1α,25-dihydroxyvitamin D3 mitigates cancer cell mediated mitochondrial dysfunction in human skeletal muscle cells

Abstract

Cancer cachexia is associated with muscle weakness and atrophy. We investigated whether 1α,25-dihydroxyvitamin D₃ (1α,25(OH)₂D₃), which has previously been shown to increase skeletal myoblast oxygen consumption rate, could reverse the deleterious effects of tumor cell conditioned medium on myoblast function. Conditioned medium from Lewis lung carcinoma (LLC1) cells inhibits oxygen consumption, increases mitochondrial fragmentation, inhibits pyruvate dehydrogenase activity, and enhances proteasomal activity in human skeletal muscle myoblasts. 1α,25(OH)₂D₃ reverses the tumor cell-mediated changes in mitochondrial oxygen consumption and proteasomal activity, without changing pyruvate dehydrogenase activity. 1α,25(OH)₂D₃ might be useful in treatment of weakness seen in association with CC.

Keywords: 1α,25-dihydroxyvitamin D(3); Cancer; Gene expression; Mitochondria; Oxygen consumption; Skeletal muscle.

Fig. 1

Oxygen consumption rate (OCR) was measured in human myoblasts following the addition of LLC1 non-conditioned medium (NCM, □) or LLC1 conditioned medium (CM, ▲) for 24 h. A. OCR in myoblasts in the presence or absence of indicated reagents. B: Basal respiration. C: maximal respiration. D: coupled OCR. E: reserve capacity. ^* = statistically significant change.

Fig. 2

OCR was measured in myoblasts following the addition of LLC1 non-conditioned medium (NCM, □) or LLC1 conditioned medium to which was added 1α,25(OH)₂D₃ (CM + 1α,25(OH)₂D₃, ▲) for period of 24 h. A. OCR was measured in human skeletal muscle myoblasts in the presence or absence of re-agents as indicated. B: Basal respiration. C: maximal respiration. D: coupled OCR. E: reserve capacity.

Fig. 3

Upper panel: A Morphology of labeled myoblast mitochondria following addition of LLC1 non-CM to cells. B: Morphology of mitochondria in myoblasts treated with LLC1 non-CM using EM. C: Morphology of labeled myoblast mitochondria following addition of LLC1 CM to cells. D: Morphology of mitochondria in myoblasts treated with LLC1 CM using EM. Note presence of filamentous mitochondria in myo-blasts treated with LLC1 non-CM, panels A and B. Following treatment of myoblasts with LLC1 CM, panels C and D, appear fragmented. Lower panel: A: Morphology of labeled myoblast mitochondria following addition of LLC1 CM to cells. B: Morphology of mitochondria in myoblasts treated with LLC1 CM using EM. C: Morphology of labeled myoblast mitochondria following addition of LLC1 CM + 1α,25(OH)₂D₃, 10⁻⁸M to cells. D: Morphology of mitochondria in myoblasts treated with LLC1 CM + 1α,25(OH)₂D₃, 10⁻⁸M using EM. Note presence of fragmented mitochondria in myoblasts treated with LLC1 CM, panels A and B. Following treatment of myoblasts with LLC1 CM + 1α,25(OH)₂D₃, 10⁻⁸M, panels C and D, mitochondria , appear filamentous.

Fig. 4

A. Aspect ratio of labeled myoblast mitochondria B. Form factor of labeled myoblast mitochondria following addition of LLC1 non-conditioned medium (NCM), LLC1 conditioned medium (CM) or LLC1 conditioned medium (CM) + 1α,25(OH)₂D₃,10⁻⁸M.