Cytoskeletal Requirements for Lymphocyte Entry into the Central Nervous System

Lay Summary

Seeing how autoimmune T cells enter the brain and spinal cord may lead to new MS therapies

Investigators will use real-time fluorescent multi-photon microscopy imaging in a mouse model of multiple sclerosis to define the routes that autoimmune T cells use to enter the brain and spinal cord and attack the myelin sheaths that insulate nerve cell axons (communication cables).

Multiple sclerosis (MS) is an autoimmune disease. Autoimmune T cells manage to travel through the bloodstream, cross the blood-brain barrier (BBB) to enter the central nervous system (CNS), and attack the myelin sheath that insulates brain cell axons and helps the axons conduct electrochemical messages from one cell to another. Recent therapies have been developed that inhibit immune T cell “trafficking” into the CNS (brain and spinal cord) but these therapies also impair the immune system’s ability to fight infections generally.  Autoimmune T cells cross the BBB, most likely by a process called “transcellular extravasation.” The investigators hypothesize that specific molecules on T cells that control the cells’ shape and movement enable the cells to pass through the elaborate BBB walls.

They will test this hypothesis by using multi-photon fluorescent microscopy to visualize the actions of these molecules on T cells as the cells cross the BBB. This imaging technique will provide valuable spatial and temporal information on the routes used by T cells and the routes’ relative frequencies. Investigators will determine whether and, if so, how the molecules regulate this process and whether inhibiting these molecules prevents T cell migration into the brain and spinal cord. If so, the research would lead to identification of therapeutic agents that specifically inhibit these molecules to prevent T cells from damaging the CNS. Such agents then could be studied in MS patients.

Significance: The study could lead to identification of MS therapies that are more effective and produce fewer side effects compared to currently available treatments.

Abstract

Cytoskeletal requirements for lymphocyte entry into the central nervous system

Multiple sclerosis (MS) is a chronic autoimmune disease caused by immune cell infiltration and damage to the central nervous system (CNS). Therapies that target lymphocyte trafficking in MS patients have shown promise, but current approaches can have major side-effects, caused in part by lack of specificity for homing to the CNS. Therefore, more specific tools to inhibit lymphocyte recruitment to the CNS without affecting systemic trafficking of immune cells are needed for the treatment of MS. Using cutting-edge in vivo multi-photon microscopy to image lymphocyte infiltration into the CNS, this project will test a novel approach aimed at more specifically preventing lymphocyte extravasation into the CNS. Our goal is to determine how the lymphocyte cytoskeleton mediates the steps required for T cell infiltration through the blood-brain barrier and into the CNS during autoimmunity. We hypothesize that lymphocyte extravasation through the specialized CNS vasculature walls relies on transcellular migration, utilizing linear actin network remodeling. Employing a multi-pronged approach, we will determine how cytoskeletal effectors of linear actin network remodeling regulate trans-endothelial migration and the route of extravasation through CNS vascular walls. Previous data as well as our preliminary data suggest that the cytoskeleton plays a role in regulating extravasation, validating the study of distinct cytoskeletal regulators in this process. In this proposal, we will examine how T cell trans-endothelial migration through CNS endothelial cells is regulated by Formin and Ena/Vasp cytoskeletal effectors both in vivo and in vitro. Our data will define the extravasation routes (transcellular vs. paracellular) utilized by T cells through the CNS vasculature and their relative frequencies. The proposed studies will also determine the specific roles and steps in which Formin and Ena/Vasp effectors of actin network remodeling are required for extravasation and infiltration into the CNS. Characterizing the molecular basis by which the lymphocyte’s cytoskeleton regulates transcellular extravasation can identify molecular targets that more specifically inhibit homing of lymphocytes to the CNS. Importantly, our approach examining the dynamics of extravasation in real time, in vitro as well as in vivo using multi-photon microscopy, will provide critical spatio-temporal information that would not be possible using standard techniques. The data obtained from this project can ultimately lead to the design of valuable new therapeutic tools for MS that could offer better specificity with fewer side effects.