Insulin-regulated aminopeptidase in adipocyte is Cys-specific and affected by obesity

Abstract

Insulin-regulated aminopeptidase (IRAP, EC 3.4.11.3) in adipocytes is well known to traffic between high (HDM) and low (LDM) density microsomal fractions toward the plasma membrane (MF) under stimulation by insulin. However, its catalytic preference for aminoacyl substrates with N-terminal Leu or Cys is controversial. Furthermore, possible changes in its traffic under metabolic challenges are unknown. The present study investigated the catalytic activity attributable to EC 3.4.11.3 in HDM, LDM and MF from isolated adipocytes of healthy (C), food deprived (FD) and monosodium glutamate (MSG) obese rats on aminoacyl substrates with N-terminal Cys or Leu, in absence or presence of insulin. Efficacy and reproducibility of subcellular adipocyte fractionation procedure were demonstrated. Comparison among HDM vs LDM vs MF intragroup revealed that hydrolytic activity trafficking from LDM to MF under influence of insulin in C, MSG and FD is only on N-terminal Cys. In MSG the same pattern of anterograde traffic and aminoacyl preference occurred independently of insulin stimulation. The pathophysiological significance of IRAP in adipocytes seems to be linked to comprehensive energy metabolism related roles of endogenous substrates with N-terminal cysteine pair such as vasopressin and oxytocin.

Insulin-Regulated Aminopeptidase Inhibition Ameliorates Metabolism in Obese Zucker Rats

“…The genetically obese Zucker rats (fa/fa) represent a model of insulin resistance and prediabetes characterized by hyperinsulinemia, hyperlipidemia and peripheral glucose intolerance which is caused largely by an impairment of insulin-stimulated glucose uptake into skeletal muscle, the major site of insulin-mediated glucose disposal (Ionescu et al, 1985;King et al, 1992). We and other authors have previously shown that obesity is associated with dysregulation of IRAP activity in adipose tissue and skeletal muscle along with reduced plasma oxytocin due to increased peptide degradation by peripheral tissues (Gajdosechova et al, 2014;Alponti et al, 2015). A study on IRAP-knockout mice showed protective effect of aminopeptidase deficiency against development of obesity (Niwa et al, 2015).…”

“…Several studies have examined the role of IRAP in obesity and glucose handling using various animal models. Results have revealed that insulin regulated traffic of IRAP toward membrane fraction in adipocytes is disturbed by monosodium glutamate-induced obesity (Alponti et al, 2015) and IRAP deficiency in mice fed high-fat diet lead to prevention of development of obesity (Niwa et al, 2015). On the other hand, acute inhibition of IRAP aminopeptidase activity with specific inhibitor, HFI-419, does not affect glucose homeostasis in the streptozotocin-induced experimental rat model of diabetes mellitus (Albiston et al, 2017).…”

Resistance training restores metabolic alterations induced by monosodium glutamate in a sex‐dependent manner in male and female rats

“…53 It has been already demonstrated that MSG administration increases the cysteine levels in the plasma of the rats, which could be associated with insulin resistance and development of obesity. 55 In addition, the excess of G6P could favor pyruvate and acetyl-CoA generation, by stimulating the Krebs cycle. 52 The present findings demonstrate that MSG administration to male rats increased the hepatic citrate synthase activity, thus generating an excess of citrate that could be redirected to the triacylglycerol synthesis, demonstrated in this study by the increase in the triglycerides (TG) content.…”

“…Another possible explanation is that high levels of cysteine could deregulate the tyrosine metabolism and decrease the TAT activity in the liver . It has been already demonstrated that MSG administration increases the cysteine levels in the plasma of the rats, which could be associated with insulin resistance and development of obesity …”