CD4+ T-Cell Legumain Deficiency Attenuates Hypertensive Damage via Preservation of TRAF6

Abstract

BACKGROUND: T cells are central to the immune responses contributing to hypertension. LGMN (legumain) is highly expressed in T cells; however, its role in the pathogenesis of hypertension remains unclear. METHODS: Peripheral blood samples were collected from patients with hypertension, and CD4+ T cells were sorted for gene expression and Western blotting analysis. TLGMNKO (T cell–specific LGMN-knockout) mice (Lgmn f/f /CD4 Cre ), regulatory T cell (Treg)–specific LGMN-knockout mice (Lgmn f/f /Foxp3 YFP Cre ), and RR-11a (LGMN inhibitor)–treated C57BL/6 mice were infused with Ang II (angiotensin II) or deoxycorticosterone acetate/salt to establish hypertensive animal models. Flow cytometry, 4-dimensional label-free proteomics, coimmunoprecipitation, Treg suppression, and in vivo Treg depletion or adoptive transfer were used to delineate the functional importance of T-cell LGMN in hypertension development. RESULTS: LGMN mRNA expression was increased in CD4+ T cells isolated from hypertensive patients and mice, was positively correlated with both systolic and diastolic blood pressure, and was negatively correlated with serum IL (interleukin)-10 levels. TLGMNKO mice exhibited reduced Ang II–induced or deoxycorticosterone acetate/salt–induced hypertension and target organ damage relative to WT (wild-type) mice. Genetic and pharmacological inhibition of LGMN blocked Ang II–induced or deoxycorticosterone acetate/salt–induced immunoinhibitory Treg reduction in the kidneys and blood. Anti-CD25 antibody depletion of Tregs abolished the protective effects against Ang II–induced hypertension in TLGMNKO mice, and LGMN deletion in Tregs prevented Ang II–induced hypertension in mice. Mechanistically, endogenous LGMN impaired Treg differentiation and function by directly interacting with and facilitating the degradation of TRAF6 (tumor necrosis factor receptor–associated factor 6) via chaperone-mediated autophagy, thereby inhibiting NF-κB (nuclear factor kappa B) activation. Adoptive transfer of LGMN-deficient Tregs reversed Ang II–induced hypertension, whereas depletion of TRAF6 in LGMN-deficient Tregs blocked the protective effects. CONCLUSIONS: LGMN deficiency in T cells prevents hypertension and its complications by promoting Treg differentiation and function. Specifically targeting LGMN in Tregs may be an innovative approach for hypertension treatment.

Legumain Regulates Regulatory T Cells in Hypertension

“…Knockdown of TRAF6 blunted the protective effects of LGMN-deficient Tregs after adoptive transfer to hypertensive mice, implicating TRAF6 degradation in LGMN-mediated Treg dysfunction. 1 Taken together, findings by He et al reveal a pathogenic role for LGMN induction in Tregs in hypertension by reducing FOXP3 expression leading to defective immunosuppressive function of these cells (Figure).…”

“…In additional mechanistic studies, He et al 1 demonstrated that LGMN promotes TRAF6 (Tumor Necrosis Factor Receptor-Associated Factor 6) degradation via chaperone-mediated autophagy. Consistent with prior evidence that TRAF6 promotes NFκB (Nuclear Factor kappa B) activation to induce FOXP3 expression, 3 the loss of TRAF6 resulted in decreased binding of NFκB subunits to the FOXP3 promoter and decreased FOXP3 expression in Tregs.…”

“…Matthew R. Alexander , David G. Harrison I n this issue of Circulation Research, He et al 1 demonstrate a previously undefined role for the cysteine protease LGMN (legumain) in CD4 + (Cluster of Differentiation 4 + ) helper T cells, and specifically regulatory T cells (Tregs), in the pathogenesis of hypertension. LGMN, also known as asparaginyl endopeptidase, is an endosomal and lysosomal cysteine protease that cleaves asparagine residues of proteins such as matrix metalloproteinases, cathepsins, and fibronectin.…”

“…First, the authors provide evidence for a mechanism whereby LGMN mediates reduced Treg suppressive function through the degradation of TRAF6 leading to reduced FOXP3 expression. 1 Prior studies have demonstrated that LGMN can also directly cleave FOXP3 11 ; however, it remains unclear whether this mechanism is also operative in Tregs in hypertension. In addition, whether LGMN can silence FOXP3 expression leading to exTreg formation in hypertension deserves further exploration.…”

“…Given that the expansion of endogenous Tregs and adoptive transfer of Tregs or CAR (Chimeric Antigen Receptor)-Tregs have been proposed for the treatment of cardiovascular diseases including hypertension, 15 the findings by He et al have important implications for these approaches by identifying potential targets for enhanced Treg function. 1…”