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Targeting the blood-brain barrier endothelium to increase hematopoietic stem cell engraftment for ly

Supervisors: Dr Sara Benedetti, Dr Giorgina Santilli

Targeting the blood-brain barrier endothelium to increase hematopoietic stem cell engraftment for lysosomal storage disease gene and cell therapy.

Background:

Lysosomal storage diseases (LSDs) are are single-gene defect multisystem diseases caused by dysfunctional enzymes and consequent accumulation of undegraded macromolecules in a variety of organs/tissues, including the central nervous system (CNS)1.  Treatments include enzyme replacement therapy (ERT), hematopoietic stem cell gene therapy (HSC-GT) and in vivo gene therapy. However, these treatments are not fully effective in treating the damaged CNS as neither enzymes, stem cells nor viral vectors efficiently cross the blood-brain barrier (BBB). Nevertheless, in the last decade HSC-GT has been shown effective in preventing or attenuating neurological symptoms in LSD patients, with CNS engraftment of HSC-derived microglial cells being a critical process2. Understanding and improving this process, may help boost HSC transmigration across the BBB allowing a greater therapeutic effect.

Aims/Objectives:

HSCs use in correcting neurodegenerative disorders has been dramatically shown by HSC-GT clinical trials in neurological LSDs. Indeed, an HSC subpopulation of the monocyte lineage can cross the BBB, engraft as microglia in the brain and secrete enzymes that can then be taken up by neurons and thus prevent neuronal damage. One essential component of this process, which is poorly understood, is the passage of this HSC subpopulation across the BBB. Indeed, manipulation of BBB permeability may increase HSC transmigration thereby improving their therapeutic effect. The BBB is a dynamic interface mainly composed of brain microvascular endothelial cells that separate the CNS from the circulation; it controls molecular/cellular traffic, and its permeability is regulated by tight junctions (TJs) and its associated proteins3. One protein that plays a major role in TJ formation/function is Junctional Adhesion Molecule-A (JAM-A). We previously showed that transient alteration of JAM-A remodelled TJ conformation, increasing transendothelial migration of stem cells to diseased tissues in muscular dystrophy mice4. In addition, HSC engraftment to CNS in neurological LSDs patients was improved by busulfan pre-conditioning compared to irradiation2, with busulfan potentially responsible for vascular injury and disrupted BBB, indicating that a perturbed BBB could be accountable for an increased HSC
subpopulation engraftment to CNS5, although the role of busulfan on TJs or JAM-A is unknown. Together, these data strongly indicate an important role for the BBB and TJ proteins in regulating HSC engraftment to the CNS. We propose here that targeting TJ molecules, and specifically JAM-A, will increase HSC-selective transmigration through BBB, improve CNS engraftment and increase generation of healthy microglia. The major objectives of this project are: 1) To assess JAM-A role in HSPC ability to cross the BBB; 2) To modulate JAM-A function to increase HSPC engraftment to CNS; 3) To understand the effect of conditioning regimes on BBB integrity/permeability.

Methods:

We plan to use a combined approach of in vitro assays and in vivo monogenic neurodegeneration model to address these issues. In vitro experiments will revolve around cell culture, transendothelial migration experiments, flow cytometry, gene editing/gene therapy and microfluidics to mimic the BBB barrier and its interaction with HSCs and monocytes/macrophages. A substantial part of the project will be consisting in performing in vivo bone marrow transplantation studies in different murine models to study HSCs engraftment to the brain when JAM-A is modulated and the effect of conditioning regimes on
BBB integrity and permeability.

References:
1Ferreira, C.R. & Gahl, W.A. Transl Sci Rare Dis 2, 1-71(2017)
2Capotondo, A. et al. Proc Natl Acad Sci U S A 109, 15018-15023 (2012)
3Haseloff, R.F. et al. Semin Cell Dev Biol 38, 16-25 (2015)
4Giannotta, M. et al. EMBO Mol Med 6, 239-258 (2014)
5Zeng, L. et al. Transplant Proc 42, 2720-2724 (2010)