Effect of Systemic Iron Loading on Skeletal Muscle Function and Redox Status in Mice

Abstract

An increase in the skeletal muscle iron status was reported in animal models of various pathophysiological states as well as aging. Notably, skeletal muscle iron levels of approximately 1.4‐ and 2.1‐fold greater were shown in models of diabetes and hemochromatosis, respectively. Additionally, an iron level of 7.0‐fold greater was reported previously in a rat model of aging. Such increment in the muscle iron level could be detrimental, as associations with increased muscle fatigability, atrophy, and oxidative stress were reported. Previous studies that investigated the direct effects of iron on muscle strength and its relevance to oxidative stress induced a high degree of muscle iron loading (i.e. 60‐fold). However, the skeletal muscle functional and redox status implications of a lower degree of muscle iron loading remain unclear. Thus, the purpose of this study was to examine whether a more moderate degree of systemic iron loading results in changes in muscle contractile characteristics and measures of antioxidant and redox status. Twenty, 8‐week‐old male mice received subcutaneous injections of iron (4 mg iron dextran/200 μL) or vehicle 5 days/week for 2 weeks (n=10/group). One day following the last injection, the soleus and gastrocnemius muscles were harvested and the functional response of the soleus was also assessed in vitro. Multivariate analysis of variance along with Wilk's Lambda were used to test the force‐frequency response of the soleus. Biochemical dependent measures of the gastrocnemius and soleus were analyzed by independent sample t‐test and Box‐Cox transformation was used if the assumption of normality was violated. Data are expressed as mean ± SD for control and iron‐loaded rats, respectively. The systemic iron loading regimen resulted in non‐heme iron (NHI) concentration elevations of approximately 3.7‐fold in the soleus (700.8 ± 202.7 vs. 2619.7 ± 663.0 nmol/gww; P < 0.001) and gastrocnemius (702.5 ± 351.0 nmol/gww vs. 2850.3 ± 937.7 nmol/gww; P < 0.01). Although the overall muscle function response was similar between groups (P = 0.43), soleus muscle from iron‐loaded mice displayed lower force values at stimulation frequencies ranging between 30 to 250 Hz (P < 0.05). Key antioxidant protein measures of the gastrocnemius including catalase (CAT: 0.60 ± 0.14 vs. 0.60 ± 0.06 O.D.; P = 0.99), manganese superoxide dismutase (MnSOD: 0.81 ± 0.11 vs. 0.71 ± 0.12 O.D.; P = 0.47) and copper‐zinc superoxide dismutase (Cu‐ZnSOD: 0.20 ± 0.01 vs. 0.22 ± 0.01 O.D.; P = 0.70) were similar between groups, as well as total SOD activity (2.72 ± 0.39 vs. 2.79 ± 1.02 A.U.; P = 0.85). However, the protein expression of thioredoxin (TRX), an indicator of the cellular redox status, was higher in iron‐loaded muscle than control (0.19 ± 0.004 vs. 0.31 ± 0.016 O.D.; P = 0.01). In summary, a degree of iron loading similar to levels reported to occur with aging and several disease states resulted in a lower skeletal muscle force generating ability that could stem from alterations in redox signaling. We are continuing to explore potential mechanisms by which iron loading contributes to skeletal muscle contractile dysfunction.Support or Funding InformationSupported by the Syracuse University SOEThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.