Mitochondrial metabolism changes following diet and exercise modifications in type 1 PSSM (PSSM1)

Polysaccharide storage myopathy (PSSM) constitutes an inherited form of glycogen storage disorder and is a cause of exertional rhabdomyolysis. A previous study analysing mitochondrial function via high-resolution respirometry (HRR) of PSSM type-1 horses showed significant bioenergetics impairment with decreased electron transfer capacity. We hypothesised that appropriate management of PSSM type-1 horses may influence mitochondrial bioenergetics. Therefore, microbiopsies were sampled from gluteus medius as well as triceps brachii muscles. We performed HRR measurements in duplicate on two confirmed PSSM type-1 horses before and after 6 months adaptation. During this period, horses were fed a low-carbohydrate (<10% non-structural carbohydrates), fat-supplemented diet and sustained a daily aerobic exercise. After this period, a 1.5 fold change in complex II-sustained respiration using pyruvate & glutamate as substrates and malate as co-substrate was recorded in both horses. A lesser effect was noticed when glutamate (with malate) was the sole substrate used. Also, the effect seemed to be enhanced in the triceps brachii vs gluteus medius muscle which leads to the hypothesis of a different use of pyruvate depending on the fibre type composition. Since the metabolic stress in form of muscle damage is more important during submaximal exercise, the use of protocols using fatty acids as substrates for HRR is the next step. This descriptive case study suggests a modification in energy conversion after PSSM1 management. The decreased metabolic stress impacting mitochondrial function may enhance mitochondrial respiratory capacity after a 6-months period of adapted nutrition and exercise.