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Mitochondria are highly dynamic organelles along with continuous fission, fusion and transport. Mitochondria dynamics not only control their morphology and number, but also affect their distribution and function. Mitochondria are also the basis for neuronal survival and involved in numbers of neuronal functions. Mitochondrial dynamic abnormalities accompanied by dysfunction have been reported in a wide range of neurological disorders, especially neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS) and Huntington’s disease (HD). In this review, we will briefly describe the molecular mechanisms of mitochondrial dynamics and their critical roles in regulating neuronal function. We will also review the studies about mitochondrial dynamic abnormalities found in neurodegenerative diseases, and discuss the possibility of targeting mitochondrial dynamics as a likely novel therapeutic strategy for treating neurodegenerative diseases.

Mutations in PINK1 (PTEN-induced putative kinase 1) are associated with autosomal recessive early-onset Parkinson's disease. Full-length PINK1 (PINK1-l) has been extensively studied in mitophagy; however, the functions of the short form of PINK1 (PINK1-s) remain poorly understood. Here, we report that PINK1-s is recruited to ribosome fractions after short-term inhibition of proteasomes. The expression of PINK1-s greatly inhibits protein synthesis even without proteasomal stress. Mechanistically, PINK1-s phosphorylates the translation elongation factor eEF1A1 during proteasome inhibition. The expression of the phosphorylation mimic mutation eEF1A1S396E rescues protein synthesis defects and cell viability caused by PINK1 knockout. These findings implicate an important role for PINK1-s in protecting cells against proteasome stress through inhibiting protein synthesis.

Aggrephagy, the aggresome-related protein degradation system, represents a protective cellular response to shuttle misfolded proteins into the microtubule-organizing center for degradation through the autophagic pathway during stress conditions, including heat shock, oxidative stress and proteasome inhibition. In response to proteasome failure, many genes are transcriptionally activated to facilitate ubiquitinated proteins to be cleared via the aggrephagy pathway. Although many regulators involved in aggresome formation have been identified, the mechanism how transcriptional activation promotes aggresome formation remains unknown. Here, we have demonstrated that nuclear factor erythroid 2-related factor 2 (Nrf2) accumulated in the nucleus and activated the transcription of sequestosome-1 (p62) during proteasome inhibition in 293 cells. Loss of Nrf2 resulted in failure of aggresome formation and cell death; whereas overexpression of p62 alleviated Nrf2 knockdown-induced aggresome formation defects and promoted cell survival. Notably, blocking Nrf2 activation using a p38/MAPK inhibitor prevented proteasome inhibitor-induced aggresome formation. These findings suggested that Nrf2 may be a critical regulator of aggresome formation, which protects cells from proteasome dysfunction-induced stress.

The study was aimed to provide better understanding on how plant cultivation affects Se distribution, transformation, and bioavailabilty in soil treated with exogenous selenite or selenate. Pak choi (Brassica chinensis L.) was planted in loess soil (Eum-Orthic Anthrosol) spiked with different concentrations of exogenous selenite or selenate. Soil samples were collected from all pots before planting and after harvest to determine Se fraction and speciation. Se concentrations in pak choi were measured after harvest. The influence of pak choi on Se distribution differed among various soil fractions in selenite- or selenate-treated soil. Se distribution and speciation remained constant between selenite-treated soil after harvest and before planting, and Se mainly existed as exchangeable Se(IV) (59.8 %–61.6 %). By contrast, a considerable transformation of soluble Se(VI) to exchangeable Se(IV) was observed in selenate-treated soil. In addition, I R values increased, which quantitatively described the relative binding intensity of Se with soil, and MF values (mobility factor) decreased under selenate treatment. Changes in these two parameters indicated the reduced bioavailability of Se in soil after plant cultivation. Moreover, soluble Se(VI) content, organic Se content in soil, and Se concentrations in pak choi shoots and roots exhibited significant correlation in selenate-treated soil. Furthermore, the contents of soluble and exchangeable Se(IV) in selenite-treated soil were significantly correlated with Se concentration in pak choi roots, whereas soluble Se(VI) content was correlated with Se concentration in the shoots. Plant cultivation decreased Se bioavailability in selenate-treated soil but only minimally influenced the bioavailability of this element in selenite-treated soil. Moreover, soluble Se(VI) content was considered a suitable indicator for assessment of soil Se bioavailability. Organic matter-bound Se also can be a source of available Se in selenate-treated soil, but only exchangeable Se(IV) content can be used to assess Se availability in selenite-treated soil.

The ubiquitin ligase Parkin and autophagic adapter protein p62 are known to function in a common pathway controlling mitochondrial autophagy (mitophagy). However, the evidence supporting that p62 is directly recruited by ubiquitinated proteins remains undetermined. Here, we demonstrate that mitochondrial fission factor (Mff) associates with Parkin and carbonyl cyanide m-chlorophenyl hydrazone treatment significantly increases the affinity of Parkin with Mff. After recruitment to depolarized mitochondria, Parkin mediates poly-ubiquitination of Mff at lysine 251. Replacement of lysine 251 by arginine (K251R) totally abrogates Parkin-stimulated ubiquitination of Mff. Subsequently, the ubiquitinated Mff promotes its association with p62. Mff knockout interferes with p62 translocation to damaged mitochondria. Only re-transfection of Mff WT, but not K251R mutant, rescues this phenotype. Furthermore, loss of Mff results in failure of Parkin translocation and final clearance of damaged mitochondria. Thus, our data reveal functional links among Mff, p62, and the selective autophagy of mitochondria, which are implicated in the pathogenesis of neurodegeneration diseases.

