Aging-related increase of cGMP disrupts mitochondrial homeostasis in Leydig cells.

Since mitochondria play an essential role in the testosterone biosynthesis, serve as power centers and are a source of oxidative stress, a possible mitochondrial dysfunction could be connected with decreased activity of Leydig cells and lowered testosterone production during aging. Here we chronologically analyzed age-related alterations of mitochondrial function in Leydig cells correlated by the progressive rise of cGMP-signaling and with respect to testosterone synthesis. To target cGMP-signaling in Leydig cells, acute or long-term in vivo or ex vivo treatments with sildenafil (PDE5 inhibitor) were performed. Aging-related accumulation of cGMP in the Leydig cells is associated with mitochondrial dysfunction illustrated by reduced ATP and steroid production, lowered O2 consumption, increased mitochondrial abundance and mtDNA copies number, decreased expression of genes that regulate mitochondrial biogenesis (Ppargc1a/PGC1a-Tfam-Nrf1/NRF1), mitophagy (Pink1), fusion (Mfn1, Opa1) and increased Nrf2/NRF2. Acute in vivo PDE5-inhibition overaccumulated cGMP and stimulated testosterone but reduced ATP production in Leydig cells from adult, middle-aged and old rats. The increased ATP/O ratio observed in cells from old compared to adult rats was diminished after stimulation of cGMP-signaling. Opposite, long-term-PDE5-inhibition decreased cGMP-signaling and improved mitochondrial function/dynamics in Leydig cells from old rats. Mitochondrial abundance in Leydig cells decreased while ATP levels increased. Chronic-treatment elevated Tfam, Nrf1, Nrf2, Opa1, Mfn1, Drp1 and normalized Pink1 expression. Altogether, long-term-PDE5-inhibition prevented age-related NO and cGMP elevation, improved mitochondrial dynamics/function, and testosterone production. The results pointed on cGMP-signaling in Leydig cells as a target for pharmacological manipulation of aging-associated changes in mitochondrial function and testosterone production.