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Metabolism is a major regulator of immune cell function, but it remains difficult to study the metabolic status of individual cells. Here, we present Compass, an algorithm to characterize cellular metabolic states based on single-cell RNA sequencing and flux balance analysis. We applied Compass to associate metabolic states with T helper 17 (Th17) functional variability (pathogenic potential) and recovered a metabolic switch between glycolysis and fatty acid oxidation, akin to known Th17/regulatory T cell (Treg) differences, which we validated by metabolic assays. Compass also predicted that Th17 pathogenicity was associated with arginine and downstream polyamine metabolism. Indeed, polyamine-related enzyme expression was enhanced in pathogenic Th17 and suppressed in Treg cells. Chemical and genetic perturbation of polyamine metabolism inhibited Th17 cytokines, promoted Foxp3 expression, and remodeled the transcriptome and epigenome of Th17 cells toward a Treg-like state. In vivo perturbations of the polyamine pathway altered the phenotype of encephalitogenic T cells and attenuated tissue inflammation in CNS autoimmunity.

Cystic fibrosis (CF) is the most common life-threatening genetic disease in the United States and among people of European descent. Despite the widespread distribution of the cystic fibrosis transmembrane conductance regulator (CFTR) along kidney tubules, specific renal phenotypes attributable to CF have not been well documented. Recent studies have demonstrated the downregulation of the apical Cl-/HCO3 - exchanger pendrin (Slc26a4) in kidney B-intercalated cells of CF mouse models. These studies have shown that kidneys of both mice and humans with CF have an impaired ability to excrete excess HCO3 -, thus developing metabolic alkalosis when subjected to excess HCO3 - intake. The purpose of this minireview is to discuss the latest advances on the role of pendrin as a molecule with dual critical roles in acid base regulation and systemic vascular volume homeostasis, specifically in CF. Given the immense prevalence of vascular volume depletion, which is primarily precipitated via enhanced chloride loss through perspiration, we suggest that the dominant presentation of metabolic alkalosis in CF is due to the impaired function of pendrin, which plays a critical role in systemic vascular volume and acid base homeostasis. [ABSTRACT FROM AUTHOR]

OBJECTIVE: Cold and β3-adrenergic receptor (AR) agonists activate beige adipocyte biogenesis in white adipose tissue (WAT). The two stimuli also induce expression of inflammatory cytokines in WAT. The low-grade inflammation may further promote WAT browning. However, the mechanisms to reconcile these two biological processes remain to be elucidated. In this study, we aim to investigate the roles of the rate-limiting polyamine catabolic enzyme spermidine/spermine N1-acetyltransferase (SAT1) in regulating beige adipocyte biogenesis and inflammation. METHODS: Adipose-specific SAT1 knockout mice (SAT1-aKO) were generated by crossing adiponectin-cre to SAT1-lox/lox mice. Metabolic phenotype was investigated. Primary pre-adipocytes were isolated from inguinal WAT (iWAT) and differentiated to adipocytes for studying beige adipocyte biogenesis. RESULT: The expression and enzymatic activity of SAT1 were up-regulated in iWAT upon cold and β3-AR stimulation. SAT1-aKO mice developed late-onset obesity on a high-fat diet with impaired cold-induced beige adipocyte biogenesis and energy expenditure. RNA-seq analysis of iWAT from cold-challenged SAT1-aKO mice revealed that, in addition to beige adipocyte biogenesis signatures, the immune response markers were highly enriched among reduced genes. In cultured adipocytes, SAT1 overexpression or pharmacological activation with N1, N11-diethylnorspermine (DENSpm) elevated oxygen consumption and increased the expression of beige adipocyte marker UCP1 and PGC-1α. DENSpm treatment of adipocytes also increased the expression of inflammatory genes. SAT1 activation enhanced hydrogen peroxide production in adipocytes. Antioxidant N-acetylcysteine abrogated the elevated UCP1 expression and reversed some inflammatory genes induced by SAT1 activation. CONCLUSIONS: SAT1 activation plays a key role in cold and β3-AR agonist-induced beige adipocyte biogenesis and low-grade inflammation.

Tuberous sclerosis complex (TSC) presents with renal cysts and benign tumors, which eventually lead to kidney failure. The factors promoting kidney cyst formation in TSC are poorly understood. Inactivation of carbonic anhydrase 2 (Car2) significantly reduced, whereas, deletion of Foxi1 completely abrogated the cyst burden in Tsc1 KO mice. In these studies, we contrasted the ontogeny of cyst burden in Tsc1/Car2 dKO mice vs. Tsc1/Foxi1 dKO mice. Compared to Tsc1 KO, the Tsc1/Car2 dKO mice showed few small cysts at 47 days of age. However, by 110 days, the kidneys showed frequent and large cysts with overwhelming numbers of A-intercalated cells in their linings. The magnitude of cyst burden in Tsc1/Car2 dKO mice correlated with the expression levels of Foxi1 and was proportional to mTORC1 activation. This is in stark contrast to Tsc1/Foxi1 dKO mice, which showed a remarkable absence of kidney cysts at both 47 and 110 days of age. RNA-seq data pointed to profound upregulation of Foxi1 and kidney-collecting duct-specific H+-ATPase subunits in 110-day-old Tsc1/Car2 dKO mice. We conclude that Car2 inactivation temporarily decreases the kidney cyst burden in Tsc1 KO mice but the cysts increase with advancing age, along with enhanced Foxi1 expression. [ABSTRACT FROM AUTHOR]

