Post-Translational Modifications in Mammalian Folliculogenesis and Ovarian Pathologies

Abstract

Post-translational modifications (PTMs) of proteins, as the core mechanism for dynamically regulating follicular development, affect the maintenance of mammalian fertility by precisely coordinating granulosa cell-oocyte interaction, metabolic reprogramming, and epigenetic remodeling. Dysregulation of these modifications directly contributes to major reproductive diseases, including polycystic ovary syndrome (PCOS) and premature ovarian insufficiency (POI). Post-translational modifications regulate follicular development through intricate mechanisms. Thus, this review systematically synthesizes recent advances in PTMs, encompassing traditional ones such as phosphorylation, ubiquitination, and acetylation, alongside emerging modifications including lactylation, SUMOylation, and ISGylation, thereby constructing a more comprehensive PTM landscape of follicular development. Furthermore, this study dissects the molecular interaction networks of these PTMs during follicular activation, maturation, and ovulation, and uncovers the common mechanisms through which PTM dysregulation contributes to pathological conditions, including hyperandrogenism in PCOS and follicular depletion in POI. Finally, this review ultimately provides a theoretical basis for improving livestock reproductive efficiency and precise intervention in clinical ovarian diseases.

Keywords: follicular development; polycystic ovary syndrome; post-translational modification; premature ovarian insufficiency.

Figure 1

Effects of protein post-translational modifications on follicles at different developmental stages. The process of follicular development is divided into primordial follicles, primary follicles, secondary follicles, and pre-ovulatory follicles, which are distinguished by follicular size as well as the number and structure of granulosa cell layers. At each developmental stage, histone or protein phosphorylation (p), ubiquitination (ub), acetylation (ac), lactylation (la), SUMOylation (sumo), and ISGylation (isg), as listed in the plot, maintain follicular development by regulating granulosa cell proliferation, hormone secretion function, and oocyte meiosis, preventing follicular exhaustion and abnormal follicular development. Blue arrows represent the promotion of follicular development, and red ball-and-stick structures represent the inhibition of follicular development.

Figure 2

The main modification mechanisms of phosphorylation, acetylation, lactylation, ubiquitination, ISGylation, and SUMOylation. (A) Phosphorylation is primarily a process mediated by kinases, which transfer a phosphate group from ATP to substrate proteins. This process can be reversed by phosphatases. (B) Acetylation is a process mediated by histone acetyltransferases (HATs) with the involvement of acetyl-CoA, transferring an acetyl group to lysine residues on substrate proteins. Deacetylation is mainly mediated by the HDAC family, which removes the acetyl group from acetylated proteins. Specifically, HDAC classes I, II, and IV utilize H₂O to hydrolyze the acetyl group, while the HDAC class III family (Sirtuins) employs NAD+ as a cofactor to remove the acetyl group. (C) Lactylation is a process that modifies substrate proteins using lactate derived from intracellular uptake or glucose metabolism. Current research primarily indicates that lactate can be converted to lactoyl-CoA via P300/CBP, facilitating the lactylation of substrate proteins. Similarly, delactylation is mainly mediated by the HDAC and SIRT families. (D–F) Ubiquitination, ISGylation, and SUMOylation are all enzymatic cascade reactions involving E1 activating enzymes, E2 conjugating enzymes, and E3 ligases. The key differences lie in the specific E1/E2/E3 enzymes and the conjugated modifier groups (ubiquitin, ISG15, or SUMO). Additionally, removal of ubiquitination is primarily performed by deubiquitinating enzymes (DUBs), while removal of ISGylation is mainly mediated by USP18, and removal of SUMOylation is predominantly carried out by SENP proteases.

Figure 3

The mechanisms and roles of protein phosphorylation in follicular development. In this figure, BPA perturbs phosphorylation balance of AMPK Thr487, mTOR Ser2448, and ULK1 Ser556, inducing granulosa cell autophagy, apoptosis, and reduced steroidogenesis. AMH transmits signals via AMHR2-mediated phosphorylation of SMAD1/5/8; abnormalities (e.g., I209N mutation) or vitamin D regulation affect follicle reserve. Reduced CFTR expression blocks the HCO₃⁻/sAC/PKA pathway, decreasing ERK1/2 phosphorylation and cyclin D2 expression to inhibit granulosa cell proliferation. Conversely, PIM2-mediated phosphorylation of DAPK3 enhances cell survival. BMP15 Ser6 phosphorylation by Golgi casein kinase strengthens receptor binding, providing paracrine support for early follicular development. In bovine oocytes, GSK3β Ser9 phosphorylation (inactive form) reduces phospho-MAPK3/1 while maintaining high phospho-MAPK14, impairing meiotic progression. MAPK and SMAD phosphorylation cascades are central to follicular remodeling and fate determination. FGF2-induced DUSP6 dephosphorylates MAPK8 (JNK) Thr183/Tyr185 to inhibit apoptosis, whereas Orexin-A promotes granulosa cell proliferation via AKT Thr308 and ERK1/2 Thr202/Tyr204 phosphorylation. TGFβ3-mediated SMAD2/3 phosphorylation induces COX-2 expression for follicular wall remodeling during ovulation, while BMP-4 reduces StAR expression through SMAD1 phosphorylation and SF-1 inhibition. Energy metabolism-related pathways include the AMPK/mTOR/ULK1 axis in BPA-induced autophagy and IGF-1-activated PI3K/AKT signaling regulating primordial follicle activation via FOXO3a phosphorylation. Collectively, these phosphorylated proteins form a multilevel network maintaining dynamic balance in follicular development, with dysregulation leading to functional abnormalities. p means phosphorylation. The red cross means de-modification.

