BMAL1 regulates tubular epithelial-derived exosomal miR-27a-3p to inhibit macrophage-myofibroblast transition and alleviate ischemia/reperfusion-induced renal fibrosis.

RATIONALE: During ischemia‒reperfusion injury (IRI), BMAL1 has been shown to alleviate inflammation and kidney damage. However, the function of the tubular epithelium-macrophage interaction mediated by BMAL1 in IRI-induced renal fibrosis is still unclear.

METHODS

A mouse model of kidney-specific BMAL1 overexpression was developed to study how BMAL1 affects renal fibrosis, exosome production, and the macrophage-to-myofibroblast transition (MMT). The role of exosomes in the MMT and renal fibrosis was examined in both in vitro and in vivo studies using exosomes extracted from TCMK-1 cells. Exosomes from BMAL1-overexpressing TCMK-1 cells subjected to hypoxia-reoxygenation (H/R) were isolated and subjected to miRNA sequencing to identify key exosomal components. Exosomal miR-27a-3p regulation by BMAL1 and its downstream effects on TGFBR1/smad3 in macrophages were investigated using a variety of experimental methods. To assess the effect of exosomal miR-27a-3p on MMT and renal fibrosis, additional in vitro and in vivo investigations were conducted.

RESULTS

Renal IRI increased exosome secretion, promoted MMT, and exacerbated renal fibrosis, whereas BMAL1 overexpression or Rab27a knockout significantly attenuated IRI-induced MMT and fibrotic progression. Exosomes derived from H/R-treated tubular epithelial cells further exacerbated MMT and renal fibrosis in an IRI model. Notably, tubular-specific overexpression of BMAL1, elevation of exosomal miR-27a-3p levels, or inhibition of exosome secretion significantly attenuated the progression of both MMT and fibrosis. Mechanistic studies demonstrated that BMAL1 binds directly to the miR-27a-3p promoter region, enhancing transcription. Exosomal miR-27a-3p subsequently targets TGFBR1 mRNA in macrophages, thereby suppressing the TGFBR1/smad3 signaling pathway and ultimately attenuating MMT and renal fibrosis.

CONCLUSIONS

BMAL1 expression was suppressed in IRI, which promoted MMT and renal fibrosis via the exosomal miR-27a-3p-TGFBR1/smad3 pathway. Targeting this signaling pathway may offer a potential therapeutic strategy for alleviating IRI-induced renal fibrosis.