Neuronal and axonal degeneration in experimental spinal cord injury: in vivo proton magnetic resonance spectroscopy and histology.

Longitudinal in vivo proton magnetic resonance spectroscopy (1H-MRS) and immunohistochemistry were performed to investigate the tissue degeneration in traumatically injured rat spinal cord rostral and caudal to the lesion epicenter. On 1H-MRS significant decreases in N-acetyl aspartate (NAA) and total creatine (Cr) levels in the rostral, epicenter, and caudal segments were observed by 14 days, and levels remained depressed up to 56 days post-injury (PI). In contrast, the total choline (Cho) levels increased significantly in all three segments by 14 days PI, but recovered in the epicenter and caudal, but not the rostral region, at 56 days PI. Immunohistochemistry demonstrated neuronal cell death in the gray matter, and reactive astrocytes and axonal degeneration in the dorsal, lateral, and ventral white-matter columns. These results suggest delayed tissue degeneration in regions both rostrally and caudally from the epicenter in the injured spinal cord tissue. A rostral-caudal asymmetry in tissue recovery was seen both on MRI-observed hyperintense lesion volume and the Cho, but not NAA and Cr, levels at 56 days PI. These studies suggest that dynamic metabolic changes take place in regions away from the epicenter in injured spinal cord.

The Role of the Androgen Receptor Cofactor p44/WDR77 in Astrocyte Activation

Astrogliosis is induced by neuronal damage and is also a pathological feature of the major aging-related neurodegenerative disorders. The mechanisms that control the cascade of astrogliosis have not been well established. In a previous study, we identified a novel androgen receptor (AR)-interacting protein (p44/WDR77) and found that it plays a critical role in the control of proliferation and differentiation of prostate epithelial cells. In the present study, we found that deletion of the p44 gene in the mouse brain caused accelerated aging with dramatic astrogliosis. The p44/WDR77 is expressed in astrocytes and loss of p44/WDR77 expression in astrocytes leads to astrogliosis. Our results reveal a novel role of p44/WDR77 in astrocytes, which may explain the well-documented role of androgens in suppression of astrogliosis. While many of detailed mechanisms of astrocyte activation remain to be elucidated, a number pathways have been implicated in astrocyte activation including p21Cip1 and the NF-kB pathway. Astrocytic activation induced by p44/WDR77 gene deletion was associated with a significant increase of p21Cip1 expression and NF-kB activation characterized by p65 nuclear localization. We found that down-regulation of p21Cip1 expression inhibited astrocyte activation induced by the p44/WDR77 deletion and was accompanied by a decreased p65 nuclear localization. While p21Cip1 role in astrocyte activation and NF-kB activation is not well understood, studies of other cell cycle regulators have implicated cell cycle control systems as modulators of astrocyte activation, thus p21Cip1 could induce secondary effect to induce p65 nuclear localization. However, p65 knockdown completely relieved the inhibition of astrocyte growth induced by the p44/WDR77 deletion, while p21Cip1 knockdown only partially recovered this inhibition. Thus, NF-kB activity performs additional regulatory actions not mediated by p21Cip1. These analyses imply that p4/WDR77 suppresses astrocyte activation through modulating p21Cip1 expression and NF-kB activation.

Upregulation of Reactive Oxygen Species During the Retrovirus Life Cycle and Their Roles in a Mutant of Moloney Murine Leukemia Virus, ts1-Mediated Neurodegeneration

