Nox2-deficient Tregs improve heart transplant outcomes via their increased graft recruitment and enhanced potency

In adult X-CGD patients, regulatory T cells are expanded while activated T cells display a NOX2-independent ROS increase

The X-linked chronic granulomatous disease (X-CGD), a rare genetic disease characterised by recurrent infections, is caused by mutations of NOX2. Significant proportions of X-CGD patients display signs of immune dysregulation. Regulatory T cells (Tregs) are CD4+T lymphocytes that expand in active inflammation and prevent autoimmune disorders. Here we asked whether X-CGD is associated to Treg dysfunctions in adult patients. To this aim, the frequency of Tregs was analysed through intracellular flow cytometry in a cohort of adult X-CGD patients, carriers and controls. We found that Tregs were significantly expanded and activated in blood of adult X-CGD patients, and this was associated with activation of conventional CD4+T cells (Tconvs). T cell activation was characterised by accumulation of intracellular ROS, not derived from NOX2 but likely produced by cellular metabolism. The higher TNF production by Tconvs in X-CGD patients might contribute to the expansion of Tregs through the TNFR2 receptor. In summary, our data indicate that Tregs expand in adult X-CGD in response to immune activation, and that the increase of NOX2-independent ROS content is a feature of activated T cells.

Immunoregulation: the interplay between metabolism and redox homeostasis

Regulatory T cells are fundamental for the induction and maintenance of immune homeostasis, with their dysfunction resulting in uncontrolled immune responses and tissue destruction predisposing to autoimmunity, transplant rejection and several inflammatory and metabolic disorders. Recent discoveries have demonstrated that metabolic processes and mitochondrial function are critical for the appropriate functioning of these cells in health, with their metabolic adaptation, influenced by microenvironmental factors, seen in several pathological processes. Upon activation regulatory T cells rearrange their oxidation-reduction (redox) system, which in turn supports their metabolic reprogramming, adding a layer of complexity to our understanding of cellular metabolism. Here we review the literature surrounding redox homeostasis and metabolism of regulatory T cells to highlight new mechanistic insights of these interlinked pathways in immune regulation.

Dysregulated anti-oxidant signalling and compromised mitochondrial integrity negatively influence regulatory T cell function and viability in liver disease

BACKGROUND

Dysregulated inflammatory responses and oxidative stress are key pathogenic drivers of chronic inflammatory diseases such as liver cirrhosis (LC). Regulatory T cells (Tregs) are essential to prevent excessive immune activation and maintain tissue homeostasis. While inflammatory cues are well known to modulate the function and stability of Tregs, the extent to which Tregs are influenced by oxidative stress has not been fully explored.

METHODS

The phenotypic and functional properties of CD4+CD25+CD127lo/- Tregs isolated from patients with LC were compared to healthy controls (HC). Treg redox state was investigated by characterizing intracellular reactive oxygen species (ROS), NADPH oxidase-2 (Nox2) activity, mitochondrial function, morphology, and nuclear factor-erythroid 2-related factor (Nrf2) antioxidant signalling. The relevance of Nrf2 and its downstream target, Heme-oxygenase-1 (HO-1), in Treg function, stability, and survival, was further assessed using mouse models and CRISPR/Cas9-mediated HO-1 knock-out.

FINDINGS

Circulating Tregs from LC patients displayed a reduced suppressive function, correlating with liver disease severity, associated with phenotypic abnormalities and increased apoptosis. Mechanistically, this was linked to a dysregulated Nrf2 signalling with resultant lower levels of HO-1, enhanced Nox2 activation, and impaired mitochondrial respiration and integrity. The functional deficit in LC Tregs could be partially recapitulated by culturing control Tregs in patient sera.

INTERPRETATION

Our findings reveal that Tregs rely on functional redox homeostasis for their function, stability, and survival. Targeting Treg specific anti-oxidant pathways may have therapeutic potential to reverse the Treg impairment in conditions of oxidative damage such as advanced liver disease.

