The hypothalamic-pituitary-gonadal axis
In trying to understand the pathophysiology of the condition, much of the latest research has zeroed in on potential mechanisms in the hypothalamic-pituitary-gonadal axis. “A consistent feature of PCOS is disordered gonadotropin secretion with elevated mean LH [luteinizing hormone], low or low normal FSH [follicle-stimulating hormone], and a persistently rapid frequency of GnRH [gonadotropin-releasing hormone] pulse secretion,” wrote authors of a scientific statement on aspects of PCOS.
“I think the balance is heading more to central neurologic control of the reproductive system and that disturbances there impact the GnRH cells in the hypothalamus, which then go on to give us the findings that we can measure peripherally with the LH-FSH ratio,” Dr. Hudson said in an interview.
The increased LH levels are thought to be a major driver of increased androgen levels. Current thinking suggests that the primary driver of increased LH is GnRH pulsatility, supported not only by human studies but by animal models as well. This leads to the question of what drives GnRH dysregulation. One hypothesis posits that GABA neurons play a role here, given findings that GABA levels in cerebrospinal fluid were higher in women with PCOS than those with normal ovulation.
But the culprit garnering the most attention is kisspeptin, a protein encoded by the KISS1 gene that stimulates GnRH neurons and has been linked to regulation of LH and FSH secretion. Kisspeptin, along with neurokinin B and dynorphin, is part of the triumvirate that comprises KNDy neurons, also recently implicated in menopausal vasomotor symptoms. Multiple systematic reviewsand meta-analyses have found a correlation between higher kisspeptin levels in the blood and higher circulating LH levels, regardless of body mass index. While kisspeptin is expressed in several tissues, including liver, pancreas, gonad, and adipose, it’s neural kisspeptin signaling that appears most likely to play a role in activating GnRH hormones and disrupting normal function of the hypothalamic-pituitary-gonadal axis.
But as noted, in at least one systematic review of kisspeptin and PCOS, “findings from animal studies suggest that kisspeptin levels are not increased in all subtypes of PCOS.” And another review found “altered” levels of kisspeptin levels in non-PCOS patients who had obesity, potentially raising questions about any associations between kisspeptin and obesity or insulin resistance.
Remaining chicken-and-egg questions
A hallmark of PCOS has long been, and continues to be, the string of chicken-or-egg questions that plague understanding of it. One of these is how depression and anxiety fit into the etiology of PCOS. Exploring the role of specific neurons that may overstimulate GnRH pulsatility may hold clues to a common underlying mechanism for the involvement of depression and anxiety in patients with PCOS, Dr. Hudson speculated. While previous assumptions often attributed depression and anxiety in PCOS to the symptoms – such as thin scalp hair and increased facial hair, excess weight, acne, and irregular periods – Dr. Hudson pointed out that women can address many of these symptoms with laser hair removal, weight loss, acne treatment, and similar interventions, yet they still have a lot of underlying mental health issues.
It’s also unclear whether metabolic factors so common with PCOS, particularly insulin resistance and obesity, are a result of the condition or are contributors to it. Is insulin resistance contributing to dysregulation in the neurons that interferes with normal functioning of the hypothalamic-pituitary-adrenal axis? Is abnormal functioning along this axis contributing to insulin resistance? Or neither? Or both? Or does it depend? The authors of one paper wrote that “insulin may play both direct and indirect roles in the pathogenesis of androgen excess in PCOS,” since insulin can “stimulate ovarian androgen production” and “enhance ovarian growth and follicular cyst formation in rats.”
Dr. Pal noted that “obesity itself can evolve into a PCOS-like picture,” raising questions about whether obesity or insulin resistance might be part of the causal pathway to PCOS, or whether either can trigger its development in those genetically predisposed.
“Obesity does appear to exacerbate many aspects of the PCOS phenotype, particularly those risk factors related to metabolic syndrome,” wrote the authors of a scientific statement on aspects of PCOS, but they add that “it is currently debated whether obesity per se can cause PCOS.” While massive weight loss in those with PCOS and obesity has improved multiple reproductive and metabolic issues, it hasn’t resolved all of them, they write.
Dr. Hudson said she expects there’s “some degree of appetite dysregulation and metabolic dysregulation” that contributes, but then there are other women who don’t have much of an appetite or overeat and still struggle with their weight. Evidence has also found insulin resistance in women of normal weight with PCOS. “There may be some kind of metabolic dysregulation that they have at some level, and others are clearly bothered by overeating,” Dr. Hudson said.
Similarly, it’s not clear whether the recent discovery of increased cardiovascular risks in people with PCOS is a result of the comorbidities so common with PCOS, such as obesity, or whether an underlying mechanism links the cardiovascular risk and the dysregulation of hormones. Dr. Pal would argue that, again, it’s probably both, depending on the patient.
Then there is the key feature of hyperandrogenemia. “An outstanding debate is whether the elevated androgens in PCOS women are merely a downstream endocrine response to hyperactive GnRH and LH secretion driving the ovary, or do the elevated androgens themselves act in the brain (or pituitary) during development and/or adulthood to sculpt and maintain the hypersecretion of GnRH and LH?” wrote Eulalia A. Coutinho, PhD, and Alexander S. Kauffman, PhD, in a 2019 review of the brain’s role in PCOS.
These problems may be bidirectional or part of various feedback loops. Sleep apnea is more common in people with PCOS, Dr. Tyson noted, but sleep apnea is also linked to cardiovascular, metabolic, and depression risks, and depression can play a role in obesity, which increases the risk of obstructive sleep apnea. “So you’re in this vicious cycle,” Dr. Tyson said. That’s why she also believes it’s important to change the dialogue and perspective on PCOS, to reduce the stigma attached to it, and work with patients to empower them in treating its symptoms and reducing their risk of comorbidities.