Viral invasion of the central nervous system (CNS) and development of neurological symptoms is a characteristic of many retroviruses. The mechanism by which retrovirus infection causes neurological dysfunction has yet to be fully elucidated. Given the complexity of the retrovirus-mediated neuropathogenesis, studies using small animal models are extremely valuable. Our laboratory has used a mutant moloney murine leukemia retrovirus, ts1-mediated neurodegneration. We hypothesize that astrocytes play an important role in ts1-induced neurodegeneration since they are retroviral reservoirs and supporting cells for neurons. It has been shown that ts1 is able to infect astrocytes in vivo and in vitro. Astrocytes, the dominant cell population in the CNS, extend their end feet to endothelial cells and neuronal synapse to provide neuronal support. Signs of oxidative stress in the ts1-infected CNS have been well-documented from previous studies. After viral infection, retroviral DNA is generated from its RNA genome and integrated into the host genome. In this study, we identified the life cycle of ts1 in the infected astrocytes. During the infection, we observed reactive oxygen species (ROS) upregulations: one at low levels during the early infection phase and another at high levels during the late infection phase. Initially we hypothesized that p53 might play an important role in ts1-mediated astrocytic cell death. Subsequently, we found that p53 is unlikely to be involved in the ts1-mediated astrocytic cell death. Instead, p53 phosphorylation was increased by the early ROS upregulation via ATM, the protein encoded by the ataxia-telangiectasia (A-T) mutated gene. The early upregulation of p53 delayed viral gene expression by suppressing expression of the catalytic subunit of NADPH oxidase (NOX). We further demonstrated that the ROS upregulation induced by NOX activation plays an important role in establishing retroviral genome into the host. Inhibition of NOX decreased viral replication and delayed the onset of pathological symptoms in ts1-infected mice. These observations lead us to conclude that suppression of NOX not only prevents the establishment of the retrovirus but also decreases oxidative stress in the CNS. This study provides us with new perspectives on the retrovirus-host cell interaction and sheds light on retrovirus-induced neurodegeneration as a result of the astrocyte-neuron interaction.

Relationships between the alterations of tumor suppressor genes, risk factors and clinical outcomes of gliomas

The relationship between MMAC/PTEN, DMBT1 and the progression and prognosis of glioma, and the association between the alterations of MMAC/PTEN, p53, p16, and Rb and some cancer risk factors, such as smoking, exposure to radiation, family cancer history, and previous cancer history, were assessed in 4 studies. ^ By allelic deletion analysis, MMAC/PTEN locus was shown to be frequently lost in glioblastomas multiforme (GM) but maintained in most lower-grade astrocytic tumors. DMBT1 locus, however, was frequently lost in all grades of gliomas examined. The potential biological significance of these two regions was frontier assessed by examining microcell-hybrids that contained various fragments of 10q. Somatic cell hybrid clones that retained the MMAC/PTEN locus have less transformed phenotypes, exhibiting an inability to grow in soft agarose. On the other hand, the presence or absence of DAMT1 did not correlate with any in vitro phenotype assessed in our model system. Further, Cox proportional hazards regression analysis, adjusted for age at surgery and histologic grades (GM, and non-GM), showed that without LOH at the MMAC/PTEN locus had a significantly better prognosis than did patients with LOH at MMAC/ PTEN (hazard ratio = 0.5; 95% Cl = 0.28–0.89; P = 0.018). Furthermore, status of LOH at MMAC/PTEN was found to be significantly associated with age, while that for DMBT1 was not. These results suggest that the DMBT1 may be involved early in the oncogenesis of gliomas, while alterations in the MMAC /PTEN may be a late event in the oncogenesis related with progression of gliomas and provide a significant prognostic marker for patient survival. ^ The associations between 4 cancer risk factors and 4 tumor suppressor genes were assessed. The expression of p16 was observed to be associated with current smoking (adjusted OR = 1.9, 95% CI = 1.02–3.6) but not the former smoking (adjusted OR = 1.1, 95% Cl = 0.5–3.5). The expression of p53 was found to be associated with the family cancer history (OR = 3.5, 95% Cl = 1.07–11 for patients with first-degree family history of cancer). MMAC/ PTEN was associated with the histologic grade (OR = 2.8, 95% CI = 1.2–6.6) and age (P = 0.035). Also, the OR for LOH around MMAC/PTEN in patients with a family history of cancer was elevated (OR = 1.9, 95% CI = 0.8–4.6 for patients with first-degree family history of cancer). The associations between exposure and the alterations of tumor suppressor genes, between smoking and p16, between family history of cancer and p53 and MMAC/PTEN, provide suggestive evidences that those exposures are related to the development of gliomas. ^