Correlation of Nr4a2 expression with the neuron progenitors in adult zebrafish brain.

Our previous study showed that although Nr4a2b transcripts have little co-localization with tyrosine hydroxylase (TH) in the posterior tuberculum area, knockdown of Nr4a2 caused a decrease in the number of TH-positive (TH(+)) neurons in the posterior tuberculum area. It suggests that Nr4a2 expression in the progenitors may play an important role in regulating differentiation rather than survival of TH(+) progenitors in the posterior tuberculum area during early zebrafish embryogenesis. In this study, we determined the correlation between TH and Nr4a2 in adult zebrafish brain and found that Nr4a2b was co-localized with the spindle-shaped TH(+) cells in the posterior tuberculum area and some small round TH(+) cells in the pretectum area, but not with large pear-shaped TH(+) cells in adult zebrafish diencephalon. In the pretectum area, Nr4a2(+) cells were localized next to the dorsal side of TH(+) cells. Furthermore, we demonstrated that Nr4a2 was co-expressed with nestin in the progenitors of pretectum area and caudal periventricular hypothalamic zones with a lateral symmetry pattern beside the diencephalic ventricle. Co-expression of Nr4a2 and nestin in these areas was remarkably declined with aging. These findings indicate that Nr4a2 is expressed in the neuronal progenitors and plays a crucial role in the differentiation process of dopamine neuron from the stem cell. The change in Nr4a2 expression with aging suggests its possible association with neurodegenerative diseases.

Collective roles of molecular chaperones in protein degradation pathways associated with neurodegenerative diseases.

The homeostasis of the protein synthesis and degradation is crucial for cell survival. Most age-related neurodegenerative diseases are characterized by accumulation of aberrant protein aggregates in affected brain regions. The principal routes of intracellular protein metabolism are the ubiquitin proteasome system (UPS) and the autophagy-lysosome pathway (ALP). They collaborate to degrade wasted proteins and interact each other to cope with the pathological conditions, in which molecular chaperones play collective roles by assisting the protein targeting to the proteasome or autophagy. It is known that intracellular protein degradation functions are decreased with aging in many tissues and organs. Failure to perform their functions could underlie the inability of cells to adapt to stress conditions, lead to accelerated course of misfolding protein deposit and the inclusion body formation, and eventually result in neurodegeneration.One of the functions of the molecular chaperones is to help the new synthesized or the misfolding toxic proteins fold to their native and nontoxic formation, as our common conception. In this review, we analyze the recent perceptions and findings of molecular chaperones biology in the two degradation pathways and their pathological attribution in several neurodegenerative diseases such as Parkinson's disease (PD), Alzheimer's disease (AD), Huntington's disease (HD), and others. It is worthy noticing that some of the HSPs can not only block the protein aggregation in the early stages, but also have promising effect on attenuating the formation of fibrils. Further more, when the degradation pathways are too weak to degrade all the toxic soluble proteins, molecular chaperones can also help to sequenstrate the toxic proteins into inclusion bodies. However, whether it is good or bad is still unclear. Therefore, the study of HSPs might shed new light on not only the mechanisms of protein synthesis and degradation, but also the possible therapeutic targets of fibril formation associating diseases.

Nr4a2 is essential for the differentiation of dopaminergic neurons during zebrafish embryogenesis.

Nr4a2 is a member of the orphan nuclear receptor gene superfamily, which has been found to be critical for the development and maintenance of mesencephalic dopaminergic (DA) neurons. To uncover the molecular mechanisms by which Nr4a2 contributes to the development of DA neurons, we have applied zebrafish to study the topographic distribution of nr4a2b transcripts, as well as its correlation with neuronal progenitor marker (neurogenin 1) and DA neuron markers (tyrosine hydroxylase, TH and DA transporter, DAT) during neurogenesis. Our studies showed that although nr4a2b transcripts did not co-localize with TH and DAT transcripts in the posterior tuberculum (PT area), knockdown of Nr4a2 resulted in a significant decrease of TH(+) and DAT(+) DA neurons in the PT area, accompanied by a reduction of DA transmitter, which were partially rescued by the injection of mouse Nr4a2 mRNA. Surprisingly, the number of nr4a2b(+) cells in Nr4a2-deficient embryos was increased by 1.6 fold. These results suggest that Nr4a2 may play an important role in the differentiation and maturation rather than the survival of DA progenitors in the PT area during zebrafish early embryogenesis.

Are heat shock proteins therapeutic target for Parkinson's disease?

Heat shock proteins (HSPs), known as molecular chaperone to assist protein folding, have recently become a research focus in Parkinson's disease (PD) because the pathogenesis of this disease is highlighted by the intracellular protein misfolding and inclusion body formation. The present review will focus on the functions of different HSPs and their protective roles in PD. It is postulated that HSPs may serve as protein folding machinery and work together with ubiquitin-proteasome system (UPS) to assist in decomposing aberrant proteins. Failure of UPS is thought to play a key role in the pathogenesis of PD. In addition, HSPs may possess anti-apoptotic effects and keep the homeostasis of dopaminergic neurons against stress conditions. The critical role of HSPs and recent discovery of some novel HSPs inducers suggest that HSPs may be potential therapeutic targets for PD and other neurodegenerative disorders.

Estrogen provides neuroprotection against activated microglia-induced dopaminergic neuronal injury through both estrogen receptor-alpha and estrogen receptor-beta in microglia.

Estrogen provides neuroprotection against neurodegenerative diseases, including Parkinson's disease. Its effects may stem from interactions with neurons, astrocytes, and microglia. We demonstrate here in primary cultures of rat mesencephalic neurons that estrogen protects them from injury induced by conditioned medium obtained from lipopolysaccharide (LPS)-activated microglia. LPS-induced nitrite production and tumor necrosis factor-alpha up-regulation in microglia were blocked by estrogen pretreatment. Estrogen neuroprotection was related to microglial activation of estrogen receptors (ERs), insofar as the protective effect of the microglia-conditioned medium was overridden by pretreatment of microglia with the ER antagonist ICI 182,780. On the other hand, the specific ERalpha antagonist, MPP dihydrochloride, only partially blocked the effects of estrogen, suggesting that estrogen protection was mediated via both ERalpha and ERbeta. LPS treatment did not change ERalpha mRNA levels in microglia, astrocytes, and neurons, but it up-regulated ERbeta mRNA levels in microglia and astrocytes. Similarly, increased ERbeta protein levels were detected in LPS-activated microglia. More interesting was that immunocytochemical analysis revealed that ERbeta was localized in the cytoplasm of microglia and in the cell nucleus of astrocytes and neurons. In summary, our results support the notion that estrogen inhibits microglial activation and thus exhibits neuroprotective effects through both ERalpha and ERbeta activation. The cytoplasm location of microglial ERbeta suggests the possible involvement of nonclassical effects of estrogen on microglia. Changes in microglial ERbeta expression levels may modulate such effects of estrogen.