ATP activation of peritubular cells drives testicular sperm transport

Abstract

Spermatogenesis, the complex developmental process of male germ cell proliferation, differentiation, and maturation, is the basis of male fertility and reproductive fitness. In the seminiferous tubules of the testes, spermatozoa are constantly generated from spermatogonial stem cells through a stereotyped sequence of mitotic and meiotic divisions. The basic physiological principles, however, that control both maturation and luminal transport of the still immotile spermatozoa within the seminiferous tubules remain poorly, if at all, defined. Here, we show that coordinated contractions of smooth muscle-like testicular peritubular cells provide the propulsive force for luminal sperm transport towards the rete testis and epididymis. Using a mouse model for in vivo imaging, we describe and quantify spontaneous tubular contractions and show a causal relationship between peritubular Ca2+ waves and peristaltic transport. Moreover, we identify P2 receptor-dependent purinergic signaling pathways as physiological triggers of tubular contractions both in vitro and in vivo. When challenged with extracellular ATP, transport of luminal content inside the seminiferous tubules displays stage-dependent directionality. We thus suggest that paracrine purinergic signaling coordinates peristaltic recurrent contractions of the mouse seminiferous tubules to propel immotile spermatozoa to the rete testis. Consequently, our findings could have substantial pharmaceutical implications for both infertility treatment and / or male contraception.

Purinergic Signaling in Spermatogenesis

“…Adapted from: Fleck, Kenzler et al. ( 3 ). Right: Distribution of P2 isoforms in various cell types of the seminiferous tubule.…”

“…Upon release, spermatozoa remain immotile and, thus, need to be actively transported towards rete testis and epididymis, where they gain the capacity for motility but remain quiescent ( 13 – 15 ). Sperm transport is mediated by coordinated smooth muscle contractions of TPCs that surround individual tubules ( 3 , 16 ).…”

“…Negative current indicates cation influx through P2X receptors. (A I ) Slowly desensitizing P2X2 and/or P2X4 current in a mouse TPC ( 3 ). (A II ) ATP activates P2X2 in murine Sertoli cells ( 33 ).…”

“…Notably, we also identified purinergic signaling pathways as physiological triggers of tubular contractions both in vitro and in vivo . By acting on ionotropic (P2X2 and/or P2X4) and metabotropic (P2Y2) purinoceptors ( Figure 2 ), extracellular ATP elevates cytosolic Ca 2+ ( Figure 2B ), activates TPC contractions, and triggers stage-dependent directional sperm movement within the mouse seminiferous tubules ( 3 ). Combining recordings from primary mouse and human TPC cultures as well as acute mouse seminiferous tubule slices with intravital multiphoton imaging of intact tubules, we provide direct and quantitative evidence for purinergic TPC signaling that triggers robust peristaltic movement of luminal sperm ( 3 ).…”

Three-dimensional analysis and in vivo imaging for sperm release and transport in the murine seminiferous tubule

“…When the function of the peritubular myoid cell (PMC) is disrupted, the luminal flow in the ST is modulated, resulting in dilation of the ST (Uchida et al ., 2020). Most recently, unidirectional movement of the spermatozoa transported in the lumina of the ST was shown by an in vivo imaging method (Fleck et al ., 2021). Motile cilia on the epithelial cells of the efferent tubules are also found to generate luminal flow using in vivo imaging (Yuan et al ., 2019).…”