Plzf Regulates Germline Progenitor Self-Renewal by Opposing mTORC1

SummaryHyperactivity of mTORC1, a key mediator of cell growth, leads to stem cell depletion, although the underlying mechanisms are poorly defined. Using spermatogonial progenitor cells (SPCs) as a model system, we show that mTORC1 impairs stem cell maintenance by a negative feedback from mTORC1 to receptors required to transduce niche-derived signals. We find that SPCs lacking Plzf, a transcription factor essential for SPC maintenance, have enhanced mTORC1 activity. Aberrant mTORC1 activation in Plzf −/− SPCs inhibits their response to GDNF, a growth factor critical for SPC self-renewal, via negative feedback at the level of the GDNF receptor. Plzf opposes mTORC1 activity by inducing expression of the mTORC1 inhibitor Redd1. Thus, we identify the mTORC1-Plzf functional interaction as a critical rheostat for maintenance of the spermatogonial pool and propose a model whereby negative feedback from mTORC1 to the GDNF receptor balances SPC growth with self-renewal

Epigenetic profiles signify cell fate plasticity in unipotent spermatogonial stem and progenitor cells

Spermatogonial stem and progenitor cells (SSCs) generate adult male gametes. During in vitro expansion, these unipotent murine cells spontaneously convert to multipotent adult spermatogonial-derived stem cells (MASCs). Here we investigate this conversion process through integrative transcriptomic and epigenomic analyses. We find in SSCs that promoters essential to maintenance and differentiation of embryonic stem cells (ESCs) are enriched with histone H3-lysine4 and -lysine 27 trimethylations. These bivalent modifications are maintained at most somatic promoters after conversion, bestowing MASCs an ESC-like promoter chromatin. At enhancers, the core pluripotency circuitry is activated partially in SSCs and completely in MASCs, concomitant with loss of germ cell-specific gene expression and initiation of embryonic-like programs. Furthermore, SSCs in vitro maintain the epigenomic characteristics of germ cells in vivo. Our observations suggest that SSCs encode innate plasticity through the epigenome and that both conversion of promoter chromatin states and activation of cell type-specific enhancers are prominent features of reprogramming

Low-dose irradiation promotes tissue revascularization through VEGF release from mast cells and MMP-9–mediated progenitor cell mobilization

Mast cells accumulate in tissues undergoing angiogenesis during tumor growth, wound healing, and tissue repair. Mast cells can secrete angiogenic factors such as vascular endothelial growth factor (VEGF). Ionizing irradiation has also been shown to have angiogenic potential in malignant and nonmalignant diseases. We observed that low-dose irradiation fosters mast cell–dependent vascular regeneration in a limb ischemia model. Irradiation promoted VEGF production by mast cells in a matrix metalloproteinase-9 (MMP-9)–dependent manner. Irradiation, through MMP-9 up-regulated by VEGF in stromal and endothelial cells, induced the release of Kit-ligand (KitL). Irradiation-induced VEGF promoted migration of mast cells from the bone marrow to the ischemic site. Irradiation-mediated release of KitL and VEGF was impaired in MMP-9–deficient mice, resulting in a reduced number of tissue mast cells and delayed vessel formation in the ischemic limb. Irradiation-induced vasculogenesis was abrogated in mice deficient in mast cells (steel mutant, Sl/Sld mice) and in mice in which the VEGF pathway was blocked. Irradiation did not induce progenitor mobilization in Sl/Sld mice. We conclude that increased recruitment and activation of mast cells following irradiation alters the ischemic microenvironment and promotes vascular regeneration in an ischemia model. These data show a novel mechanism of neovascularization and suggest that low-dose irradiation may be used for therapeutic angiogenesis to augment vasculogenesis in ischemic tissues

Retinal Pigment Epithelium-Secreted VEGF-A Induces Alpha-2-Macroglobulin Expression in Endothelial Cells.

Alpha-2-macroglobulin (A2M) is a protease inhibitor that regulates extracellular matrix (ECM) stability and turnover. Here, we show that A2M is expressed by endothelial cells (ECs) from human eye choroid. We demonstrate that retinal pigment epithelium (RPE)-conditioned medium induces A2M expression specifically in ECs. Experiments using chemical inhibitors, blocking antibodies, and recombinant proteins revealed a key role of VEGF-A in RPE-mediated A2M induction in ECs. Furthermore, incubation of ECs with RPE-conditioned medium reduces matrix metalloproteinase-2 gelatinase activity of culture supernatants, which is partially restored after A2M knockdown in ECs. We propose that dysfunctional RPE or choroidal blood vessels, as observed in retinal diseases such as age-related macular degeneration, may disrupt the crosstalk mechanism we describe here leading to alterations in the homeostasis of choroidal ECM, Bruch's membrane and visual function.This work was funded by grants EY08538 and GM34107 from NIH, award 2013-028 by the Tri-Institutional Stem Cell Initiative established by a grant from The Starr Foundation and by Departmental grants from Research to Prevent Blindness and Dyson Foundations (E.R.-B.). I.B. was supported by the Comunidad Autónoma de Madrid (grants 2017-T1/BMD-5247 and 2021-5A/BMD20944). The CNIC is supported by the Ministerio de Ciencia e Innovación (MCIN), the Instituto de Salud Carlos III, and the Pro-CNIC Foundation and is a Severo Ochoa Center of Excellence (grant CEX2020-001041-S funded by MCIN/AEI/10.13039/501100011033). R.F.M. and S.Z. were supported by grant EY024605 from NIH. J.M.-G. was supported by grant RTI2018-094727-B-100 funded by MCIN/AEI/10.13039/501100011033.S

Retinal Pigment Epithelium-Secreted VEGF-A Induces Alpha-2-Macroglobulin Expression in Endothelial Cells

Altres ajuts: NIH (EY08538, GM34107, EY024605); Tri-Institutional Stem Cell Initiative established by a grant from The Starr Foundation and by Departmental grants from Research to Prevent Blindness and Dyson Foundations (award 2013-028); Comunidad Autónoma de Madrid (2017-T1/BMD-5247, 2021-5A/BMD-20944); Instituto de Salud Carlos III; Pro-CNIC Foundation.Alpha-2-macroglobulin (A2M) is a protease inhibitor that regulates extracellular matrix (ECM) stability and turnover. Here, we show that A2M is expressed by endothelial cells (ECs) from human eye choroid. We demonstrate that retinal pigment epithelium (RPE)-conditioned medium induces A2M expression specifically in ECs. Experiments using chemical inhibitors, blocking antibodies, and recombinant proteins revealed a key role of VEGF-A in RPE-mediated A2M induction in ECs. Furthermore, incubation of ECs with RPE-conditioned medium reduces matrix metalloproteinase-2 gelatinase activity of culture supernatants, which is partially restored after A2M knockdown in ECs. We propose that dysfunctional RPE or choroidal blood vessels, as observed in retinal diseases such as age-related macular degeneration, may disrupt the crosstalk mechanism we describe here leading to alterations in the homeostasis of choroidal ECM, Bruch's membrane and visual function