A magic kick for regeneration: role of mesenchymal stromal cell secretome in spermatogonial stem cell niche recovery

Injury of stem cell niches may disturb tissue homeostasis and regeneration coordinated by specific niche components. Yet, the mechanisms of stem cell niche restoration remain poorly understood. Herein, we examined the role of mesenchymal stromal cells (MSCs) as pivotal regulators of stem cell niche recovery focusing on the effects of their secretome. The spermatogonial stem cell (SSC) niche was selected as a model. SSC niches were injured by inducing abdominal cryptorchidism in rats. Briefly, testes of anesthetized rats were elevated into the abdominal cavity through the inguinal canal for 14 days. After descent of testes, MSC or MSC secretome treatment was applied to the animals by local subtunical injections. Local administration of MSC or MSC secretome was sufficient to recover spermatogenesis and production of functional germ cells. The effects of MSC and their secreted components were comparable, leading to restoration of Sertoli cell pools and recovery of Leydig cell secretory functions. Our data suggest that MSCs mimic the functions of lost supportive cells within the stem cell niche, transiently providing paracrine stimuli for target cells and triggering tissue regenerative processes after damage.