Assessing the role of the Caprin-2 RNA binding protein in supraoptic nucleus function

Abstract

The expression of the gene encoding the RNA binding protein Caprin-2 is robustly upregulated by dehydration in the hypothalamic supraoptic nucleus (SON). Caprin-2 has previously been reported to play a key role in the osmotic defense response by binding to the vasopressin (Avp) mRNA and modulating the length of its poly(A) tail. Increased polyadenylation is thought to promote transcript stability and to control translation. In order to define the network of genes regulated by Caprin-2 in the SON, virally delivered shRNAs were used to knock down Caprin-2 expression in the SON of both euhydrated and dehydrated rats. RNA sequencing was then used to identify global alterations in gene expression consequential to Caprin-2 knockdown. Genes which are known to be upregulated in the SON as a consequence of dehydration were significantly downregulated by Caprin-2 knockdown. To validate these findings, immunohistochemistry was conducted on the brain slices to map several neuropeptides known to be secreted from the SON-pituitary axis. AVP, oxytocin (OXT), VGF, and cellular markers for the endoplasmic reticulum (ER) and Golgi apparatus (GA) compartments responsible for neuropeptide trafficking were examined. It was observed that as Caprin-2 was knocked down, higher accumulation of AVP precursor protein was observed in the SON. In contrast, the neuropeptide OXT decreases within the SON following Caprin-2 knockdown. Caprin-2 knockdown resulted in compromised increase of soma size, ER and GA which are normally observed following dehydration. In the intact SON, dehydration evokes enhanced soma-somatic membrane apposition driven mainly by astrocytic retraction. However, when Caprin-2 was knocked down, this glial retraction was compromised. Previous studies have suggested a pivotal role of SON RNA binding protein Caprin-2 in osmoregulatory. Here it was shown that knockdown of Caprin-2 expression massively alters the SON transcriptome under both euhydrated and dehydrated conditions. These data suggest that Caprin-2 is vital for the preservation of overall SON function during osmotic stress.

Date of Award	20 Jun 2023
Original language	English
Awarding Institution	University of Bristol
Supervisor	Paul Bishop (Supervisor) & David Murphy (Supervisor)