Cellular senescence promotes macrophage-to-myofibroblast transition in chronic ischemic renal disease

Cellular senescence participates in the pathophysiology of post-stenotic kidney damage, but how it regulates tissue remodeling is incompletely understood. Macrophage-myofibroblast transition (MMT) contributes to the development of tissue fibrosis. We hypothesized that cellular senescence contributes to MMT and renal fibrosis in mice with renal artery stenosis (RAS). INK-ATTAC mice expressing p16^INK-4a and green fluorescent protein in senescent cells were assigned to control or unilateral RAS, untreated or treated with AP20187 (an apoptosis inducer in p16^INK-4a-expressing cells) for 4 weeks. Renal perfusion was studied in vivo using micro-MRI, and kidney morphology, senescence, and MMT ex vivo. Cellular senescence was induced in human renal proximal tubular epithelial cells (HRPTEpiC) in vitro, and interferon-induced transmembrane protein-3 (IFITM3), a cellular senescence vector, was silenced (siRNA) or over-expressed (plasmid). HRPTEpiC were then co-incubated with macrophages with silenced integrin-3 (ITGB3), a regulator of mesenchymal transitions. CD68/p16^INK-4a/α-SMA co-expression and senescence markers were studied. Murine RAS kidneys showed increased expression of p16^INK-4a and MMT markers (F4/80, α-SMA) vs. controls, which decreased after AP20187, as did renal fibrosis and plasma creatinine, whereas renal perfusion increased. IFITM3 and ITGB3 expression were upregulated in senescent HRPTEpiC or co-cultured macrophages, respectively. MMT markers and TGF-β/Smad3 expression also rose in these macrophages and decreased after IFITM3 or ITGB3 silencing. p16^INK-4a-expressing macrophages may regulate interstitial fibrosis in RAS via MMT. This process is associated with elevated expression of ITGB3 and TGF-β/Smad3 pathway activation through neighboring senescent cell-derived IFITM3. These findings may implicate MMT as a therapeutic target in ischemic kidneys.