The idea that CNS ramified microglia are quiescent has been challenged by studies that show that microglia without the classic signs of activation can be phagocytic and appear with shorter, thicker ramifications. These semi-activated cells may constitute a form of microglia that has not been previously recognized in neuropathological conditions and may contribute to the pathology and dysfunction in these disorders. This study investigated the expression of CD 163, a cell surface marker whose normal expression is restricted to monocytes/macrophages, in cases of HIV or SIV encephalitis (HIVE/SIVE), Alzheimer disease, and variant Creutzfeldt-Jakob disease. In HIVE/SIVE, in addition to reacting with CNS macrophages, CD163 antibody staining was shown to highlight ramified microglia. Such reactivity was especially notable in grey matter ramified microglia and was greater than that of another typically used marker, HLA-DR. CD163 expression was only observed in infected/affected tissue, in contrast to that shown with another microglia marker, GLUT5, which has recently been shown to identify all microglia regardless of disease state. Although activated microglia were present in the other disorders, as evidenced by strong HLA-DR expression, there was very little CD163 immunoreactivity. The activation state identified by CD163 has not been previously recognized and may have a positive or negative impact on neuronal damage shown in HIV-associated dementia.

Synucleins are small proteins associated with neurodegenerative diseases and some forms of cancer. Most studies of this group of proteins have been directed to the elucidation of their role in the brain and their connection to the formation of depositions in brain tissues. Here we describe the localization of different types of synucleins in ocular tissues. By Western blot analysis, all members of the synuclein family are found in the retina and optic nerve, where their relative ratio varies. The data on immunohistochemical staining show that different members of the synuclein family have different localizations in ocular tissues. Alpha-synucleins and beta-synucleins are present predominantly in the inner plexiform layer, whereas gamma-synuclein is in the nerve fiber layer. In transgenic mice overexpressing alpha-synuclein, a different pattern of localization depending on the promoter used for the expression was observed. In Alzheimer's disease patients, immunohistochemical staining for gamma-synuclein revealed the loss of immunoreactivity in the nerve fiber layer and the nerve fiber layer and the appearance of immunopositive cells in or near the outer nuclear layer. We conclude that, in mature eyes, synucleins are present predominantly in the retina and optic nerve, and the immunoreactivity of gamma-synuclein changes specifically in the retina of Alzheimer's disease patients. In transgenic mice overexpressing alpha-synuclein, immunopositive deposits in the optic nerve and accumulation of immunoreactivity in specific retinal cells were found.

The accumulation of aggregated ␣-synuclein is thought to contribute to the pathogenesis of Parkinson's disease. Recent studies indicate that aggregated ␣-synuclein binds to S6, a component of the 19 S subunit in the 26 S proteasome and inhibits 26 S proteasomal degradation, both ubiquitin-independent and ubiquitindependent. The IC 50 of aggregated ␣-synuclein for inhibition of the 26 S ubiquitin-independent proteasomal activity is ϳ1 nM. ␣-Synuclein has two close homologues, termed ␤-synuclein and ␥-synuclein. In the present study we compared the effects of the three synuclein homologues on proteasomal activity. The proteasome exists as a 26 S and a 20 S species, with the 26 S proteasome containing the 20 S core and 19 S cap. Monomeric ␣-and ␤-synucleins inhibited the 20 S and 26 S proteasomal activities only weakly, but monomeric ␥-synuclein strongly inhibited ubiquitin-independent proteolysis. The IC 50 of monomeric ␥-synuclein for the 20 S proteolysis was 400 nM. In monomeric form, none of the three synuclein proteins inhibited 26 S ubiquitin-dependent proteasomal activity. Although ␤-synuclein had no direct effect on proteasomal activity, co-incubating monomeric ␤-synuclein with aggregated ␣-synuclein antagonized the inhibition of the 26 S ubiquitin-independent proteasome by aggregated ␣-synuclein when added before the aggregated ␣-synuclein. Co-incubating ␤-synuclein with ␥-synuclein had no effect on the inhibition of the 20 S proteasome by monomeric ␥-synuclein. Immunoprecipitation and pull-down experiments suggested that antagonism by ␤-synuclein resulted from binding to ␣-synuclein rather than binding to S6. Pull-down experiments demonstrated that recombinant monomeric ␤-synuclein does not interact with the proteasomal subunit S6, unlike ␣-synuclein, but ␤-synuclein does bind ␣-synuclein and competes with S6 for binding to ␣-synuclein. Based on these data, we hypothesize that the ␣-and ␥-synucleins regulate proteasomal function and that ␤-synuclein acts as a negative regulator of ␣-synuclein.

No abstract

No abstract