Upregulation of glial clusterin in brains of patients with AIDs

Accelerated Neuroimmune Dysfunction in Aged HIV-1-Infected Humanized Mice

Disordered immunity, aging, human immunodeficiency virus type one (HIV-1) infection, and responses to antiretroviral therapy are linked. However, how each factor is linked with the other(s) remains incompletely understood. It has been reported that accelerated aging, advanced HIV-1 infection, inflammation, and host genetic factors are associated with host cellular, mitochondrial, and metabolic alterations. However, the underlying mechanism remains elusive. With these questions in mind, we used chronically HIV-1-infected CD34-NSG humanized mice (hu-mice) to model older people living with HIV and uncover associations between HIV-1 infection and aging. Adult humanized mice were infected with HIV-1 at the age of 20 weeks and maintained for another 40 weeks before sacrifice. Animal brains were collected and subjected to transcriptomics, qPCR, and immunofluorescence assays to uncover immune disease-based biomarkers. CD4+ T cell decline was associated with viral level and age. Upregulated C1QA, CD163, and CXCL16 and downregulated LMNA and CLU were identified as age-associated genes tied to HIV-1 infection. Ingenuity pathway analysis affirmed links to innate immune activation, pyroptosis signaling, neuroinflammation, mitochondrial dysfunction, cellular senescence, and neuronal dysfunction. In summary, CD34-NSG humanized mice are identified as a valuable model for studying HIV-1-associated aging. Biomarkers of immune senescence and neuronal signaling are both age- and virus-associated. By exploring the underlying biological mechanisms that are linked to these biomarkers, interventions for next generation HIV-1-infected patients can be realized.

Development- and activity-dependent expression of clusterin in the mouse olfactory bulb

Clusterin, a protein involved in many biological processes, is expressed broadly in the central nervous system, but its functions remain largely unknown. As preparations for elucidating some possible functions, we examined the spatiotemporal expression patterns of clusterin in the mouse olfactory bulb at different developmental stages and under different neuronal activity levels. Our results revealed a dynamic expression of the protein during development. Clusterin signal was seemingly diffuse during the early stages of development, shifted to the cell somas later and then predominantly to the axons of projection neurons in the adult stage, with a transition point at approximately postnatal day 18. The effects of olfactory deficits on the clusterin expression level in an anosmic mouse model were neuron-specific: the signals increased remarkably from faint to strong in olfactory sensory neurons, reduced considerably from moderate/strong to faint in the centrifugal projection neurons, decreased moderately from moderate to faint in the local bulbar projection neurons, and remained intense in long-distance bulbar projection neurons. These results showed that clusterin expression is modulated dynamically during development and by sensory activity. These findings deepen our understanding of this broadly expressed protein.

Gene expression profiles of HIV-1-infected glia and brain: toward better understanding of the role of astrocytes in HIV-1-associated neurocognitive disorders

Astrocytes are the major cellular component of the central nervous system (CNS), and they play multiple roles in brain development, normal brain function, and CNS responses to pathogens and injury. The functional versatility of astrocytes is linked to their ability to respond to a wide array of biological stimuli through finely orchestrated changes in cellular gene expression. Dysregulation of gene expression programs, generally by chronic exposure to pathogenic stimuli, may lead to dysfunction of astrocytes and contribute to neuropathogenesis. Here, we review studies that employ functional genomics to characterize the effects of HIV-1 and viral pathogenic proteins on cellular gene expression in astrocytes in vitro. We also present the first microarray analysis of primary mouse astrocytes exposed to HIV-1 in culture. In spite of different experimental conditions and microarray platforms used, comparison of the astrocyte array data sets reveals several common gene-regulatory changes that may underlie responses of these cells to HIV-1 and its proteins. We also compared the transcriptional profiles of astrocytes with those obtained in analyses of brain tissues of patients with HIV-1 dementia and macaques infected with simian immunodeficiency virus (SIV). Notably, many of the gene characteristics of responses to HIV-1 in cultured astrocytes were also altered in HIV-1 or SIV-infected brains. Functional genomics, in conjunction with other approaches, may help clarify the role of astrocytes in HIV-1 neuropathogenesis.

