PKR-like ER kinase (PERK) Haplotypes Are Associated with Depressive Symptoms in People with HIV

Background

Depression is a debilitating and difficult-to-treat condition in people with HIV (PWH) despite viral suppression on antiretroviral therapy (ART). Depression is associated with activation of the PKR-like ER kinase (PERK) pathway, which regulates protein synthesis in response to metabolic stress. We evaluated common PERK haplotypes that influence PERK expression in relation to depressed mood in PWH.

Methods

PWH from 6 research centers were enrolled in the study. Genotyping was conducted using targeted sequencing with TaqMan. The major PERK haplotypes A, B, and D were identified. Depressive symptom severity was assessed using the Beck Depression Inventory-II (BDI-II). Covariates including genetically-defined ancestry, demographics, HIV disease/treatment parameters and antidepressant treatments were assessed. Data were analyzed using multivariable regression models.

Results

A total of 287 PWH with a mean (SD) age of 57.1±7.8 years were enrolled. Although the largest ethnic group was non-Hispanic white (n=129, 45.3%), African-American (n=124, 43.5%) and Hispanic (n=30, 10.5%) made up over half the sample. 20.3% were female and 96.5% were virally suppressed. Mean BDI-II was 9.6±9.5, and 28.9% scored above the cutoff for mild depression (BDI-II>13). PERK haplotype frequencies were AA57.8%, AB25.8%, AD 10.1%, and BB4.88%. PERK haplotypes were differentially represented according to genetic ancestry (p=6.84e-6). BDI-II scores were significantly higher in participants with the AB haplotype (F=4.45, p=0.0007).This finding was robust to consideration of potential confounds.

Conclusion

PERK haplotypes were associated with depressed mood in PWH.Consequently, pharmacological targeting of PERK-related pathways might amelioratedepression in PWH.

Activation status of integrated stress response pathways in neurones and astrocytes of HIV-associated neurocognitive disorders (HAND) cortex

C. Akay, K. A. Lindl, N. Shyam, B. Nabet, Y. Goenaga‐Vazquez, J. Ruzbarsky, Y. Wang, D. L. Kolson and K. L. Jordan‐Sciutto (2012) Neuropathology and Applied Neurobiology38, 175–200

Activation status of integrated stress response pathways in neurones and astrocytes of HIV‐associated neurocognitive disorders (HAND) cortex

Aims: Combined anti‐retroviral therapy (cART) has led to a reduction in the incidence of HIV‐associated dementia (HAD), a severe motor/cognitive disorder afflicting HIV(+) patients. However, the prevalence of subtler forms of neurocognitive dysfunction, which together with HAD are termed HIV‐associated neurocognitive disorders (HAND), continues to escalate in the post‐cART era. The microgliosis, astrogliosis, dendritic damage, and synaptic and neuronal loss observed in autopsy cases suggest an underlying neuroinflammatory process, due to the neurotoxic factors released by HIV‐infected/activated macrophages/microglia in the brain, might underlie the pathogenesis of HAND in the post‐cART era. These factors are known to induce the integrated stress response (ISR) in several neurodegenerative diseases; we have previously shown that BiP, an indicator of general ISR activation, is upregulated in cortical autopsy tissue from HIV‐infected patients. The ISR is composed of three pathways, each with its own initiator protein: PERK, IRE1α and ATF6. Methods: To further elucidate the specific ISR pathways activated in the central nervous system of HAND patients, we examined the protein levels of several ISR proteins, including ATF6, peIF2α and ATF4, in cortical tissue from HIV‐infected patients. Results: The ISR does not respond in an all‐or‐none fashion in HAND, but rather demonstrates a nuanced activation pattern. Specifically, our studies implicate the ATF6 pathway of the ISR as a more likely candidate than the PERK pathway for increases in BiP levels in astrocytes. Conclusion: These findings begin to characterize the nature of the ISR response in HAND and provide potential targets for therapeutic intervention in this disease.

