Combination Gene Therapy with AAV-Based Vectors Ameliorates the Phenotype of Type 2 Diabetes in Diet-Induced Obese and db/db Mice

Type 2 diabetes mellitus (T2DM) has significant treatment challenges due to its complex pathophysiology and associated comorbidities. In recent years, hepatokine fibroblast growth factor 21 (FGF21) has gained significant attention for treatment of metabolic disorders. Its translation potential is hindered by a short half-life and adverse effects on skeletal muscle. To address this, we developed an engineered AAV8 vector encoding codon-optimized human FGF21 ( co.hFGF21 ) transgene either alone or in combination with AAV9-miR411 to sustain FGF21 expression and to preserve muscle function. Our analysis over a 41 week follow-up period in diet-induced obese (DIO) mice showed that co.hFGF21 gene therapy led to a substantial reduction in body weight (∼38%), improved glycemic profile (blood glucose 80–108 vs 116–150 mg/dL, in control vector group), preserved glucose-stimulated insulin secretion, and attenuated hepatic steatosis. The combination of co.hFGF21 and miR-411 enhanced insulin responsiveness and muscle histology. To further validate the therapeutic efficacy of hFGF21, we used diabetic Lepr db /J ( db / db ) mice. co.hFGF21 gene therapy controlled obesity (body weight reduction of ∼31%), reversed hyperglycemia, and improved insulin sensitivity over a 30 week period. Additionally, co.hFGF21 expression significantly improved energy expenditure in db / db mice without any adverse effects on skeletal muscles. These findings support the use of optimized AAV8 human codon-optimized FGF21 as a viable, long-lasting therapeutic strategy for T2DM.