Basic fibroblast growth factor induces proliferation and collagen production by fibroblasts derived from the bovine corpus luteum

Abstract

Cyclic regression of the ovarian corpus luteum, the endocrine gland responsible for progesterone production, involves rapid matrix remodeling. Despite fibroblasts in other systems being known for producing and maintaining extracellular matrix, little is known about fibroblasts in the functional or regressing corpus luteum. Vast transcriptomic changes occur in the regressing corpus luteum, among which are reduced levels of vascular endothelial growth factor a (VEGFA) and increased expression of fibroblast growth factor 2 (FGF2) after 4 and 12 h of induced regression, when progesterone is declining, and the microvasculature is destabilizing. We hypothesized that FGF2 activates luteal fibroblasts. Analysis of transcriptomic changes during induced luteal regression revealed elevations in markers of fibroblast activation and fibrosis, including fibroblast activation protein (FAP), serpin family E member 1 (SERPINE1), and secreted phosphoprotein 1 (SPP1). To test our hypothesis, we treated bovine luteal fibroblasts with FGF2 to measure downstream signaling, type 1 collagen production, and proliferation. We observed rapid and robust phosphorylation of various signaling pathways involved in proliferation, such as ERK, AKT, and STAT1. From our longer-term treatments, we determined that FGF2 has a concentration-dependent collagen-inducing effect, and that FGF2 acts as a mitogen for luteal fibroblasts. FGF2-induced proliferation was greatly blunted by inhibition of AKT or STAT1 signaling. Our results suggest that luteal fibroblasts are responsive to factors that are released by the regressing bovine corpus luteum, an insight into the contribution of fibroblasts to the microenvironment in the regressing corpus luteum.

Single-cell and spatiotemporal profile of ovulation in the mouse ovary

“…Additionally, we observed an enriched interaction between Fgf2 (ligand) and Sdc3 (receptor) from stroma/granulosa cells and luteal cells, respectively ( Figure 6D, 6F ), with their co-localization observed spatially ( Figure 6H ). FGF2 acts as a mitogenic factor in promoting luteal cell proliferation and extracellular matrix remodeling during luteal angioregression 108 . Sdc3, which encodes for the proteoglycan syndecan-3, is expressed in the corpus lutea and is suggested to be involved in inflammation 109 .…”

Mechanisms of angioregression of the corpus luteum

“…Unlike VEGF, FGF2 expression is increased during luteal regression ( Neuvians et al, 2004a ; Neuvians et al, 2004b ; Zalman et al, 2012 ; Monaco et al, 2023 ). These findings indicate that an elevation in luteal FGF2 is not sufficient to prevent the loss of endothelial cells and capillaries that occurs during early luteal regression, nor does FGF2 cotreatment affect progesterone levels of cows treated with PGF2α in vivo ( Piotrowska - Tomala et al, 2021 ).…”

“…In support of this idea, using smooth muscle actin as a marker, Reynolds and Redmer observed that fibroblast number was elevated in the corpus luteum during the late luteal phase of sheep, and collagen production was also elevated following PGF2α treatment ( Reynolds and Redmer, 1999 ; Vonnahme et al, 2006 ). A recent study showed that FGF2 induced both proliferation and collagen production of bovine luteal fibroblasts ( Monaco et al, 2023 ). Furthermore, in vitro studies reveal that the presence of type 1 collagen causes endothelial cells to become more sensitive to TGFB1 ( Maroni and Davis, 2011 ).…”

“…As reviewed above, many endothelial-reactive factors may contribute to fibrosis. Fibroblast activation by TGFB1 and FGF2 ( Monaco et al, 2023 ) and deposition of matrix may be a major contributor to this process. EDN1 has been implicated in pulmonary fibrosis and TNF-induced EndMT in cardiac fibrosis ( Swigris and Brown, 2010 ; Hu et al, 2023 ).…”