Antisense Oligonucleotide-Based Therapeutic Strategy for Genetic Obesity Caused by MC4R Mutations

About This Grant

Project Summary The leptin-melanocortin pathway, an endocrine circuit linking adipocyte metabolism to brain circuits that govern appetite and energy expenditure, is considered a critical target for developing obesity treatments. Obesity syndromes that develop in early childhood frequently increase burden of comorbidities including hypertension, cardiovascular disease, type 2 diabetes, and cancer. Mutations in the MC4R gene, a critical node in the leptin- melanocortin pathway, are the most common genetic cause of early-onset obesity with a mean age of onset of approximately 2.5 to 7.3 years. The MC4R gene encodes for melanocortin-4 receptor (MC4R), which is a G protein-coupled receptor expressed by neurons in the hypothalamus and central nervous system that governs appetite and energy expenditure. Heterozygous loss-of-function MC4R mutations result in hyperphagia, increases in fat and lean mass, increased linear growth, severe obesity (BMI>35), and increased risk for type 2 diabetes. While there are approved drugs for early-onset obesity caused by mutation in MC4R and other genes in the leptin-melanocortin pathway for older age groups, there is currently no approved treatment for children under 10 years of age with MC4R mutations. Moreover, the MC4R agonist drug setmelanotide is only partially selective and “off-target” activation of other melanocortin receptors (MC1R and MC3R) contributes to side effects such as nausea and hyperpigmentation. Thus, there remains a critical need for developing treatments that are effective at selectively targeting MC4R. This proposal focuses on developing and testing a novel therapeutic strategy that specifically amplifies endogenous MC4R signaling. Antisense oligonucleotides (ASOs) are emerging as a promising therapeutic modality, and we have recently developed an ASO strategy that increases levels of a target protein in a dose-dependent manner in the central nervous system. This strategy uses ASOs to sterically block microRNA binding sites in the target mRNA and thereby derepress translation. Applying this ASO-based approach to MC4R has the potential to directly address the underlying genetic defect by restoring normal MC4R protein levels, in the setting of MC4R haploinsufficiency. We have identified two regions in the MC4R mRNA that may be amenable to targeting, and our preliminary data show that ASOs targeting these regions can increase MC4R protein levels in cultured cells. In this proposal, we will: 1) design additional MC4R- targeting ASOs and test them in cultured cells and iPSC-derived neurons, 2) generate and characterize a humanized MC4R mouse model of genetic obesity, and 3) test if ASO-mediated increase of MC4R can reverse hyperphagia and obesity in heterozygous humanized MC4R mice. Completion of these studies will generate important preclinical data that provide insights into the utility of this ASO-based therapeutic approach for genetic obesity caused by MC4R mutations.