Rac GTPases are involved in development, survival and homeostasis of T cells

Kurarinone regulates Th17/Treg balance and ameliorates autoimmune uveitis via Rac1 inhibition

INTRODUCTION

Autoimmune uveitis (AU) is a severe intraocular autoimmune disorder with a chronic disease course and a high rate of blindness. Kurarinone (KU), a major component of the traditional Chinese medicine Sophorae Flavescentis Radix, possesses a wide spectrum of activities and has been used to treat several inflammation-related diseases.

OBJECTIVE

We aimed to investigate the effects of KU on AU and its modulatory mechanisms.

METHODS

We used an experimental autoimmune uveitis (EAU) animal model and characterized the comprehensive immune landscape of KU-treated EAU mice using single-cell RNA sequencing (scRNA-seq). The retina and lymph nodes were analyzed. The siRNAs and selective inhibitors were used to study the signaling pathway. The effect of KU on peripheral blood mononuclear cells (PBMCs) from uveitis patients was also examined.

RESULTS

We found that KU relieved chorioretinal lesions and immune cell infiltration in EAU model mice. Subsequent single-cell analysis revealed that KU downregulated the EAU-upregulated expression of inflammatory and autoimmune-related genes and suppressed pathways associated with immune cell differentiation, activation, and migration in a cell-specific manner. KU was implicated in restoring T helper 17 (Th17)/regulatory T (Treg) cell balance by alleviating inflammatory injury and elevating the expression of modulatory mediators in Tregs, while simultaneously ameliorating excessive inflammation by Th17 cells. Furthermore, Rac1 and the Id2/Pim1 axis potentiated the pathogenicity of Th17 cells during EAU, which was inhibited by KU treatment, contributing to the amelioration of EAU-induced inflammation and treatment of AU. In addition, KU suppressed inflammatory cytokine production in activated human PBMCs by inhibiting Rac1. Integration of the glucocorticoid-treated transcriptome suggests that KU has immunomodulatory effects on lymphocytes.

CONCLUSION

Our study constructed a high-resolution atlas of the immunoregulatory effects of KU treatment on EAU and identified its potential therapeutic mechanisms, which hold great promise in treating autoimmune disorders.

Rho-GTPase pathways may differentiate treatment response to TNF-alpha and IL-17A inhibitors in psoriatic arthritis

Biological therapies have dramatically improved the therapeutic landscape of psoriatic arthritis (PsA); however, 40–50% of patients are primary non-responders with response rates declining significantly with each successive biological therapy. Therefore, there is a pressing need to develop a coherent strategy for effective initial and subsequent selection of biologic agents. We interrogated 40 PsA patients initiating either tumour necrosis factor inhibitors (TNFi) or interleukin-17A inhibitors (17Ai) for active PsA. Patients achieving low disease activity according to the Disease Activity Index for PsA (DAPSA) at 3 months were classified as responders. Baseline and 3-month CD4⁺ transcript profiling were performed, and novel signaling pathways were identified using a multi-omics profiling and integrative computational analysis approach. Using transcriptomic data at initiation of therapy, we identified over 100 differentially expressed genes (DEGs) that differentiated IL-17Ai response from non-response and TNFi response from non-response. Integration of cell-type-specific DEGs with protein–protein interactions and further comprehensive pathway enrichment analysis revealed several pathways. Rho GTPase signaling pathway exhibited a strong signal specific to IL-17Ai response and the genes, RAC1 and ROCKs, are supported by results from prior research. Our detailed network and pathway analyses have identified the rewiring of Rho GTPase pathways as potential markers of response to IL17Ai but not TNFi. These results need further verification.

FLT3-ITD cooperates with Rac1 to modulate the sensitivity of leukemic cells to chemotherapeutic agents via regulation of DNA repair pathways

Acute myeloid leukemia (AML) is an aggressive hematologic neoplasm, and patients with an internal tandem duplication (ITD) mutation of the FMS-like tyrosine kinase-3 (FLT3) receptor gene have a poor prognosis. FLT3-ITD interacts with DOCK2, a G effector protein that activates Rac1/2. Previously, we showed that knockdown of DOCK2 leads to decreased survival of FLT3-ITD leukemic cells. We further investigated the mechanisms by which Rac1/DOCK2 activity affects cell survival and chemotherapeutic response in FLT3-ITD leukemic cells. Exogenous expression of FLT3-ITD led to increased Rac1 activity, reactive oxygen species, phosphorylated STAT5, DNA damage response factors and cytarabine resistance. Conversely, DOCK2 knockdown resulted in a decrease in these factors. Consistent with the reduction in DNA damage response factors, FLT3-ITD cells with DOCK2 knockdown exhibited significantly increased sensitivity to DNA damage response inhibitors. Moreover, in a mouse model of FLT3-ITD AML, animals treated with the CHK1 inhibitor MK8776 + cytarabine survived longer than those treated with cytarabine alone. These findings suggest that FLT3-ITD and Rac1 activity cooperatively modulate DNA repair activity, the addition of DNA damage response inhibitors to conventional chemotherapy may be useful in the treatment of FLT3-ITD AML, and inhibition of the Rac signaling pathways via DOCK2 may provide a novel and promising therapeutic target for FLT3-ITD AML.

miR-21 is a negative modulator of T-cell activation

microRNAs (miRNAs) are a class of small non-coding RNAs acting as post-transcriptional regulators of gene expression and play fundamental roles in regulating immune response and autoimmunity. We show that memory T-lymphocytes express higher levels of miR-21 compared to naïve T-lymphocytes and that miR-21 expression is induced upon TCR engagement of naïve T-cells. We identify bona fide miR-21 targets by direct immuno-purification and profiling of AGO2-associated mRNAs in Jurkat cells over-expressing miR-21. Our analysis shows that, in T-lymphocytes, miR-21 targets genes are involved in signal transduction. Coherently, TCR signalling is dampened upon miR-21 over-expression in Jurkat cells, resulting in lower ERK phosphorylation, AP-1 activation and CD69 expression. Primary human lymphocytes in which we impaired miR-21 activity, display IFN-γ production enhancement and stronger activation in response to TCR engagement as assessed by CD69, OX40, CD25 and CD127 analysis. By intracellular staining of the endogenous protein in primary T-lymphocytes we validate three key regulators of lymphocyte activation as novel miR-21 targets. Our results highlight an unexpected function of miR-21 as a negative modulator of signal transduction downstream of TCR in T-lymphocytes.