Altered mitochondrial dynamics as a consequence of Venezuelan Equine encephalitis virus infection

Abstract

Mitochondria are sentinel organelles that are impacted by various forms of cellular stress, including viral infections. While signaling events associated with mitochondria, including those activated by pathogen associated molecular patterns (PAMPs), are widely studied, alterations in mitochondrial distribution and changes in mitochondrial dynamics are also beginning to be associated with cellular insult. Cells of neuronal origin have been demonstrated to display remarkable alterations in several instances, including neurodegenerative disorders. Venezuelan Equine Encephalitis Virus (VEEV) is a New World alphavirus that infects neuronal cells and contributes to an encephalitic phenotype. We demonstrate that upon infection by the vaccine strain of VEEV (TC-83), astrocytoma cells experience a robust drop in mitochondrial activity, which corresponds with an increased accumulation of reactive oxygen species (ROS) in an infection-dependent manner. Infection status also corresponds with a prominent perinuclear accumulation of mitochondria. Cellular enzymatic machinery, including PINK1 and Parkin, appears to be enriched in mitochondrial fractions as compared with uninfected cells, which is indicative of mitochondrial damage. Dynamin related protein 1 (Drp1), a protein that is associated with mitochondrial fission, demonstrated a modest enrichment in mitochondrial fractions of infected cells. Treatment with an inhibitor of mitochondrial fission, Mdivi-1, led to a decrease in caspase cleavage, suggesting that mitochondrial fission was likely to contribute to apoptosis of infected cells. Finally, our data demonstrate that mitophagy ensues in infected cells. In combination, our data suggest that VEEV infection results in significant changes in the mitochondrial landscape that may influence pathological outcomes in the infected cell.

Viral strategies for triggering and manipulating mitophagy

“…Likewise, in Venezuelan equine encephalitis virus (VEEV)infected cells, DNM1L, PRKN, and PINK1 are enriched in mitochondrial fractions as compared with uninfected cells, and mitophagy ensues in infected cells [38]. Similar findings were reported for coxsackievirus B (CVB), classical swine fever virus (CSFV), and porcine reproductive and respiratory syndrome virus (PRRSV) [39][40][41].…”

“…The inhibition of apoptosis by mitophagy favors viral replication and promotes the pathogenesis of viral infection [56]. Similar findings have been reported with HBV, HCV, VEEV, CSFV, PRRSV, Newcastle disease virus (NDV), and transmissible gastroenteritis virus (TGEV) [35,37,38,40,41,57,58]. These examples share 2 concurrent phenomena: (1) upon infection, viruses induce mitophagy via different mechanisms, and (2) subsequent mitophagy mitigates apoptosis to promote viral infection.…”

Direct and indirect pro-inflammatory cytokine response resulting from TC-83 infection of glial cells

“…Our previous study indicated that TC-83 induced mitochondrial dysfunction ultimately contributes to cell death via increased activation of the caspase response [24]. In astrocytes, the activation of caspase-3/7 is seen as early as 12 hours post infection (hpi) (Figure 1(c)).…”

“…In addition to this accepted marker of mitochondrial stress, maintenance of the mitochondrial membrane potential (MMP) is also utilized as a marker of mitochondrial function [17,18,24,38]. We have shown that these two events correlate with increased mitochondrial fission and mitophagy, contributing to cell death in an infection dependent manner [24]. …”

“…In these instances, alterations to mitochondrial homeostasis abrogate its function resulting in altered cellular redox status, accumulation of reactive oxygen species (ROS), dysregulated energy metabolism, mitophagy, increased neuroinflammation, collapsed mitochondrial networks, and axonal demyelination. We have previously reported that TC-83 can induce structural and functional changes to the mitochondria, which ultimately contributes to neuronal death [24]. …”