Suzanne M. de la Monte

Conversion of p35 to p25 deregulates Cdk5 activity and promotes neurodegeneration

Cyclin-dependent kinase 5 (Cdk5) is required for proper development of the mammalian central nervous system. To be activated, Cdk5 has to associate with its regulatory subunit, p35. We have found that p25, a truncated form of p35, accumulates in neurons in the brains of patients with Alzheimers disease. This accumulation correlates with an increase in Cdk5 kinase activity. Unlike p35, p25 is not readily degraded, and binding of p25 to Cdk5 constitutively activates Cdk5, changes its cellular location and alters its substrate specificity. In vivo the p25/Cdk5 complex hyperphosphorylates tau, which reduces taus ability to associate with microtubules. Moreover, expression of the p25/Cdk5 complex in cultured primary neurons induces cytoskeletal disruption, morphological degeneration and apoptosis. These findings indicate that cleavage of p35, followed by accumulation of p25, may be involved in the pathogenesis of cytoskeletal abnormalities and neuronal death in neurodegenerative diseases.

Human and rat brain-derived neurotrophic factor and neurotrophin-3: gene structures, distributions, and chromosomal localizations.

The development and maintenance of the vertebrate nervous system depends upon neuronal survival proteins known as neurotrophic factors. Nerve growth factor (NGF) remains the best characterized neurotrophic molecule. Brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) are two recently cloned neurotrophic factors that are homologous to NGF. Here we describe the molecular cloning of the human and rat genes encoding BDNF, as well as the isolation of the human NT-3 gene. On the basis of comparison of our genomic and cDNA clones with those of previously isolated BDNF and NT-3 genes and cDNAs, we make inferences about the structures of processed transcripts derived from the neurotrophin genes and the protein precursors they encode. We demonstrate that the mature form of BDNF is identical in all mammals examined, and that the same is true of the mature form of NT-3. Furthermore, the respective tissue-distributions and neuronal specificities of NT-3 and BDNF are also conserved among mammals. Finally, we localize the gene encoding human BDNF (gene symbol designated BDNF) to chromosome 11, band p13, and the gene encoding human NT-3 (gene symbol designated NTF3) to chromosome 12, band p13.

p53 mutation in hepatocellular carcinoma after aflatoxin exposure

Mutations of the p53 gene are found in hepatocellular carcinoma (HCC), the most common form of primary liver cancer. Specific mutations might reflect exposure to specific carcinogens and we have screened HCC samples from patients in 14 different countries to determine the frequency of a hotspot mutation at codon 249 of the tumour suppressor p53 gene. We detected mutations in 17% of tumours (12/72) from four countries in south Africa and the southeast coast of Asia. There was no codon 249 mutation in 95 specimens of HCC from other geographical locations including North America, Europe, Middle East, and Japan. Worldwide, the presence of the codon 249 mutation in HCCs correlated with high risk of exposure to aflatoxins and the hepatitis B virus (HBV). Further studies were completed in two groups of HBV-infected patients at different risks of exposure to aflatoxins. 53% of patients (8/15) from Mozambique at high risk of aflatoxin exposure had a tumour with a codon 249 mutation, in contrast with 8% of patients from Transkei (1/12) who were at low risk. HCC is an endemic disease in Mozambique and accounts for up to two thirds of all tumours in men. A codon 249 mutation of the p53 gene identifies an endemic form of HCC strongly associated with dietary aflatoxin intake.

