Abumoawad, Abdelrhman M

AbstractCell stress may give rise to insuperable growth arrest, which is defined as cellular senescence. Stenotic kidney (STK) ischemia and injury induced by renal artery stenosis (RAS) may be associated with cellular senescence. Mesenchymal stem cells (MSCs) decrease some forms of STK injury, but their ability to reverse senescence in RAS remains unknown. We hypothesized that RAS evokes STK senescence, which would be ameliorated by MSCs. Mice were studied after 4 weeks of RAS, RAS treated with adipose tissue‐derived MSCs 2 weeks earlier, or sham. STK senescence‐associated β‐galactosidase (SA‐β‐Gal) activity was measured. Protein and gene expression was used to assess senescence and the senescence‐associated secretory phenotype (SASP), and staining for renal fibrosis, inflammation, and capillary density. In addition, senescence was assessed as p16+ and p21+ urinary exosomes in patients with renovascular hypertension (RVH) without or 3 months after autologous adipose tissue‐derived MSC delivery, and in healthy volunteers (HV). In RAS mice, STK SA‐β‐Gal activity increased, and senescence and SASP marker expression was markedly elevated. MSCs improved renal function, fibrosis, inflammation, and capillary density, and attenuated SA‐β‐Gal activity, but most senescence and SASP levels remained unchanged. Congruently, in human RVH, p21+ urinary exosomes were elevated compared to HV, and only slightly improved by MSC, whereas p16+ exosomes remained unchanged. Therefore, RAS triggers renal senescence in both mice and human subjects. MSCs decrease renal injury, but only partly mitigate renal senescence. These observations support exploration of targeted senolytic therapy in RAS.

Background Hypertension may be associated with renal cellular injury. Cells in distress release extracellular vesicles ( EV s), and their numbers in urine may reflect renal injury. Cellular senescence, an irreversible growth arrest in response to a noxious milieu, is characterized by release of proinflammatory cytokines. We hypothesized that EV s released by senescent nephron cells can be identified in urine of patients with hypertension. Methods and Results We recruited patients with essential hypertension ( EH ) or renovascular hypertension and healthy volunteers (n=14 each). Renal oxygenation was assessed using magnetic resonance imaging and blood samples collected from both renal veins for cytokine‐level measurements. EV s isolated from urine samples were characterized by imaging flow cytometry based on specific markers, including p16 (senescence marker), calyxin (podocytes), urate transporter 1 (proximal tubules), uromodulin (ascending limb of Henle's loop), and prominin‐2 (distal tubules). Overall percentage of urinary p16+ EV s was elevated in EH and renovascular hypertension patients compared with healthy volunteers and correlated inversely with renal function and directly with renal vein cytokine levels. Urinary levels of p16 + /urate transporter 1 + were elevated in all hypertensive subjects compared with healthy volunteers, whereas p16 + /prominin‐2 + levels were elevated only in EH versus healthy volunteers and p16 + /uromodulin + in renovascular hypertension versus EH . Conclusions Levels of p16 + EV s are elevated in urine of hypertensive patients and may reflect increased proximal tubular cellular senescence. In EH , EV s originate also from distal tubules and in renovascular hypertension from Henle's loop. Hence, urinary EV s levels may be useful to identify intrarenal sites of cellular senescence.