Veronica Lifshitz

Neuroprotective and neurotoxic properties of glial cells in the pathogenesis of Alzheimer's disease

•  Introduction •  Innate immune response in the AD brain ‐  Microglia ‐  Astrocyte •  Glial cells mediate the peripheral immune response in AD ‐  Glial cell interaction with endothelial cells ‐  Glial cell interaction with T cells •  Glial cell activation as a therapeutic target in AD •  Conclusion

Tumor-Microenvironment Interactions The Fucose-Generating FX Enzyme Controls Adhesive Properties of Colorectal Cancer Cells

Extravasation of tumor cells is a pivotal step in metastasis formation. This step is initiated by an interaction of extravasating tumor cells with endothelial cells. Among the molecules mediating tumor-endothelium interactions are selectins and their fucosylated ligands. In a previous study, we demonstrated that the fucose-generating FX enzyme regulates the expression of selectin ligands by B and T lymphocytes and by head and neck squamous cell carcinoma cells. It was also shown that the FX enzyme regulated important interaction parameters between these cancer cells and endothelial cells. The present study was aimed to determine whether the FX enzyme controls adhesive interactions between colorectal cancer cells and endothelial cells. The results clearly indicate that this is indeed the case. Overexpressing the FX enzyme by the transfer of FX cDNA to low FX-expressing colorectal cancer cells resulted in an increased adhesive capacity of the transfectants to activated endothelial cells and to recombinant E-selectin. Down-regulating FX levels in colorectal cancer cells expressing high levels of endogenous FX by transfection with small-interfering RNA resulted in a down-regulated expression of the selectin ligand sialyl Lewis-a and a decrease in the adhesive capacity of the transfectants to activated endothelial cells and to recombinant E-selectin. These transfection experiments also indicated that manipulating the levels of the FX enzyme affected global cellular fucosylation and altered the interaction of colorectal cancer cells with some extracellular matrix components such as fibronectin. We also found that highly metastatic colorectal cancer variants express higher levels of FX and of sialyl Lewis-a than low metastatic variants originating in the same tumors. These results lead us to hypothesize that the FX enzyme controls the capacity of colorectal cancer to extravasate and form metastasis. If this hypothesis will be confirmed the FX enzyme could become a target molecule for metastasis prevention.

Immunotherapy of cerebrovascular amyloidosis in a transgenic mouse model.

Cerebrovascular amyloidosis is caused by amyloid accumulation in walls of blood vessel walls leading to hemorrhagic stroke and cognitive impairment. Transforming growth factor-β1 (TGF-β1) expression levels correlate with the degree of cerebrovascular amyloid deposition in Alzheimers disease (AD) and TGF-β1 immunoreactivity in such cases is increased along the cerebral blood vessels. Here we show that a nasally administered proteosome-based adjuvant activates macrophages and decreases vascular amyloid in TGF-β1 mice. Animals were nasally treated with a proteosome-based adjuvant on a weekly basis for 3 months beginning at age 13 months. Using magnetic resonance imaging (MRI) we found that while control animals showed a significant cerebrovascular pathology, proteosome-based adjuvant prevents further brain damage and prevents pathological changes in the blood-brain barrier. Using an object recognition test and Y-maze, we found significant improvement in cognition in the treated group. Our findings support the potential use of a macrophage immunomodulator as a novel approach to reduce cerebrovascular amyloid, prevent microhemorrhage, and improve cognition.

TGF-β1 affects endothelial cell interaction with macrophages and T cells leading to the development of cerebrovascular amyloidosis.

Astrocyte-endothelial cell (EC) interactions play a major role in the function of the neurovascular unit. Dysfunction in these interactions may lead to amyloid accumulation in blood vessels and may cause microhemorrhage and cognitive impairment. Transforming growth factor-β1 (TGF-β1) expression levels positively correlate with the degree of cerebrovascular amyloid in Alzheimers disease (AD) cases. Furthermore, expression of TGF-β1 driven by the GFAP promoter in mice leads to an age-related deposition of amyloid, such as β-amyloid (Aβ), around cerebral blood vessels. Here, we demonstrate that TGF-β1 affects the cross talk between EC and inflammation, leading to a reduction in macrophage activity as measured by protein levels and migration ability. Changes in EC secreted factors following TGF-β1 stimulation also affect CD4(+) T cell activation, as shown by a reduction in the levels of IFN-γ. Moreover, while medium from EC can stimulate macrophages to clear insoluble cerebrovascular amyloid from an AD mouse brain, pre-incubation of EC with TGF-β1 reduces the ability of EC to affect macrophage activity. Our findings support the importance of cross talk between EC, macrophages and CD4(+) T cells in preventing cerebrovascular amyloid deposition. Understanding EC-immune system interactions may pave the way to new therapeutic approaches for cerebrovascular amyloidosis diseases.