Morphometric Demonstration of Atrophic Changes in the Cerebral Cortex, White Matter, and Neostriatum in Huntington's Disease

We performed morphometric analysis of five standardized coronal brain slices at anterior frontal (AF), caudate-putamen-accumbens (CAP), globus pallidus (GP), lateral geniculate nucleus (LGN), and parieto-occipital fissure (OCP) levels in 30 patients with Huntingtons disease (HD) and 13 controls. Associated with the 30% mean reduction in brain weight in HDpatients (p<0.001) were significantly smaller overall cross-sectional areas of brain at all five levels studied, with striking losses in cerebral cortex (21-29%), white matter (29-34%), caudate (57%), putamen (64%), and thalamus (28%) (all p<0.005). In addition, the ventricular system was dilated up to 2.5 times normal at CAP, GP, and LGN levels, 9.5 times normal at the OCP level, and 13 times normal at the AFlevel. Higher grades of severity of HDhad greater reductions in the cross-sectional area of the caudate, putamen, thalamus, and cerebral cortex (p<0.005-0.001), and larger ventricles (p=0.08) compared to lower (less severe) grades of HD. The findings confirm and quantitate the severe atrophy of the neostriatum, in addition to demonstrating a severe loss of cerebral cortex and subcortical white matter in HD. The global atrophy of cerebral cortex and white matter observed in all degrees of HD may account for the cognitive and neuropsychiatric impairments which often precede the onset of chorea.

Correlates of p53- and Fas (CD95)-mediated apoptosis in Alzheimer's disease.

Apoptosis may be an important mechanism of cell loss in Alzheimers disease (AD). Experimentally, apoptosis is preceded by nuclear accumulation of p53, and increased expression of Fas (CD95) antigen. In the present study, quantitative Western blot analysis of postmortem frontal and temporal lobe tissue demonstrated significantly higher mean levels of p53 and Fas in AD relative to age-matched controls. Immunohistochemical staining and in situ apoptosis assays demonstrated increased p53 and Fas expression and DNA fragmentation in overlapping populations of cortical neurons, and cortical and white matter glial cells distributed in regions damaged by neurodegeneration. Double-label immunohistochemical staining studies revealed p53 immunoreactivity in: 1) cortical neurons without tau-immunoreactive neurofibrillary tangles; 2) numerous, but not all tau-immunoreactive neuropil neurites and white matter axons; 3) dystrophic fibrils surrounding amyloid-beta-immunoreactive plaques; and 4) glial cells characterized as A2B5+ protoplasmic astrocytes or oligodendrocytes. The prominent distribution of dystrophic p53-immunoreactive processes around amyloid-beta-containing plaques suggests that amyloid deposits are associated with local neuritic degeneration. In addition, the results suggest that many tau-immunoreactive neuritic processes originate from degenerating (p53) as well as regenerating neurons. Finally, apoptosis of glial cells (A2B5+) required to maintain the functional integrity of axons and dendrites may represent an important pathogenic mechanism of axonal loss and synaptic disconnection in AD.

Infection of the Retina by Human Immunodeficiency Virus Type I

HUMAN immunodeficiency virus (HIV) is the etiologic agent of the acquired immunodeficiency syndrome (AIDS).1 2 3 4 HIV penetrates specific cells bearing the CD4 surface antigen5 , 6 and has been observed in helper T lymphocytes, monocytes, Langerhans cells, and recently, astrocytes, endothelial cells, oligodendrocytes, and neurons.7 8 9 10 11 HIV-infected cells have been found in the blood, semen, vaginal secretions, breast milk, lymph nodes, brain, spinal cord, and peripheral nerves.7 8 9 10 11 12 13 14 15 16 17 18 19 Many patients with HIV infection have a variety of ocular abnormalities not associated with obvious opportunistic infections; these abnormalities include cotton-wool spots and microvascular changes of the retina.20 21 22 23 24 25 26 27 These observations, together with the established neurotropism of HIV, .xa0.xa0.

