Proinflammatory NFkB signalling promotes mitochondrial dysfunction in skeletal muscle in response to cellular fuel overloading

Abstract

Sustained nutrient (fuel) excess, as occurs during obesity and diabetes, has been linked to increased inflammation, impaired mitochondrial homeostasis, lipotoxicity, and insulin resistance in skeletal muscle. Precisely how mitochondrial dysfunction is initiated and whether it contributes to insulin resistance in this tissue remains a poorly resolved issue. Herein, we examine the contribution that an increase in proinflammatory NFkB signalling makes towards regulation of mitochondrial bioenergetics, morphology, and dynamics and its impact upon insulin action in skeletal muscle cells subject to chronic fuel (glucose and palmitate) overloading. We show sustained nutrient excess of L6 myotubes promotes activation of the IKKβ-NFkB pathway (as judged by a six-fold increase in IL-6 mRNA expression; an NFkB target gene) and that this was associated with a marked reduction in mitochondrial respiratory capacity (>50%), a threefold increase in mitochondrial fragmentation and 2.5-fold increase in mitophagy. Under these circumstances, we also noted a reduction in the mRNA and protein abundance of PGC1α and that of key mitochondrial components (SDHA, ANT-1, UCP3, and MFN2) as well as an increase in cellular ROS and impaired insulin action in myotubes. Strikingly, pharmacological or genetic repression of NFkB activity ameliorated disturbances in mitochondrial respiratory function/morphology, attenuated loss of SDHA, ANT-1, UCP3, and MFN2 and mitigated the increase in ROS and the associated reduction in myotube insulin sensitivity. Our findings indicate that sustained oversupply of metabolic fuel to skeletal muscle cells induces heightened NFkB signalling and that this serves as a critical driver for disturbances in mitochondrial function and morphology, redox status, and insulin signalling.

Caveolin‐3 deficiency associated with the dystrophy P104L mutation impairs skeletal muscle mitochondrial form and function

“…In healthy cells, ROS production is normally low and rapidly neutralized by ROS detoxifying enzymes such as MnSOD. However, ROS generation can exceed the anti‐oxidant capacity of cells in numerous circumstances as seen, for example, during periods of excessive mitochondrial fuel supply and/or conditions that reduce expression/activity of anti‐oxidant enzymes . Our work indicates that muscle of Cav3 −/− mice and myoblasts expressing Cav3 P104L or those genetically depleted in Cav3 exhibit a significant reduction in MnSOD, which may contribute to the rise in mitochondrial superoxide.…”

“…Interestingly, this fragmentation can be ameliorated by cell treatment with MitoTempo, a mitochondrial‐targeted superoxide scavenger. Notably, while mitochondrial fission is blunted by MitoTempo in fuel‐overloaded myotubes, it fails to mitigate the associated loss in mitochondrial respiratory capacity, which is likely sustained because of the failure to recover expression of key functional proteins, such as SDHA, ANT‐1, and UCP3 . Based on these latter observations, the increase in oxidative stress seen in Cav3 P104L expressing myoblasts (and that reported in numerous muscular dystrophies) may be important in influencing the morphology of the mitochondrial network.…”

“…Previous work in C2C12 myoblasts has shown that acute exposure to H 2 O 2 initiates mitochondrial fragmentation and that this is preceded by depolarisation of the mitochondrial membrane and a reduction in maximal respiration . Mitochondrial fragmentation is also a feature of muscle cells subjected to sustained fuel overloading . Interestingly, this fragmentation can be ameliorated by cell treatment with MitoTempo, a mitochondrial‐targeted superoxide scavenger.…”

Elucidating the mechanism of action of alpha-1-antitrypsin using retinal pigment epithelium cells exposed to high glucose. Potential use in diabetic retinopathy

“…NFκB is a DNA binding protein related to inflammation. This protein is overexpressed in diabetes [41] and DR pathogenesis [42] in different cell lines and animal models of diabetes. NFκB regulates the expression of pro-inflammatory molecules like TNF-α and iNOS [43].…”

Cellular Senescence as the Pathogenic Hub of Diabetes-Related Wound Chronicity

“…Mitochondria, routinely identified as the powerhouse of the cell are the major generator of members of the ROS family such as superoxide anion, hydroxyl and peroxyl radicals, and hydrogen peroxide (150)(151)(152)(153). Furthermore, ROS/oxidative stress/mitochondrial dysfunction and inflammation behave as an indissoluble, interconnected nosogenic unit that links organismal aging, T2DM, and poor wound healing (73,(154)(155)(156)(157)(158). Converging evidences demonstrate that high levels of ROS disrupt the normal healing process (159)(160)(161) and constitute a hallmark in chronic wounds including recalcitrant DFU (147,159,162).…”