Parkin loss of function contributes to RTP801 elevation and neurodegeneration in Parkinson's disease.

Mutations in the PARK2 gene are associated with an autosomal recessive form of juvenile parkinsonism (AR-JP). These mutations affect parkin solubility and impair its E3 ligase activity, leading to a toxic accumulation of proteins within susceptible neurons that results in a slow but progressive neuronal degeneration and cell death. Here, we report that RTP801/REDD1, a pro-apoptotic negative regulator of survival kinases mTOR and Akt, is one of such parkin substrates. We observed that parkin knockdown elevated RTP801 in sympathetic neurons and neuronal PC12 cells, whereas ectopic parkin enhanced RTP801 poly-ubiquitination and proteasomal degradation. In parkin knockout mouse brains and in human fibroblasts from AR-JP patients with parkin mutations, RTP801 levels were elevated. Moreover, in human postmortem PD brains with mutated parkin, nigral neurons were highly positive for RTP801. Further consistent with the idea that RTP801 is a substrate for parkin, the two endogenous proteins interacted in reciprocal co-immunoprecipitates of cell lysates. A potential physiological role for parkin-mediated RTP801 degradation is indicated by observations that parkin protects neuronal cells from death caused by RTP801 overexpression by mediating its degradation, whereas parkin knockdown exacerbates such death. Similarly, parkin knockdown enhanced RTP801 induction in neuronal cells exposed to the Parkinson's disease mimetic 6-hydroxydopamine and increased sensitivity to this toxin. This response to parkin loss of function appeared to be mediated by RTP801 as it was abolished by RTP801 knockdown. Taken together these results indicate that RTP801 is a novel parkin substrate that may contribute to neurodegeneration caused by loss of parkin expression or activity.

Inflammatory processes in the aging mouse brain: participation of dendritic cells and T-cells.

Increased inflammatory activity accompanies normal brain aging. Whereas local glial cell activation, upregulation of cytokines and transcriptional alterations of inflammatory factors are well-documented components of this complex process, it is unclear whether blood-derived leukocytes also contribute to the age-related changes. The present study of normal mouse brain applied single and double immunohistochemistry to reveal for the first time that dendritic cells (DCs) and T-cells are important components of the general increased inflammatory state, which was documented by upregulation of reactive astrocytes and microglia. B-cells and mast cells do not contribute to this inflammatory response. Dendritic cells and T-cells appeared at about 12 months of age and their number increased further during aging. In 24-month-old animals a dense network of DCs interspersed with T-cells pervaded brain areas where substantial histopathological changes and a volumetric decrease have been reported. All CD11c(+)-DCs displayed the typical dendritic shape and expressed the myeloid specific integrin CD11b. Some of the DCs were also CD205- or MIDC8-immunoreactive and expressed the cathepsins S and X. The emergence and prolonged presence of leukocytes might indicate a crucial role of these cells in local, age-related immune responses in the brain.

Expression of MUPP1 protein in mouse brain.

Localizing cell surface receptors to specific subcellular sites can be crucial for proper functioning. PDZ proteins apparently play central roles in such protein localizations. 5-HT(2C) receptors have previously been shown to interact with MUPP1, a multi PDZ domain protein, in heterologous systems and in rat choroid plexus. We now report the generation and characterization of two independent MUPP1 antisera, which recognise distinct areas of the mouse brain in agreement with previous in-situ hybridization studies. Our results indicate that MUPP1 immunoreactivity co-localizes with 5-HT(2A) or 5-HT(2C) receptor expression in all regions of the mouse brain, including the choroid plexus where 5-HT(2C) receptors are highly enriched.

A genome survey indicates a possible susceptibility locus for bipolar disorder on chromosome 22.

Bipolar disorder or manic depressive illness is a major psychiatric disorder that is characterized by fluctuation between two abnormal mood states. Mania is accompanied by symptoms of euphoria, irritability, or excitation, whereas depression is associated with low mood and decreased motivation and energy. The etiology is currently unknown; however, numerous family, twin, and adoption studies have argued for a substantial genetic contribution. We have conducted a genome survey of bipolar disorder using 443 microsatellite markers in a set of 20 families from the general North American population to identify possible susceptibility loci. A maximum logarithm of odds score of 3.8 was obtained at D22S278 on 22q. Positive scores were found spanning a region of nearly 32 centimorgans (cM) on 22q, with a possible secondary peak at D22S419. Six other chromosomal regions yielded suggestive evidence for linkage: 3p21, 3q27, 5p15, 10q, 13q31-q34, and 21q22. The regions on 22q, 13q, and 10q have been implicated in studies of schizophrenia, suggesting the possible presence of susceptibility genes common to both disorders.