Nardilysin-Dependent Proteolysis of Cell-Associated VTCN1 (B7-H4) Marks Type 1 Diabetes Development

Abstract

T-cell responses directed against insulin-secreting pancreatic β-cells are the key events highlighting type 1 diabetes (T1D). Therefore, a defective control of T-cell activation is thought to underlie T1D development. Recent studies implicated a B7-like negative costimulatory protein, V-set domain-containing T-cell activation inhibitor-1 (VTCN1), as a molecule capable of inhibiting T-cell activation and, potentially, an important constituent in experimental models of T1D. Here, we unravel a general deficiency within the VTCN1 pathway that is shared between diabetes-prone mice and a subset of T1D patients. Gradual loss of membrane-tethered VTCN1 from antigen-presenting cells combined with an increased release of soluble VTCN1 (sVTCN1) occurs in parallel to natural T1D development, potentiating hyperproliferation of diabetogenic T cells. Mechanistically, we demonstrate that the loss of membrane-tethered VTCN1 is linked to proteolytic cleavage mediated by the metalloproteinase nardilysin. The cleaved sVTCN1 fragment was detected at high levels in the peripheral blood of 53% T1D patients compared with only 9% of the healthy subjects. Elevated blood sVTCN1 levels appeared early in the disease progression and correlated with the aggressive pace of disease, highlighting the potential use of sVTCN1 as a new T1D biomarker, and identifying nardilysin as a potential therapeutic target.

Loss of Peripheral Protection in Pancreatic Islets by Proteolysis-Driven Impairment of VTCN1 (B7-H4) Presentation Is Associated with the Development of Autoimmune Diabetes

“…1C). These findings echoed our recent report describing a highly similar phenotype of progressive VTCN1 protein loss (coupled with compensatory VTCN1 mRNA up-regulation) in MФs and DCs from T1D-succeptible subjects, which occurred due to proteolysis of cell-associated VTCN1 by the metalloproteinase NRD1 (22). Hence, we compared dynamics of islet NRD1 expression and observed a significant age-dependent elevation of NRD1 mRNA in NOD, but not B6 g7 islets (Fig.…”

“…RT-qPCR analysis using primers specific for VTCN1 , NRD1 , PCSK1, or PCSK2 was performed as previously described (22). …”

“…Cell lysates were prepared in RIPA buffer as described before (22). The samples (5 μg total protein) were subjected to electrophoresis through a 4 – 12% NuPAGE Bis-Tris polyacrylamide gel.…”

“…Recently, we unveiled an endogenous pathway of functional VTCN1 inactivation in APCs (particularly in macrophages – MФs, and dendritic cells – DCs) of NOD mice and T1D patients. Specifically, a gradual loss of membrane-tethered VTCN1 due to a proteolytic cleavage mediated by metalloproteinase nardilysin (NRD1), progressed alongside natural T1D development, and triggered hyper-proliferation of diabetogenic T cells (22). Here, we extend our previous findings and dissect a pattern of VTCN1 expression and presentation on islet cells in connection with diabetogenesis.…”

B7-H4 as a protective shield for pancreatic islet beta cells

“…Our results showed a trend of higher sB7-H4 in diabetic children, though not statistically significant. This data agreed with a more recent study, which confirmed that sB7-H4 were elevated in newly-onset T1D patients [62] . Previous characterization of the B7-H4 gene using human multiple cDNA panels demonstrated that there are two major versions of B7-H4 transcripts from the pancreas tissue: A full-length (2.0 kb) transcript which is shared with other organs, and a shorter (1.2 kb) transcript version which is specific for pancreas [23,24] .…”