Crosstalk between the aryl hydrocarbon receptor and hypoxia-inducible factor 1α pathways in human islet models

We previously showed that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD - a persistent organic pollutant) activates the aryl hydrocarbon receptor (AHR) in pancreatic islets. The AHR is known to crosstalk with hypoxia-inducible factor 1α (HIF1α) in other cell types but AHR-HIF1α crosstalk has not been previously examined in islet cells. Islet cell function is sensitive to hypoxia; we hypothesize that AHR activation by environmental pollutant(s) will interfere with the HIF1α pathway response in islets, which may be detrimental to islet cell function and survival during periods of hypoxia.

We assessed AHR-HIF1α crosstalk by treating human donor islets and stem cell-derived islets (SC-islets) with 10 nM TCDD ± 1% O₂ and measuring gene expression of downstream targets of AHR (e.g. CYP1A1) and HIF1α (e.g. HMOX1).

In SC-islets, co-treatment with TCDD + hypoxia consistently suppressed CYP1A1 induction compared with TCDD treatment alone. In human islets, TCDD + hypoxia co-treatment suppressed CYP1A1 induction, but only in 2 of 6 donors. Both SC-islets and human donor islets displayed hypoxia-mediated suppression of glucose-6-phosphate catalytic subunit 2 (G6PC2) expression. Glucose-stimulated insulin secretion (GSIS) in human donor islets was impaired by hypoxia exposure, but unaffected by TCDD exposure.

Our study shows consistent AHR-HIF1α crosstalk in SC-islets and variable crosstalk in primary human islets, depending on the donor. In both cell models, hypoxia exposure interfered with activation of the AHR pathway by TCDD but there was no evidence that AHR activation interfered with the HIF1α pathway. In summary, our data show that co-exposure to an environmental pollutant and hypoxia results in molecular crosstalk in islets.