Selenate and selenite are two main kinds of inorganic selenium (Se) sources in soil, but these substances can pose threats to the environment. Phytoextraction is an emerging technology to remove Se from polluted soils by using a hyper-accumulator. In this study, a pot experiment was conducted to investigate Se phytoextraction potential of pak choi (Brassica chinensis L.) and to determine the effects of Se on growth and Se accumulation of pak choi under successive planting conditions (four crops). Results showed that Se concentration in pak choi shoots significantly increased as selenate and selenite rates increased. Se concentration increased in successive crops on soil treated with selenite; by contrast, Se concentration decreased in crops on soil treated with selenate. Se concentrations of pak choi on soil treated with selenate were higher than those on soil treated with selenite. The maximum Se accumulations amount in crops on selenite- and selenate-treated soil were 7818 and 8828 μg · pot(-1), respectively. High bioconcentration factor (BCF) values indicated that pak choi could accumulate more Se from Se-contaminated soil. The Se phytoextraction efficiency of pak choi increased under successive planting conditions in selenite and selenate treatments; the maximum Se phytoextraction efficiencies of four successive crops of pak choi on selenite- and selenate-treated soil were 4.91 and 31.90 %, respectively. These differences between selenate and selenite treatments were attributed to the differences in Se forms in soil. Total and available Se contents in soil decreased significantly during repeated planting crops on soil treated with selenate; conversely, total and available Se contents decreased slightly in crops on soil treated with selenite. These results suggested that pak choi could highly tolerate and accumulate Se. Thus, pak choi may remove Se from contaminated soil; indeed, pak choi can be used in the phytoextraction of Se in polluted soil.

The aim of this study is to determine the regulatory mechanism of PTEN-induced putative kinase protein 1 short isoform (PINK1S) in cytoplasm. By co-immunoprecipitation (Co-IP) assay, we identified that PINK1S interacted with the beta regulatory subunit of Casein Kinase 2 (CK2β), but not with the catalytic subunits CK2α1 and CK2α2. Furthermore, cells were transfected with PINK1S and CK2β, and then PINK1S was purified by immunoprecipitation. After detecting the phosphorylated proteins by Phos-tag Biotin, we found that CK2β overexpression increased auto-phosphorylation of PINK1S. Finally, we generated CK2β knockdown cell lines by RNA interference. Purified PINK1S from CK2β knockdown cells significantly reduced its auto-phosphorylation compared with control cells. These results suggested that CK2β functions as a regulatory subunit of PINK1S kinase complex promoted its activation by self-phosphorylation.

During proteasomal stress, cells can alleviate the accumulation of polyubiquitinated proteins by targeting them to perinuclear aggresomes for autophagic degradation, but the mechanism underlying the activation of this compensatory pathway remains unclear. Here we report that PINK1-s, a short form of Parkinson disease (PD)-related protein kinase PINK1 (PTEN induced putative kinase 1), is a major regulator of aggresome formation. PINK1-s is extremely unstable due to its recognition by the N-end rule pathway, and tends to accumulate in the cytosol during proteasomal stress. Overexpression of PINK1-s induces aggresome formation in cells with normal proteasomal activities, while loss of PINK1-s function leads to a significant decrease in the efficiency of aggresome formation induced by proteasomal inhibition. PINK1-s exerts its effect through phosphorylation of the ubiquitin-binding protein SQSTM1 (sequestosome 1) and increasing its ability to sequester polyubiquitinated proteins into aggresomes. These findings pinpoint PINK1-s as a sensor of proteasomal activities that transduces the proteasomal impairment signal to the aggresome formation machinery.

PTEN-induced putative kinase 1 (PINK1), a Parkinson's disease (PD)-related protein, has two isoforms, the mitochondria-localized full-length isoform PINK1FL and the cytoplasm-localized short isoform PINK1-cyto. Studies have suggested that PINK1FL can selectively accumulate at the surface of damaged mitochondria and cooperate with another Parkinson's Disease-related protein PARKIN to trigger the degradation of MIRO1, a mitochondria trafficking regulator. The functions of PINK1-cyto are, however, not yet clear. To investigate the functions of PINK1-cyto, we expressed different proteins in cultured HEK293 cells by transfecting it with different plasmids, and detected the protein levels by Western blot after expressing for 24 h. We found that in cultured HEK293 cells, PINK1-cyto could also cooperate with PARKIN degrade MIRO1 in the presence of CK23, and the regulatory subunit of Casein Kinase II. Interestingly, this function of CK2P was not dependent on CK2alpha, the catalytic subunit of Casein Kinase II. We also found that CK2P could promote the direct interaction between PINK1-cyto and MIRO1 by immunocoprecipitation analysis. This result suggested that in addition to CK2alpha, CK2beta could also form a kinase complex.