Determinants of plasma levels of gcg and metabolic impact of glucagon receptor signalling – a UK Biobank study

Aims/hypotheses Glucagon and Glucagon-like peptide-1 (GLP-1) are derived from the same precursor; proglucagon (gcg), and dual agonists of their receptors are currently explored for the treatment of obesity and steatotic liver disease. Elevated levels of endogenous glucagon (hyperglucagonaemia) have been linked with hyperglycaemia in individuals with type 2 diabetes but are also observed in individuals with obesity and metabolic dysfunction-associated steatotic liver disease (MASLD). It is unknown whether type 2 diabetes, obesity or MASLD causes hyperglucagonaemia or vice versa. We investigated potential determinants of plasma gcg and associations of glucagon receptor signalling with metabolic diseases based on data from the UK Biobank. Methods We used exome sequencing data from the UK Biobank for ∼410,000 Caucasians to identify glucagon receptor variants and grouped them based on their known or predicted signalling. Plasma levels of gcg estimated using Olink technology was available for a subset of the cohort (∼40,000). We determined associations between glucagon receptor variants and gcg with BMI, type 2 diabetes, and liver fat (quantified by liver MRI) and performed survival analyses to investigate if elevated gcg predicts type 2 diabetes development. Results Obesity, MASLD, and type 2 diabetes independently associated with elevated plasma levels of gcg. Baseline gcg levels were statistically significantly associated with the risk of type 2 diabetes development over a 14-year follow-up period (hazard ratio = 1.13; 95% confidence interval (CI) = 1.09, 1.17, p < 0.0001). This association was of the same magnitude across strata of BMI. Carriers of glucagon receptor variants with reduced cAMP signalling had elevated levels of gcg (β = 0.847; CI = 0.04, 1.66; p = 0.04), and carriers of variants with a predicted frameshift mutation had significantly higher levels of liver fat compared to wild-type controls (β = 0.504; CI = 0.03, 0.98; p = 0.04). Conclusions/interpretation Our findings support that glucagon receptor signalling is involved in MASLD and type 2 diabetes, and that plasma levels of gcg are determined by genetic variation in the glucagon receptor, obesity, type 2 diabetes, and MASLD. Determining the molecular signalling pathways downstream of glucagon receptor activation may guide the development of biased GLP-1/glucagon co-agonist with improved metabolic benefits. Research in context What is already known about this subject? What is the key question? What are key determinants of plasma proglucagon (gcg) and is elevated plasma gcg a cause or consequence (or both) of type 2 diabetes? What are the new findings? How might this impact on clinical practice in the foreseeable future? ### Competing Interest Statement NJWA has received research support and speaker fees from Mercodia, Novo Nordisk, Merck, MSD, and Boehringer Ingelheim. LLG has received research support and speaker fees from Novo Nordisk, Pfizer, Becton, Dickinson, Alexion, Gilead, Sobi, Alexion, Immunovia, Norgine, Pfizer, Astra Zeneca. ### Funding Statement NJWA is supported by NNF Excellence Emerging Investigator Grant: Endocrinology and Metabolism (Application No. NNF19OC0055001), EFSD Future Leader Award (NNF21SA0072746) and DFF Sapere Aude (1052 00003B). NNF Center for Protein Research is supported financially by the NNF (grant agreements NNF14CC0001 and NNF17OC0027594). Access to UK Biobank data was funded by the Augustinus Foundation (grants 20 1914 and 21 1518). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This research has been conducted using the UK Biobank Resource under Application Number 61785. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes * Gcg : proglucagon GLP-1 : Glucagon-like peptide-1 LoF : loss-of-function MASLD : metabolic dysfunction-associated steatotic liver disease NPX : Normalized Protein eXpression PDFF : Proton density fat-fraction UKB : UK Biobank