ROS constitute a convergence nexus in the development of IGF1 resistance and impaired wound healing in a rat model of type 2 diabetes

Abstract

SUMMARYAn indolent non-healing wound and insulin and/or insulin-like growth factor (IGF1) resistance are cardinal features of diabetes, inflammation and hypercortisolemia. Little is known about why these phenomena occur in so many contexts. Do the various triggers that induce insulin and/or IGF1 resistance and retard wound healing act through a common mechanism? Cultured dermal fibroblasts from rats and full-thickness excisional wounds were used as models to test the premise that reactive oxygen species (ROS) play a causal role in the development of IGF1 resistance and impaired wound healing under different but pathophysiologically relevant clinical settings, including diabetes, dexamethasone-induced hypercortisolemia and TNFα-induced inflammation. In normal fibroblasts, IGF1 initiated a strong degree of phosphorylation of insulin receptor substrate 1 (IRS1) (Tyr612) and Akt (Ser473), concomitantly with increased PI3K activity. This phenomenon seemed to be attenuated in fibroblasts that had phenotypic features of diabetes, inflammation or hypercortisolemia. Notably, these cells also exhibited an increase in the activity of the ROS–phospho-JNK (p-JNK)–p-IRS1 (Ser307) axis. The above-mentioned defects were reflected functionally by attenuation in IGF1-dependent stimulation of key fibroblast functions, including collagen synthesis and cell proliferation, migration and contraction. The effects of IGF1 on glucose disposal and cutaneous wound healing were also impaired in diabetic or hypercortisolemic rats. The ROS suppressors EUK-134 and α-lipoic acid, or small interfering RNA (siRNA)-mediated silencing of JNK expression, restored IGF1 sensitivity both in vitro and in vivo, and also ameliorated the impairment in IGF1-mediated wound responses during diabetes, inflammation and hypercortisolemia. Our data advance the notion that ROS constitute a convergence nexus for the development of IGF1 resistance and impaired wound healing under different but pathophysiologically relevant clinical settings, with a proof of concept for the beneficial effect of ROS suppressors.

Oxygen Modulates the Glutathione Peroxidase Activity during the L6 Myoblast Early Differentiation Process

“…Majmundar et al [7] found a loss of sensitivity of the IGF-1 receptor at 0.5% O 2 in C2C12 cells. Such a loss of sensitivity has been correlated with an accumulation of ROS in cultured fibroblasts from diabetic rats [17]. In our study, cultured L6 myoblasts at both 21% and 1% O 2 exhibit a higher TBAR accumulation compared to 5% O 2 .…”

“…In L6 myoblasts 5% O 2 seems to be the optimal condition for the best balance between the TBARS production and detoxification. At 1% O 2 we can suggest that the oxidative stress is very high and the low activity of GPx does not allow the removing of ROS, which bind to cellular molecules such as IRS and alter the differentiation [17]. At 21% O 2 the high production of TBARS is detoxified by glutathione peroxidase, which allows the differentiation to occur.…”

“…The oxidative intracellular environment appears to be an important differentiation factor depending on the ambient O 2 level. Interestingly, the role of ROS as a regulator of the IGF-1/Akt pathway was proposed in rat cultured dermal fibroblasts [17]. In normal fibroblasts, IGF-1 induced a strong phosphorylation of Akt whereas phosphorylation is attenuated in fibroblasts expressing the phenotypic characteristics of diabetes, inflammation or hypercortisolemia [17].…”

“…Interestingly, the role of ROS as a regulator of the IGF-1/Akt pathway was proposed in rat cultured dermal fibroblasts [17]. In normal fibroblasts, IGF-1 induced a strong phosphorylation of Akt whereas phosphorylation is attenuated in fibroblasts expressing the phenotypic characteristics of diabetes, inflammation or hypercortisolemia [17]. This work proposes to study whether oxygen at hyperoxic (21% O 2 ), physiological (5% O 2 ) and hypoxic (1% O 2 ) levels can regulate the L6 myoblast differentiation by modulating the activity of two important enzymes involved in the detoxification of ROS such as glutathione peroxidase and catalase.…”

Insulin resistance and cancer: the role of insulin and IGFs

“…Immune response alterations and carcinogenesis ILP molecules have been reported to play a crucial role in altered inflammatory responses to infectious challenge commonly observed in insulin resistance-related metabolic disorders (Fenton et al 2009, Bitar & Al-Mulla 2012.…”