Polycystic Ovary Syndrome as a Multi-System Disorder: A Comprehensive Review of Hormonal, Metabolic, and Inflammatory Crosstalk at the Cellular and Molecular Level

1.1 Definition and Global Prevalence of PCOS

Polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders affecting women of reproductive age, characterized by a constellation of reproductive, metabolic, and hormonal abnormalities (Teede et al., 2018). It is defined by chronic anovulation, hyperandrogenism, and polycystic ovarian morphology, though clinical presentation can vary significantly among individuals. Globally, PCOS affects approximately 6–20% of women, depending on the diagnostic criteria applied and population studied (Bozdag et al., 2016; Lizneva et al., 2016). Such variation in prevalence highlights the complexity and heterogeneity of the disorder across different ethnic and geographic populations.

1.2 Clinical Heterogeneity and Diagnostic Criteria (Rotterdam, NIH, AE-PCOS)

PCOS is clinically heterogeneous, and multiple diagnostic frameworks have been developed. The NIH 1990 criteria define PCOS based on hyperandrogenism and chronic anovulation after exclusion of related disorders (Zawadski & Dunaif, 1992). The Rotterdam 2003 criteria expanded the definition by requiring the presence of any two of the following: oligo-/anovulation, clinical or biochemical hyperandrogenism, and polycystic ovarian morphology (ESHRE/ASRM, 2004). The Androgen Excess-PCOS Society (AE-PCOS) 2006 criteria emphasize androgen excess as a central feature, along with ovarian dysfunction (Azziz et al., 2006). While these differing criteria allow for broader identification, they also contribute to variability in reported prevalence and phenotypic subgroups.

1.3 Burden of PCOS as a Multi-System Disorder Beyond Reproduction

Although initially described as a reproductive condition, PCOS is now recognized as a multi-system disorder with implications extending beyond fertility. Women with PCOS often present with insulin resistance, obesity, dyslipidemia, and increased risk of metabolic syndrome and type 2 diabetes mellitus (Diamanti-Kandarakis & Dunaif, 2012). Cardiovascular risks such as hypertension and endothelial dysfunction are also heightened in this population (Escobar-Morreale, 2018). Moreover, PCOS has been associated with psychological consequences including anxiety, depression, and diminished quality of life (Cooney & Dokras, 2018). These systemic associations highlight the importance of understanding PCOS within a broader hormonal, metabolic, and inflammatory framework.

1.4 Aim and Scope of the Review

The aim of this review is to provide a comprehensive analysis of PCOS as a multi-system disorder, focusing on the interplay between hormonal, metabolic, and inflammatory pathways at the cellular and molecular levels. By synthesizing current knowledge, this review seeks to clarify mechanisms underlying disease pathophysiology, highlight clinical implications, and identify emerging therapeutic strategies. Particular emphasis is placed on the crosstalk among endocrine, metabolic, and immune systems, which collectively shape the heterogeneity and progression of PCOS.

2. Pathophysiology of PCOS: An Overview

PCOS pathophysiology is multifactorial, involving a complex interplay of genetic, hormonal, metabolic, and inflammatory mechanisms that disrupt ovarian function. This dysregulation leads to hyperandrogenism, anovulation, and systemic metabolic disturbances, manifesting as a multi-system disorder.

Figure 1. Schematic representation of the pathophysiology of polycystic ovary syndrome (PCOS)

PCOS is considered a polygenic disorder with heritability estimates ranging from 40–70% (Day et al., 2018). Genome-wide association studies (GWAS) have identified susceptibility loci linked to gonadotropin secretion, insulin signaling, and androgen biosynthesis, including LHCGR, DENND1A, THADA, and FSHR genes (Goodarzi et al., 2015). Epigenetic modifications, such as DNA methylation, histone acetylation, and non-coding RNAs, have also been implicated in dysregulated ovarian and metabolic pathways (Xu et al., 2020).

Beyond genetics, environmental and lifestyle factors significantly influence PCOS onset and severity. Sedentary lifestyle, obesity, and dietary habits exacerbate insulin resistance and hyperandrogenism (Lim et al., 2019). Prenatal androgen exposure and endocrine-disrupting chemicals (EDCs), such as bisphenol A (BPA), have been linked to altered ovarian development and neuroendocrine programming (Rattan et al., 2021). These findings support the “developmental origins” hypothesis, suggesting that early-life exposures may predispose women to PCOS later in life.