The involvement of the sLe-a selectin ligand in the extravasation of human colorectal carcinoma cells

The extravasation of tumor cells is a pivotal stage in the formation of hematogenous metastasis. An interaction of selectins expressed on endothelial cells and selectin ligands expressed by tumor cells has been implicated to play a role in extravasation. In the present study we used a human-mouse model to prove the hypothesis that the selectin ligand sialyl Lewis-a (sLe-a) is indeed involved in the in vivo extravasation of colorectal carcinoma (CRC) cells. The results indicated that highly metastatic CRC cells expressing high levels of sLe-a extravasate more efficiently than non-metastatic CRC cells expressing low levels of sLe-a. It was also demonstrated that down regulating the expression levels of sLe-a in CRC cells by genetic manipulations, significantly reduced CRC extravasation. Non-specific effects of these manipulations were ruled out. The results of this study indicate that the arrest and adhesion of CRC cells, and possibly of other types of cancer cells as well, to endothelium depend on the expression of the selectin ligand sLe-a by the tumor cells.

Astrocyte Dysfunction Associated with Cerebellar Attrition in a Nijmegen Breakage Syndrome Animal Model

Nijmegen breakage syndrome (NBS) is a genomic instability disorder caused by hypomorphic mutations in the Nbs1 gene. When Nbs1 is conditionally inactivated in the central nervous system of mice (Nbs1-CNS-Δ), they suffer from severe cerebellar atrophy, ataxia, and white matter damage. Here, we show that conditional inactivation of the murine Nbs1 gene has a profound effect on the integrity and the functionality of the glial cells, which suggests their crucial role in the pathogenesis of NBS. Interestingly, in Nbs1-CNS-Δ mice, the dramatic reduction in the numbers of Purkinje and granule cells was also linked to a reduction of microglial cells but not to astrocytes (GFAP+), suggesting an impairment in astrocytic functionality. Nbs1 levels were dramatically reduced in adult astrocyte isolated from Nbs1-CNS-Δ mice, suggesting a major role in cerebellar pathology. In order to investigate the effect of Nbs1 deletion on astrocyte activity, we investigated glutamine synthetase levels in astrocyte and discovered 40% reduction as compared to WT. Furthermore, we found a significant reduction in the secretion of neurotrophic factors, such as brain-derived neurotrophic factor and neurotrophin 3. Understanding the contribution of malfunctioning astrocytes to the etiology of NBS can elucidate a hitherto unknown aspect of this disorder.

Insulin-degrading enzyme deficiency accelerates cerebrovascular amyloidosis in an animal model

Cerebrovascular amyloidosis (CA) may result in intraparenchymal bleeding and cognitive impairment. It was previously shown that transforming growth factor-β1 (TGF-β1) expression under an astrocyte promoter resulted in congophilic vascular deposits and vascular pathology. A reduction in insulin-degrading enzyme (IDE) activity was previously suggested to play a role in the accumulation of congophilic vascular deposits in the microvasculature of Alzheimers disease (AD) cases. Here, we aim to investigate the link between TGF-β1 and IDE activity in the development of CA. We found that TGF-β1 can reduce IDE expression in a mouse brain endothelial cell line (ECs). Furthermore, we discovered that IDE activity in the brains of TGF-β1 transgenic (Tg) mice was significantly reduced compared with that of the control mice in an age-dependent manner. In addition, TGF-β1/IDE(-/-) mice showed significantly greater levels of cerebrovascular pathology compared with TGF-β1 mice. We have previously shown that 16-month-old TGF-β1 mice have a significant reduction in synaptophysin protein levels, which may lead to cognitive impairment. Here we discovered a significant reduction in synaptophysin protein already at the age of seven in the hippocampus of TGF-β1/IDE(-/-) mice compared with TGF-β1 mice. Further investigation of TGF-β1-mediated IDE activity in ECs may provide useful therapeutic intervention targets for cerebrovascular diseases such as CA.