[ad_1]
In a recent study published in nature metabolism, researchers conducted clinical studies in murine animals and humans to evaluate the impact of high protein intake on the mammalian amino acid target of rapamycin complex 1 (mTORC1) autophagy signaling pathway. They also evaluated the dose-response relationship, downstream effects, and amino acid specificity of mTORC1 activation.
Background
Animal studies have reported that high protein intake is associated with cardiovascular disease in Western nations. High-protein diets enhance atherogenesis through amino acid-mediated mTORC1 signaling and impair autophagy and mitophagy in macrophages. The specific joint processes underlying this activation remain unknown, although the authors speculate that the stimulatory impact may be related to certain “pathogenic” amino acids.
About the study
In the present study, the researchers performed two clinical experiments to investigate the dose-response connection between dietary protein consumption and the amino acid specificity of the amino acid-mTOR-autophagy pathway in human monocytes or macrophages.
The first experiment examined the extremes of protein consumption by assessing the impact of liquid meals containing 50% or 10% protein content on activation of the mTORC1 pathway in monocytes. The second experiment used a more realistic setting and evaluated these results in subjects receiving standard protein meals or mixed meals with more protein (15% kilocalories vs. 22% kilocalories). The study looked at monocytes that express cluster of differentiation 14 (CD14+), but not CD16, as they represent the majority of monocytes in circulation and are more likely to become atherosclerotic macrophages.
The team performed flow cytometry and isolation of monocytes from platelets. They used Western blotting, fluorescence-activated cell sorting (FACS), and immunofluorescence to investigate the impact of different protein-containing meals on serological amino acid levels, monocyte mTORC1 signaling, and downstream consequences.
The team investigated 14 overweight people. [based on body mass index (BMI)] twice after a 12-hour overnight fast. Participants ate meals with low and very high levels of protein. The researchers used cultured macrophages derived from human monocytes to investigate the macrophage-specific mTORC1 response to amino acids and evaluate dose effects.
They measured amino acid concentrations in plasma and macrophages by gas chromatography-mass spectrometry and quantified the amounts of arginine in plasma by liquid chromatography-mass spectrometry. They determined the size of the atherosclerotic lesions by Oil Red O staining of aortic root sections.
The researchers investigated whether leucine-dependent mTORC1 activation occurs in vivo in mice and cultured murine macrophages. ApoE knockout mice were fed six meals for eight weeks, including a moderate-protein Western diet, a high-protein Western diet, a moderate-protein Western diet with leucine and amino acids, plus amino acids, and a nitrogen-adjusted version of the diet. moderate. -proteins plus amino acids.
They investigated whether serum amino acids were present in C57BL/6J mice weaned at three weeks of age. LiveResearch related to atherosclerosis began at eight weeks using male mice of the given genotype fed varied diets.
Results
The study identified leucine as the main activator of mTOR signaling in macrophages, showing a threshold impact of high protein consumption and circulation of leucine in monocytes or macrophages. Only proteins greater than 25 g per meal activate mTOR and have functional consequences. Protein ingestion above 22% of dietary energy requirements triggers the harmful amino acid mTORC1 autophagy signaling pathway in human monocytes and macrophages, causing atherosclerosis in male mice. The study found a strong link between high protein consumption and the risk of atherosclerotic cardiovascular disease, indicating the possibility of dietary advice and treatment measures.
Total plasma amino acid content increased after eating the high-protein liquid meal, but not after drinking the low-protein meal. During the three-hour postprandial interval, consumption of a very high level of protein boosted mTORC1 signaling and gradually reduced LC3 signal intensity, indicating suppression of mTORC1-mediated autophagy. Western blot analysis showed a strong dose-dependent impact of leucine-mediated mTORC1 activation in HMDM, as assessed by phosphorylation of ribosomal protein S6 and ribosomal protein S6 kinase (p-S6K).
The team also found a dose-dependent threshold effect for mTOR-LAMP2 colocalization, suppression of autophagy (decreased LC3 dot formation), and mitophagy (reduced colocalization of the mitochondrial marker COXIV with the autophagosome marker LC3). They observed significantly higher levels of four amino acids (Leu, Ile, Val and Thr) in mice after protein gavage compared to control gavage.
Leucine was the most effective mTORC1 activator, with 1.6 g of protein per kg of gavage resulting in greater mTORC1 activation than 0.8 g of protein per kg of gavage. The study revealed that an increase in dietary leucine is necessary and sufficient to produce the proatherogenic impact of a high-protein diet. live.
The study findings showed that high protein intake, particularly through elevated plasma leucine levels, could suppress mTORC1-mediated autophagy and atherogenesis in monocytes and macrophages, with critical clinical and public health implications.
Although protein consumption above the recommended amount of 0.8 grams/kg/day is considered safe, the study suggests caution and further clinical studies. Leucine was the main amino acid responsible for activating mTOR in macrophages, and increased protein consumption had a threshold effect on the detrimental signaling pathway.
A thorough examination is required to determine the exact threshold between the benefits of dietary protein and the negative health impacts.