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Phosphatases modified by LH signaling in ovarian follicles: testing their role in regulating the NPR2 guanylyl cyclase

ABSTRACT: In response to luteinizing hormone (LH), multiple proteins in rat and mouse granulosa cells are rapidly dephosphorylated, but the responsible phosphatases remain to be identified. Because the phosphorylation state of phosphatases can regulate their interaction with substrates, we searched for phosphatases that might function in LH signaling by using quantitative mass spectrometry. We identified all proteins in rat ovarian follicles whose phosphorylation state changed detectably in response to a 30-min exposure to LH, and within this list, identified protein phosphatases or phosphatase regulatory subunits that showed changes in phosphorylation. Phosphatases in the phosphoprotein phosphatase (PPP) family were of particular interest because of their requirement for dephosphorylating the natriuretic peptide receptor 2 (NPR2) guanylyl cyclase in the granulosa cells, which triggers oocyte meiotic resumption. Among the PPP family regulatory subunits, PPP1R12A and PPP2R5D showed the largest increases in phosphorylation, with 4–10 fold increases in signal intensity on several sites. Although follicles from mice in which these phosphorylations were prevented by serine-to-alanine mutations in either Ppp1r12a or Ppp2r5d showed normal LH-induced NPR2 dephosphorylation, these regulatory subunits and others could act redundantly to dephosphorylate NPR2. Our identification of phosphatases and other proteins whose phosphorylation state is rapidly modified by LH provides clues about multiple signaling pathways in ovarian follicles.

INSTRUMENT(S): Orbitrap Fusion

ORGANISM(S): Rattus Norvegicus (rat)

TISSUE(S): Ovarian Follicle

SUBMITTER: Henning Urlaub

LAB HEAD: Prof. Dr.

PROVIDER: PXD033878 | Pride | 2023-11-20

REPOSITORIES: Pride

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Project description:Determining the spatial and temporal expression of genes involved in the ovulatory pathway is critical for the understanding of the role of each estrogen receptor in the modulation of folliculogenesis and ovulation. Estrogen receptor (ER) b is highly expressed in ovarian granulosa cells and mice lacking ERb (bERKO) are subfertile due to inefficient ovulation. Previous work has focused on isolated granulosa cells or cultured follicles and while informative, provides confounding results due to the heterogeneous cell types present including granulosa, theca and oocytes and exposure to in vitro conditions. Herein, we isolated preovulatory granulosa cells from WT and ERb-null mice using laser capture microdissection to examine the genomic transcriptional response downstream of PMSG (mimicking FSH) and PMSG/hCG (mimicking LH) stimulation. This allows for a direct comparison of in vivo granulosa cells at the same stage of development from both WT and ERb-null ovaries. ERb-null granulosa cells showed altered expression of genes known to be regulated by FSH (Akap12 and Runx2) as well as not previously reported (Arnt2 and Pou5f1) in WT granulosa cells. Our analysis also identified 304 genes not previously associated with ERb in granulosa cells. LH responsive genes including Abcb1b and Fam110c show reduced expression in ERb-null granulosa cells; however novel genes including Rassf2 and Megf10 were also identified as being downstream of LH signaling in granulosa cells. Collectively, our data suggests that granulosa cells from ERb-null ovaries may not be appropriately differentiated and are unable to respond properly to gonadotropin stimulation We used microarray to compare the gene expression profiles of wiltype (WT) and Erb-null (bERKO) preovulatory granulosa cells as they respond to either PMSG or PMSG+hCG treatments. Laser microdissection was used to collect a purified population of granulosa cells only from preovulatory follicles. We chose to compre the response to PMSG or PMSG+hCG of granulosa cells collected from either WT and bERKO preovulatory follicles. We chose to collect cells 48h after mice were treated with PMSG to compare the gene expression profile ot preovulatory granulosa cells. We also studied the response of these cells to LH (or hCG) as we collected cells 4h after mice were treated with hCG (peak of transcriptional response to hCG).

Project description:The molecular mechanisms that regulate the pivotal transformation processes observed in the follicular wall following the pre-ovulatory LH-surge, are still not established, particularly for cells of the thecal layer. To elucidate thecal and granulosa cell type-specific biological functions and signaling pathways, large dominant bovine follicles were collected before and 21 hrs after an exogenous GnRH induced LH surge. Because LH receptor density varies within the granulosa cell populations, antral granulosa (aGC; those aspirated by follicular puncture) and membrane associated granulosa (mGC; those scraped from the follicular wall) were compared to thecal cell expression profiles determined by mRNA microarrays. Thecal cell gene expression was less affected in the peri-ovulatory follicle when compared to granulosa cells, as evidenced by only 2% versus 25% of the ~11,000 genes expressed changing in response to the LH surge, respectively. The majority of the 203 LH-regulated thecal genes were also LH regulated in granulosa cells, leaving a total of 58 genes as LH-regulated theca cell specific genes. Most of the 58 genes (i.e., 74%) thecal specific genes including several known thecal markers (CYP17A1, NR5A1) were downregulated, while most genes identified are new to theca. Many of the newly identified upregulated thecal genes (e.g., PTX3, RND3, PPP4R4) were also upregulated in granulosa. Minimal expression differences were observed between aGC and mGC, however, transcripts encoding extracellular proteins (NID2) and matrix modulators (ADAMTS1, SASH1) predominated these differences. We also identified large numbers of unknown LH-regulated granulosa cell genes and discuss their putative roles in ovarian function. The single dominant ovarian follicle was collected from each cow before the LH surge or 22 hours after GnRH (used to induce LH surge). RNA was extracted from three independent cells within each follicle and there were hybridized on Affymetrix microarrays.

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Phosphatases modified by LH signaling in ovarian follicles: testing their role in regulating the NPR2 guanylyl cyclase

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