GAP-43 gene expression during development: persistence in a distinctive set of neurons in the mature central nervous system

GAP-43 is a rapidly transported axonal protein most prominently expressed in regenerating and developing nerves. However, the low level persistence of GAP-43 in the adult CNS where growth and regenerative capacity are minimal may additionally indicate a role for this molecule in neuronal remodeling. Previous studies have revealed GAP-43 immunoreactivity in neurites throughout many regions of the CNS. To identify the CNS neurons that express GAP-43 at different stages of development, we utilized in situ hybridization and immunocytochemistry; the latter was performed with an antibody that recognizes GAP-43 immunoreactivity in both perikarya and neurites. In the perinatal period GAP-43 is expressed in all neurons. Subsequently its expression becomes progressively restricted such that by maturity most neurons no longer express detectable levels, although GAP-43 expression is still moderately high in the adult entorhinal cortex, and strikingly high in the adult hippocampus and olfactory bulb. In light of current notions about the function of GAP-43, it is tempting to speculate that this anatomy denotes neurons engaged in structural remodeling and functional plasticity.

Cloning of human GAP 43: Growth association and ischemic resurgence

GAP-43 is a growth cone protein expressed in neurons especially during periods of axonal elongation. Poor repair in the adult mammalian CNS has been ascribed to restraints upon its expression. We have cloned human GAP-43 cDNA to investigate its potential involvement in neurological illness. Analysis of postmortem human brain tissue disclosed uniformly high expression of GAP-43 throughout the neonatal brain, whereas in the adult brain high levels of GAP-43 persist only in discrete regions. However, in the wake of ischemic injury in the adult brain, regions normally low in GAP-43 reexpress it at high levels, suggesting a role for GAP-43 in remodeling and repair of mature CNS neurons.

Human Immunodeficiency Virus (HIV) Infection of the Uterine Cervix

Human immunodeficiency virus (HIV) has been detected in cervical secretions from HIV-infected women. We report the isolation of HIV from four cervical biopsy specimens. Cervicitis was shown by immunohistochemical staining in cervical biopsy specimens from four HIV-seropositive women; cervicitis was not found in cervical biopsy specimens from four HIV-seronegative women. We found HIV antigens in monocyte-macrophages and endothelial cells within the submucosa of three of these cervices by specific immunohistochemical staining. Small numbers of HIV-infected cells resembling lymphocytes also were found in the cervical mucosa. The virus was not shown by culture or immunohistochemistry in cervical biopsy specimens from the four HIV-seronegative women. These findings suggest that HIV enters cervical secretions from selected infected cell populations within the cervical tissue. The HIV-infected cells in cervical tissue may be involved in transmission of HIV by heterosexual contact and to neonates born to HIV-infected women.

Aspartyl‐asparagyl β hydroxylase over‐expression in human hepatoma is linked to activation of insulin‐like growth factor and notch signaling mechanisms

Aspartyl‐(Asparagyl)‐β‐hydroxylase (AAH) is overexpressed in various malignant neoplasms, including hepatocellular carcinomas (HCCs). The upstream regulation of AAH and its functional role in Notch‐mediated signaling and motility in HCC cells was accessed. The mRNA transcript levels of AAH, insulin receptor substrate (IRS), insulin and insulin‐like growth factor (IGF) receptors and polypeptides, Notch, Jagged, and HES were measured in 15 paired samples of HCC and adjacent HCC‐free human liver biopsy specimens using real‐time quantitative RT‐PCR and Western blot analysis. Overexpression of AAH was detected in 87% of the HCC relative to the paired HCC‐free liver tissue. IRS‐1, IRS‐2, and IRS‐4 were each overexpressed in 80% of the HCC samples, and IGF‐I and IGF‐2 receptors were overexpressed in 40% and 100% of the HCCs, respectively. All HCC samples had relatively increased levels of Notch‐1 and HES‐1 gene expression. Overexpression of AAH led to increased levels of Notch, and co‐immunoprecipitation experiments demonstrated a direct interaction between AAH and Notch as well as its ligand Jagged. In conclusion, contributions to the malignant phenotype of HCC is due to activation of IGF‐I and IGF‐II signaling that results in over‐expression of both AAH and Notch. The functional role of AAH in relation to cell motility has been linked to increased activation of the Notch signaling pathway. (HEPATOLOGY 2006;44:446–457.)