Autophagy Associated Gene Expression and Protein Levels in Neuronal Cells Infected with Herpes Simplex Virus Type One and Chlamydia Pneumoniae May Suggest Infection-Induced Mechanisms of Alzheimer's Disease

Date of Award

9-2013

Degree Type

Thesis

Degree Name

Master of Science (MS)

First Advisor

Susan T Hingley, PhD

Second Advisor

Denah M Appelt, PhD

Third Advisor

Brian J Balin, PhD

Fourth Advisor

Marcus G Bell, PhD

Abstract

While the etiology of Alzheimer's disease (AD) is not known, studies have proposed a possible role for infectious agents in triggering the events culminating in AD. Two possible candidates, Herpes simplex virus type l (HSV-1) and Chlamydia pneumoniae, have been detected in AD brains. Other studies have postulated that disruption of autophagy, a cellular process that promotes cell survival, might contribute to some of the pathological changes that occur in neurodegeneration. To determine whether these potential mechanisms for inducing neuropathology can be interconnected, this study evaluates changes in the expression of several genes and proteins involved in the autophagic pathway following infection of neurona I cells by HSV-1 and C. pneumoniae, either alone or together. Experiments were designed to investigate whether either pathogen inhibits replication of the other, as well as examine whether the two pathogens together exacerbate changes elicited by either one alone. Neuronal cells were inoculated with HSV-1 and/or C. pneumoniae at an MOI of 1; culture supernates and infected cell lysates were obtained at 18, 24 and 30 hours post infection. Data suggest that productive infection of neuronal cells with HSV-1 may inhibit replication by C. pneumoniae. Conversely C. pneumoniae does not appear to alter the infectivity of HSV-1. Previous data using microarrays to detect changes in expression of autophagy-associated genes revealed increased expression of several genes upon infection of neuronal cells by HSV-1 and Cpn. This current study indicates that expression of two such genes, FAM176A and PI3Kᵞ, is elevated to a greater extent in co-infected cells than in cells infected by either HSV-1 or C. pneumoniae alone; expression of a third gene, ATG7, is slightly increased in co-infected cells over that seen in single infections. Changes in gene expression due to infection may disrupt normal cellular signaling pathways, including those associated with autophagy. LC3-2 protein levels, commnonly assessed as a marker for autophagy, were increased while PI3Kᵞ protein levels decreased. Thus, our data support the hypothesis that disruption of autophagy by infection may contribute to the pathological changes observed in neurodegenerative disease.

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