Neurovascular structures in human vastus lateralis muscle and the ideal biopsy site.

A density model of neurovascular structures was generated from 28 human vastus lateralis muscles isolated from embalmed cadavers. The intramuscular portion of arteries, veins, and nerves was dissected, traced on transparencies, and digitized before adjustment to an average muscle shape using Procrustes analysis to generate density distributions for the relative positions of these structures. The course of arteries, veins, and nerves was highly variable between individual muscles. Nevertheless, a zone of lower average neurovascular density was found between the tributaries from the lateral circumflex femoral and the deep femoral arteries. While the area with the lowest density was covered by the iliotibial tract and would therefore not be suitable for biopsies, another low-density area was located in the distal portion of vastus lateralis. This was just anterior to the iliotibial tract, in a zone that has been described as a good needle biopsy site. The reported complication rates of needle biopsies (0.1%-4%) are in the range of expectations when simulated based on this model. It is concluded that the optimal human vastus lateralis biopsy site is in the distal portion of the muscle, between ½ and ¾ of the length from the greater trochanter to the lateral epicondyle, just anterior to the iliotibial band.

Independent and combined effects of acute physiological hyperglycaemia and hyperinsulinaemia on metabolic gene expression in human skeletal muscle.

Physiological hyperglycaemia and hyperinsulinaemia are strong modulators of gene expression, which underpins some of their well-known effects on insulin action and energy metabolism. The aim of the present study was to examine whether acute in vivo exposure of healthy humans to hyperinsulinaemia and hyperglycaemia have independent or additive effects on expression of key metabolic genes in skeletal muscle. On three randomized occasions, seven young subjects underwent a 4 h (i) hyperinsulinaemic (50 m-units·m⁻²·min⁻¹) hyperglycaemic (10 mmol/l) clamp (HIHG), (ii) hyperglycaemic (10 mmol/l) euinsulinaemic (5 m-units·m⁻²·min⁻¹) clamp (LIHG) and (iii) hyperinsulinaemic (50 m-units·m⁻²·min⁻¹) euglycaemic (4.5 mmol/l) clamp (HING). Muscle biopsies were obtained before and after each clamp for the determination of expression of genes involved in energy metabolism, and phosphorylation of key insulin signalling proteins. Hyperinsulinaemia and hyperglycaemia exerted independent effects with similar direction of modulation on PI3KR1 (phosphatidylinositol 3-kinase, regulatory 1), LXRα (liver X receptor α), PDK4 (pyruvate dehydrogenase kinase 4) and FOXO1 (forkhead box O1A) and produced an additive effect on PI3KR1, the gene that encodes the p85α subunit of PI3K in human skeletal muscle. Acute hyperglycaemia itself altered the expression of genes involved in fatty acid transport and oxidation [fatty acid transporter (CD36), LCAD (long-chain acyl-CoA dehydrogenase) and FOXO1], and lipogenesis [LXRα, ChREBP (carbohydrate-responseelement-binding protein), ABCA1 (ATP-binding cassette transporter A1) and G6PD (glucose-6-phosphate dehydrogenase). Surperimposing hyperinsulinaemia on hyperglycaemia modulated a number of genes involved in insulin signalling, glucose metabolism and intracellular lipid accumulation and exerted an additive effect on PI3KR1. These may be early molecular events that precede the development of glucolipotoxicity and insulin resistance normally associated with more prolonged periods of hyperglycaemia and hyperinsulinaemia.

Similar changes of gene expression in human skeletal muscle after resistance exercise and multiple fine needle biopsies.