Site-specific hyperphosphorylation of pRb in HIV-induced neurotoxicity

HIV-Associated Neurocognitive Disorder (HAND) remains a serious complication of HIV infection, despite combined Anti-Retroviral Therapy (cART). Neuronal dysfunction and death are attributed to soluble factors released from activated and/or HIV-infected macrophages. Most of these factors affect the cell cycle machinery, determining cellular outcomes even in the absence of cell division. One of the earliest events in cell cycle activation is hyperphosphorylation of the retinoblastoma protein, pRb (ppRb). We and others have previously shown increased ppRb expression in the CNS of patients with HIV encephalitis (HIVE) and in neurons in an in vitro model of HIV-induced neurodegeneration. However, trophic factors also lead to an increase in neuronal ppRb with an absence of cell death, suggesting that, depending on the stimulus, hyperphosphorylation of pRb can have different outcomes on neuronal fate. pRb has multiple serines and threonines targeted for phosphorylation by distinct kinases, and we hypothesized that different stimuli may target separate sites for phosphorylation. Thus, to determine whether pRb is differentially phosphorylated in response to different stimuli and whether any of these sites is preferentially phosphorylated in association with HIV-induced neurotoxicity, we treated primary rat mixed cortical cultures with trophic factors, BDNF or RANTES, or with the neurotoxic factor, N-methyl-d-aspartate (NMDA), or with supernatants containing factors secreted by HIV-infected monocyte-derived macrophages (HIV-MDM), our in vitro model of HIV-induced neurodegeneration. We found that, while BDNF and RANTES phosphorylated serine807/811 and serine608 in vitro, treatment with HIV-MDM did not, even though these trophic factors are components of HIV-MDM. Rather, HIV-MDM targets a specific phosphorylation site, serine795, of pRb for phosphorylation in vitro and this ppRb isoform is also increased in HIV-infected brains in vivo. Further, overexpression of a nonphosphorylatable pRb (ppRb S795A) attenuated HIV-MDM-induced neurotoxicity. These findings indicate that HIV-infection in the brain is associated with site-specific hyperphosphorylation of pRb at serine795, which is not induced by other tested stimuli, and that this phosphorylation contributes to neuronal death in this disease, demonstrating that specific pRb sites are differentially targeted and may have diverse impacts on the viability of post-mitotic neurons.

Expression of the endoplasmic reticulum stress response marker, BiP, in the central nervous system of HIV-positive individuals

The prevalence of HIV-associated neurocognitive impairment (NCI), which includes HIV-associated dementia (HAD) and minor cognitive and motor disorder (MCMD), has been increasing. HIV-infected and/or activated macrophages/microglia in the brain initiate the neurodegeneration seen in HIV-associated NCI via soluble neurotoxic mediators, including reactive oxygen species, viral proteins and excitotoxins. Neurotoxic factors released by macrophages/microglia injure neurones directly and alter astrocytic homeostatic functions, which can lead to excitotoxicity and oxidative stress-mediated neuronal injury. Often, cells respond to oxidative stress by initiating the endoplasmic reticulum (ER) stress response. Thus, we hypothesize that ER stress response is activated in HIV-infected cortex. We used immunofluorescence and immunoblotting to assess expression patterns of the ER stress proteins, BiP and ATF6, in HIV-positive cortical autopsy tissue. Additionally, we performed immunofluorescence using cell type-specific markers to examine BiP staining in different cell types, including neurones, astrocytes and macrophages/microglia. We observed a significant increase in BiP expression by both immunoblotting and immunofluorescence in HIV-positive cortex compared with control tissue. Additionally, phenotypic analysis of immunofluorescence showed cell type-specific increases in BiP levels in neurones and astrocytes. Further, ATF-6beta, an ER stress response initiator, is up-regulated in the same patient group, as assessed by immunoblotting. These results suggest that ER stress response is activated in HIV-infected cortex. Moreover, data presented here indicate for the first time that numbers of macrophages/microglia increase in brains of MCMD patients, as has been observed in HAD.

