Higher insulin sensitivity in EDL muscle of rats fed a low-protein, high-carbohydrate diet inhibits the caspase-3 and ubiquitin-proteasome proteolytic systems but does not increase protein synthesis

Abstract

+ 55 to 65 to 3615 to 8765; Fax: +55 to 65 to 3615 to 8005. E-mail address: nairhonda@terra.com.br (N. H. Kawashita). AbstractCompared with the extensor longus digitorum (EDL) muscle of control rats (C), the EDL muscle of rats fed a low-protein, high-carbohydrate (LPHC) diet showed a 36% reduction in mass. Muscle mass is determined by the balance between protein synthesis and proteolysis; thus, the aim of this work was to evaluate the components involved in these processes. Compared with the muscle from C rats, the EDL muscle from LPHC diet-fed rats showed a reduction (34%) in the in vitro basal protein synthesis and a 22% reduction in the in vitro basal proteolysis suggesting that the reduction in the mass can be associated with a change in the rate of the two processes. Soon after euthanasia, in the EDL muscles of the rats fed the LPHC or C diet for 15 days, the activity of caspase-3 and of components of the ubiquitin-proteasome system (atrogin-1 content and chymotrypsin-like activity) were decreased. The phosphorylation of p70 S6K and 4E-BP1, proteins involved in protein synthesis, was also decreased. We observed an increase in the insulin-stimulated protein content of p-Akt. Thus, the higher insulin sensitivity in the EDL muscle of LPHC rats seemed to contribute to the lower proteolysis in LPHC rats. However, even with the higher insulin sensitivity, the reduction in p-E4-BP1 and p70 S6Kindicates a reduction in protein synthesis, showing that factors other than insulin can have a greater effect on the control of protein synthesis.

A low-protein, high-carbohydrate diet increases browning in perirenal adipose tissue but not in inguinal adipose tissue

“…We have previously shown that rats from the LPHC group have higher levels of nonessential amino acids (data are shown in Supplementary Table 2) [19] can be synthesized from glycolysis (pyruvate) and Krebs cycle (alpha ketoglutarate) intermediaries [19]. Additionally, other studies show that the protein synthesis in the soleus [19] and EDL muscles is reduced [22]. So, an important pathway that uses amino acids is inhibited in LPHC rats.…”

“…Male Wistar rats weighing approximately 100 g (30 to 32 d old) were randomized into either the C group or the LPHC group. Rats in the C group were fed a diet containing 17% protein, 63% carbohydrates, and 7% lipids [25], and those in the LPHC group were fed a diet containing 6% protein, 74% carbohydrates, and 7% lipids for 15 d. The diets were isocaloric (16.3 kJ$g -1 ), with the energy difference from the reduction in dietary protein compensated for by increasing the carbohydrate content [13][14][15][16][17][18][19][20][21][22][23]25] (Table 1). The rats were individually housed in metabolic cages in an environmentally controlled room (lights on from 0600 to 1800; temperature 22 AE 1 C).…”

“…We have been steadily focusing on the effects of administering a low-protein, high-carbohydrate (LPHC) diet to rats, introduced during the early phase of life [13][14][15][16][17][18][19][20][21][22] because children in occidental societies are often fed diets with these characteristics, introduced soon after weaning [23]. Fifteen days after introducing this diet, alterations in the energy balance occur, along with increased food intake and energy gain; these changes increase the amount of body lipids [13].…”

“…Additionally, the LPHC diet increases energy expenditure by increasing thermogenesis in the interscapular brown adipose tissue (iBAT), enhancing UCP1 content, and resulting in a higher response to adrenaline stimulation; this attenuates the energetic gains in these animals as they ingest 18% more calories than rats fed a control (C) diet [13]. Elucidation of major changes in the hormonal profiles and specific responses from these tissues have improved the understanding of the mechanisms involved in thermogenesis in iBAT and other alterations and processes in the adipose tissues, liver, and muscles of these animals [13][14][15][16][17][18][19][20][21][22].…”

Goji Berry (Lycium barbarum) Extract Improves Biometric, Plasmatic and Hepatic Parameters of Rats Fed a High-Carbohydrate Diet

“…Body weight gain promoted by the HC diet can be ascribed to the higher adiposity index of the animals, as they had reduced muscle mass indicated by the weight of the gastrocnemius and that can be the result of the lower protein content of the diet [34]. The observation of decreased body weight gain with the daily supplementation with GB, without change in daily chow ingestion was similar to those in mice [35] and rats [36] fed with HF diet and treated with polysaccharides isolated from GB.…”