Epidermal growth factor receptor is involved in clusterin-induced astrocyte proliferation

We previously reported that clusterin enhances astrocyte proliferation and extracellular signal-regulated kinase (ERK) activity. It, however, remains largely unknown how clusterin promotes cell growth. Here, we investigate the signaling pathway and related molecules underlying astrocyte proliferation by clusterin. Exogenous clusterin stimulates Ras-dependent Raf-1/mitogen-activated protein kinase kinase (MEK)/ERK activation. Clusterin-induced astrocyte proliferation and ERK1/2 phosphorylation were abrogated by either AG1478 (an inhibitor of epidermal growth factor receptor, EGFR) or EGFR small interfering RNA. Furthermore, clusterin treatment provoked tyrosine phosphorylation of EGFR (pY(1173)), which was also blocked by AG1478. These results suggest that clusterin requires EGFR activation to deliver its mitogenic signal through the Ras/Raf-1/MEK/ERK signaling cascade in astrocytes.

Clusterin increases post-ischemic damages in organotypic hippocampal slice cultures

Clusterin or apolipoprotein J is a heterodimeric glycoprotein which is known to be increased during tissue involution in response to hormonal changes or injury and under circumstances leading to apoptosis. Previous studies in wild-type (WT) and clusterin-null (Clu-/-) mice indicated a protective role of clusterin over-expression in astrocytes lasting up to 90 days post-ischemia. However, in in vitro and in vivo models of neonatal hypoxia-ischemia, clusterin exacerbates necrotic cell death. We developed recombinant forms of clusterin and examined their effect on propidium iodide uptake, neuronal and synaptic markers as well as electrophysiological recordings in hippocampal slice cultures from Clu-/- and WT mice subjected to oxygen-glucose deprivation (OGD). WT mice displayed a marked up-regulation of clusterin associated with electrophysiological deficits and dramatic increase of propidium iodide uptake 5 days post-OGD. Immunocytochemical and western blot analyses revealed a substantial decrease of neuronal nuclei and synaptophysin immunoreactivity that predominated in WT mice. These findings contrasted with the relative post-OGD resistance of Clu-/- mice. The addition of biologically active recombinant forms of human clusterin for 24 h post-OGD led to the abolishment of the ischemic tolerance in Clu-/- slices. This deleterious effect of clusterin was reverted by the concomitant administration of the NMDA receptor antagonist, d-2-amino-5-phosphonopentanoate. The present data indicate that in an in vitro model of ischemia characterized by the predominance of NMDA-mediated cell death, clusterin exerts a negative effect on the structural integrity and functionality of hippocampal neurons.

Clusterin expression during fetal and postnatal CNS development in mouse

Clusterin (or apolipoprotein J) is a widely distributed multifunctional glycoprotein involved in CNS plasticity and post-traumatic remodeling. Using biochemical and morphological approaches, we investigated the clusterin ontogeny in the CNS of wild-type (WT) mice and explored developmental consequences of clusterin gene knock-out in clusterin null (Clu-/-) mice. A punctiform expression of clusterin mRNA was detected through the hypothalamic region, neocortex and hippocampus at embryonic stages E14/E15. From embryonic stage E16 to the first week of the postnatal life, the vast majority of CNS neurons expressed low levels of clusterin mRNA. In contrast, a very strong hybridizing signal mainly localized in pontobulbar and spinal cord motor nuclei was observed from the end of the first postnatal week to adulthood. Astrocytes expressing clusterin mRNA were often detected through the hippocampus and neocortex in neonatal mice. Real-time polymerase chain amplification and clusterin-immunoreactivity dot-blot analyses indicated that clusterin levels paralleled mRNA expression. Comparative analyses between WT and Clu-/- mice during postnatal development showed no significant differences in brain weight, neuronal, synaptic and astrocyte markers as well myelin basic protein expression. However, quantitative estimation of large motor neuron populations in the facial nucleus revealed a significant deficit in motor cells (-16%) in Clu-/- compared with WT mice. Our data suggest that clusterin expression is already present in fetal life mainly in subcortical structures. Although the lack of this protein does not significantly alter basic aspects of the CNS development, it may have a negative impact on neuronal development in certain motor nuclei.

