Transcriptional Regulation of Thrombospondins and Its Functional Validation through CRISPR/Cas9 Mediated Gene Editing in Corpus Luteum of Water Buffalo (Bubalus Bubalis)

Abstract

Background/aims: Thrombospondins (TSPs) are large multi-modular proteins, identified as natural angiogenesis inhibitors that exert their activity by binding to CD36 and CD47 receptors. The anti-angiogenic effect of TSPs in luteal regression of water buffalo has not been addressed. The present study characterized the expression pattern and localization of TSPs and their receptors in ovarian corpus luteum during different stages of development in buffalo. This study also elucidated the effect of exogenous Thrombospondin1 (TSP1) or the knocking out of the endogenous protein on luteal cell viability and function. Further, the in vitro transcriptional interaction of TSP1 with hormones, LH, PGF2α and angiogenic growth factors, VEGF and FGF2 were also evaluated.

Methods: First, the CLs were classified into four groups based on macroscopic observation and progesterone concentration. mRNA expression of examined factors was measured by qPCR, localization by immunoblotting and immunohistochemistry. TSP1 was knocked out (KO) in cultured luteal cells isolated from late luteal stage CLs (day 1116) by CRISPR/Cas9 mediated gene editing technology in order to functionally validate the TSP1 gene. Isolated cells from late stage CLs were also stimulated with different doses of TSP1, LH, PGF2α, VEGF and FGF2 for various time intervals to determine transcriptional regulation of thrombospondins.

Results: mRNA expression of TSPs and their receptors were found to be significantly higher in late and regressed stage of CL as compared to other groups which was consistent with the findings of immunoblotting and immunolocalization experiments. It was observed that TSP1 induced apoptosis, down regulated angiogenic growth factors, VEGF and FGF2 and attenuated progesterone production in cultured luteal cells. However, knocking out of endogenous TSP1 with CRISPR/Cas9 system improved the viability of luteal cells, progesterone synthesis and upregulated the expression of VEGF and FGF2 in the KO luteal cells. PGF2α induced the upregulation of TSPs and Caspase 3 transcripts, whereas treatment with LH and angiogenic growth factors (VEGF and FGF2) down regulated the TSP system in luteal cells.

Conclusion: Collectively, these data provide evidence that thrombospondins along with their receptors are expressed at varying levels in different stages of CL progression with maximum expression during the late and regressing stages. These results are consistent with the hypothesis that thrombospondins stimulated by PGF2α plays an essential modulatory role in bringing about structural and functional luteolysis in buffalo.