2.3 Central Role of Ovarian Dysfunction and Neuroendocrine Abnormalities

Ovarian dysfunction remains central to PCOS pathogenesis. Theca cells exhibit increased steroidogenic activity, producing excess androgens due to upregulation of enzymes such as CYP17A1 (Nelson et al., 2019). Granulosa cells show impaired aromatase activity, disrupting estrogen production and follicular maturation. Neuroendocrine alterations include increased GnRH pulsatility and elevated LH/FSH ratio, leading to chronic anovulation (Pastor et al., 2016). This dysregulation establishes a vicious cycle of androgen excess and impaired folliculogenesis.

2.4 PCOS as an Interplay of Hormonal, Metabolic, and Inflammatory Factors

PCOS is increasingly recognized as a multi-system disorder where hormonal, metabolic, and inflammatory pathways converge. Hyperinsulinemia amplifies ovarian androgen production and suppresses sex hormone-binding globulin (SHBG), worsening hyperandrogenism (Diamanti-Kandarakis & Dunaif, 2012). Chronic low-grade inflammation, characterized by elevated CRP, TNF-α, and IL-6, further contributes to insulin resistance and ovarian dysfunction (Escobar-Morreale, 2018). Adipose tissue dysfunction, oxidative stress, and gut microbiota dysbiosis are emerging factors reinforcing this systemic interplay.

3.1 Hypothalamic–Pituitary–Ovarian (HPO) Axis Dysfunction

The HPO axis plays a central role in PCOS pathogenesis. Women with PCOS exhibit altered GnRH pulsatility, favoring rapid pulses that preferentially stimulate luteinizing hormone (LH) over follicle-stimulating hormone (FSH) secretion (Pastor et al., 2016). This results in an elevated LH/FSH ratio, promoting theca cell androgen synthesis while impairing granulosa cell function. Consequently, folliculogenesis is disrupted, leading to anovulation and the accumulation of immature follicles within the ovary (Rosenfield & Ehrmann, 2016).

3.2 Hyperandrogenism

i) Ovarian Theca Cell Hyperactivity

Theca cells in PCOS exhibit intrinsic abnormalities, including upregulated expression of CYP17A1 (17α-hydroxylase/17,20-lyase), leading to excess androgen production (Nelson et al., 2019).

ii) Role of Insulin in Androgen Synthesis

Insulin acts synergistically with LH to stimulate theca cell steroidogenesis, while simultaneously suppressing hepatic sex hormone–binding globulin (SHBG), thereby increasing bioavailable testosterone (Diamanti-Kandarakis & Dunaif, 2012).

iii) Molecular Pathways

Dysregulation of CYP17A1, steroidogenic acute regulatory protein (STAR), and downstream AKT/PI3K signaling pathways has been implicated in enhanced androgen biosynthesis. Crosstalk between insulin receptor signaling and LH receptor pathways amplifies androgen excess, contributing to follicular arrest (Sen et al., 2020).

3.3 Progesterone Resistance and Impaired Endometrial Receptivity

Progesterone resistance is a hallmark of PCOS, characterized by reduced responsiveness of the endometrium to progesterone signaling (Piltonen et al., 2015). Impaired expression of progesterone receptors and altered downstream gene transcription lead to endometrial dysfunction, contributing to infertility, recurrent miscarriage, and increased risk of endometrial hyperplasia and cancer (Hu et al., 2018).

3.4 Adrenal Contribution to Androgen Excess

Although ovarian hyperandrogenism predominates, the adrenal glands contribute up to 30% of circulating androgens in women with PCOS (Azziz, 2016). Dysregulated adrenal steroidogenesis, involving 21-hydroxylase and 11β-hydroxylase pathways, results in elevated dehydroepiandrosterone sulfate (DHEAS) levels in a subset of patients (Yildiz et al., 2010). This adrenal contribution is particularly evident in lean PCOS phenotypes.