Beneficial effects of r-h-CLU on disease severity in different animal models of peripheral neuropathies

Clusterin is a protein involved in multiple biological events, including neuronal cytoprotection, membrane recycling and regulation of complement-mediated membrane attack after injury. We investigated the effect of recombinant human clusterin in preclinical models of peripheral neuropathies. Daily treatment with clusterin accelerated the recovery of nerve motor evoked potential parameters after sciatic nerve injury. Prophylactic or therapeutic treatment of experimental autoimmune neuritis rats with clusterin also accelerated the rate of recovery from the disease, associated with remyelination of demyelinated nerve fibers. These data demonstrate that clusterin is capable of ameliorating clinical, neurophysiological and pathological signs in models of peripheral neuropathies.

Clusterin enhances proliferation of primary astrocytes through extracellular signal-regulated kinase activation

Clusterin, a secretory glycoprotein, has been shown to be up-regulated in the reactive astrocytes in response to brain injury and neurodegenerative diseases, but its function has not been clearly elucidated. In this study, we investigate whether clusterin has growth-stimulatory activity in astrocytes. Suppression of clusterin with antisense oligonucleotide induced growth arrest, whereas transient overexpression of clusterin by cDNA transfection or exogenous treatment with purified clusterin promoted proliferation of the primary astrocytes in culture. This clusterin-stimulated proliferation was abrogated by PD98059, an inhibitor of mitogen-activated protein kinase kinase. These results suggest that clusterin might play an important role in astrogliosis by stimulating the proliferation of astrocytes through activation of the extracellular signal-regulated kinase 1/2 signaling pathway.

Sustained astrocytic clusterin expression improves remodeling after brain ischemia

Clusterin is a glycoprotein highly expressed in response to tissue injury. Using clusterin-deficient (Clu-/-) mice, we investigated the role of clusterin after permanent middle cerebral artery occlusion (MCAO). In wild-type (WT) mice, clusterin mRNA displayed a sustained increase in the peri-infarct area from 14 to 30 days post-MCAO. Clusterin transcript was still present up to 90 days post-ischemia in astrocytes surrounding the core infarct. Western blot analysis also revealed an increase of clusterin in the ischemic hemisphere of WT mice, which culminates up to 30 days post-MCAO. Concomitantly, a worse structural restoration and higher number of GFAP-reactive astrocytes in the vicinity of the infarct scar were observed in Clu-/- as compared to WT mice. These findings go beyond previous data supporting a neuroprotective role of clusterin in early ischemic events in that they demonstrate that this glycoprotein plays a central role in the remodeling of ischemic damage.

Expression of the Antiapoptotic Proteins Clusterin and Bcl-2 in Laryngeal Squamous Cell Carcinomas

Bcl-2 and clusterin genes have been related to the inhibition of apoptosis, an event that plays a key role in malignant transformation and in invasive disease. In this work, we determine the significance of clusterin and bcl-2 expression in a large series of laryngeal carcinomas. We used immunohistochemical methods and in situ hybridization to examine the expression of these proteins. Nontumoral epithelial laryngeal tissues did not express clusterin and bcl-2 proteins. However, 9% (14 out of 154) and 25% of these tumors (39 of 154) had positive clusterin and bcl-2 staining, respectively. Clusterin expression was significantly related to the degree of local invasion and higher bcl-2 expression was found in these clusterin-positive tumors (p < 0.05). Bcl-2 expression was significantly correlated with supraglottic localization, nodal metastases, invasion in depth, and poorly differentiated tumors. However, by multivariate analysis, bcl-2 was shown to be an independent predictor of good prognosis in these tumors (OR = 0.12, 95% CI = 0.02-0.91). These findings indicate that clusterin and bcl-2 are upregulated in laryngeal carcinomas and their expression is related to the invasiveness of these tumors.