Diet-Induced Obesity Affects Muscle Regeneration After Murine Blunt Muscle Trauma—A Broad Spectrum Analysis

Abstract

Injury to skeletal muscle affects millions of people worldwide. The underlying regenerative process however, is a very complex mechanism, time-wise highly coordinated, and subdivided in an initial inflammatory, a regenerative and a remodeling phase. Muscle regeneration can be impaired by several factors, among them diet-induced obesity (DIO). In order to evaluate if obesity negatively affects healing processes after trauma, we utilized a blunt injury approach to damage the extensor iliotibialis anticus muscle on the left hind limb of obese and normal weight C57BL/6J without showing any significant differences in force input between normal weight and obese mice. Magnetic resonance imaging (MRI) of the injury and regeneration process revealed edema formation and hemorrhage exudate in muscle tissue of normal weight and obese mice. In addition, morphological analysis of physiological changes revealed tissue necrosis, immune cell infiltration, extracellular matrix (ECM) remodeling, and fibrosis formation in the damaged muscle tissue. Regeneration was delayed in muscles of obese mice, with a higher incidence of fibrosis formation due to hampered expression levels of genes involved in ECM organization. Furthermore, a detailed molecular fingerprint in different stages of muscle regeneration underlined a delay or even lack of a regenerative response to injury in obese mice. A time-lapse heatmap determined 81 differentially expressed genes (DEG) with at least three hits in our model at all-time points, suggesting key candidates with a high impact on muscle regeneration. Pathway analysis of the DEG revealed five pathways with a high confidence level: myeloid leukocyte migration, regulation of tumor necrosis factor production, CD4-positive, alpha-beta T cell differentiation, ECM organization, and toll-like receptor (TLR) signaling. Moreover, changes in complement-, Wnt-, and satellite cell-related genes were found to be impaired in obese animals after trauma. Furthermore, histological satellite cell evaluation showed lower satellite cell numbers in the obese model upon injury. Ankrd1, C3ar1, Ccl8, Mpeg1, and Myog expression levels were also verified by qPCR. In summary, increased fibrosis formation, the reduction of Pax7+ satellite cells as well as specific changes in gene expression and signaling pathways could explain the delay of tissue regeneration in obese mice post trauma.

High‐fat diet pre‐conditioning improves microvascular remodelling during regeneration of ischaemic mouse skeletal muscle

“…It will be valuable for future studies to decipher the relative importance of specific dietary components, overall caloric content and fat mass of the individual prior to the ischaemic insult, in establishing the efficacy of post‐ischemic vascular remodelling and muscle regeneration. It is also important to note that a substantially greater degree of inflammation in ischaemic muscle injury has been reported by studies employing longer periods of HF diet feeding and in aged mice . Thus, it is probable that the initial physiological adaptations that enable skeletal muscle to cope with excess fatty acids can eventually be overwhelmed, resulting in accumulation of intramuscular triglycerides and development of inflammation and fibrosis, and this transition is likely influenced by age, genetics, diet composition and duration.…”

Loss of CD36 protects against diet‐induced obesity but results in impaired muscle stem cell function, delayed muscle regeneration and hepatic steatosis

“…49 Limited data suggest that skeletal muscle ectopic lipid infiltration impairs satellite cell activation, leading to a decrease of skeletal muscle regeneration potential. 7,27 We observed a significant reduction in cultured satellite cell numbers in WT HF diet mice. Moreover, we showed that obesity impairs satellite cell activation during early proliferation (ie 24 hours).…”

“…Satellite cells, the myogenic precursor stem cell population of the skeletal muscle, are of pivotal importance for skeletal muscle homeostasis and regeneration . Sparse evidence suggests that skeletal muscle regeneration is severely impaired in obese individuals possibly because of increased lipid deposition and perturbed satellite cell function . The fatty acid transporter CD36 plays an important role in skeletal muscle fatty acid transport and utilization .…”

“…2 Sparse evidence suggests that skeletal muscle regeneration is severely impaired in obese individuals possibly because of increased lipid deposition and perturbed satellite cell function. 7,10,27,43 The fatty acid transporter CD36 plays an important role in skeletal muscle fatty acid transport and utilization. 22,24,44 In this study, we show that CD36-deficient mice are protected from HF diet-induced weight gain, which is in line with previous findings, 45,46 but results in impaired satellite cell function, compromised myogenic differentiation, delayed muscle regeneration after acute injury and hepatic steatosis.…”

Influence of obesity on remodeling of lung tissue and organization of extracellular matrix after blunt thorax trauma

“…5 μm thick tissue-sections were deparaffinized, rehydrated in decreasing alcohol series and subsequently stained in hematoxylin for three minutes. Afterwards the sections were blued using running water for 10 min and subsequently stained in eosin for 10 s [32]. The staining was completed by implementing dehydration of the slides in increasing alcohol series with incubation in Roti®-Histol.…”