The Characterization of Sex Differences in Hypoglycemia-Induced Activation of HPA Axis on the Transcriptomic Level

Activation of the hypothalamic-pituitary-adrenal (HPA) axis using an insulin tolerance test (ITT) is a medical diagnostic procedure that is frequently used in humans to assess the HPA and growth-hormone (GH) axes. Whether sex differences exist in the response to ITT stress is unknown. Thus, investigations into the analysis of transcripts during activation of the HPA axis in response to hypoglycemia have revealed the underlying influences of sex in signaling pathways that stimulate the HPA axis. We assessed four time points of ITT application in Balb/c mice. After insulin injection, expression levels of 192 microRNAs and 41 mRNAs associated with the HPA, GH and hypothalamic-pituitary-gonadal (HPG) axes were determined by real-time RT-PCR in the hypothalamus, pituitary and adrenal tissues, as well as blood samples (Raw data accession: https://drive.google.com/drive/folders/10qI00NAtjxOepcNKxSJnQbJeBFa6zgHK?usp=sharing ). Although the ITT is commonly used as a gold standard for evaluating the HPA axis, we found completely different responses between males and females with respect to activation of the HPA axis. While activation of several transcripts in the hypothalamus and pituitary was observed after performing the ITT in males within 10 min, females responded via the pituitary and adrenal immediately and durably over 40 min. Additionally, we found that microRNA alterations precede mRNA responses in the HPA axis. Furthermore, robust changes in the levels of several transcripts including Avpr1b and Avpr2 observed at all time points strongly suggest that transcriptional control of these genes occurs mostly via differential signaling in pituitary and blood between males and females. Male and female HPA axis responses to ITT involve a number of sophisticated regulatory signaling pathways of miRNAs and mRNAs. Our results highlight the first robust markers in several layers of HPA, HPG and GH axis involved in ITT/hypoglycemia stress-induced dynamics.