4.1 Insulin Resistance: Systemic and Tissue-Specific Mechanisms

Insulin resistance (IR) is present in up to 70% of women with PCOS, independent of obesity (Dunaif, 2012). It manifests in multiple tissues, including muscle, adipose, and liver, leading to impaired glucose utilization and compensatory hyperinsulinemia.

• Adipose tissue inflammation: PCOS adipose tissue exhibits infiltration of macrophages and increased secretion of TNF-α, IL-6, and MCP-1, which impair insulin sensitivity and exacerbate systemic inflammation (Gambineri et al., 2012).
• Impaired PI3K-AKT signaling: Post-receptor defects, particularly serine phosphorylation of insulin receptor substrate (IRS-1/2), blunt downstream PI3K-AKT signaling, reducing glucose uptake and glycogen synthesis (Diamanti-Kandarakis & Dunaif, 2012).
• Mitochondrial dysfunction: Abnormalities in mitochondrial oxidative phosphorylation and increased ROS generation further compromise insulin sensitivity and energy homeostasis (Victor et al., 2009).

4.2 Hyperinsulinemia and Its Impact on Ovarian and Adrenal Androgen Production

Hyperinsulinemia acts synergistically with LH to enhance ovarian theca cell androgen biosynthesis through upregulation of CYP17A1 and STAR (Nelson et al., 2019). Insulin also decreases hepatic sex hormone–binding globulin (SHBG), increasing free testosterone levels (Diamanti-Kandarakis et al., 2006). In the adrenal cortex, hyperinsulinemia enhances androgen secretion by sensitizing steroidogenic enzymes, thereby contributing to elevated DHEAS in a subset of women (Azziz, 2016).

Figue 2. Schematic representation of Insulin resistance & hyperinsulinemia across tissues

PCOS is strongly associated with dyslipidemia, independent of BMI. Women typically present with elevated triglycerides, reduced HDL-C, and small dense LDL particles (Wild et al., 2011). Insulin resistance and hyperandrogenism alter hepatic lipoprotein metabolism by increasing VLDL synthesis and impairing lipolysis. These lipid disturbances contribute to long-term cardiovascular risks in PCOS.

4.4 Obesity, Adipokines (Leptin, Adiponectin, Resistin), and Energy Homeostasis

Obesity exacerbates metabolic dysfunction in PCOS, but even lean women can exhibit adipose tissue abnormalities. Adipokines play a crucial role in metabolic regulation:

• Leptin: Hyperleptinemia is common, reflecting leptin resistance, which contributes to disrupted appetite control and reproductive dysfunction (Carmina et al., 2020).
• Adiponectin: Levels are reduced in PCOS, independent of BMI, impairing insulin sensitivity and lipid oxidation (Panidis et al., 2003).
• Resistin and visfatin: Elevated levels promote systemic inflammation and further aggravate IR (Tan et al., 2008).

This dysregulated adipokine profile contributes to a vicious cycle of energy imbalance, inflammation, and hormonal disruption in PCOS.

Figue 3: Adipokines (leptin, adiponectin, chemerin, resistin, etc.) in PCOS

5.1 Chronic Low-Grade Inflammation as a Hallmark of PCOS

Chronic low-grade inflammation is widely recognized as a core feature of PCOS and is observed across phenotypes, including lean and obese patients (Escobar-Morreale, 2018). Inflammatory activation in PCOS is systemic but also local (ovarian and adipose microenvironments), and it contributes to insulin resistance, altered steroidogenesis, and adverse reproductive outcomes (Diamanti-Kandarakis & Dunaif, 2012). Elevated markers of low-grade inflammation correlate with metabolic dysfunction and are thought to participate in the feed-forward cycle that links metabolic and reproductive abnormalities in PCOS.

5.2 Pro-inflammatory Cytokines (TNF-α, IL-6, IL-18, CRP)

Key circulating and tissue cytokines implicated in PCOS include tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), interleukin-18 (IL-18), and C-reactive protein (CRP). These mediators:

• Impair insulin signaling via serine phosphorylation of IRS proteins and suppression of PI3K-AKT activity (Diamanti-Kandarakis & Dunaif, 2012).
• Promote ovarian steroidogenic changes by modulating theca and granulosa cell function (Escobar-Morreale, 2018).
• Associate with cardiometabolic risk markers (e.g., dyslipidemia, endothelial dysfunction) in women with PCOS (Escobar-Morreale, 2018).

