Propionate functions as a feeding state-dependent regulatory metabolite to counter proinflammatory signaling linked to nutrient load and obesity.

Generally, fasting and refeeding confer anti- and proinflammatory effects, respectively. In humans, these caloric-load interventions function, in part, via regulation of CD4+ T cell biology. However, mechanisms orchestrating this regulation remain incomplete. We employed integrative bioinformatics of RNA sequencing and high-performance liquid chromatography-mass spectrometry data to measure serum metabolites and gene expression of peripheral blood mononuclear cells isolated from fasting and refeeding in volunteers to identify nutrient-load metabolite-driven immunoregulation. Propionate, a short chain fatty acid (SCFA), and the SCFA-sensing G protein-coupled receptor 43 (ffar2) were coordinately and inversely regulated by fasting and refeeding. Propionate and free fatty acid receptor agonists decreased interferon-γ and interleukin-17 and significantly blunted histone deacetylase activity in CD4+ T cells. Furthermore, propionate blunted nuclear factor κB activity and diminished interleukin-6 release. In parallel, propionate reduced phosphorylation of canonical T helper 1 (TH1) and TH17 regulators, STAT1 and STAT3, respectively. Conversely, knockdown of free fatty acid receptors significantly attenuated the anti-inflammatory role of propionate. Interestingly, propionate recapitulated the blunting of CD4+ TH cell activation in primary cells from obese individuals, extending the role of this metabolite to a disease associated with low-grade inflammation. Together, these data identify a nutrient-load responsive SCFA-G protein-coupled receptor linked pathway to regulate CD4+ TH cell immune responsiveness.

Identification and Validation of Nutrient State-Dependent Serum Protein Mediators of Human CD4+ T Cell Responsiveness.

Intermittent fasting and fasting mimetic diets ameliorate inflammation. Similarly, serum extracted from fasted healthy and asthmatic subjects' blunt inflammation in vitro, implicating serum components in this immunomodulation. To identify the proteins orchestrating these effects, SOMAScan technology was employed to evaluate serum protein levels in healthy subjects following an overnight, 24-h fast and 3 h after refeeding. Partial least square discriminant analysis identified several serum proteins as potential candidates to confer feeding status immunomodulation. The characterization of recombinant IGFBP1 (elevated following 24 h of fasting) and PYY (elevated following refeeding) in primary human CD4+ T cells found that they blunted and induced immune activation, respectively. Furthermore, integrated univariate serum protein analysis compared to RNA-seq analysis from peripheral blood mononuclear cells identified the induction of IL1RL1 and MFGE8 levels in refeeding compared to the 24-h fasting in the same study. Subsequent quantitation of these candidate proteins in lean versus obese individuals identified an inverse regulation of serum levels in the fasted subjects compared to the obese subjects. In parallel, IL1RL1 and MFGE8 supplementation promoted increased CD4+ T responsiveness to T cell receptor activation. Together, these data show that caloric load-linked conditions evoke serological protein changes, which in turn confer biological effects on circulating CD4+ T cell immune responsiveness.

Fasting-induced FOXO4 blunts human CD4+ T helper cell responsiveness.

Intermittent fasting blunts inflammation in asthma1 and rheumatoid arthritis2, suggesting that fasting may be exploited as an immune-modulatory intervention. However, the mechanisms underpinning the anti-inflammatory effects of fasting are poorly characterized3-5. Here, we show that fasting in humans is sufficient to blunt CD4+ T helper cell responsiveness. RNA sequencing and flow cytometry immunophenotyping of peripheral blood mononuclear cells from volunteers subjected to overnight or 24-h fasting and 3 h of refeeding suggest that fasting blunts CD4+ T helper cell activation and differentiation. Transcriptomic analysis reveals that longer fasting has a more robust effect on CD4+ T-cell biology. Through bioinformatics analyses, we identify the transcription factor FOXO4 and its canonical target FK506-binding protein 5 (FKBP5) as a potential fasting-responsive regulatory axis. Genetic gain- or loss-of-function of FOXO4 and FKBP5 is sufficient to modulate TH1 and TH17 cytokine production. Moreover, we find that fasting-induced or genetic overexpression of FOXO4 and FKBP5 is sufficient to downregulate mammalian target of rapamycin complex 1 signalling and suppress signal transducer and activator of transcription 1/3 activation. Our results identify FOXO4-FKBP5 as a new fasting-induced, signal transducer and activator of transcription-mediated regulatory pathway to blunt human CD4+ T helper cell responsiveness.