The protective potential of mild hypoxia on inflammatory demyelinating disease

Milner, D

Abstract

Multiple sclerosis (MS) is a chronic inflammatory disease that results in demyelination and degeneration of axons in the central nervous system (CNS). Compelling evidence suggests that breakdown of the blood-brain barrier (BBB) occurs at an early stage of MS (as well as in the animal model of MS, experimental autoimmune encephalomyelitis (EAE)), and plays a central role in the initiation and maintenance of this pathology. While it has been known for some time that hypoxic pre-conditioning protects against the development of ischemic stroke, only recently has it been suggested that mild hypoxia may also protect against the development of inflammatory demyelinating disease. Recently, we studied this protection in more detail, and we now have strong preliminary data showing that mild hypoxia (8% O2) applied before EAE induction, prevents vascular breakdown and reduces leukocyte infiltration during the early stages of EAE development. More importantly, mild hypoxia applied to mice with well-developed EAE profoundly protects against disease progression. Furthermore, findings from our lab and others have shown that mild hypoxia induces beneficial physiological adaptations in cerebral vessels that include: (i) marked angiogenic and arteriogenic responses, resulting in increased vessel density, (ii) elevated expression levels of tight junction proteins, suggesting increased BBB integrity, and (iii) reduced leukocyte adherence to cerebral vessels in stroke and EAE. In light of this accumulating data, the goal of this application is to test the hypothesis that mild hypoxia inhibits the progression o inflammatory demyelinating disease by promoting blood-brain barrier integrity and beneficial remodeling of cerebral blood vessels. Our hypothesis will be tested in two specific aims: (1) define the optimal dose, daily duration and frequency of hypoxia that most effectively prevents EAE progression, 2) define the influence of mild hypoxia on vascular protective mechanisms during EAE. First, we will define the dose, duration and frequency of hypoxia that inhibits disease progression in mice that already have well-established EAE. Second, we will investigate how the defined optimized hypoxic regimen influences vascular protective mechanisms, including BBB integrity, vascular remodeling, endothelial inflammatory status, TGF-? signaling and activation of the HIF-1?-VEGF axis. We anticipate these studies will define the optimal dose, daily duration and frequency of mild hypoxia that most effectively prevents EAE progression, and identify the key vascular mechanisms that underlie this protection. Successful completion of these studies will further our goal of developing this approach for the treatment of MS. This may take the form of a hypoxic therapy regimen, or more likely, result in the identification of molecular targets that could be exploited pharmacologically.

Public Health Relevance

Compelling evidence suggests that breakdown of the blood-brain barrier (BBB) occurs at an early stage of multiple sclerosis (MS) and plays a central role in the initiation and maintenance of this pathology. Given that short-term mild hypoxia promotes beneficial adaptations in cerebrovascular structure and function, here we will test the hypothesis that mild hypoxia inhibits the progression of inflammatory demyelinating disease by promoting blood-brain barrier integrity and beneficial remodeling of cerebral blood vessels. The proposed research is relevant to public health and the mission of NIH because it is expected to lead to the development of novel therapeutic approaches aimed at treating inflammatory demyelinating disease; these findings would have major implications for the treatment strategy of MS patients.