Mast Cells and the Pancreas in Human Type 1 and Type 2 Diabetes

The evolving role of mast cells in wound healing: insights from recent research and diverse models

Chronic wounds significantly burden health care systems worldwide, requiring novel strategies to ease their impact. Many physiological processes underlying wound healing are well studied but the role of mast cells remains controversial. Mast cells are innate immune cells and play an essential role in barrier function by inducing inflammation to defend the host against chemical irritants and infections, among others. Many mast cell-derived mediators have proposed roles in wound healing; however, in vivo evidence using mouse models has produced conflicting results. Recently, studies involving more complex wound models such as infected wounds, diabetic wounds and wounds healing under psychological stress suggest that mast cells play critical roles in these processes. This review briefly summarizes the existing literature regarding mast cells in normal wounds and the potential reasons for the contradictory results. Focus will be placed on examining more recent work emerging in the last 5 years that explores mast cells in more complex systems of wound healing, including infection, psychological stress and diabetes, with a discussion of how these discoveries may inspire future work in the field.

Mast Cells are Dependent on Glucose Transporter 1 (GLUT1) and GLUT3 for IgE-mediated Activation

Mast cells (MCs) are known to have a pathological impact in a variety of settings, in particular in allergic conditions. There is also limited evidence implicating MCs in diabetes, raising the possibility that MC function may be influenced by alterations in glucose levels. However, it is not known whether MCs are directly affected by elevated glucose concentrations. Moreover, it is not known which glucose transporters that are expressed by MCs, and whether MCs are dependent on glucose transporters for activation. Here we addressed these issues. We show that MCs express high levels of both glucose transporter 1 (GLUT1/Slc2A1) and GLUT3 (Slc2A3). Further, we show that the inhibition of either GLUT1 or GLUT3 dampens both MC degranulation and cytokine induction in response to IgE receptor crosslinking, and that combined GLUT1 and GLUT3 inhibition causes an even more pronounced inhibition of these parameters. In contrast, the inhibition of GLUT1 or GLUT3, or combined GLUT1 and GLUT3 inhibition, had less impact on the ability of the MCs to respond to activation via compound 48/80. Elevated glucose concentrations did not affect MC viability, and had no stimulatory effect on MC responses to either IgE receptor crosslinking or compound 48/80. Altogether, these findings reveal that MCs are strongly dependent on glucose transport via GLUT1 and/or GLUT3 for optimal responses towards IgE-mediated activation, whereas MC functionality is minimally affected by elevated glucose levels. Based on these findings, antagonists of GLUT1 and GLUT3 may be considered for therapeutic intervention in allergic conditions.

The effect of intrauterine growth restriction on the developing pancreatic immune system

Immune cells in the pancreas are known to participate in organ development. However, the resident pancreatic immune system has yet to be fully defined. Immune cells also play a role in pathology and are implicated in diseases such as diabetes induced by intrauterine growth restriction (IUGR). We hypothesized that the resident immune system is established during neonatal development and disrupted by IUGR. Using single cell RNAseq and flow cytometry we identified many immune cell populations in the near-term fetus (at embryologic day 22) and neonatal (postnatal day 1, 7, &14) islets, non-endocrine pancreas, and the spleen in the rat. Using flow cytometry, we observed the resident immune system is established during neonatal development in the pancreas and spleen. We identified 9 distinct immune populations in the pancreatic islets and 8 distinct immune populations in the spleen by single cell RNAseq. There were no sex-specific differences in the relative proportion of immune cells in the pancreas or spleen. Finally, we tested if IUGR disrupted the neonatal immune system using bilateral uterine artery ligation. We found significant changes to the percentage of CD11B+ HIS48- and CD8+ T cells in the islets and non-endocrine pancreas and in the spleen. IUGR-induced alterations were influenced by the tissue environment and the sex of the offspring. Future research to define the role of these immune cells in pancreatic development may identify disrupted pathways that contribute to the development of diabetes following IUGR.

The transcriptional characteristics of mast cells derived from skin tissue in type 2 diabetes patients at the single-cell level

OBJECTIVES

The mechanisms underlying the role of mast cells in wound healing have not been thoroughly studied, and even fewer data are available on studies related to mast cells in the skin of patients with type 2 diabetes mellitus (T2DM). Therefore, this study aims to explore the transcriptional characteristics of mast cells at the single-cell level in patients with T2DM and provide experimental data for studying mast cell behaviors under abnormal glucose metabolism.

METHODS

Two patients with T2DM and one trauma patient without diabetes were enrolled. Samples were derived from skin tissue resected at the time of surgery and were isolated by single cell capture technology on BD platform to prepare single cell cDNA library. Seurat was used to process raw reads and analyze data downstream of single-cell RNA sequencing, including removal of low-quality cells, identification of cell clusters at the single-cell level, and screening for differential genes with fold change > 1.5 and p < 0.05 by two-sided t-test. We performed single-cell RNA sequencing on skin tissues of T2DM patients and non-diabetics and identified the cell cluster of skin, single-cell subsets, and transcriptional characteristics of mast cells at a single-cell level. Meanwhile, gene set enrichment(GSEA) analysis was performed on the differentially expressed genes.

RESULTS

A total of 8888 cells were obtained from skin tissue. Clustering analysis revealed eight-cell clusters, identified as smooth muscle cells, dendritic cells, mast cells, and T cells, respectively. Cluster 6 was identified as mast cells with the marker genes TPSAB1, CPA3, TPSB2, MS4A2,KIT, etc., which accounting for 2.7% of the total cell number.Compared with the control group, the genes highly expressed in MCs from T2DM patients, include ADH1C, PAXIP1, HAS1, ARG1, etc., and the low expression genes include PHACTR2, GGA1, RASSF2, etc. GSEA analysis suggested that the signal pathways of MCS in T2DM patients included VEGF signaling pathway, Fc gamma R-mediated phagocytosis, the B cell receptor signaling pathway, natural killer cell-mediated cytotoxicity.

CONCLUSIONS

The characteristic genes of MCs in the skin tissues of T2DM patients were described at the single-cell level. These genes and enriched signaling pathways provide a theoretical basis and data support for further researches on dermatopathy in patients with diabetes mellitus.