PACAP27 is Protective Against Tat-Induced Neurotoxicity

Abstract

Human immunodeficiency virus type-1 (HIV) infection of the central nervous system promotes neuronal injury and apoptosis that culminate in HIV-associated neurocognitive disorders. Viral proteins, such as transactivator of transcription (Tat), have emerged as leading candidates to explain HIV-mediated neurotoxicity, though the mechanism remains unclear. To determine the effects of Tat, rat cortical neurons were exposed to nanomolar concentrations of Tat for various time points. Within a few hours, Tat induced the production of reactive oxygen species (ROS), and other indices of mitochondrial destabilization. In addition, we observed a significant induction of DNA double strand breaks (DSBs) by Tat. We next investigated the neuroprotective activity of the pituitary adenylate cyclase-activating polypeptide 27 (PACAP27) against these cardinal features of Tat-induced neurodegeneration. PACAP27 (100 nM) inhibited all Tat-mediated toxic effects including DNA DSBs. Importantly, PACAP27 prevented the induction of neuronal loss induced by Tat. The neuroprotective effect of PACAP27 is correlated with its ability to release the anti-apoptotic chemokine CCL5. Our data support a mechanism of Tat neurotoxicity in which Tat induces mitochondrial destabilization, thus increasing the release of ROS, which causes DNA DSBs leading to cell death. PACAP27, through CCL5, mitigates the effects of Tat-induced neuronal dysfunction, suggesting that PACAP27 could be a new strategy for an adjunct therapy against HIV-associated neurocognitive disorders.

Pharmacological induction of CCL5 in vivo prevents gp120-mediated neuronal injury

“…Moreover, two ligands of CCR5, CCL5 and CCL4, block the neurotoxic effect of gp120 (Kaul et al, 2007) suggesting that CCL5 may prevent/displace gp120BaL from binding to neuronal CCR5. However, CCL5 has also been shown to be protective against numerous neurotoxic insults including N-methyl-D-aspartic acid (Bruno et al, 2000), β-amyloid (Tripathy et al, 2010), and glutamate (Brenneman et al, 2002; Lin et al, 2011) as well as other HIV proteins (Brenneman et al, 2002; Kaul et al, 2007; Rozzi et al, 2014). Moreover, CCL5 enhances neurite formation and dendritic arborization (Chou et al, 2008), two hallmarks shared by neurotrophic factors.…”

“…For instance, CCL5 promotes survival of human astrocytes (Bakhiet et al, 2001), inhibits the neurotoxic effect of amyloid-β peptide (Ignatov et al, 2006), a hallmark of Alzheimer's disease (Stokin et al, 2005), as well as glutamate toxicity (Bruno et al, 2000). Importantly, CCL5 has been shown to exhibit a neuroprotective profile against various HIV proteins including gp120 and Tat (Brenneman et al, 2002; Kaul and Lipton, 1999; Meucci et al, 1998; Rozzi et al, 2014). Therefore, CCL5 could be a valid adjunct therapy to prevent neurodegeneration caused by HIV.…”

Identification of a binding site of the human immunodeficiency virus envelope protein gp120 to neuronal‐specific tubulin

“…The viability of primary cortical neurons was estimated by Hoechst 33258 and propidium iodide (Hoechst/PI; Sigma‐Adrich) co‐staining and visualized using a fluorescence microscope Olympus IX71 as previously described (Rozzi et al . ). Hoechst/PI‐positive cells were then counted using ImageJ and expressed as a percentage of the total number of neurons.…”

Human Immunodeficiency Virus Promotes Mitochondrial Toxicity

“…Tat induces DNA double strand breaks (Rozzi et al 2014). This Tat property could be arising from its function as viral transcriptional regulator in the nucleus (Liu et al 2000; Stauber and Pavlakis 1998).…”

“…However, in vitro or in vivo investigations have identified potential therapeutic avenues that can mitigate the effects of viral protein-induced mitochondrial toxicity. Antioxidants, including Trolox, Cu/Zn SOD1, GPx1, and PACAP27 have been found in multiple in vitro experimental approaches to reduce Tat- and gp120 induced oxidative stress and prevent neuronal apoptosis (Agrawal et al 2006; Agrawal et al 2012; Butler et al 2011; Pocernich et al 2005; Rozzi et al 2014). Ascorbate supplementation (ascorbate-2-O-phosphate) prevents the deleterious upregulation of iNOS and associated neuronal injury caused by gp120 in brain cell cultures (Walsh et al 2004).…”