Early-life thymectomy upregulates proinflammatory chemokine signaling in visceral adipose tissue

Abstract

We have previously reported that early-life thymectomy (thymex) induces an aged T cell phenotype (i.e. shift from naïve to memory) and subsequent glucose intolerance at 9mo compared to control mice. To determine potential mechanisms of inflammation and glucose intolerance in these mice, we preformed RNA sequencing (RNAseq) on the perigonadal white adipose tissue (pWAT) from thymex and control mice. We hypothesized that thymex mice would exhibit an upregulation of inflammatory genes compared to controls. This study was approved by the IACUC at the University of Texas Arlington. Male C57BL/6 mice underwent thymectomy (n=4-10) at 3wks of age or were left with their thymus intact (control n=4-10). At 9mo of age, mice were euthanized and both pWAT fat pads were dissected. One fat pad was used to determine T cell phenotype via flow cytometry, RNA was extracted from the other fat pat for RNAseq. Group differences were assessed by a students t test; RNAseq p values were adjusted for false discovery rate. RNAseq data is reported as a fold change (normalized to control group gene expression); T cell data reported as mean ± SEM (control vs thymex). There were no statistical differences in the total weight of the pWAT nor the total number of T cells in the fat pads. Gene ontology and KEGG analysis revealed that the adaptive immune response, chemokine signaling, chemokine binding and chemokine receptor binding pathways, all markers of inflammation, were upregulated in the pWAT of thymex mice compared to controls. Further analysis of these pathways revealed that gene expression for the chemokines ccl2 (MCP-1) (3.2 times greater than control; p=<0.01) and ccl5 (RANTES)(2.3 times greater than control; p=<0.01) were significantly upregulated in thymex mice compared to controls. In addition, gene expression for the receptors of these chemokines, ccr2 (1.7 times greater than control; p=<0.01) and ccr5 (4.9 times greater than control; p<0.01) were up-regulated in the pWAT of thymex mice. To determine if these chemokines were actively recruiting T cells to the pWAT, we assessed CCR2 and CCR5 expression on CD4+ (Helper) and CD8+ (Cytotoxic) T cells in the pWAT using flow cytometery. Thymex mice had significantly greater proportions of CD4+ CCR2+ (54.4±4.7%, 72.2±4.3%; p=<0.01) and CCR5+ (57.4±5.1%, 75.4±5.0%; p=0.01) cells compared to controls. Similarly, thymex mice had significantly greater proportions of CD8+ CCR2+ (23.1±4.3%, 43.3±5.4%; p=<0.01) and CCR5+(22.7±5.1%, 41.8±7.1%; p=0.02) cells. These results indicate that early life thymectomy induces upregulation of proinflammatory chemokine signaling in the pWAT. These chemokines appear to recruit T cells and potentially other immune cells to the pWAT, contributing to inflammation and potentially metabolic dysfunction. Funding: AHA 940023, NIH R01AG060395, K01AG061271. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.