ACKR1 favors transcellular over paracellular T‐cell diapedesis across the blood‐brain barrier in neuroinflammation in vitro

Abstract

The migration of CD4 + effector/memory T cells across the blood-brain barrier (BBB) is a critical step in MS or its animal model, EAE. T-cell diapedesis across the BBB can occur paracellular, via the complex BBB tight junctions or transcellular via a pore through the brain endothelial cell body. Making use of primary mouse brain microvascular endothelial cells (pMBMECs) as in vitro model of the BBB, we here directly compared the transcriptome profile of pMBMECs favoring transcellular or paracellular T-cell diapedesis by RNA sequencing (RNA-seq). We identified the atypical chemokine receptor 1 (Ackr1) as one of the main candidate genes upregulated in pMBMECs favoring transcellular T-cell diapedesis. We confirmed upregulation of ACKR1 protein in pMBMECs promoting transcellular T-cell diapedesis and in venular endothelial cells in the CNS during EAE. Lack of endothelial ACKR1 reduced transcellular T-cell diapedesis across pMBMECs under physiological flow in vitro. Combining our previous observation that endothelial ACKR1 contributes to EAE pathogenesis by shuttling chemokines across the BBB, the present data support that ACKR1 mediated chemokine shuttling enhances transcellular T-cell diapedesis across the BBB during autoimmune neuroinflammation.Keywords: atypical chemokine receptor 1 r blood-brain barrier r transcellular diapedesis r T cell Additional supporting information may be found online in the Supporting Information section at the end of the article.

Neuroimmune Crosstalk Between the Peripheral and the Central Immune System in Amyotrophic Lateral Sclerosis

“…Increasing evidence shows that many peripheral leukocytes are first activated in PIS and then migrate into the CNS in ALS ( Angelini et al, 2020 ). The regulation of leukocyte trafficking to the CNS is multifaceted and depends on the activation state of the leukocytes, TJ complexes at the endothelial interface, and the inflammatory microenvironment in the CNS and PNS ( Congdon et al, 2019 ; Trolese et al, 2020 ; Marchetti et al, 2022 ). As peripheral leukocytes can be easily monitored, and intrathecal or intracerebroventricular is associated with several risks, targeting peripheral leukocytes may be feasible in ALS treatment.…”

Gene Signatures Associated with Temporal Rhythm as Diagnostic Markers of Major Depressive Disorder and Their Role in Immune Infiltration

“…Another gene, ACKR1 , binds more than 20 inflammatory CC and CXC chemokines and is expressed specifically in erythrocytes, venular endothelial cells, and cerebellar Purkinje neurons [ 28 ]. It is known that ACKR1 is involved in neuroinflammation in the brain [ 29 ]. Notably, inflammation is also involved in the pathogenesis of MDD, hence, we speculated that ACKR1 might participate in the progression of MDD by regulating neuroinflammation.…”

How Does the Immune System Enter the Brain?

“…The unique barrier characteristics of the BBB extend to its characteristic immune quiescent phenotype. In contrast to peripheral endothelial cells, BBB endothelial cells lack storage of P-selectin protein in their endothelial Weibel Palade bodies [summarized in ( 61 )] and constitutive expression of the atypical chemokine receptor 1 (ACKR1), which transports chemokines from the abluminal to the luminal surface of endothelial cells ( 62 , 63 ). Thus, immune cell entry into the CNS is very low and limited to activated T cells that do not depend on these trafficking cues.…”

“…After their arrest, the T cells polarize and were observed to crawl over extended distances against the direction of the bloodstream on endothelial ICAM-1 and ICAM-2, obviously to find rare tricellular junctions as sites permissive for diapedesis across the BBB endothelium ( 58 , 66 , 67 ). Under neuroinflammatory conditions, high cell surface levels of endothelial ICAM-1 and de novo expression of ACKR-1 were shown to reduce T cell crawling distances and increase transcellular T-cell diapedesis across the BBB ( 62 , 66 ). Importantly, although the BBB junctions become leaky under neuroinflammatory conditions and allow for uncontrolled diffusion of blood-borne molecules across the BBB, this is not accompanied by increased paracellular T cell diapedesis but rather leads to enhanced transcellular T cell diapedesis across the BBB.…”

“…Individuals lacking expression of the atypical chemokine receptor 1 (ACKR1), formally referred to as DARC (Duffy blood group antigen receptor for chemokines) are for example resistant to malaria. ACKR1 mediates inflammatory chemokine shuttling across the BBB and enhances transcellular T-cell diapedesis across the BBB during EAE ( 62 , 63 ). Lack of ACKR1 ameliorates development of EAE and it remains to be shown if individuals lacking functional ACKR1 are protected from MS. Alternatively, also different ACKR1 haplotypes could affect susceptibility to MS. To this end over 900 ACKR1 haplotypes were identified ( 136 ).…”