Figure 4

Mechanistic pathway map of post-translational modifications regulating PCOS and POI. (A) In polycystic ovary syndrome (PCOS), key pathogenic pathways involve dysregulated PTMs. Phosphorylation-related perturbations include hyperphosphorylation of IRS-1, which impairs PI3K/Akt signaling and induces insulin resistance in granulosa cells (GCs); constitutive phosphorylation of luteinizing hormone (LH) receptors aberrantly activates the cAMP-PKA cascade, exacerbating hyperandrogenemia and anovulation; and reduced CFTR expression blocks the HCO₃⁻/sAC/PKA pathway, decreasing ERK1/2 phosphorylation and inhibiting cyclin D2 expression, thereby arresting granulosa cell proliferation and follicle development. Ubiquitination dysfunction is characterized by abnormally elevated phosphoglycerate kinase 1 (PGK1), which binds to the E3 ubiquitin ligase Skp2 and inhibits its activity, preventing ubiquitination and degradation of the androgen receptor (AR), leading to AR accumulation, increased local ovarian androgen synthesis via CYP17A1 activation, and chronic inflammatory microenvironment formation. Acetylation dysregulation involves hyperandrogen-induced inhibition of the AMPK/SIRT1 axis, elevating PDK4 acetylation and disrupting granulosa cell glycolysis, along with diminished H3K9 acetylation that impairs transcription of androgen-synthesizing enzymes. The red upward arrow means the increased androgen level. (B) In premature ovarian insufficiency (POI), critical pathogenic mechanisms are linked to defective PTMs. Phosphorylation abnormalities include the I209N mutation of AMHR2, which blocks SMAD1/5/8 phosphorylation, interrupts anti-Müllerian hormone (AMH) signaling, and impairs primordial follicle reserve maintenance; bisphenol A (BPA) activates AMPK (Thr487), inhibits mTOR (Ser2448), and activates ULK1 (Ser556), inducing granulosa cell autophagy and accelerating follicle reserve depletion. Ubiquitination dysfunction involves reduced HDAC6, which leads to insufficient deacetylation of nerve growth factor (NGF), impairing its ubiquitination and degradation, thereby over-activating the PI3K/Akt/mTOR pathway and causing excessive primordial follicle activation; Skp2 deficiency hinders ubiquitination and degradation of p27, inhibiting granulosa cell transition from G1 to S phase and impairing proliferation; FBXW7 mutation reduces ubiquitination efficiency of connexin 37, disrupting oocyte–granulosa cell communication. UBE2I deficiency downregulates maternal effect genes and disrupts zygotic genome activation, leading to follicle depletion. Lactylation dysregulation involves AARS2 (R199C mutation) increasing lactylation levels of downstream proteins and inhibiting CPT2-mediated fatty acid oxidation and PDHA1-driven pyruvate entry into the tricarboxylic acid cycle, thus accelerating follicle recruitment and depletion. p means phosphorylation; Ub means ubiquitination; Ac means acetylation; La means lactylation; the red cross means de-modification.

Figure 5

The roles of post-translational modifications (PTMs) in folliculogenesis and ovarian diseases. The PTMs, including phosphorylation, ubiquitination, lactylation, acetylation, ISGylation, and SUMOylation, regulate multiple normal functions during folliculogenesis, such as granulosa cells (GCs) proliferation, steroid synthesis, autophagy, meiosis, follicle recruitment, follicle activation, and cell paracrine interactions. However, when PTMs become aberrant, normal folliculogenesis processes are disrupted. This abnormality, for instance, high androgen, follicular depletion, GCs apoptosis, can induce various ovarian diseases including premature ovarian insufficiency (POI) and polycystic ovary syndrome (PCOS).