Iron Supplementation Improves Skeletal Muscle Contractile Properties in Mice with CKD

Abstract

Background: Chronic kidney disease (CKD) patients frequently have compromised physical performance, which increases their mortality; however, their skeletal muscle dysfunction has not been characterized at the single fiber and molecular levels. Notably, interventions to mitigate CKD myopathy are scarce. Methods: The impact of CKD in the absence and presence of iron supplementation on the contractile function of individual skeletal muscle fibers from the soleus and extensor digitorum longus muscles was evaluated in 16 week old mice. CKD was induced by adenine diet and iron supplementation was by weekly iron dextran injections. Results: Maximally activated and fatigued fiber force production was decreased 24-52% in untreated CKD, independent of size, by reducing strongly-bound myosin-actin cross-bridges and/or decreasing myofilament stiffness in myosin heavy chain (MHC) I, IIA and IIB fibers. Additionally, myosin-actin interactions in untreated CKD were slower for MHC I and IIA fibers and unchanged or faster in MHC IIB fibers. Iron supplementation improved anemia and did not change overall muscle mass in CKD mice. Iron supplementation ameliorated CKD-induced myopathy by increasing strongly-bound cross-bridges, leading to improved specific tension, and/or returning the rate of myosin-actin interactions towards or equivalent to control values in MHC IIA and IIB fibers. Conclusions: Skeletal muscle force production was significantly reduced in untreated CKD, independent of fiber size, indicating that compromised physical function in patients is not solely due to muscle mass loss. Iron supplementation improved multiple aspects of CKD-induced myopathy, suggesting that timely correction of iron imbalance may aid in ameliorating contractile deficits in CKD patients.

Effects of counteracting measures on muscle contraction determinants in CKD: what muscle biopsy studies tell us?

“…However, a host of counteracting measures have shown to improve muscle performance in CKD patients or animal models and could be also assessed at the muscle biopsy level of CKD patients (alone or in combination with other interventions). For example, a recent study (45) with iron supplementation in an animal model of CKD showed significant improvements in muscle contraction properties of single muscle fibers indicating that timely maintenance of iron balance in CKD patients could also maintain or improve skeletal muscle quality and quantity. Therefore, future studies could verify the results in muscle biopsies of human patients (preferably during catheter insertion or transplantation to avoid further discomfort of patients).…”

Skeletal muscle single fiber force production declines early in juvenile male mice with chronic kidney disease

“…We have previously validated the use of the adenine diet in juvenile male mice indicating that various phenotypes are similar to humans including growth retardation, cachexia, anemia, iron deficiency and inflammation (Akchurin et al, 2016 ). Both groups received intraperitoneal injections of iron dextran at 0.5 g/kg weekly to eliminate the potential confounding effect of iron deficiency and anemia on muscle contractile function (Dziegala et al, 2018 ; Finch et al, 1976 ; Momb et al, 2022 ; Patino et al, 2020 ). Mouse body length was measured by the nose (snout) to tail tip length of anesthetized mice.…”

“…Determining the individual impact of each of these components using whole body and whole muscle function can be difficult, so a reductionist approach may be needed to determine the specific mechanisms behind the loss of physical capacity. One means of examining myopathy independent of neuropathy and other confounders is to examine single fiber contractile function as these measurements are performed on fibers without an excitable membrane, due to being chemically skinned, and within their normal three‐dimensional structure, protein content, and ionic conditions (Höök et al, 2001 ; Miller et al, 2013 ; Miller et al, 2015 ; Mitrou et al, 2019 ; Momb et al, 2022 ; Toth et al, 2013 ). Single fiber force production (cellular level) and the underlying myofilament mechanical properties (molecular level), including myosin‐actin cross‐bridge kinetics, can be assessed within the same fiber (Kawai & Halvorson, 1991 ; Miller et al, 2010 ; Momb et al, 2022 ; Zhao & Kawai, 1994 ).…”

“…One means of examining myopathy independent of neuropathy and other confounders is to examine single fiber contractile function as these measurements are performed on fibers without an excitable membrane, due to being chemically skinned, and within their normal three‐dimensional structure, protein content, and ionic conditions (Höök et al, 2001 ; Miller et al, 2013 ; Miller et al, 2015 ; Mitrou et al, 2019 ; Momb et al, 2022 ; Toth et al, 2013 ). Single fiber force production (cellular level) and the underlying myofilament mechanical properties (molecular level), including myosin‐actin cross‐bridge kinetics, can be assessed within the same fiber (Kawai & Halvorson, 1991 ; Miller et al, 2010 ; Momb et al, 2022 ; Zhao & Kawai, 1994 ). To our knowledge, no human studies have examined cellular and molecular contractile function in children with CKD, potentially due to the difficulties of performing skeletal muscle biopsies in this population.…”

“…These prior studies using animal models (Mitrou et al, 2019 ; Momb et al, 2022 ) have provided initial insights into the underlying contractile deficits of advanced CKD in adults as, to our knowledge, no human studies have reported these measures. Furthermore, no human or animal studies have examined the impacts of early‐stage CKD on cellular and molecular contractile function.…”