# The ExPAND Study: A Prospective Association Study into Endometriosis-Associated Pain, Neurosteroid Synthesis, and TRPM3

## TL;DR

The ExPAND study explores how neurosteroids and TRPM3 may contribute to endometriosis-related pain, offering new insights into its causes.

## Contribution

The study identifies increased CYP17A1 expression and demonstrates that neurosteroids PS and DHEAS activate TRPM3 in sensory neurons, linking them to endometriosis pain.

## Key findings

- CYP17A1 mRNA levels are significantly higher in endometrium of patients with severe pain symptoms.
- PS and DHEAS concentrations in peritoneal fluid are sufficient to stimulate TRPM3 activity in vitro.
- DHEAS and PS activate human sensory neurons in a TRPM3-dependent manner.

## Abstract

Endometriosis-associated pain has debilitating effects on the quality of life of patients. Despite its high prevalence in reproductive-aged women, the pathophysiology is still unknown, impeding the development of targeted treatment approaches. The prospective ExPAND study proposes the neurosteroids pregnenolone sulphate (PS) and dehydroepiandrosterone sulphate (DHEAS) as potential contributors to endometriosis-associated pain, due to their agonistic action at the pain-related ion channel TRPM3. To this end, endometrium, deep endometriosis lesions, and peritoneal fluid were prospectively collected in four demarcated patient groups, which were characterised based on their pain symptoms, as scored via the WERF-EPHect questionnaire, i.e., (1) control (n = 44), (2) endometriosis patients with no pain symptoms (n = 24), (3) with only severe dysmenorrhea (n = 54), or (4) with both severe dysmenorrhea and non-cyclic pelvic pain (n = 78). Tissue mRNA expression levels of steroidogenic enzymes were investigated and showed significantly increased levels of CYP17A1 in the endometrium of patients with severe pain symptoms compared to control tissue. In addition, liquid chromatography with tandem mass spectrometry (LC-MS/MS) was performed to investigate neurosteroid concentrations in the peritoneal fluid. Both neurosteroids PS and DHEAS were present in the peritoneal fluid at concentrations that are known to stimulate TRPM3 activity in vitro. Finally, using microfluorimetric Ca2+ imaging, we demonstrate that both DHEAS and PS stimulate human stem-cell-derived sensory neurons in a TRPM3-dependent manner. Taken together, these data indicate a potential contribution of steroidogenesis and TRPM3 in endometriosis-associated pain.