Niacin Alleviates Dairy Cow Mastitis by Regulating the GPR109A/AMPK/NRF2 Signaling Pathway.

Wenjin Guo,Wen Li,Shoupeng Fu,Yu Cao,Juxiong Liu,Xingchi Kan,He Ma,Qian Gong,Jianfa Wang

doi:10.3390/ijms21093321

Abstract

Mastitis is one of three bovine diseases recognized as a cause of substantial economic losses every year throughout the world. Niacin is an important feed additive that is used extensively for dairy cow nutrition. However, the mechanism by which niacin acts on mastitis is not clear. The aim of this study is to investigate the mechanism of niacin in alleviating the inflammatory response of mammary epithelial cells and in anti-mastitis. Mammary glands, milk, and blood samples were collected from mastitis cows not treated with niacin (n = 3) and treated with niacin (30 g/d, n = 3) and healthy cows (n = 3). The expression of GPR109A, IL-6, IL-1β, and TNF-α in the mammary glands of the dairy cows with mastitis was significantly higher than it was in the glands of the healthy dairy cows. We also conducted animal experiments in vivo by feeding rumen-bypassed niacin. Compared with those in the untreated mastitis group, the somatic cell counts (SCCs) and the expression of IL-6, IL-1β, and TNF-α in the blood and milk were lower. In vitro, we isolated the primary bovine mammary epithelial cells (BMECs) from the mammary glands of the healthy cows. The mRNA levels of IL-6, IL-1β, TNF-α, and autophagy-related genes were detected after adding niacin, shRNA, compound C, trans retinoic acid, 3-methyladenine to BMECs. Then GPR109A, AMPK, NRF-2, and autophagy-related proteins were detected by Western blot. We found that niacin can activate GPR109A and phosphorylate AMPK, and promote NRF-2 nuclear import and autophagy to alleviate LPS-induced inflammatory response in BMECs. In summary, we found that niacin can reduce the inflammatory response of BMECs through GPR109A/AMPK/NRF-2/autophagy. We also preliminarily explored the alleviative effect of niacin on mastitis in dairy cows.

Highlights

Dairy cow mastitis is an inflammatory disease caused by the co-infection of various pathogenic microorganisms
To examine the reliability of the mammary gland samples, pathological changes and the mRNA levels of pro-inflammatory factors (IL-6, TNF-α, and IL-1β) in the mammary gland were detected by hematoxylin and eosin (H&E) staining or real-time (RT)-PCR, respectively
The H&E staining analysis revealed that a large number of neutrophils had infiltrated the mammary acini of mastitis dairy cows, but neutrophils did not invade the mammary acini of healthy cows

Summary

Introduction

Dairy cow mastitis is an inflammatory disease caused by the co-infection of various pathogenic microorganisms. The problem of dairy cow mastitis has not been well resolved, and it still causes tremendous economic losses to the world’s dairy industry [2,3]. The main cause of mastitis in dairy cows is the invasion of pathogenic microorganisms into the mammary glands of dairy cows. The main components of these endotoxins are lipopolysaccharides (LPS) It can cause a strong immunogenic response [8]. LPS can trigger the immune response of bovine mammary epithelial cells (BMECs) or macrophages, thereby releasing a large number of pro-inflammatory factors, damaging the BMECs and leading to mastitis [9,10]. In follow-up experiments, we used LPS to construct an inflammation response model of BMECs in vitro

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Results