The peroxisome proliferator-activated receptors (PPARs) are a family of nuclear receptors involved in metabolic processes comprising lipid and glucose metabolism, energy homeostasis, cell proliferation and differentiation. Granulosa cells (GC) of developing ovarian follicles have been shown to predominantly express PPARgamma (PPARγ). However, its role is unclear in normal ovarian biology. Thiazolidinediones (TZD) are a class of exogeneous PPARγ agonists that include the anti-diabetic drug rosiglitazone (RGZ). This study investigated the underlying molecular mechanisms of PPARγ activation which may affect ovarian function.
A transformed non-luteinised human GC cell line, hGrC1, was treated with either vehicle or RGZ and retinoic acid (the ligand for PPARγ heterodimeric partner RXRα). RNA was extracted to generate RNA-seq libraries, then sequenced (average of 50 million reads/sample). For data analysis, we utilised the RNASik pipeline (Monash Bioinformatics Platform), followed by DEGUST analysis to establish transcriptomic profiles.
Preliminary analysis identified 350 differentially expressed genes in PPARγ-activated GC cells, 67% of which were upregulated (FDR 0.05, fold change>1.5). The following genes were of interest: CREB3L3 (6-fold increase), IL1B (4-fold), PDGFB (2-fold), VEGFA (1.7-fold), ID1 (2-fold) and PTGER2 (2-fold). KEGG pathway analysis revealed these genes contributed to critical signalling pathways: AMPK, PI3K-Akt, MAPK, Ras, Rap1 and cAMP, all of which are key regulators of basic cellular functions such as proliferation, differentiation and/or cell energy homeostasis. Furthermore, regulation of lipid metabolism including steroid hormone biosynthesis (CYP11A1, CYP26B1 and HSD3B1 genes, >2-fold); suggests that activation of PPARγ plays a key transcriptional link between energy metabolic and signal transduction functions in normal ovarian GC biology.
Transcriptomic data can provide valuable insight into how PPARγ modulation may impact normal basal ovarian physiology. Given its almost exclusive expression in GC, disruption in PPARγ could potentially effect GC development and normal oocyte maturation, which may have functional implications in ovarian pathology.