Phytomodulatory proteins isolated from Calotropis procera latex promote glycemic control by improving hepatic mitochondrial function in HepG2 cells

The medicinal uses of Calotropis procera are diverse, yet some of them are based on effects that still lack scientific support. Control of diabetes is one of them. Recently, latex proteins from C. procera latex (LP) have been shown to promote in vivo glycemic control by the inhibition of hepatic glucose production via AMP-activated protein kinase (AMPK). Glycemic control has been attributed to an isolated fraction of LP (CpPII), which is composed of cysteine peptidases (95%) and osmotin (5%) isoforms. Those proteins are extensively characterized in terms of chemistry, biochemistry and structural aspects. Furthermore, we evaluated some aspects of the mitochondrial function and cellular mechanisms involved in CpPII activity. The effect of CpPII on glycemic control was evaluated in fasting mice by glycemic curve and glucose and pyruvate tolerance tests. HepG2 cells was treated with CpPII, and cell viability, oxygen consumption, PPAR activity, production of lactate and reactive oxygen species, mitochondrial density and protein and gene expression were analyzed. CpPII reduced fasting glycemia, improved glucose tolerance and inhibited hepatic glucose production in control animals. Additionally, CpPII increased the consumption of ATP-linked oxygen and mitochondrial uncoupling, reduced lactate concentration, increased protein expression of mitochondrial complexes I, III and V, and activity of peroxisome-proliferator-responsive elements (PPRE), reduced the presence of reactive oxygen species (ROS) and increased mitochondrial density in HepG2 cells by activation of AMPK/PPAR. Our findings strongly support the medicinal use of the plant and suggest that CpPII is a potential therapy for prevention and/or treatment of type-2 diabetes. A common epitope sequence shared among the proteases and osmotin is possibly the responsible for the beneficial effects of CpPII.

Leucine can modulate the expression of proteins related to protein degradation signalling under mTOR inhibition in C2C12 cells

Many metabolic syndromes lead to energetic disturbs which ends to an intense catabolic state. The branched-chain amino acid leucine shows very positive effects on muscle protein metabolism. However, it is still not clear how leucine acts improving the protein turnover. This study aimed to evaluate in vitro the effects of leucine supplementation in minimising the signalling pathway of protein degradation when mTOR was inhibited. Our studies were conducted in murine C2C12 myotubes exposed to 2mM leucine or 2mM isoleucine in control situation and compared to the inhibition of mTOR by rapamycin. Then, the expression of proteins related to protein synthesis and degradation signalling pathway was obtained by Western Blot. At this concentration, the leucine was sufficient to maintain the expression of proteins evaluated as in control situation. However, when the cells were exposed to rapamycin (80nM), leucine inhibited the expression of SMAD and FoxO3a, showing that leucine was able to modulate the degradation pathway when protein synthesis is compromised. Furthermore, leucine had no effect in modifying the expression of subunits of ubiquitin-proteasome system, showing that leucine had no direct effect in ubiquitin-proteasome system, but acted leading to the phosphorylation of SMAD and FoxO3, which inhibited the activity of transcriptional of these proteins. No similar results were observed in cells exposed to isoleucine under the same experimental protocol, likely showing that leucine has specific action over another branched-chain amino acids. In conclusion, the present study shows that leucine can modulate degradation pathways even under inhibition of mTOR by rapamycin.

Leucine can modulate the expression of proteins related to protein degradation signalling under mTOR inhibition in C2C12 cells

Many metabolic syndromes lead to energetic disturbs which ends to an intense catabolic state. The branched-chain amino acid leucine shows very positive effects on muscle protein metabolism. However, it is still not clear how leucine acts improving the protein turnover. This study aimed to evaluate in vitro the effects of leucine supplementation in minimising the signalling pathway of protein degradation when mTOR was inhibited. Our studies were conducted in murine C2C12 myotubes exposed to 2mM leucine or 2mM isoleucine in control situation and compared to the inhibition of mTOR by rapamycin. Then, the expression of proteins related to protein synthesis and degradation signalling pathway was obtained by Western Blot. At this concentration, the leucine was sufficient to maintain the expression of proteins evaluated as in control situation. However, when the cells were exposed to rapamycin (80nM), leucine inhibited the expression of SMAD and FoxO3a, showing that leucine was able to modulate the degradation pathway when protein synthesis is compromised. Furthermore, leucine had no effect in modifying the expression of subunits of ubiquitin-proteasome system, showing that leucine had no direct effect in ubiquitin-proteasome system, but acted leading to the phosphorylation of SMAD and FoxO3, which inhibited the activity of transcriptional of these proteins. No similar results were observed in cells exposed to isoleucine under the same experimental protocol, likely showing that leucine has specific action over another branched-chain amino acids. In conclusion, the present study shows that leucine can modulate degradation pathways even under inhibition of mTOR by rapamycin.