Testicular endothelial cells are a critical population in the germline stem cell niche

Abstract

Maintenance of adult tissues depends on stem cell self-renewal in local niches. Spermatogonial stem cells (SSC) are germline adult stem cells necessary for spermatogenesis and fertility. We show that testicular endothelial cells (TECs) are part of the SSC niche producing glial cell line-derived neurotrophic factor (GDNF) and other factors to support human and mouse SSCs in long-term culture. We demonstrate that FGF-2 binding to FGFR1 on TECs activates the calcineurin pathway to produce GDNF. Comparison of the TEC secretome to lung and liver endothelial cells identified 5 factors sufficient for long-term maintenance of human and mouse SSC colonies in feeder-free cultures. Male cancer survivors after chemotherapy are often infertile since SSCs are highly susceptible to cytotoxic injury. Transplantation of TECs alone restores spermatogenesis in mice after chemotherapy-induced depletion of SSCs. Identifying TECs as a niche population necessary for SSC self-renewal may facilitate fertility preservation for prepubertal boys diagnosed with cancer.

Tcf21+mesenchymal cells contribute to testis somatic cell development, homeostasis, and regeneration

“…In addition to cell types with defined functions, such as testosterone-producing Leydig, contractile myoid, vessel-forming endothelial, immune-response macrophage, and FSHsensing Sertoli cells, the testis also harbors poorly defined interstitial cell populations (Combes et al, 2009). Emerging studies have highlighted the important roles somatic cells play in germ cell homeostasis and regeneration (Bhang et al, 2018;Green et al, 2018;Kitadate et al, 2019) and how their disruption can dramatically alter testes function. For instance, genetic ablation of macrophages in the adult testis leads to disruption of spermatogonial proliferation and differentiation (DeFalco et al, 2015).…”

<p>Role of stem cells in fertility preservation: current insights</p>

“…Subsequently, several teams attempted to find a culture system of dissociated testicular cell suspensions (TCSs) able to propagate human SSCs in vitro (Table 1). [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] Sadri-Ardekani et al adapted the protocol developed by Kanatsu-Shinohara et al for human testicular cells (TCs). Briefly, this culture system relies on the capacity of somatic cells to adhere to the plate while the germ-cell fraction stays in suspension, allowing enrichment of SSCs after differential plating.…”

“…32,33 This technique led to an 18,450-fold enrichment of adult SSCs after 64 days and to a 9.6-fold enrichment of prepubertal SSCs after 11 days of culture using xenotransplantation as the gold standard to identify SSCs able to migrate along the basement membrane of the STs, colonize their niches, and generate germ-cell colonies. Among researchers who have xenotransplanted long-term cultured human SSCs, 32,33,39,40,42,43,51 only Sadri-Ardekani et al and Nickkholgh et al quantified SSCs in STs after transplantation and demonstrated SSC enrichment. 32,33,43 However, several other teams using the same protocol could not reproduce such results due to the complexity and skills needed to distinguish between SSCs and human embryonic stem cell-like (hESC-like) cells, 34 because of low germ-cell survival and overgrowth of remaining somatic cells.…”

“…Recently, Bhang et al discovered that human endothelial TCs secreted GDNF, bFGF, stromal cell-derived factor-1 (SDF-1), macrophage inflammatory protein 2, and insulin-like growth factor-binding protein 2 and could support SSC growth for at least 150 days. 51 It also appeared that cells with MSC characteristics were able to support spermatogonia in vitro. Indeed, Smith et al showed that a THY1 + fraction isolated from TCSs was of mesenchymal origin and could support SSEA-4 + SSC growth, while mouse embryonic fibroblasts and human placental and fetal testicular stromal cells could not.…”

Recent advances in oncofertility address a serious side effect of cancer therapy

“…“In the presence of these endothelial cells, and specifically from the testes—not from lung or liver or any other organ—you can get gallons of SSCs produced and grown,” she says. For the first time, as she and Dr. Ginsberg showed in a 2018 study, researchers could reproducibly expand the human stem cells in vitro until they numbered in the millions …”