Response of cell cycle proteins to neurotrophic factor and chemokine stimulation in human neuroglia

Increased expression of neurotrophins (e.g., NGF, BDNF) and chemokines (e.g., RANTES) has been observed in neurodegenerative diseases. We examined the effect of these factors on intracellular signaling cascades inducing cell cycle proteins p53, pRb, and E2F1 in human fetal mixed neuronal and glial cells. Comparing neurotrophin- and chemokine-treated cultures with untreated controls showed altered subcellular localization and expression of hyperphosphorylated retinoblastoma protein (ppRb), E2F1, and p53. Using immunofluorescent laser confocal microscopy, E2F1 and ppRb were detected exclusively in neuronal nuclei in control cultures while p53 was cytoplasmic in astrocytes and nuclear in neurons. Following treatment with neurotrophins, E2F1 and ppRb were observed in the cytoplasm of neurons, while p53 was observed in both neuronal and astrocytic nuclei. Similar findings were observed following treatment with RANTES. Semiquantitative analysis using immunoblots showed an increase in the amount of phosphorylated pRb in treated cultures. Induction of cell cycle proteins may play a role in neurodegeneration associated with neurotrophin and chemokine stimulation.

Induction of cell-cycle regulators in simian immunodeficiency virus encephalitis

Neuronal degeneration associated with human immunodeficiency virus encephalitis has been attributed to neurotoxicity of signaling molecules secreted by activated, infected macrophages. We hypothesized that the barrage of signals present in the extracellular milieu of human immunodeficiency virus-infiltrated brain causes inappropriate activation of neuronal cell-cycle machinery. We examined the presence of three members of the cell-cycle control machinery: pRb, E2F1, and p53 in the simian immunodeficiency virus encephalitis (SIVE) model. Compared to noninfected and simian immunodeficiency virus-infected, nonencephalitic controls, we observed increased protein expression of E2F1 and p53 and aberrant cellular localization of E2F1 and pRb. In SIVE, E2F1 was abundant in the cytoplasm of neurons in both neurons and astrocytes proximal to SIVE pathology in the basal ganglia. pRb staining was nuclear and cytoplasmic in cortical neurons of SIVE cases. Antibodies to phosphorylated pRb also labeled the cytoplasm of cortical neurons. These data suggest that in SIVE, cell signaling results in phosphorylation of pRb which may result in subsequent alteration in E2F1 activity. As increased E2F1 and p53 activities have been linked to cell death, these data suggest that the neurodegeneration in SIVE could in part be because of changes in expression and activity of cell-cycle machinery.

Fetal Alz-50 clone 1 (FAC1) protein interacts with the Myc-associated zinc finger protein (ZF87/MAZ) and alters its transcriptional activity

Transcription factors mediate their regulatory effects through interaction with DNA and numerous nuclear proteins. The fetal Alz-50 clone 1 (FAC1) protein, a novel DNA-binding protein with the capacity to repress transcription, is likely to function through a similar mechanism (1). Using the two-hybrid yeast screen, we have shown that FAC1 interacts with the myc-associated zinc finger protein (ZF87/MAZ). This association was confirmed in vitro with recombinant protein. The ZF87/MAZ interaction domain was mapped to the region containing a putative nuclear localization signal (NLS) and nuclear export sequence (NES) of FAC1, using deletion mutants of the FAC1 protein. FAC1, on the other hand, recognizes a conformational interface that includes the proline/alanine-rich domain of ZF87/MAZ and the first zinc finger. Cotransfection of NIH3T3 cells with ZF87/MAZ and a luciferase reporter containing the SV40 promoter and enhancer results in an increase in transcriptional activation, suggesting ZF87/MAZ is able to recognize its consensus binding site present in the SV40 promoter. Cotransfection with FAC1 reduces the level of ZF87/MAZ-induced activation of the SV40 promoter in a dose dependent manner. A mutant FAC1, lacking the ZF87/MAZ interaction domain, does not alter ZF87/MAZ activation of the SV40 promoter. These data demonstrate that interaction between FAC1 and ZF87/MAZ alters the transactivation capacity of ZF87/MAZ. By immunoblot analysis, FAC1 and ZF87/MAZ exhibit similar tissue distribution and co-localize to pathologic structures in Alzheimer's disease brain. Coexpression of FAC1 and ZF87/MAZ suggest that interaction of these two proteins will have biological implications for gene regulation in neurodegeneration.

