Nevenka Juretić

L‐arginine induces the expression of utrophin in skeletal muscle cells, so it has been proposed as a pharmacological treatment to attenuate the symptoms of Duchenne muscular dystrophy (DMD). On the other hand, it has been described that one of the pathways that participates in the expression of utrophin in muscle is the Neuregulin‐1 (NRG‐1)/ErbB receptors pathway. Several studies have postulated that disintegrin and metalloprotease‐17 (ADAM17) causes the proteolytic processing of NRG of transmembrane, allowing the release of NRG to the medium, which when joining its ErbB receptor activates the signaling pathway that triggers utrophin transcription. The aim of this study was to evaluate the effect of L‐arginine in the activation of NRG‐1/ErbB pathway and utrophin mRNA levels in C2C12 cells, and the participation of ADAM17 in this process. Our results indicate that L‐arginine induces phosphorylation of ErbB2 and increases utrophin mRNA levels in C2C12 myotubes, with a maximum increase of 2‐fold at 4 h post‐stimulation. This effect is not observed when the myotubes are stimulated in the presence of GM6001 (general metalloprotease inhibitor) or PD‐158780 (specific inhibitor of ErbB receptor phosphorylation). Experiments performed by flow cytometry suggest that L‐arginine stimulates ADAM17 activation in our study model. Furthermore, immunofluorescence analysis supports our findings that L‐arginine stimulates ADAM17 increase in treated myotubes. However, our results using pharmacological inhibitors suggest that ADAM17 does not participate in utrophin expression in C2C12 cells treated with L‐arginine. The results obtained help to clarify the mechanism of action of L‐arginine in the expression of utrophin in muscle cells, which will contribute to the design of new therapeutic strategies in pathologies such as DMD.

Neuregulins (NRGs) are a family of signaling proteins that bind to receptor tyrosine kinases of the ErbB family (ErbB2 to ErbB4), which can homo- or heterodimerize depending on their structural features and cell type. Many studies have proposed that decreased NRG levels are a common characteristic of obesity. In liver and adipose tissue, the increase in NRG expression has protective effects against obesity. However, it is still unknown whether ErbBs expression is altered in this pathology. We hypothesized that high fat diet-induced obesity downregulates ErbB receptors expression in obese mice compared to normal weight mice. Males C57BL/6 mice (n=6-7 for each group) were fed for 12 weeks and divided into: (i) control diet (CD; 10%-kcal fat, 20%-kcal protein, 70%-kcal carbohydrates), and (ii) high fat diet (HFD; 60%-kcal fat, 20%-kcal protein, 20%-kcal carbohydrates). General parameters and ErbBs expression (qPCR, immunohistochemistry and Western blot) were evaluated. We observed a significant increase in final body weight (47%), adipose tissue to body weight ratio (244%) and HOMA-IR (69%), among other parameters, in obese mice. In HFD group significantly decreased ErbB2 (48%) and ErbB3 (66%) mRNA levels in liver (no change in ErbB4), and ErbB2 (43%), ErbB3 (76%) and ErbB4 (35%) in adipose tissue, compared to CD. Furthermore, ErbB2 and ErbB3 protein levels decreased significantly in HFD group compared to the CD in liver. Therefore, our results suggest that HFD-induced obesity significantly decreases ErbBs expression in liver and adipose tissue in this murine model, that may be associated with alterations in the NRG pathway in obese mice.

Increase in body fat contributes to loss of function and changes in skeletal muscle, accelerating sarcopenia, a phenomenon known as sarco-obesity or sarcopenic obesity. Studies suggest that obesity decreases the skeletal muscle (SM)’s ability to oxidize glucose, increases fatty acid oxidation and reactive oxygen species production, due to mitochondrial dysfunction. Exercise improves mitochondrial dysfunction in obesity; however, it is not known if exercise regulates the mitochondrial unfolded protein response (UPRmt) in the SM. Our study aimed to determine the mito-nuclear UPRmt in response to exercise in a model of obesity, and how this response is associated with the improvement in SM functioning after exercise training. C57BL/6 mice were fed a normal diet and high-fat diet (HFD) for 12 weeks. After 8 weeks, animals were subdivided into sedentary and exercised for the remaining 4 weeks. Grip strength and maximal velocity of mice submitted to HFD improved after training. Our results show an increase in the activation of UPRmt after exercise while in obese mice, proteostasis is basally decreased but shows a more pronounced increase with exercise. These results correlate with improvement in the circulating triglycerides, suggesting mitochondrial proteostasis could be protective and could be related to mitochondrial fuel utilization in SM.

Flavor is a determining attribute in the choice of foods and culinary preparations. Taste and preferences for different flavors have been little explored in the Chilean population. The aim of this exploratory study was to determine the liking opinion and preferences for primary flavors and their combinations, aromatic flavors and ethnic flavors in 149 university students. The most liked flavors were salty (91.2%), sweet (89.5%), fruity (83.8%) and Chinese (80.0%) with some differences according to sex. On the contrary, the least liked flavors were bitter and its combinations, spicy (39.9%) and Indian (8.32%), without differences between sex We hope that this information will contribute to improve the current understanding about the acceptability for new gastronomic trends derived from increased migratory phenomenon in Chile, to increase culinary diversity of the national diet.

Inositol 1,4,5‐trisphosphate (IP ₃ ) receptors (IP ₃ Rs) drive calcium signals involved in skeletal muscle excitation‐transcription coupling and plasticity; IP ₃ R subtype distribution and downstream events evoked by their activation have not been studied in human muscle nor has their possible alteration in Duchenne muscular dystrophy (DMD). We studied the expression and localization of IP ₃ R subtypes in normal and DMD human muscle and in normal (RCMH) and dystrophic (RCDMD) human muscle cell lines. In normal muscle, both type 1 IP ₃ Rs (IP ₃ R1) and type 2 IP ₃ Rs (IP ₃ R2) show a higher expression in type II fibers, whereas type 3 IP ₃ Rs (IP ₃ R3) show uniform distribution. In DMD biopsies, all fibers display a homogeneous IP ₃ R2 label, whereas 24 ± 7% of type II fibers have lost the IP ₃ R1 label. RCDMD cells show 5‐fold overexpression of IP ₃ R2 and down‐regulation of IP ₃ R3 compared with RCMH cells. A tetanic stimulus induces IP ₃ ‐dependent slow Ca ²⁺ transients significantly larger and faster in RCDMD cells than in RCMH cells as well as significant ERK1/2 phosphorylation in normal but not in dystrophic cells. Excitation‐driven gene expression was different among cell lines; 44 common genes were repressed in RCMH cells and expressed in RCDMD cells or vice versa . IP ₃ ‐dependent Ca ²⁺ release may play a significant role in DMD pathophysiology.—Cárdenas, C., Juretić, N., Bevilacqua, J. A., García, I. E., Figueroa, R., Hartley, R., Taratuto, A. L., Gejman, R., Riveros, N., Molgó, J., Jaimovich, E. Abnormal distribution of inositol 1,4,5‐trisphosphate receptors in human muscle can be related to altered calcium signals and gene expression in Duchenne dystrophy‐derived cells. FASEB J . 24, 3210–3221 (2010). www.fasebj.org