Diacylglycerol kinase synthesized by commensal Lactobacillus reuteri diminishes protein kinase C phosphorylation and histamine-mediated signaling in the mammalian intestinal epithelium

Abstract

Lactobacillus reuteri 6475 (Lr) of the human microbiome synthesizes histamine and can suppress inflammation via type 2 histamine receptor (H2R) activation in the mammalian intestine. Gut microbes such as Lr promote H2R signaling and may suppress H1R pro-inflammatory signaling pathways in parallel by unknown mechanisms. In this study, we identified a soluble bacterial enzyme known as diacylglycerol kinase (Dgk) from Lr that is secreted into the extracellular milieu and presumably into the intestinal lumen. DgK diminishes diacylglycerol (DAG) quantities in mammalian cells by promoting its metabolic conversion and causing reduced PKC phosphorylation (pPKC) as a net effect in mammalian cells. We demonstrated that histamine synthesized by gut microbes (Lr) activates both mammalian H1R and H2R, but Lr-derived Dgk suppresses the H1R signaling pathway. Phospho-PKC and IκBα were diminished within the intestinal epithelium of mice and humans treated by WT Lr, but pPKC and IκBα were not decreased in treatment with ΔdgkA Lr. Mucosal IL-6 and systemic IL-1α, eotaxin and G-CSF were suppressed in WT Lr, but not in ΔdgkA Lr colonized mice. Collectively, the commensal microbe Lr may act as a “microbial antihistamine” by suppressing intestinal H1R mediated pro-inflammatory responses via diminished pPKC-mediated mammalian cell signaling.

The vagino-cervical microbiome as a woman’s life history

“…While lacking significant association with the vagino-cervical microbial composition, the immune repertoire data, especially TRBV7.3 and TRBV7.4, showed multiple associations with functional pathways in the vagino-cervical microbiome, such as purine and pyrimidine metabolism, synthesis of branched-chain amino acids, histidine and arginine (Figure S7). Red blood cell counts, plasma vitamin A and plasma hydroxyl vitamin D levels negatively associated with CDP-diacylglycerol biosynthesis pathways, consistent with presence of diacylglycerol kinase in Lactobacilli with anti-inflammatory functions (Andrada et al, 2017; Ganesh et al, 2017). Fecal Coprococcus comes , a bacterium previously reported to associate with cytokine response to Candida albicans (Schirmer et al, 2016), was seen here to associate with isoleucine pathways in the vagino-cervical microbiome (Figure S7).…”

Two‐carbon folate cycle of commensalLactobacillus reuteri6475 gives rise to immunomodulatory ethionine, a source for histone ethylation

“…reuteri culture L. reuteri was cultured in Lactobacillus defined medium (LDM) 3 or 4 in an anaerobic hood (Bactron IV; Sheldon Manufacturing, Cornelius, OR, USA). Colonies were transferred from De Man, Rogosa, and Sharpe medium plates to liquid De Man, Rogosa, and Sharpe medium to grow a preculture (20,26,27). Cell densities corresponding to 0.1 optical density of preculture were used to inoculate experimental cultures that were grown in LDM3 or LDM4.…”

“…In contrast to mast cell-derived histamine and allergic inflammation, bacterial-derived histamines yielded anti-inflammatory effects in mammalian hosts, depending on the relative distribution of histamine receptors. Specifically, histamine production by L. reuteri ATCC 6475 suppresses the production of proinflammatory cytokines in intestinal epithelial cells and macrophages in vitro (17,19,20). Administration of live L. reuteri 6475, cellfree culture supernatants, or histamine suppresses the intestinal inflammation in mouse colitis models (19)(20)(21).…”

Probiotics in Disease Prevention and Treatment

“…Some human‐derived L. reuteri strains, for example, L. reuteri strain ATCC PTA 6475, synthesize histamine, which can suppress inflammation via type 2 histamine receptor activation in the mammalian intestine, resulting in suppression of chronic intestinal inflammation and colorectal tumorigenesis …”

“…97 Some human-derived L. reuteri strains, for example, L. reuteri strain ATCC PTA 6475, synthesize histamine, which can suppress inflammation via type 2 histamine receptor activation in the mammalian intestine, resulting in suppression of chronic intestinal inflammation and colorectal tumorigenesis. 98,99 Probiotics have the ability to ferment certain types of fibers, thus increasing the production of short-chain fatty acids (SCFAs), such as propionate, acetic acid, and butyrate. Short-chain fatty acids play multiple critical roles in host defense and immunity, including anticancer, anti-inflammation, and antioxidant activities, as well as outcompetition of enteric bacterial pathogens.…”