Characterizing 24-Hour Skeletal Muscle Gene Expression Alongside Metabolic and Endocrine Responses Under Diurnal Conditions

Abstract

Context: Skeletal muscle plays a central role in the storage, synthesis, and breakdown of nutrients, yet little research has explored temporal responses of this human tissue, especially with concurrent measures of systemic biomarkers of metabolism.

Objective: To characterize temporal profiles in skeletal muscle expression of genes involved in carbohydrate metabolism, lipid metabolism, circadian clocks, and autophagy and descriptively relate them to systemic metabolites and hormones during a controlled laboratory protocol.

Methods: Ten healthy adults (9M/1F, [mean ± SD] age 30 ± 10 years; BMI 24.1 ± 2.7 kg·m-2) rested in the laboratory for 37 hours with all data collected during the final 24 hours (08:00-08:00 hours). Participants ingested hourly isocaloric liquid meal replacements alongside appetite assessments during waking before a sleep opportunity from 22:00 to 07:00 hours. Blood samples were collected hourly for endocrine and metabolite analyses, with muscle biopsies occurring every 4 hours from 12:00 to 08:00 hours the following day to quantify gene expression.

Results: Plasma insulin displayed diurnal rhythmicity peaking at 18:04 hours. Expression of skeletal muscle genes involved in carbohydrate metabolism (Name, Acrophase [hours]: GLUT4, 14:40; PPARGC1A, 16:13; HK2, 18:24) and lipid metabolism (FABP3, 12:37; PDK4, 05:30; CPT1B, 12:58) displayed 24-hour rhythmicity that reflected the temporal rhythm of insulin. Equally, circulating glucose (00:19 hours), nonesterified fatty acids (04:56), glycerol (04:32), triglyceride (23:14), urea (00:46), C-terminal telopeptide (05:07), and cortisol (22:50) concentrations also all displayed diurnal rhythmicity.

Conclusion: Diurnal rhythms were present in human skeletal muscle gene expression as well systemic metabolites and hormones under controlled diurnal conditions. The temporal patterns of genes relating to carbohydrate and lipid metabolism alongside circulating insulin are consistent with diurnal rhythms being driven in part by the diurnal influence of cyclic feeding and fasting.

Keywords: circadian rhythms; diurnal; gene expression; glucose; lipids; skeletal muscle.

Figure 1.

Schematic representation of the study protocol.

Figure 2.

24-hour profile for melatonin onset adjusted (A) plasma glucose, (B) plasma NEFA, (C) plasma glycerol, (D) plasma triglycerides, and (E) plasma urea. Solid lines denote the regression that best fits the data with the horizontal dotted line representing the 24-hour mean concentration used for the null comparison. The dotted vertical line denotes melatonin onset. The shaded areas represent 24-hour melatonin profile.

Figure 3.

24-hour profile for melatonin onset adjusted (A) plasma insulin, (B) plasma C-terminal telopeptide (CTX), (C) serum cortisol, and (D) serum testosterone. Solid lines denote the regression that best fits the data with the horizontal dotted line representing the 24-hour mean concentration used for the null comparison. The dotted vertical line denotes melatonin onset. The shaded areas represent 24-hour melatonin profile.

Figure 4.

Relative changes in skeletal muscle RNA expression across the 24-hour semi-constant routine. Diurnal rhythmicity (as determined by cosinor analysis) is denoted by a clock symbol.

Figure 5.

Peak (circles) and nadir (triangles) timings of circulating metabolites, hormones, telopeptides, and skeletal muscle genes displaying significant diurnal rhythmicity. The dark/fasted period is depicted in the shaded gray region.