Researchers here provide evidence that the presence in the urine of extracellular vesicles carrying p16 as a part of their cargo might be used as a way to assess cellular senescence levels in the kidney. The presence of lingering senescent cells increases with age, and these cells cause chronic inflammation and tissue dysfunction in proportion to their numbers. With rapid growth in the clinical development of senolytic drugs capable of clearing senescent cells from aged tissues, and the present availability of a few proven and potential senolytic treatments such as the dasatinib and quercetin combination, there is a strong need for ways to quantify the burden of senescent cells in humans. Simple, low-cost tests that can run before and after a senolytic treatment would go a long way towards quantifying the degree to which the presently available approaches actually work.
Hypertension may be associated with renal cellular injury. Cells in distress release extracellular vesicles (EVs), 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 EVs released by senescent nephron cells can be identified in urine of patients with hypertension.
We recruited patients with essential hypertension (EH) or renovascular hypertension and healthy volunteers. Renal oxygenation was assessed using magnetic resonance imaging and blood samples collected from both renal veins for cytokine-level measurements. EVs 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+ EVs 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.
In conclusion, levels of p16+ EVs are elevated in urine of hypertensive patients and may reflect increased proximal tubular cellular senescence. In EH, EVs originate also from distal tubules and in renovascular hypertension from Henle's loop. Hence, urinary EVs levels may be useful to identify intrarenal sites of cellular senescence.