Folliculogenesis and corresponding abnormalities

ABSTRACT

Despite Research progress in the last decades, many mechanisms involved in the formation, growth, and survival of oocytes remain poorly understood.

This article focuses on recent findings related to the creation of the founding cells of the follicular structure, the evolution of follicular structures during folliculogenesis, and to the pathological conditions that can affect follicular maturation. Indeed, not only the number and functionality of primordial follicles (PFs) is important for fertility, but also the process of activation and maturation of the follicles.

Folliculogenesis is the process by which ovarian follicles mature from a primordial stage to a mature one. The primordial follicles are the only source of oocytes during a woman’s reproductive life. The maturation of oocytes is influenced by several autocrine and paracrine signals.

Folliculogenesis occurs through several stages, from primordial to primary, secondary, and tertiary follicles. Follicular maturation is regulated by a significant number of genes, transcription factors, and hormones secreted by the hypothalamic-pituitary-ovarian axis. Primordial follicles contain oocytes arrested in the prophase I of meiosis and are surrounded by a layer of flattened granulosa cells. As follicles progress to primary, secondary, and tertiary stages, they accumulate follicular fluid and acquire the ability to produce estrogen.

Abnormalities in folliculogenesis can lead to reproductive dysfunctions, as seen in polycystic ovary syndrome (PCOS), which can cause anovulatory infertility. Women with PCOS show an increased number of follicles but abnormal growth and maturation, not allowing proper ovulation. Women with PCOS often show a reduction in serum levels of circulating FSH and increased serum LH levels.

Recent discoveries on the regulation of folliculogenesis and the pathological mechanisms affecting follicular maturation offer new treatment perspectives, particularly for women with PCOS The aim is to regulate underlying folliculogenesis mechanisms, promoting proper follicular maturation. However, several challenges persist in identifying and correcting factors that limit ovulation and oocyte quality, so further studies are needed.