Clinical studies and meta-analyses show modest but consistent elevations of CRP, IL-6, and TNF-α in PCOS versus matched controls, independent of BMI in many reports (Escobar-Morreale, 2018).

5.3 Oxidative Stress and ROS Generation

Oxidative stress—marked by increased reactive oxygen species (ROS) production and reduced antioxidant defenses—is prevalent in PCOS and interrelates with inflammation and metabolic dysfunction (Victor et al., 2009). ROS contribute to:

• Damage of cellular macromolecules (lipids, proteins, DNA) in ovarian and metabolic tissues.
• Impaired insulin signaling via oxidative modification of insulin pathway components.
• Exacerbation of local ovarian inflammation and follicular arrest.

Biomarkers such as increased lipid peroxidation products, lower glutathione levels, and altered antioxidant enzyme activity have been reported in multiple PCOS cohorts (Victor et al., 2009; Escobar-Morreale, 2018).

5.4 Immune Cell Involvement: Macrophages, T-cells, and NK Cells in Ovarian Microenvironment

Innate and adaptive immune cells are active participants in PCOS pathophysiology:

• Macrophages: Increased infiltration and altered polarization (shift toward pro-inflammatory M1 phenotype) in adipose tissue and the ovarian stroma contribute to local cytokine production and insulin resistance (Gambineri et al., 2012).
• T-cells: Dysregulated T-cell subsets (e.g., altered Th17/Treg balance) have been reported and may promote chronic inflammation and auto-inflammatory tendencies within reproductive tissues (Escobar-Morreale, 2018).
• Natural killer (NK) cells: Changes in NK cell number/function in the endometrium and ovary have been linked to impaired follicular development and endometrial receptivity, although findings are heterogeneous and phenotype-dependent.

These immune changes create an inflammatory ovarian milieu that disrupts folliculogenesis, steroidogenesis, and endometrial function, thereby linking immune dysregulation with both metabolic and reproductive PCOS manifestations.

5.5 Gut Microbiota Dysbiosis and Systemic Inflammation

Emerging evidence implicates gut microbiota alterations (dysbiosis) in PCOS pathogenesis. Changes in microbial composition and reduced diversity have been associated with systemic inflammation, increased intestinal permeability, and metabolic dysregulation (Lindheim et al., 2017). Proposed mechanisms include:

• Microbial-derived metabolites (e.g., lipopolysaccharide) triggering systemic innate immune activation and cytokine release.
• Effects on bile acid metabolism and short-chain fatty acid profiles that regulate insulin sensitivity and adipose inflammation.
• Interaction between diet, obesity, and the gut microbiome, amplifying inflammatory and metabolic disturbances in PCOS.

Although causality remains under investigation, microbiome modulation (probiotics, prebiotics, dietary interventions) is an active area for therapeutic exploration.

Table 6. Therapeutic Strategies Targeting Inflammation and Oxidative Stress

6. Cellular and Molecular Interactions

6.1 Theca and Granulosa Cell Dysfunction

PCOS ovaries exhibit intrinsic cellular abnormalities, particularly in theca and granulosa cells, which underpin altered folliculogenesis and steroidogenesis.

• Altered steroidogenesis: Theca cells show upregulated expression of steroidogenic enzymes (CYP17A1, CYP11A1), resulting in excess androgen production (Ehrmann, 2005). Granulosa cells, conversely, demonstrate impaired aromatase (CYP19A1) activity, reducing estradiol biosynthesis and contributing to follicular arrest (Franks et al., 2008).
• Growth factor signaling disruption: Key paracrine regulators such as insulin-like growth factor (IGF), vascular endothelial growth factor (VEGF), and anti-Müllerian hormone (AMH) are dysregulated. Elevated AMH reflects increased pre-antral follicle number but also inhibits granulosa cell sensitivity to FSH, impairing follicle maturation (Dewailly et al., 2016). Increased ovarian VEGF is linked to abnormal angiogenesis and contributes to the risk of ovarian hyperstimulation in PCOS patients undergoing assisted reproduction.

