Scalable 3D Printed Molds for Human Tissue Engineered Skeletal Muscle.

Tissue engineered skeletal muscle allows investigation of the cellular and molecular mechanisms that regulate skeletal muscle pathology. The fabricated model must resemble characteristics of in vivo tissue and incorporate cost-effective and high content primary human tissue. Current models are limited by low throughput due to the complexities associated with recruiting tissue donors, donor specific variations, as well as cellular senescence associated with passaging. This research presents a method using fused deposition modeling (FDM) and laser sintering (LS) 3D printing to generate reproducible and scalable tissue engineered primary human muscle, possessing aligned mature myotubes reminiscent of in vivo tissue. Many existing models are bespoke causing variability when translated between laboratories. To this end, a scalable model has been developed (25-500 μL construct volumes) allowing fabrication of mature primary human skeletal muscle. This research provides a strategy to overcome limited biopsy cell numbers, enabling high throughput screening of functional human tissue

A 7‐day high‐fat, high‐calorie diet induces fibre‐specific increases in intramuscular triglyceride and perilipin protein expression in human skeletal muscle

KEY POINTS: We have recently shown that a high-fat high-calorie (HFHC) diet decreases whole body glucose clearance without impairing skeletal muscle insulin signalling, in healthy lean individuals. These diets are also known to increase skeletal muscle IMTG stores, but the effect on lipid metabolites leading to skeletal muscle insulin resistance has not been investigated. This study measured the effect of 7 days HFHC diet on: 1) skeletal muscle concentration of lipid metabolites, and 2) potential changes in the perilipin (PLIN) content of the lipid droplets (LD) storing IMTG. The HFHC diet increased PLIN3 protein expression and redistributed PLIN2 to LD stores in type I fibres. The HFHC diet increased IMTG content in type I fibres, while lipid metabolite concentrations remained the same. The data suggest that the increases in IMTG stores assists reducing the accumulation of lipid metabolites known to contribute to skeletal muscle insulin resistance. ABSTRACT: A HFHC diet reduces whole body glucose clearance without impairing skeletal muscle insulin signalling in healthy lean individuals. HFHC diets also increase skeletal muscle lipid stores. However, unlike certain lipid metabolites, intramuscular triglyceride (IMTG) stored within lipid droplets (LD) does not directly contribute to skeletal muscle insulin resistance. Increased expression of perilipin (PLIN) proteins and colocalisation to LD has been shown to assist in IMTG storage. We aimed to test the hypothesis that 7 days on a HFHC diet increases IMTG content while minimising accumulation of lipid metabolites known to disrupt skeletal muscle insulin signalling in sedentary and obese individuals. We also aimed to identify changes in expression and subcellular distribution of proteins involved in IMTG storage. Muscle biopsies were obtained from the m. vastus lateralis of 13 (n = 11 males, n = 2 females) healthy lean individuals (age: 23 ± 2.5 y, BMI: 24.5 ± 2.4 kg m-2 ), following an overnight fast, before and after consuming a high-fat (64% energy) high-calorie (+47% kcal) diet for 7 days. After the HFHC diet, IMTG content increased in type I fibres only (+10%; P < 0.001), whereas there was no change in the concentration of either total diacylglycerol (P = 0.123) or total ceramides (P = 0.150). Of the PLINs investigated, only PLIN3 content increased (+50%; P < 0.01) solely in type I fibres. LDs labelled with PLIN2 increased (80%; P < 0.01), also in type I fibres only. We propose that these adaptations to LD support IMTG storage and minimise accumulation of lipid metabolites to protect skeletal muscle insulin signalling following 7 days HFHC diet