Vitamin D (VitD) deficiency is common in ~25% of the population, and is considered to have actions upon skeletal muscle metabolism and health, and is associated with age-related sarcopenia (1). VitD regulates and exerts its effects through the ubiquitously expressed VitD receptor (VDR); a potent transcription factor, controlling the expression of multiple genes at VitD response elements initiating transcription (2). Recent investigations have established a VDR autonomous role in muscle function and regeneration (3). Thus, we aimed to investigate whether VDR has a functional role in modulating key regulatory pathways/ genesets important to muscle growth and homeostasis. To examine the role of VDR in muscle mass regulation, Tibialis Cranialis(TC) muscles of Wistar rats were electroporated (under 2.5% isofluorane, 50mg/kg carprofen) to continuously over-express (VDR-OE) or knockdown (VDR-KD) VDR by cDNA or shRNA lentiviral transfection; contralateral TC’s were sham treated internal controls. RNA from muscles underwent RNA-Seq using the Illumina HiSeq system, before analysis of differential gene expression, geneset enrichment and pathway analysis. False discovery rates were applied throughout. VDR-OE stimulated fibre hypertrophy (cross-sectional area (CSA) +17±7%, P<0.05) and enhanced muscle protein synthesis (+69±7%, P<0.05). This was matched by an upregulation in key growth-related extracellular remodeling, Paxand integrinpathway genesets. Comparatively, VDR-KD induced myofibre atrophy(CSA -8±2%, P<0.001)and autophagy related processes (e.g. LC3B-II +84±43%, P<0.05). This was complemented by an upregulation in multiple lysosome and vesicle biogenesis genesets. Moreover, many energy metabolism related genes were downregulated, i.e. multiple electron transport complex, oxidative phosphorylation, glycolysis and citric acid cycle genesets. Thus, the VDR acts autonomously to regulate muscle mass; operating through reciprocal geneset modulation to facilitate hypertrophy by enhanced remodeling and anabolic signalling pathways, whilst limiting atrophy through regulating energy metabolism and autophagy. Therefore, the VDR has an essential role in the coordination of genesets key to the maintenance of muscle mass.