Semaglutide-induced weight loss improves mitochondrial energy efficiency in skeletal muscle

Abstract

Objective: Glucagon-like peptide-1 receptor agonists (e.g., semaglutide) potently induce weight loss, thereby reducing obesity-related complications. However, weight regain occurs when treatment is discontinued. An increase in skeletal muscle oxidative phosphorylation (OXPHOS) efficiency upon diet-mediated weight loss has been described, which may contribute to reduced systemic energy expenditure and weight regain. We set out to determine the unknown effect of semaglutide on muscle OXPHOS efficiency.

Methods: C57BL/6J mice were fed a high-fat diet for 12 weeks before receiving semaglutide or vehicle for 1 or 3 weeks. The rates of ATP production and oxygen (O₂) consumption were measured via high-resolution respirometry and fluorometry to determine OXPHOS efficiency in muscle at these two time points.

Results: Semaglutide treatment led to significant reductions in fat and lean mass. Semaglutide improved skeletal muscle OXPHOS efficiency, measured as ATP produced per O₂ consumed in permeabilized muscle fibers. Mitochondrial proteomic analysis revealed changes restricted to two proteins linked to complex III assembly (LYRM7 and TTC19; p < 0.05 without multiple corrections) without substantial changes in the abundance of OXPHOS subunits.

Conclusions: These data indicate that weight loss with semaglutide treatment increases skeletal muscle mitochondrial efficiency. Future studies could test whether it contributes to weight regain.

FIGURE 1

Semaglutide induces weight loss in overweight mice. (A) Schematic of the experimental design. Twenty‐week‐old C57BL/6J mice were fed a 42% HFD for 12 weeks before semaglutide (3 nmol/kg of body weight/day) intervention. Semaglutide was subcutaneously injected daily for 1 or 3 weeks. Vehicle groups received an equal volume of PBS. (B) Body weight was recorded every week. (C) Percent change in body weight after semaglutide treatment was calculated from the baseline of 12 weeks of an HFD. (D) Fat mass was determined by NMR before and after treatment. (E) Percentage change in fat mass was analyzed by NMR. (F) Lean mass was determined by NMR before and after treatment. (G) Percentage change in lean mass was calculated by NMR. (H) After the completion of semaglutide treatment, gastrocnemius muscle was harvested, and wet weight was measured. Data are represented as mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001, and ^**** p < 0.0001, significant difference vs. corresponding controls. ^## p < 0.01 and ^### p < 0.001, significant difference vs. vehicle, 3 weeks. n = 8 and 9 for 1‐week vehicle and 3‐week vehicle, respectively, and n = 11 for both 1‐week and 3‐week semaglutide. HFD, high‐fat diet.

FIGURE 2

Semaglutide treatment increases skeletal muscle OXPHOS energy efficiency. A small piece of red gastrocnemius was collected and permeabilized in the buffer with saponin (30 μg/mL). (A,B) JATP was determined by fluorometer. (C,D) JO₂ was analyzed by high‐resolution respirometry. (E,F) OXPHOS efficiency was determined as P/O ratio. (G,H) Abundance of OXPHOS subunits in whole lysate of gastrocnemius muscle was determined by Western blot. Data are represented as mean ± SEM. *p < 0.05, significant difference vs. corresponding controls. n = 10 and 13 for 1‐week vehicle and 3‐week vehicle and n = 10 and 14 for 1‐week and 3‐week semaglutide, respectively. JATP, rate of ATP production; JO₂, mitochondrial O₂ consumption; OXPHOS, oxidative phosphorylation; P/O, ATP produced per oxygen consumed.

FIGURE 3

Semaglutide‐induced increase in mitochondrial OXPHOS efficiency is not observed when quantified in isolated mitochondria from skeletal muscle. Mitochondria were isolated from whole gastrocnemius muscle. (A,B) JATP was determined by fluorometer. (C,D) JO₂ was analyzed by high‐resolution respirometry. (E,F) OXPHOS efficiency was determined as P/O ratio. (G,H) Abundance of OXPHOS subunits in isolated mitochondria from gastrocnemius muscle was determined by Western blot. Data are represented as mean ± SEM. n = 12 and 13 for 1‐week vehicle and 3‐week vehicle, respectively, and n = 15 for both 1‐week and 3‐week semaglutide. JATP, rate of ATP production; JO2, mitochondrial O₂ consumption; OXPHOS, oxidative phosphorylation; P/O, ATP produced per oxygen consumed.

FIGURE 4

Semaglutide treatment does not alter skeletal muscle mitochondrial supercomplex formation. (A–F) Mitochondrial supercomplex formation was analyzed in isolated mitochondria from gastrocnemius muscle by native polyacrylamide gel electrophoresis (PAGE) and quantified. (G) Representative mitochondrial morphology analyzed by electron microscopy. All data are from 3‐week semaglutide treatment. n = 6 for both vehicle and semaglutide for native PAGE.

FIGURE 5

Semaglutide‐induced weight loss does not robustly influence the abundance of OXPHOS subunits. (A) Relative abundance of mitochondrial lipids. (B) Principal component analysis of mitochondrial proteomic data. (C) Volcano plot of differentially abundant mitochondria proteins between vehicle and semaglutide groups. (D–H) Heat map of abundance of OXPHOS subunits determined by mass spectrometry. All data are from 3‐week semaglutide treatment. n = 6 for both vehicle and semaglutide. OXPHOS, oxidative phosphorylation.