Impact of Cryptococcus Neoformans Polysaccharide Capsule on Astrocytes
Cryptococcus neoformans is a neurotropic, opportunistic, encapsulated, yeast-like fungus that causes life-threatening meningoencephalitis in both healthy and immunocompromised individuals. C. neoformans infects 1,000,000 people and causes 210,000 deaths worldwide annually, mostly in sub-Saharan Africa. The polysaccharide capsule of C. neoformans is the fungus major virulent factor. Glucuronoxylomannan (GXM), the main component of the capsule is abundantly released into brain tissue during C. neoformans infection, causing immunosuppressive defects in the host. C. neoformans is inhaled from the environment, disseminate via bloodstream, and crosses the blood brain barrier (BBB) to cause cryptococcal meningoencephalitis (CM). Although CM causes significant mortality in HIV/AIDS patients, limited knowledge is available on the effect of secreted GXM on the cellular component of the BBB, especially astrocytes. Astrocytes are the most abundant glial cells with diverse biological functions in the brain and form a neurovascular unit at BBB regulating the water movement via their water channels, aquaporin 4 (AQP4). AQP4 is expressed exclusively in the astrocytic endfeet and is a functional regulator of glymphatic clearance, a recently discovered central nervous system (CNS) water clearance system that employs perivascular channels formed by astrocytes. AQP4 expression is depolarized during reactive astrogliosis, a morphological and a functional change seeing in astrocytes in response to CNS injury. A manifestation in some patients with CM is hydrocephalus or accumulation of cerebrospinal fluid (CSF) in the brain. Despite of high mortality in CM patients, little is known about the effects of GXM on astrocyte function and their involvement with hydrocephalus. AQP4 forms hetero tetramers with the two major isoforms, M1-AQP4 and M23, which congregate to form super-molecular structures or Orthogonal Arrays of Particles (OAPs). Formation of stable OAPs requires the expression of M23-AQP4 isoform whereas M1-AQP4 destabilizes OAP formation. We hypothesized that GXM enhances the expression of M1-AQP4 and inhibits OAP formation contributing to development of reactive astrogliosis and hydrocephalus. In this dissertation, we have quantified and characterized the GXM-mediated altered expression of AQP4 isoforms, affecting the formation of OAPs. We hope this research provides the foundation for biomedical applications in engineering glial cells as part of therapeutic treatment for cerebral cryptococcosis.
Woo, Yeon Hwa, "Impact of Cryptococcus Neoformans Polysaccharide Capsule on Astrocytes" (2020). ETD Collection for University of Texas, El Paso. AAI28262120.