DNA binding activity of the fetal Alz-50 clone 1 (FAC1) protein is enhanced by phosphorylation

Fetal Alz-50 clone 1 (FAC1) is a novel DNA binding protein with altered expression and subcellular localization during neuronal development and degeneration. FAC1 localizes to the cell body and neurites in undifferentiated neurons during development and in degenerating neurons during Alzheimer's disease progression. In the normal adult brain FAC1 is present predominantly in the nucleus of cortical neurons. When in the nucleus FAC1 has been shown to repress transcription by binding a specific DNA sequence. In the present study we demonstrate that the affinity of FAC1 for the identified DNA sequence is dramatically enhanced when FAC1 is phosphorylated. Phosphatase treatment of neuroblastoma nuclear extracts reduces FAC1 DNA binding affinity. Finally, inhibition of cellular serine/threonine phosphatases results in increased FAC1 DNA binding activity. These data suggest that FAC1 DNA binding activity is dependent upon and regulated by phosphorylation signals in the cell.

A mutant E2F-1 transcription factor that affects the phenotype of NIH3T3 fibroblasts inefficiency associates with cyclin A-cdk2

The amino-terminal domain of the E2F1 transcription factor is the site of association with cyclin A-cdk2, mapping to residues 87-94. A mutant of E2F1 lacking the first 87 amino acids (termed E2F1d87) has a number of potent effects on cellular phenotype when constitutively expressed in NIH3T3 fibroblasts. For example, in these fibroblasts the duration of S phase and the sensitivity to S phase chemotherapeutic agents are both increased. Since E2F1d87 only partially truncates the cyclin A-cdk2 binding domain, it was important to determine the level of cyclin A-cdk2 association with this mutant to correlate any reduction in association with the observed effects on the cell cycle. It was found that cyclin A-cdk2 binds E2F1d87 in an in vitro assay but that this binding is reduced approximately 8 fold compared with binding to full-length E2F1, whereas no detectable binding was seen to a mutant E2F1 that lacks the first 117 amino acids. Correspondingly, H1 kinase activity in E2F1d87 immunoprecipitates from E2F1d87-expressing cells was significantly reduced compared with that seen for full-length E2F1. From these data it appears that E2F1 with reduced cyclin A-cdk2 binding activity mediates the alteration in cell cycle parameters seen in these cells.

Reduction in fibronectin expression and alteration in cell morphology are coincident in NIH3T3 cells expressing a mutant E2F1 transcription factor

Fibronectin within the extracellular matrix plays a role in cell attachment, spreading, and shape, while it also affects aspects of cell proliferation. Transcription factors such as E2F1 are also known to regulate cell shape and cell proliferation. Yet, to date no linkage has been established between fibronectin expression and E2F1. We show here that cells constitutively expressing a mutant E2F1 protein (E2F1d87) produce reduced amounts of fibronectin mRNA and protein. The altered expression of fibronectin seen in the E2F1d87 expressing cells is due, in part, to a reduction in transcription from the fibronectin promoter. Providing exogenous fibronectin, but not Type I collagen or laminin, as a substrate for cell adhesion is sufficient to revert the altered morphology and reestablish actin-containing microfilaments lost in the mutant cell line. An additional characteristic of the cells expressing the mutant E2F1 is that they demonstrate slow growth and a doubling in S phase duration. While providing exogenous fibronectin as an adhesion substrate did not shorten the S phase duration in the mutant line, it did significantly shorten the S phase duration in the parental NIH3T3 cell line, implicating a role for the extracellular matrix in regulating S phase transit in normal cells.