Interleukin-17 as a key player in neuroimmunometabolism

In mammals, interleukin (IL)-17 cytokines are produced by innate and adaptive lymphocytes. However, the IL-17 family has widespread expression throughout evolution, dating as far back as cnidaria, molluscs and worms, which predate lymphocytes. The evolutionary conservation of IL-17 suggests that it is involved in innate defence strategies, but also that this cytokine family has a fundamental role beyond typical host defence. Throughout evolution, IL-17 seems to have a major function in homeostatic maintenance at barrier sites. Most recently, a pivotal role has been identified for IL-17 in regulating cellular metabolism, neuroimmunology and tissue physiology, particularly in adipose tissue. Here we review the emerging role of IL-17 signalling in regulating metabolic processes, which may shine a light on the evolutionary role of IL-17 beyond typical immune responses. We propose that IL-17 helps to coordinate the cross-talk among the nervous, endocrine and immune systems for whole-body energy homeostasis as a key player in neuroimmunometabolism.

Omega-3 polyunsaturated fatty acids prevent obesity by improving tricarboxylic acid cycle homeostasis

The beneficial effects of omega-3 polyunsaturated fatty acids (n-3 PUFAs) on preventing obesity are well known; however, the underlying mechanism by which n-3 PUFAs influence tricarboxylic acid (TCA) cycle under obesity remains unclear. We randomly divided male C57BL/6 mice into 5 groups (n=10) and fed for 12 weeks as follows: mice fed a normal diet (Con, 10% kcal); mice fed a high-fat diet (HFD, lard, 60% kcal); and mice fed a high-fat diet (60% kcal) substituting half the lard with safflower oil (SO), safflower oil and fish oil (SF) and fish oil (FO), respectively. Then we treated HepG2 cells with palmitic acid and DHA for 24 h. We found that body weight in FO group was significantly lower than it in HFD and SO groups. N-3 PUFAs reduced the transcription and translation of TCA cycle enzymes, including IDH1, IDH2, SDHA, FH and MDH2, to enhance mitochondrial function in vivo and vitro. DHA significantly inhibited protein expression of the mTORC1 signaling pathway, increased p-AKT protein expression to alleviate insulin resistance and improved mitochondrial oxygen consumption rate and glycolysis ability in HepG2 cells. In addition, the expressions of IDH2 and SDHB were reduced by rapamycin. N-3 PUFAs could prevent obesity by improving TCA cycle homeostasis and mTORC1 signaling pathway may be upstream.

N-3 polyunsaturated fatty acid-enriched lipid emulsion improves Paneth cell function via the IL-22/Stat3 pathway in a mouse model of total parenteral nutrition

Total parenteral nutrition (TPN) is a life-saving therapy for patients with gastrointestinal dysfunction or failure. Long-term TPN impairs gut barrier function and contributes to infections and poor clinical outcomes. However, the underlying mechanisms of TPN-related gut barrier damage have not been fully elucidated, and effective measures are still rare. Here, we compared the effects of a predominantly n-6 polyunsaturated fatty acids emulsion (PUFAs; Intralipid) and a lipid emulsion containing n-3 PUFAs (Intralipid plus Omegaven) on antimicrobial peptides produced by Paneth cells. Our results show for the first time that n-3 PUFAs markedly ameliorated intestine atrophy, and increased protein levels of lysozyme, RegIIIγ, and α-cryptdin 5, and their mRNA expression, compared to the n-6 PUFAs emulsion. Importantly, our study reveals that downregulation of IL-22 and phosphorylated Stat3 (p-Stat3) is associated with Paneth cell dysfunction, which may mediate TPN-related gut barrier damage. Lastly, n-3 PUFAs upregulated levels of IL-22 and increased the p-Stat3/Stat3 ratio in ileal tissue, suggesting that n-3 PUFAs improve Paneth cell function through activation of the IL-22/Stat3 pathway. Therefore, our study provides a cogent explanation for the beneficial effects of n-3 PUFAs, and indicates the IL-22/Stat3 pathway as a promising target in the treatment of TPN-related gut barrier damage.