Esther Hormiga Pérez

BDNF Up‐Regulates TrkB Protein and Prevents the Death of CA1 Neurons Following Transient Forebrain Ischemia

The neurotrophin family of growth factors, which includes Nerve Growth Factor (NGF), Brain‐Derived Neurotrophic Factor (BDNF), Neurotrophin‐3 (NT3) and Neurotrophin‐4/5 (NT4/5) bind and activate specific tyrosine kinase (Trk) receptors to promote cell survival and growth of different cell populations. For these reasons, growing attention has been paid to the use of neurotrophins as therapeutic agents in neurodegeneration, and to the regulation of the expression of their specific receptors by the ligands. BDNF expression, as revealed by immunohistochemistry, is found in the pre‐subiculum, CA1, CA3, and dentate gyrus of the hippocampus. Strong TrkB immunoreactivity is present in most CA3 neurons but only in scattered neurons of the CA1 area. Weak TrkB immunoreactivity is found in the granule cell layer of the dentate gyrus. Unilateral grafting of BDNF‐transfected fibroblasts into the hippocampus resulted in a marked increase in the intensity of the immunoreaction and in the number of TrkB‐immunoreactive neurons in the granule cell layer of the dentate gyrus, pre‐subiculum and CA1 area in the vicinity of the graft. No similar effects were produced after the injection of control mock‐transfected fibroblasts. Delayed cell death in the CA1 area was produced following 5 min of forebrain ischemia in the gerbil. The majority of living cells in the CA1 area at the fourth day were BDNF/TrkB immunoreactive. Unilateral grafting of control mock‐transfected or BDNF fibroblasts two days before ischemia resulted in a moderate non‐specific protection of TrkB‐negative, but not TrkB‐positive cells, in the CA1 area of the grafted side. This finding is in line with a vascular and glial reaction, as revealed, by immunohistochemistry using astroglial and microglial cell markers. This astroglial response was higher in the grafted side than in the contralateral side in ischemic gerbils, but no differences were seen between BDNF‐producing and non‐BDNF‐producing grafts. However, grafting of BDNF‐producing fibroblasts two days before ischemia significantly and specifically prevented nerve cells from dying in the CA1 area of the ipsilateral hippocampus. Cell survival was associated with increased TrkB immunoreactivity as the majority of living cells were TrkB immunoreactive. Thus, our results show that BDNF is able to up‐regulate the expression of TrkB in control and pathological states, and that BDNF prevention of neuronal death following transient forebrain ischemia is associated with increased expression of its specific receptor.

Aquaporin expression in the cerebral cortex is increased at early stages of Alzheimer disease

Abnormalities in the cerebral microvasculature are common in Alzheimer disease (AD). Expression levels of the water channels aquaporin 1 and aquaporin 4 (AQP1, AQP4) were examined in AD cases by gel electrophoresis and Western blotting, and densitometric values normalized with beta-actin were compared with corresponding values in age-matched controls processed in parallel. In addition, samples of cases with Pick disease (PiD) were examined for comparative purposes. A significant increase in the expression levels of AQP1 was observed in AD stage II (following Braak and Braak classification). Individual variations were seen in advanced stages which resulted in non-significant differences between AD stages V-VI and age-matched controls. No differences in AQP1 levels were observed between familial AD cases (FAD, all of them at advanced stages) and corresponding age-matched controls. Immunohistochemistry showed increased AQP1 in astrocytes at early stages of AD. Double-labelling immunofluorescence and confocal microscopy disclosed AQP1 immunoreactivity at the cell surface of astrocytes which were recognized with anti-glial fibrillary acidic protein antibodies. No differences in the levels of AQP4 were observed in AD, FAD and PiD when compared with corresponding controls. These results indicate abnormal expression of AQP1 in astrocytes in AD, and they add support to the idea that abnormal regulation of mechanisms involved in the control of water fluxes occurs at early stages in AD.

Abnormal levels of prohibitin and ATP synthase in the substantia nigra and frontal cortex in Parkinson's disease

Prohibitin and ATP synthase protein levels were examined in the substantia nigra and frontal cortex (area 8) in five cases of Parkinsons disease (PD), five cases of dementia with Lewy bodies pure form (pDLB), five cases of early Alzheimers disease (AD stage IIA, B), nine cases with advanced AD (stages V/VIC), and nine controls. A significant reduction of prohibitin and ATP synthase was observed in the substantia nigra in PD cases. In contrast, increased prohibitin and ATP synthase levels were found in the frontal cortex in PD, and increased prohibitin but not ATP synthase in the frontal cortex in pDLB. Superoxide dismutase 2 (SOD2) expression levels were also increased in the frontal cortex in PD and pDLB. No modifications in prohibitin and ATP synthase levels were found in the frontal cortex in sporadic AD. These findings demonstrate disease-specific modifications in the expression of mitochondrial-related proteins in the frontal cortex at stages of PD in which there is no alpha-synuclein aggregation in the form of Lewy bodies and Lewy neurites in this area. These findings emphasize the presence of mitochondrial modifications before the appearance of histological hallmarks of PD, and point to the possibility of a more extended molecular pathology in PD than currently accepted.