The role of MRAP in adipocyte metabolism
Ruoyan Xu, Queen Mary University of London
Globally, obesity is a leading cause of early death through associated co-morbidities (cardiovascular disease, cancer, type 2 diabetes and COVID-19). There is increasing interest in brown adipose tissue (BAT) activation and white adipose tissue (WAT) beigeing / browning as a therapeutic strategy for weight loss in humans. Melanocortin-2-receptor accessory protein (MRAP) is a small single transmembrane domain protein, that enables the functional expression of the Melanocortin-2-receptor (MC2R). MRAP loss-of-function mutations gives rise to Familial Glucocorticoid Deficiency type-2 (FGD2). We reported the Mrap-/- mouse phenotype which recapitulates FGD2 (Novoselova et al. 2018). Beyond the adrenal gland, MRAP is highly expressed in adipose tissue. Recent studies showed that MRAP was involved in ACTH stimulated lipolysis (Zhang et al. 2018) and expression is associated with obesity in a primate model (Murray et al. 2020). However, its function in adipocyte metabolism remains largely unknown.
The overarching aim of the proposal is to define the role of MRAP in adipose tissue biology especially adipocyte metabolism and thermogenesis. Specific aims include (1) Determine the role of MRAP in rodent 3T3-L1 MRAP knock-out (KO) and wide-type (WT) pre-adipocyte cells, (2) Develop and assess a human MRAP-KO cell model using the Simpson-Golabi-Behmel syndrome (SGBS) pre-adipocyte cell-line.
I am grateful to the Bioscientifica Trust for award of the COVID-19 response fund provided me with short bridge salary support (£4,913.43). The funding enabled me to generate some preliminary data which was used for a Barts Charity Programme Grant for which I was a named post-doc.
With the Bioscientifica Trust support, I utilised Seahorse and mitochondrial stress test assays to measure the oxygen consumption rate of the MRAP KO cells compared to wild type cells. The results confirmed the MRAP affected basal oxygen consumption rate and the maximum oxygen consumption rate of the 3T3-L1 cells in the presence of MRAP. Mitochondrial activity increased as a result of MRAP KO, which could contribute to increased thermogenesis.
Using a global MRAP KO mice model, I analysed RNA sequencing data derived from brown adipose tissue and white adipose tissue extracted from global MRAP KO mice compared to MRAP-wildtype littermates. By comparing the KO effect on (MRAP KO mice vs. wildtype) brown adipose tissue and white adipose tissues, we were able to hone down a list of upregulated and downregulated genes and pathways that place a key role in metabolism. This data supported our hypothesis that MRAP plays a key role in adipocyte metabolism.
My preliminary data was used to support the funding of a £2.7M Barts Charity programme grant (Barts Metabolism Network) for which I was a named post-doctoral associate. I am currently working on expanding the role of MRAPs in cellular metabolism to build a fellowship application in the future.
Grant awarded: £4,913.43