FUNDING

This study was funded by the Wellcome Trust (211113/A/18/Z).

Luteolin attenuates acute liver allograft rejection in rats by inhibiting T cell proliferation and regulating T cell subsets

Allograft rejection continues to be a significant cause of morbidity and graft failure for liver transplant recipients. Existing immunosuppressive regimens have many drawbacks, thus safe and effective long-term immunosuppressive regimens are still required. Luteolin (LUT), a natural component found in many plants, has a variety of biological and pharmacological effects and shows good anti-inflammatory activity in inflammatory and autoimmune diseases. Nevertheless, it remains unclear how it affects acute organ rejection after allogeneic transplantation. In this study, a rat liver transplantation model was constructed to investigate the effect of LUT on acute rejection of organ allografts. We found that LUT significantly protected the structure and function of liver grafts, prolonged recipient rat survival, ameliorated T cell infiltration, and downregulated proinflammatory cytokines. Moreover, LUT inhibited the proliferation of CD4+ T cells and Th cell differentiation but increased the proportion of Tregs, which is the key to its immunosuppressive effect. In vitro, LUT also significantly inhibited CD4+ T cell proliferation and Th1 differentiation. There may be important implications for improving immunosuppressive regimens for organ transplantation as a result of this discovery.

Effect of Extracellular Matrix Stiffness on Candesartan Efficacy in Anti-Fibrosis and Antioxidation

Myocardial fibrosis progression and imbalanced redox state are closely associated with increased extracellular matrix (ECM) stiffness. Candesartan (CAN), an angiotensin II (Ang II) receptor inhibitor, has shown promising anti-fibrosis and antioxidant efficacy in previous cardiovascular disease studies. However, the effect of ECM stiffness on CAN efficacy remains elusive. In this study, we constructed rat models with three different degrees of myocardial fibrosis and treated them with CAN, and then characterized the stiffness, cardiac function, and NADPH oxidase-2 (NOX2) expression of the myocardial tissues. Based on the obtained stiffness of myocardial tissues, we used polyacrylamide (PA) gels with three different stiffness to mimic the ECM stiffness of cardiac fibroblasts (CFs) at the early, middle, and late stages of myocardial fibrosis as the cell culture substrates and then constructed CFs mechanical microenvironment models. We studied the effects of PA gel stiffness on the migration, proliferation, and activation of CFs without and with CAN treatment, and characterized the reactive oxygen species (ROS) and glutathione (GSH) levels of CFs using fluorometry and scanning electrochemical microscopy (SECM). We found that CAN has the best amelioration efficacy in the cardiac function and NOX2 levels in rats with medium-stiffness myocardial tissue, and the most obvious anti-fibrosis and antioxidant efficacy in CFs on the medium-stiffness PA gels. Our work proves the effect of ECM stiffness on CAN efficacy in myocardial anti-fibrosis and antioxidants for the first time, and the results demonstrate that the effect of ECM stiffness on drug efficacy should also be considered in the treatment of cardiovascular diseases.

Targeting regulatory T cells for cardiovascular diseases

Cardiovascular diseases (CVDs) are the leading cause of death and disability worldwide. The CVDs are accompanied by inflammatory progression, resulting in innate and adaptive immune responses. Regulatory T cells (Tregs) have an immunosuppressive function and are one of the subsets of CD4⁺T cells that play a crucial role in inflammatory diseases. Whether using Tregs as a biomarker for CVDs or targeting Tregs to exert cardioprotective functions by regulating immune balance, suppressing inflammation, suppressing cardiac and vascular remodeling, mediating immune tolerance, and promoting cardiac regeneration in the treatment of CVDs has become an emerging research focus. However, Tregs have plasticity, and this plastic Tregs lose immunosuppressive function and produce toxic effects on target organs in some diseases. This review aims to provide an overview of Tregs' role and related mechanisms in CVDs, and reports on the research of plasticity Tregs in CVDs, to lay a foundation for further studies targeting Tregs in the prevention and treatment of CVDs.