Ovarian Collagen Regulates Granulosa Cell Proliferation Through Persistent Activation of the ERK1/2 Pathway in the Chinese Soft-Shelled Turtle (Pelodiscus sinensis)

The Chinese soft-shelled turtle (Pelodiscus sinensis) is an important aquaculture species in China, and proper follicular development is crucial for its reproduction. Collagen plays a critical role in ovarian development, yet its effects in this species remain unclear. Using primary granulosa cells and ovarian tissue, we found that collagen content varied dynamically throughout follicular development and peaked at the mid-vitellogenic stage. Collagen reduction resulted in granulosa cell detachment, inhibited proliferation, induced nuclear vacuolation, and arrested the cell cycle. Collagen reduction also caused a persistent increase in ERK1/2 phosphorylation over 24 h, which was associated with downregulation of CCNE1, CDK2, and BCL2; pharmacological inhibition of ERK1/2 phosphorylation partially restored the expression of these genes. These results indicate that collagen is involved in ovarian development, and its reduction may inhibit granulosa cell proliferation, at least in part, through persistent ERK1/2 activation. Our findings, obtained from an experimentally manipulated in vitro system, provide insights for in vitro culture of chelonian granulosa cells and ovarian tissues.