Dietary fibre regulates blood pressure (BP) through gut microbial production of acidic metabolites known as short-chain fatty acids (SCFAs). The specific mechanisms of how SCFAs regulate BP are still emerging. We hypothesised that acidic metabolites that are abundant in the large intestine may activate proton-sensing G-protein coupled receptors, such as GPR65, thus conferring BP regulating effects. Using mouse models, we found that dietary fibre levels determined the luminal pH in the large intestine, through production of SCFAs by the gut microbiota. We then investigated a new mouse model lacking GPR65, which spontaneously developed higher BP, cardiac and renal hypertrophy and fibrosis. We identified that low pH, acting via GPR65 signalling, increased cAMP production and phosphorylation of CREB, and regulated inflammatory cytokine production involved in hypertension. We showed that the benefits of diets high in fibre, which usually prevent hypertension and its associated phenotypes, were decreased in mice lacking GPR65. Finally, we provided proof-of-concept evidence that the luminal pH profile in the colon of hypertensive participants is higher than that of normotensive participants. Colonic pH was further associated with dietary fibre, particularly in the colonic regions where fibre is fermented by the gut microbiota. Together, we show that pH sensing by GPR65 underlies at least some of the cardiovascular benefits of dietary fibre.

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Dietary fibre controls blood pressure and cardiovascular risk by lowering large intestinal pH and activating the proton-sensing receptor GPR65

A major mechanism for immunomodulation: Dietary fibres and acid metabolites.

Chemically synthetic receptors that establish cells a new sense-and-respond capability to interact with outer worlds are highly desired, but rarely reported. In this work, we develop a membrane-anchored synthetic receptor (Ts-pHLIP-Pr) using DNA and peptide as the building block to equip cells with artificial signaling pathways. Upon sensing external pH stimuli, the Pr module can be translocated across the cell membrane via the conformation switch of pHLIP, enabling membrane-proximal recruitment of specific proteins to trigger downstream signaling cascades. Our experimental results demonstrate the capability of Ts-pHLIP-Pr for regulating PKCε-related signaling events upon responding to external pH reduction. With a modular feature, this receptor can be extended to elicit T cell activation through low-pH environment-induced directional movement of cytoplasmic ZAP70. Our work is expected to offer a new paradigm for intelligent synthetic biology and customized cell engineering.

Chemically Synthetic Membrane Receptors Establish Cells with Artificial Sense-and-Respond Signaling Pathways.

The inflammatory microenvironment involves changes in pH and protein phosphorylation has closely related to the occurrence and development of atherosclerosis (AS). Herein, we constructed a dual-detection fluorescence nanosensor PCN-NP-HPZ based on post modification of MOFs, which realized the simultaneous detection and imaging of pH and phosphorylation through the pH sensitive group piperazine and the Zr(IV) node of MOFs. The sensors were used to track changes in blood pH and phosphate levels at different time stages during atherosclerotic plaque formation. Two-photon fluorescence imaging was also performed in vascular endothelium. Blood tests combined with two-photon fluorescence images indicated that in the early stage of AS, blood and tissue pH levels were lower than that of the normal mice, while phosphate and tissue phosphorylation levels were higher than that of the normal mice. The present study provides a new analysis method for the assessment of early atherosclerotic disease.

Assessing the Progression of Early Atherosclerosis Mice Using a Fluorescence Nanosensor for the Simultaneous Detection and Imaging of pH and Phosphorylation.

Few studies report the microglia involvement in the pathogenesis of panic disorder (PD), although the crucial role of microglia in other neuropsychiatric diseases is being emphasized. In addition, there is no report to characterize the phenotypic and functional levels of PD patient-derived microglia to find their clinical relevance. Herein, we used a model to induce patient-derived microglia-like cells (iMGs) to clarify the molecular characteristics and function of PD-iMGs. We established iMGs from 17 PD patients and 16 healthy controls (non-psychiatric controls, HC). PD-iMGs showed increased T-cell death-associated gene-8 expression per the proposal of a previous in vivo study. In addition, we found that patient-derived iMGs showed reduced phagocytosis and increased TREM2 expression. We analyzed the phenotype of the PD-iMGs by RNA sequencing. The PD-iMGs clustered together distinct from HC-iMGs. Gene set enrichment analysis revealed the involvement of cholesterol biosynthesis and steroid metabolism in PD-iMGs. Regarding the cholesterol synthesis pathway, we discovered ACAT2 and DHCR7 as the most impacted genes related to a character of PD-iMGs compared to HC-iMGs. The ACAT2, a major cholesterol esterifier, was increased in PD-iMGs. Nevertheless, PD-iMGs did not show lipid droplet accumulation. Interestingly, ACAT2 expression was inversely correlated with the severity of depression and anxiety sensitivity to publicly observable anxiety reactions. We propose that microglia of PD patients have unique characteristics with dysregulation of cholesterol biosynthesis pathway and impaired phagocytosis, reflecting clinical phenotype. 

/pdf/a-molecular-characterization-and-clinical-relevance-of-3sa8hld4.pdf

A molecular characterization and clinical relevance of microglia-like cells derived from patients with panic disorder

Extracellular acidification occurs in inflamed tissue and the tumor microenvironment; however, a systematic study on how pH sensing contributes to tissue homeostasis is lacking. In the present study, we examine cell type-specific roles of the pH sensor G protein-coupled receptor 65 (GPR65) and its inflammatory disease-associated Ile231Leu-coding variant in inflammation control. GPR65 Ile231Leu knock-in mice are highly susceptible to both bacterial infection-induced and T cell-driven colitis. Mechanistically, GPR65 Ile231Leu elicits a cytokine imbalance through impaired helper type 17 T cell (TH17 cell) and TH22 cell differentiation and interleukin (IL)-22 production in association with altered cellular metabolism controlled through the cAMP–CREB–DGAT1 axis. In dendritic cells, GPR65 Ile231Leu elevates IL-12 and IL-23 release at acidic pH and alters endo-lysosomal fusion and degradation capacity, resulting in enhanced antigen presentation. The present study highlights GPR65 Ile231Leu as a multistep risk factor in intestinal inflammation and illuminates a mechanism by which pH sensing controls inflammatory circuits and tissue homeostasis. Extracellular microenvironments are more acidic upon tissue damage or in tumors. Xavier and colleagues identify a role for the pH-sensitive, G protein-coupled receptor GPR65 in multiple aspects of immune cell lipid metabolism, disruption of which leads to chronic inflammatory responses. 

Xiangjun Chen

Papers

pH sensing controls tissue inflammation by modulating cellular metabolism and endo-lysosomal function of immune cells