Repeated biopsy sampling from one muscle is necessary to investigate muscular adaptation to different forms of exercise as adaptation is thought to be the result of cumulative effects of transient changes in gene expression in response to single exercise bouts. In a crossover study, we obtained four fine needle biopsies from one vastus lateralis muscle of 11 male subjects (25.9 ± 3.8 yr, 179.2 ± 4.8 cm, 76.5 ± 7.0 kg), taken before (baseline), 1, 4, and 24 h after one bout of squatting exercise performed as conventional squatting or as whole body vibration exercise. To investigate if the repeated biopsy sampling has a confounding effect on the observed changes in gene expression, four fine needle biopsies from one vastus lateralis muscle were also taken from 8 male nonexercising control subjects (24.5 ± 3.7 yr, 180.6 ± 1.2 cm, 81.2 ± 1.6 kg) at the equivalent time points. Using RT-PCR, we observed similar patterns of change in the squatting as well as in the control group for the mRNAs of interleukin 6 (IL-6), IL-6 receptor, insulin-like growth factor 1, p21, phosphofructokinase, and glucose transporter in relation to the baseline biopsy. In conclusion, multiple fine needle biopsies obtained from the same muscle region can per se influence the expression of marker genes induced by an acute bout of resistance exercise.

Different molecular and structural adaptations with eccentric and conventional strength training in elderly men and women.

Reprogramming of gene expression contributes to structural and functional adaptation of muscle tissue in response to altered use. The aim of this study was to investigate mechanisms for observed improvements in leg extension strength, gain in relative thigh muscle mass and loss of body and thigh fat content in response to eccentric and conventional strength training in elderly men (n = 14) and women (n = 14; average age of the men and women: 80.1 ± 3.7 years) by means of structural and molecular analyses. Biopsies were collected from m. vastus lateralis in the resting state before and after 12 weeks of training with two weekly resistance exercise sessions (RET) or eccentric ergometer sessions (EET). Gene expression was analyzed using custom-designed low-density PCR arrays. Muscle ultrastructure was evaluated using EM morphometry. Gain in thigh muscle mass was paralleled by an increase in muscle fiber cross-sectional area (hypertrophy) with RET but not with EET, where muscle growth is likely occurring by the addition of sarcomeres in series or by hyperplasia. The expression of transcripts encoding factors involved in muscle growth, repair and remodeling (e.g., IGF-1, HGF, MYOG, MYH3) was increased to a larger extent after EET than RET. MicroRNA 1 expression was decreased independent of the training modality, and was paralleled by an increased expression of IGF-1 representing a potential target. IGF-1 is a potent promoter of muscle growth, and its regulation by microRNA 1 may have contributed to the gain of muscle mass observed in our subjects. EET depressed genes encoding mitochondrial and metabolic transcripts. The changes of several metabolic and mitochondrial transcripts correlated significantly with changes in mitochondrial volume density. Intramyocellular lipid content was decreased after EET concomitantly with total body fat. Changes in intramyocellular lipid content correlated with changes in body fat content with both RET and EET. In the elderly, RET and EET lead to distinct molecular and structural adaptations which might contribute to the observed small quantitative differences in functional tests and body composition parameters. EET seems to be particularly convenient for the elderly with regard to improvements in body composition and strength but at the expense of reducing muscular oxidative capacity.

Content of intramyocellular lipids derived by electron microscopy, biochemical assays, and (1)H-MR spectroscopy.

Three different methods to determine intramyocellular lipid (IMCL) contents in human skeletal muscle have been compared. (1)H-magnetic resonance spectroscopy (MRS) was evaluated against electron microscopic morphometry and biochemical assays of biopsy samples from m. tibialis anterior of 10 healthy subjects. The results of (1)H-MRS and morphometry were strongly correlated, proving the validity of the (1)H-MRS results for the noninvasive determination of IMCL. Biochemical assays yielded results that did not significantly correlate with the results of the other methods. When IMCL levels obtained from the three methods are expressed in common units, it was found that (1)H-MRS yielded IMCL average levels that were 1.8 times lower than those found by morphometry. Potential reasons for the discrepancy are discussed. It is expected that (1)H-MRS will be suitable to replace invasive techniques for IMCL determination, whenever noninvasiveness is crucial, e.g., for repeated investigations in studies of substrate recruitment and recovery in exercise.