High-Protein Diet Ameliorates Cardiomyopathy in a Cardiac-Specific AGL Knockout Mouse Model: Association With Upregulated Hepatic Gluconeogenesis.

Glycogen storage disease type IIIa (GSDIIIa) causes progressive cardiomyopathy, and current high-fat dietary strategies lack consensus regarding long-term cardiovascular safety. We evaluated the efficacy and safety of high-protein versus high-fat diets in a novel cardiac-specific AGL knockout (CKO; AGLflox/flox/MHC-Cre) mouse model to specifically assess isolated cardiac responses. CKO mice were randomized at weaning to High-Protein (HPD), High-Protein High-Fat (HPHFD), or Low-Protein (LPD) diets, with approximate protein/fat/carbohydrate distributions of 40%/4%/50%, 40%/50%/10%, and 10%/4%/80%, respectively; CKO mice on normal diet (ND) and AGLflox/flox mice served as controls. Cardiac phenotypes and hepatic gluconeogenic enzymes were evaluated longitudinally up to 24 weeks. CKO-ND mice developed progressive cardiomyopathy with elevated myocardial glycogen at 24 weeks (32.01 ± 3.22 vs. 5.90 ± 2.21 mg/g in controls, p < 0.001), reduced left ventricular ejection fraction, and elevated serum creatine kinase. Both HPD and HPHFD significantly reduced myocardial glycogen burden (12.82 ± 3.58 and 15.07 ± 4.40 mg/g, p < 0.001), restored systolic function, and normalized hypertrophy. However, HPHFD induced distinct hyperlipidemia, whereas HPD maintained a stable lipid profile. Furthermore, therapeutic benefits in high-protein groups were associated with upregulated hepatic rate-limiting gluconeogenic enzymes (FBP2, PCK1). In this cardiac-specific AGL knockout model, a high-protein, non-high-fat diet attenuated cardiac glycogen accumulation and systolic dysfunction without the hyperlipidemia observed with the high-fat regimen. These preclinical findings support further evaluation of high-protein dietary strategies for GSDIIIa cardiomyopathy and suggest a possible liver-heart metabolic axis involving hepatic gluconeogenesis.