Abstract
As a subgroup of CD4+ T helper cells, follicular helper T (Tfh) cells provide help to germinal center B cells and mediate the development of long-lived humoral immunity. Dysregulation of Tfh cells is associated with several major autoimmune diseases. Although recent studies showed that Tfh cell differentiation is controlled by the transcription factor Bcl6, cytokines, and cell-cell signals, limited information is available on the proteome and post-translational modifications (PTMs) of proteins in human Tfh cells. In the present study, we investigated quantitative proteome and acetylome in human naive CD4+ T cells and in vitro induced Tfh (iTfh) cells using the tandem mass tag (TMT) labeling technique, antibody-based affinity enrichment, and high-resolution liquid chromatography-mass spectrometry (LC-MS)/mass spectrometry (MS) analysis. In total, we identified 802 upregulated proteins and 598 downregulated proteins at the threshold of 1.5-fold in iTfh cells compared to naive CD4+ T cells. With the aid of intensive bioinformatics, the biological process, the cellular compartment, the molecular function, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, and protein–protein interaction of these differentially expressed proteins were revealed. Moreover, the acetylome data showed that 22 lysine (K) acetylated proteins are upregulated and 26 K acetylated proteins are downregulated in iTfh cells compared to the naive CD4+ T cells, among which 11 differentially acetylated K residues in core histones were identified, indicating that protein acetylation and epigenetic mechanism are involved in regulating Tfh cell differentiation. The study provides some important clues for investigating T cell activation and Tfh cell differentiation.
Highlights
Follicular helper T (Tfh) cells have emerged as a separate CD4+ T helper subset specialized in assisting B cells in recent times
To investigate the proteomic profile that was involved in the differentiation of follicular helper T (Tfh) cells, naive CD4+ T cells were isolated from the peripheral blood of healthy subjects (Figure 2A) and induced into Tfh cells in vitro under a Tfh-polarizing condition
The results showed that the percentage of CXCR5+PD-1+CD4+T cells was up to 90% in the induced T cells (Figure 2B), which were consistent with the characters of Tfh cells reported in previous studies, indicating that the induction of Tfh cells was successful in this study
Summary
Follicular helper T (Tfh) cells have emerged as a separate CD4+ T helper subset specialized in assisting B cells in recent times. Recent studies suggested that Tfh cell differentiation and function are essential in the control of virus infections [2,3,4,5]. Elucidating the underlying molecular biological mechanisms of Tfh cell differentiation and function is of great importance for identifying the novel targets of therapy for autoimmune diseases. Proteins perform many biological functions within organisms, including DNA replication, catalyzing metabolic reactions, response to stimuli, molecule transportation, and so on. Lysine acetylation (Kac) residues is one type of PTMs and plays a key role in cellular metabolism, chromatin remodeling, cytoplasmic and nuclear transport, and mitosis [17]. Acetylation of protein plays a vital role in the regulation of inflammasomedependent innate immune responses, toll-like receptors, and retinoic-acid-inducible gene I (RIG-I)-like receptors [18, 19]
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