drp[1] activity. Phosphorylation of serine 637 (p-Drp1S637) represses its activity and leads to mitochondrial elongation[5].

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Conclusion