Iron limitation promotes the atrophy of skeletal myocytes, whereas iron supplementation prevents this process in the hypoxic conditions

Abstract

There is clinical evidence that patients with heart failure and concomitant iron deficiency have increased skeletal muscle fatigability and impaired exercise tolerance. It was expected that a skeletal muscle cell line subjected to different degrees of iron availability and/or concomitant hypoxia would demonstrate changes in cell morphology and in the expression of atrophy markers. L6G8C5 rat skeletal myocytes were cultured in normoxia or hypoxia at optimal, reduced or increased iron concentrations. Experiments were performed to evaluate the iron content in cells, cell morphology, and the expression of muscle specific atrophy markers [Atrogin1 and muscle-specific RING-finger 1 (MuRF1)], a gene associated with the atrophy/hypertrophy balance [mothers against decapentaplegic homolog 4 (SMAD4)] and a muscle class-III intermediate filament protein (Desmin) at the mRNA and protein level. Hypoxic treatment caused, as compared to normoxic conditions, an increase in the expression of Atrogin-1 (P<0.001). Iron-deficient cells exhibited morphological abnormalities and demonstrated a significant increase in the expression of Atrogin-1 (P<0.05) and MuRF1 (P<0.05) both in normoxia and hypoxia, which indicated activation of the ubiquitin proteasome pathway associated with protein degradation during muscle atrophy. Depleted iron in cell culture combined with hypoxia also induced a decrease in SMAD4 expression (P<0.001) suggesting modifications leading to atrophy. In contrast, cells cultured in a medium enriched with iron during hypoxia exhibited inverse changes in the expression of atrophy markers (both P<0.05). Desmin was upregulated in cells subjected to both iron depletion and iron excess in normoxia and hypoxia (all P<0.05), but the greatest augmentation of mRNA expression occurred when iron depletion was combined with hypoxia. Notably, in hypoxia, an increased expression of Atrogin-1 and MuRF1 was associated with an increased expression of transferrin receptor 1, reflecting intracellular iron demand (R=0.76, P<0.01; R=0.86, P<0.01). Hypoxia and iron deficiency when combined exhibited the most detrimental impact on skeletal myocytes, especially in the context of muscle atrophy markers. Conversely, iron supplementation in in vitro conditions acted in a protective manner on these cells.

Iron Depletion Affects Genes Encoding Mitochondrial Electron Transport Chain and Genes of Non­Oxidative Metabolism, Pyruvate Kinase and Lactate Dehydrogenase, in Primary Human Cardiac Myocytes Cultured upon Mechanical Stretch

“…The intracellular iron content was assessed by means of flame atomic absorption spectroscopy assay [ 14 ], as described in detail in our previous work [ 15 ].…”

Oxidative and glycolytic skeletal muscles deploy protective mechanisms to avoid atrophy under pathophysiological iron overload

“…As ~10% of total body iron is stored in skeletal muscle, the impact of iron overload on muscle phenotype has also been explored during the last decade 18 . Previous studies reported a strong correlation between muscle iron accumulation occurring with ageing, ROS production, and muscle wasting 19–22 . Moreover, iron overload‐induced skeletal muscle atrophy has been associated with ROS‐mediated ubiquitin–proteasome system activation 22–24 .…”

“…[19][20][21][22] Moreover, iron overload-induced skeletal muscle atrophy has been associated with ROS-mediated ubiquitin-proteasome system activation. [22][23][24] However, the iron supplementation used in these studies causes systemic and cellular iron overload, [22][23][24] much higher than that observed under pathophysiological conditions, especially in patients with haemochromatosis. 25 Although extra-physiological iron overload is known to induce skeletal muscle wasting, the impacts of iron excess close to pathophysiology levels on skeletal muscle mass and cellular mechanisms involved in iron homeostasis remain unclear.…”

“… 18 Previous studies reported a strong correlation between muscle iron accumulation occurring with ageing, ROS production, and muscle wasting. 19 , 20 , 21 , 22 Moreover, iron overload‐induced skeletal muscle atrophy has been associated with ROS‐mediated ubiquitin–proteasome system activation. 22 , 23 , 24 However, the iron supplementation used in these studies causes systemic and cellular iron overload, 22 , 23 , 24 much higher than that observed under pathophysiological conditions, especially in patients with haemochromatosis.…”

Iron Deficiency in Pulmonary Arterial Hypertension: A Deep Dive into the Mechanisms

“…After 4 days of hypoxia (10% O 2 ), iron chelation in rats decreased RV hypertrophy and GATA4 expression, which plays a major role in its adaptation to pressure overload [ 89 , 90 ]. In fact, iron deficiency promoted skeletal muscle atrophy, while iron supplementation had the opposite effect, suggesting that iron is required for muscle adaptation to overload [ 91 ]. Myoglobin, which serves as a skeletal muscle iron store, plays an important role in the adaptation of the RV to pressure overload [ 92 ].…”