6.2 Insulin Receptor and Downstream Signaling Defects

Insulin resistance in PCOS extends to post-receptor signaling defects, particularly at the level of IRS-1/IRS-2 phosphorylation.

• Phosphorylation abnormalities: Enhanced serine phosphorylation and reduced tyrosine phosphorylation of insulin receptor substrates impair downstream PI3K–AKT signaling, reducing glucose uptake in skeletal muscle and adipose tissue (Diamanti-Kandarakis & Dunaif, 2012).
• Cross-regulation with androgen signaling: Hyperinsulinemia synergizes with LH to stimulate theca cell androgen production, while androgens themselves exacerbate insulin resistance, creating a self-perpetuating cycle of endocrine and metabolic dysfunction (Ehrmann, 2005).

6.3 Mitochondrial Dysfunction and Impaired Cellular Energy Metabolism

Mitochondrial defects are increasingly recognized in PCOS. Altered mitochondrial morphology, reduced mtDNA copy number, and impaired oxidative phosphorylation have been reported in ovarian, adipose, and skeletal muscle tissues (Victor et al., 2009). These abnormalities:

• Increase ROS generation and oxidative stress.
• Impair granulosa cell energy metabolism, affecting oocyte maturation.
• Contribute to systemic insulin resistance by disrupting energy utilization in metabolic tissues.

6.4 Crosstalk Between Adipose Tissue, Liver, and Ovary

The multi-organ nature of PCOS involves bidirectional communication:

• Adipose tissue secretes pro-inflammatory adipokines (TNF-α, IL-6, resistin) and has reduced adiponectin, contributing to systemic insulin resistance and ovarian dysfunction (Escobar-Morreale, 2018).
• Liver contributes via dysregulated gluconeogenesis and lipid metabolism, further amplifying hyperinsulinemia and dyslipidemia.
• Ovary responds to these systemic changes by producing excess androgens, which feedback to exacerbate adipose dysfunction and hepatic lipid disturbances.

This adipose–liver–ovary axis underscores PCOS as a systemic metabolic–reproductive disorder rather than an isolated ovarian condition.

7. Clinical Manifestations Linked to Multi-System Crosstalk

7.1 Reproductive Outcomes: Anovulation, Infertility, Miscarriage Risk

PCOS is the most common cause of anovulatory infertility. Follicular arrest due to granulosa cell dysfunction, excess AMH, and disrupted gonadotropin secretion leads to chronic anovulation (Franks et al., 2008). Infertility is compounded by impaired endometrial receptivity, and PCOS women have a higher risk of miscarriage, partly attributable to hyperinsulinemia, hyperandrogenism, and chronic inflammation (Palomba et al., 2015).

7.2 Metabolic Syndrome and Type 2 Diabetes Mellitus

PCOS is strongly associated with metabolic syndrome, defined by abdominal obesity, insulin resistance, dyslipidemia, and hypertension (Ehrmann, 2005). Longitudinal studies confirm a 3–5 fold increased risk of type 2 diabetes mellitus (T2DM) in PCOS women, independent of BMI (Legro et al., 2013).

7.3 Cardiovascular Complications: Hypertension, Atherosclerosis

Chronic low-grade inflammation, endothelial dysfunction, and dyslipidemia predispose PCOS women to hypertension and premature atherosclerosis. Although absolute cardiovascular event risk remains debated due to age-related confounding, subclinical markers (carotid intima-media thickness, coronary artery calcification) are consistently elevated in PCOS cohorts (Wild et al., 2010).

7.4 Endometrial Dysfunction and Cancer Risk

Unopposed estrogen exposure due to chronic anovulation, along with hyperinsulinemia, increases the risk of endometrial hyperplasia and carcinoma in PCOS women (Chittenden et al., 2009). Defects in progesterone signaling, chronic inflammation, and altered immune surveillance exacerbate this vulnerability.

7.5 Psychological and Neurological Aspects: Anxiety, Depression, Cognitive Changes

PCOS is associated with significantly higher prevalence of anxiety, depression, and reduced quality of life (Dokras et al., 2011). Emerging data also suggest cognitive alterations, potentially linked to chronic inflammation, insulin resistance, and hyperandrogenemia, although findings are still preliminary.