The bicarbonate transport activities of Slc26a1, Slc26a6 and Slc26a7 are essential to physiological processes in multiple organs. Although mutations of Slc26a1, Slc26a6 and Slc26a7 have not been linked to any human diseases, disruption of Slc26a1, Slc26a6 or Slc26a7 expression in animals causes severe dysregulation of acid-base balance and disorder of anion homeostasis. Amelogenesis, especially the enamel formation during maturation stage, requires complex pH regulation mechanisms based on ion transport. The disruption of stage-specific ion transporters frequently results in enamel pathosis in animals. Here we present evidence that Slc26a1, Slc26a6 and Slc26a7 are highly expressed in rodent incisor ameloblasts during maturation-stage tooth development. In maturation-stage ameloblasts, Slc26a1, Slc26a6 and Slc26a7 show a similar cellular distribution as the cystic fibrosis transmembrane conductance regulator (Cftr) to the apical region of cytoplasmic membrane, and the distribution of Slc26a7 is also seen in the cytoplasmic/subapical region, presumably on the lysosomal membrane. We have also examined Slc26a1 and Slc26a7 null mice, and although no overt abnormal enamel phenotypes were observed in Slc26a1-/- or Slc26a7-/- animals, absence of Slc26a1 or Slc26a7 results in up-regulation of Cftr, Ca2, Slc4a4, Slc4a9 and Slc26a9, all of which are involved in pH homeostasis, indicating that this might be a compensatory mechanism used by ameloblasts cells in the absence of Slc26 genes. Together, our data show that Slc26a1, Slc26a6 and Slc26a7 are novel participants in the extracellular transport of bicarbonate during enamel maturation, and that their functional roles may be achieved by forming interaction units with Cftr.

The Syndrome of Inappropriate ADH secretion (SIADH) presents with excess ADH release caused by a range of conditions; including pneumonia, brain tumors, certain lung cancers, and diseases of the hypothalamus. It presents with significant reduction in both sodium and chloride concentrations in the blood. However, reports examining the acid base status indicate a normal serum bicarbonate concentration and systemic acid base homeostasis. The mechanisms for the absence of abnormalities in acid base homeostasis remain speculative. This mini review is highlighting the recent advances in renal molecular physiology to provide answers for the maintenance of acid base status and serum bicarbonate in a physiological range. [ABSTRACT FROM AUTHOR]

Introduction The clinical syndrome of asthma has evolved as one of the most common chronic diseases in children and adults, but its pathogenesis remains incompletely understood. Th2-mediated inflammation triggered by [...]

Gastric surface pH ([pH.sub.o]) transiently increases in response to focal epithelial damage. The sources of that increase, either from paracellular leakage of interstitial fluid or transcellular acid/base fluxes, have not been determined. Using in vivo microscopy approaches we measured pHo with Cl-NERF, tissue permeability with intravenous fluorescent-dextrans to label interstitial fluid (paracellular leakage), and gastric epithelial intracellular pH ([pH.sub.i]) with SNARF-5F (cellular acid/base fluxes). In response to two-photon photodamage, we found that cell-impermeant dyes entered damaged cells from luminal or tissue compartments, suggesting a possible slow transcellular, but not paracellular, route for increased permeability after damage. Regarding cytosolic acid/base status, we found that damaged cells acidified (6.63 [+ or -] 0.03) after photo-damage, compared with healthy surface cells both near (7.12 [+ or -] 0.06) and far (7.07 [+ or -] 0.04) from damage (P < 0.05). This damaged cell acidification was further attenuated with 20 [micro]M intravenous EIPA (6.34 [+ or -] 0.05, P < 0.05) but unchanged by addition of 0.5 mM luminal [H.sub.2]DIDS (6.64 [+ or -] 0.08, P > 0.05). Raising luminal pH did not realkalinize damaged cells, suggesting that the mechanism of acidification is not attributable to leakiness to luminal protons. Inhibition of apical HC[O.sup.-.sub.3] secretion with 0.5 mM luminal [H.sub.2]DIDS or genetic deletion of the solute-like cartier 26A9 (SLC26A9) [Cl.sup.-]/HC[O.sup.-.sub.3] exchanger blocked the [pH.sub.o] increase normally observed in control animals but did not compromise repair of damaged tissue. Addition of exogenous [PGE.sub.2] significantly increased [pH.sub.o] in wild-type, but not SLC26A9 knockout, animals, suggesting that prostaglandin-stimulated HC[O.sup.-.sub.3] secretion is fully mediated by SLC26A9. We conclude that cellular HC[O.sup.-.sub.3] secretion, likely through SLC26A9, is the dominant mechanism whereby surface pH transiently increases in response to photodamage. photodamage; NAD(P)H; autofluorescence; two-photon microscopy; confocal microscopy; intracellular pH; SNARF-5F; CI-NERF; permeability; solute-like carrier 26A9 doi: 10.1152/ajpgi.00037.2010.