Propionate supplementation promotes the expansion of peripheral regulatory T-Cells in patients with end-stage renal disease

Abstract

Patients with end-stage renal disease (ESRD) suffer from a progressively increasing low-grade systemic inflammation, which is associated with higher morbidity and mortality. Regulatory T cells (Tregs) play an important role in regulation of the inflammatory process. Previously, it has been demonstrated that short-chain fatty acids reduce inflammation in the central nervous system in a murine model of multiple sclerosis through an increase in tissue infiltrating Tregs. Here, we evaluated the effect of the short-chain fatty acid propionate on the chronic inflammatory state and T-cell composition in ESRD patients. Analyzing ESRD patients and healthy blood donors before, during, and 60 days after the propionate supplementation by multiparametric flow cytometry we observed a gradual and significant expansion in the frequencies of CD25^highCD127^- Tregs in both groups. Phenotypic characterization suggests that polarization of naïve T cells towards Tregs is responsible for the observed expansion. In line with this, we observed a significant reduction of inflammatory marker CRP under propionate supplementation. Of interest, the observed anti-inflammatory surroundings did not affect the protective pathogen-specific immunity as demonstrated by the stable frequencies of effector/memory T cells specific for tetanus/diphtheria recall antigens. Collectively, our data suggest that dietary supplements with propionate have a beneficial effect on the elevated systemic inflammation of ESRD patients. The effect can be achieved through an expansion of circulating Tregs without affecting the protective pathogen-reactive immunity.

Keywords: End-stage renal disease; Propionate; Regulatory T-cells; Short-chain fatty acids.

Fig. 1

CD25^highCD127⁻ Tregs expand during propionate supplementation. Cells were analyzed ex vivo by flow cytometry. Tregs were identified as CD25^highCD127⁻ according to the gating strategy in Supplementary Fig. 2. a Frequency of Tregs during the baseline phase of the study. The average over the baseline phase was taken for each study participant and used as a single baseline value. b Frequency of Tregs during the propionate supplementation and follow-up phase of the study focusing on differences between study groups. c As in b but focusing on changes over time. d Difference of Treg frequencies over time to the base line. The downward pointing line under asterisks indicates comparison of mean to 0. e Ratio of Tregs frequency during the propionate and follow-up phase to the baseline focusing on differences between study groups. f As in e but with focus on changes over time. The downward pointing line under asterisks indicates comparison of mean to 1. The boxes represent the 25th, 50th, and 75th percentile and the whiskers represent the range of the observations excluding outliers. Each point signifies a single donor. Only significant differences are annotated. Asterisks indicate the p value (*p < 0.05; **p < 0.01; ***p < 0.001)

Fig. 2

Treg subpopulations are not altered during propionate supplementation. Tregs and their subpopulations were analyzed ex vivo by flow cytometry according to the gating strategy in Supplementary Fig. 2. a CCR7⁺CD45RA⁺ naïve like Tregs. b CCR7⁺CD45RA^– central memory like Tregs. c CCR7⁻CD45RA^– effector memory like Tregs. The boxes represent the 25th, 50th, and 75th percentile and the whiskers represent the range of the observations excluding outliers. Each point signifies a single donor. Only significant differences are annotated. Asterisks indicate the p value (*p < 0.05; **p < 0.01; ***p < 0.001)

Fig. 3

Proliferative capacity of Tregs is not modified by propionate intake. Proliferating CD25^highCD12⁷⁻ Tregs were identified by KI76-expression according to the gating strategy in Supplementary Fig. 2. The boxes represent the 25th, 50th, and 75th percentile and the whiskers represent the range of the observations excluding outliers. Each point signifies a single donor. Only significant differences are annotated. Asterisks indicate the p value (*p < 0.05; **p < 0.01; ***p < 0.001)

Fig. 4

The frequency of gut homing Tregs is increased after propionate. Gut homing CD25^highCD127⁻ Tregs were identified by the expression of α4β7⁺CCR9⁺ according to the gating strategy in Supplementary Fig. 2. The boxes represent the 25th, 50th, and 75th percentile and the whiskers represent the range of the observations excluding outliers. Each point signifies a single donor. Only significant differences are annotated. Asterisks indicate the p value (*p < 0.05; **p < 0.01; ***p < 0.001)