Dystroglycan is selectively cleaved at the parenchymal basement membrane at sites of leukocyte extravasation in experimental autoimmune encephalomyelitis

Abstract

The endothelial cell monolayer of cerebral vessels and its basement membrane (BM) are ensheathed by the astrocyte endfeet, the leptomeningeal cells, and their associated parenchymal BM, all of which contribute to establishment of the blood–brain barrier (BBB). As a consequence of this unique structure, leukocyte penetration of cerebral vessels is a multistep event. In mouse experimental autoimmune encephalomyelitis (EAE), a widely used central nervous system inflammatory model, leukocytes first penetrate the endothelial cell monolayer and underlying BM using integrin β1-mediated processes, but mechanisms used to penetrate the second barrier defined by the parenchymal BM and glia limitans remain uninvestigated. We show here that macrophage-derived gelatinase (matrix metalloproteinase [MMP]-2 and MMP-9) activity is crucial for leukocyte penetration of the parenchymal BM. Dystroglycan, a transmembrane receptor that anchors astrocyte endfeet to the parenchymal BM via high affinity interactions with laminins 1 and 2, perlecan and agrin, is identified as a specific substrate of MMP-2 and MMP-9. Ablation of both MMP-2 and MMP-9 in double knockout mice confers resistance to EAE by inhibiting dystroglycan cleavage and preventing leukocyte infiltration. This is the first description of selective in situ proteolytic damage of a BBB-specific molecule at sites of leukocyte infiltration.

Enzymatic processing of β‐dystroglycan recombinant ectodomain by MMP‐9: Identification of the main cleavage site

“…Since MMP-2 also targets b-DG in vivo (17)(18)(19), its enzymatic activity has been tested on the recombinant b-DG (654-750) and compared with the one displayed by MMP-9. MMP-2 produced four proteolytic fragments (see Fig.…”

Hydrogen Sulfide Inhalation Decreases Early Blood—Brain Barrier Permeability and Brain Edema Induced by Cardiac Arrest and Resuscitation

“…29,[35][36][37][38] Studies by Toft-Hansen et al 37 revealed that metalloproteinase enzymes are implicated in leukocyte infiltration in neuroinflammation. Agrawal et al 38 further stated that MMP-9-mediated selective cleavage of β-dystroglycan, which anchors astrocyte endfeet to the astroglial basement membrane, is critical for leukocyte penetration of the parenchymal basement membrane and the damage of BBB.…”

The Blood–Brain Barrier

“…In EAE and MS, immune cell infiltrates are in great part contained to the perivascular space, and the process of leukocyte migration across the parenchymal BM and astrocyte endfeet appears to be more tightly controlled than the diapedesis across ECs (Engelhardt and Sorokin 2009). In EAE, CD4 þ T-cell infiltration across the parenchymal BM is not laminin dependent, but rather requires focal activation of and matrix metalloproteinases (MMP)-2 and MMP-9 to selectively cleave dystroglycan, affecting the BM stability and integrity (Agrawal et al 2006). Interestingly, parenchymal BM components and other ECM-binding receptors on the astrocyte endfeet remain unaffected, indicating the existence of specific and specialized protective mechanisms under the control of astrocytes and possibly other cells within the NVU (Engelhardt and Sorokin 2009).…”