A new study reveals how estrogen fine-tunes gut cell communication to amplify serotonin-driven pain, shedding light on why women suffer more from IBS and offering new leads for targeted therapies.
Study: A Cellular Basis for Heightened Gut Sensitivity in Females. Image Credit: Prathankarnpap / Shutterstock
*Important notice: bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
A recent study posted to the bioRxiv preprint* server identified a new estrogen-responsive pathway in which two types of enteroendocrine cells (EECs) communicate to increase gut sensitivity in females.
Chronic gastrointestinal (GI) pain conditions are more common in females, which can be aggravated with changes in estrogen levels during pregnancy and the menstrual cycle. While the relevant estrogen targets remain unknown, the gut mucosa could be a potential site of action, where sensory nerve fibers interact with epithelial cells. Most epithelial cells lining the gut are enterocytes, which primarily function to absorb electrolytes, nutrients, and water from the digestive tract.
The rare, excitable EECs are interspersed among the enterocytes and detect luminal contents and release neurotransmitters and peptides, triggering physiological responses. Serotonergic enterochromaffin (EC) cells are a subtype of EEC cells that activate mucosal spinal afferents to induce visceral pain. This EC cell-sensory nerve circuit exhibits increased sensitivity in female mice, suggesting that it might be the locus for the enhancement of visceral pain.
The L-cell, another EEC subtype, is known for its role in secreting hormones, such as peptide YY (PYY) and glucagon-like peptide-1 (GLP-1), and sensing postprandial nutrients. Exogenous administration of the cleaved PYY3-36 peptide causes gastrointestinal discomfort. PYY3-36 selectively binds to neuropeptide Y2 receptors (NPY2Rs) in the brain and vagal afferents.
The larger PYY1-36 peptide also activates the NPY1R, expressed by spinal afferents and EC cells in the gut. With EC cells being the primary detectors of noxious stimuli along the gut epithelium, coupling between NPY1R and PYY1-36 could presumably lead to hypersensitivity and visceral discomfort. However, few studies have investigated paracrine coupling between EC and L cells and their consequences on visceral pain.
The study and findings
The present study demonstrated that crosstalk between EC and L cells results in visceral hypersensitivity. First, the team investigated whether estrogen is involved in the differential sensitivity of mucosal sensory afferents, which have been previously shown to exhibit higher baseline activity in female mice compared to male mice. To this end, afferent nerve fiber activity in ex vivo mucosal preparations (evMAR) was compared between male and ovariectomized (OVX) or intact female mice.
Higher responses were recorded in females compared to males, and this difference was attenuated in OVX females. Moreover, estrogen had a marked effect on behavioral measures of visceral sensitivity, determined by evaluating visceral motor responses to colorectal distension. Responses in females were significantly attenuated when OVX depleted estrogen. Notably, a single treatment of OVX females with estradiol benzoate (EB) reversed this attenuation.
Furthermore, the team observed that the estrogen receptor alpha (ERα) was expressed at relatively low levels in proximal gut regions but at markedly high levels in a sparse population of cells, especially in the distal colon, where visceral pain is most acutely perceived. This enrichment of ERα in the colon relative to the small intestine suggests regional specialization in estrogen responsiveness. Therefore, they investigated how the loss of ERα impacts visceral sensitivity and gut function.
While mutant mice lacking intestinal ERα showed no changes in gross metabolic parameters (e.g., daily food intake, body weight), colonic motility and GI transit times were significantly accelerated, particularly in females. ERα depletion also reduced mucosal afferent sensitivity in females relative to males. Interestingly, estrogen treatment failed to increase visceral sensitivity in mutant females, indicating that ERα was central to estrogen-dependent enhancement of visceral sensitivity.
Unexpectedly, EC cells lacked ERα, but ERα was found to overlap completely with Pyy-expressing cells, particularly in the distal colon. Additional experiments showed that PYY1-36 could fully restore gut sensitivity in OVX females or after the loss of estrogen signaling in the gut epithelium, and that PYY1-36 acts locally to bind to NPY1R on EC cells, triggering serotonin release that enhances activity of the EC-mucosal afferent circuit and induces gut pain.
The researchers also demonstrated that blocking this pathway pharmacologically—either at the level of NPY1R or the serotonin 5HT3R—abolished the estrogen- and PYY1-36-induced visceral hypersensitivity. These findings reinforce the pathway’s central role in mediating pain signaling.
Finally, the researchers identified estrogen-responsive targets that could modulate visceral sensitivity by profiling sorted L-cells from vehicle- or EB-treated OVX females. This revealed multiple targets sensitive to estrogen, including known ERα targets. In total, 248 genes were upregulated and 35 downregulated, highlighting a broad transcriptional response in L-cells, while only a few estrogen-responsive genes were identified in sorted EC cells.
The short-chain fatty acid (SCFA) receptor, encoded by the olfactory receptor 78 (Olfr78), emerged as the top hit, and its expression in L-cells upon estrogen treatment was confirmed. However, Olfr78 was unchanged in EC cells after estrogen treatment. Preincubating female intestinal organoids with estrogen and treating them with acetate (OLFR78 ligand) significantly increased L-cell responses to acetate.
Conclusions
Together, the findings reveal how estrogen signaling modulates paracrine interactions between two EEC subtypes, illuminating the mechanism of heightened visceral sensitivity in females. PYY1-36 from L cells initiates the cellular cascade by amplifying the serotonergic tone in EC cells, activating nearby mucosal spinal afferents. Estrogen plays a crucial role in triggering these events by enhancing PYY release and increasing the sensitivity of L cells to bacterial metabolites (SCFAs) through the upregulation of Olfr78.
The results also suggest therapeutic strategies for conditions such as irritable bowel syndrome (IBS), including combined use of NPY1R and 5HT3R antagonists, alongside dietary interventions that reduce SCFA production (e.g., low FODMAP diets).
*Important notice: bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
