Insup Choi

Pink1 deficiency attenuates astrocyte proliferation through mitochondrial dysfunction, reduced akt and increased p38 mapk activation, and downregulation of egfr

PINK1 (PTEN induced putative kinase 1), a familial Parkinsons disease (PD)‐related gene, is expressed in astrocytes, but little is known about its role in this cell type. Here, we found that astrocytes cultured from PINK1‐knockout (KO) mice exhibit defective proliferative responses to epidermal growth factor (EGF) and fetal bovine serum. In PINK1‐KO astrocytes, basal and EGF‐induced p38 activation (phosphorylation) were increased whereas EGF receptor (EGFR) expression and AKT activation were decreased. p38 inhibition (SB203580) or knockdown with small interfering RNA (siRNA) rescued EGFR expression and AKT activation in PINK1‐KO astrocytes. Proliferation defects in PINK1‐KO astrocytes appeared to be linked to mitochondrial defects, manifesting as decreased mitochondrial mass and membrane potential, increased intracellular reactive oxygen species level, decreased glucose‐uptake capacity, and decreased ATP production. Mitochondrial toxin (oligomycin) and a glucose‐uptake inhibitor (phloretin) mimicked the PINK1‐deficiency phenotype, decreasing astrocyte proliferation, EGFR expression and AKT activation, and increasing p38 activation. In addition, the proliferation defect in PINK1‐KO astrocytes resulted in a delay in the wound healing process. Taken together, these results suggest that PINK1 deficiency causes astrocytes dysfunction, which may contribute to the development of PD due to delayed astrocytes‐mediated repair of microenvironment in the brain.

LRRK2 G2019S mutation attenuates microglial motility by inhibiting focal adhesion kinase

In response to brain injury, microglia rapidly extend processes that isolate lesion sites and protect the brain from further injury. Here we report that microglia carrying a pathogenic mutation in the Parkinsons disease (PD)-associated gene, G2019S-LRRK2 (GS-Tg microglia), show retarded ADP-induced motility and delayed isolation of injury, compared with non-Tg microglia. Conversely, LRRK2 knockdown microglia are highly motile compared with control cells. In our functional assays, LRRK2 binds to focal adhesion kinase (FAK) and phosphorylates its Thr–X–Arg/Lys (TXR/K) motif(s), eventually attenuating FAK activity marked by decreased pY397 phosphorylation (pY397). GS-LRRK2 decreases the levels of pY397 in the brain, microglia and HEK cells. In addition, treatment with an inhibitor of LRRK2 kinase restores pY397 levels, decreased pTXR levels and rescued motility of GS-Tg microglia. These results collectively suggest that G2019S mutation of LRRK2 may contribute to the development of PD by inhibiting microglial response to brain injury.

PINK1 Deficiency Enhances Inflammatory Cytokine Release from Acutely Prepared Brain Slices

Parkinsons disease (PD) is the second most common neurodegenerative motor disease caused by degeneration of dopaminergic neurons in the substantia nigra. Because brain inflammation has been considered a risk factor for PD, we analyzed whether PTEN induced putative kinase 1 (PINK1), an autosomal recessive familial PD gene, regulates brain inflammation during injury states. Using acutely prepared cortical slices to mimic injury, we analyzed expression of the pro-inflammatory cytokines tumor necrosis factor-α, interleukin (IL)-1β, and IL-6 at the mRNA and protein levels. Both mRNA and protein expression of these cytokines was higher at 6-24 h after slicing in PINK1 knockout (KO) slices compared to that in wild-type (WT) slices. In serial experiments to understand the signaling pathways that increase inflammatory responses in KO slices, we found that IκB degradation was enhanced but Akt phosphorylation decreased in KO slices compared to those in WT slices. In further experiments, an inhibitor of PI3K (LY294002) upstream of Akt increased expression of pro-inflammatory cytokines. Taken together, these results suggest that PINK1 deficiency enhance brain inflammation through reduced Akt activation and enhanced IκB degradation in response to brain injury.

Astrogliosis Is a Possible Player in Preventing Delayed Neuronal Death

Mitigating secondary delayed neuronal injury has been a therapeutic strategy for minimizing neurological symptoms after several types of brain injury. Interestingly, secondary neuronal loss appeared to be closely related to functional loss and/or death of astrocytes. In the brain damage induced by agonists of two glutamate receptors, N-ethyl-D-aspartic acid (NMDA) and kainic acid (KA), NMDA induced neuronal death within 3 h, but did not increase further thereafter. However, in the KA-injected brain, neuronal death was not obviously detectable even at injection sites at 3 h, but extensively increased to encompass the entire hemisphere at 7 days. Brain inflammation, a possible cause of secondary neuronal damage, showed little differences between the two models. Importantly, however, astrocyte behavior was completely different. In the NMDA-injected cortex, the loss of glial fibrillary acidic protein-expressing (GFAP+) astrocytes was confined to the injection site until 7 days after the injection, and astrocytes around the damage sites showed extensive gliosis and appeared to isolate the damage sites. In contrast, in the KA-injected brain, GFAP+ astrocytes, like neurons, slowly, but progressively, disappeared across the entire hemisphere. Other markers of astrocytes, including S100β, glutamate transporter EAAT2, the potassium channel Kir4.1 and glutamine synthase, showed patterns similar to that of GFAP in both NMDA- and KA-injected cortexes. More importantly, astrocyte disappearance and/or functional loss preceded neuronal death in the KA-injected brain. Taken together, these results suggest that loss of astrocyte support to neurons may be a critical cause of delayed neuronal death in the injured brain.

PINK1 expression increases during brain development and stem cell differentiation, and affects the development of GFAP-positive astrocytes

BackgroundMutation of PTEN-induced putative kinase 1 (PINK1) causes autosomal recessive early-onset Parkinson’s disease (PD). Despite of its ubiquitous expression in brain, its roles in non-neuronal cells such as neural stem cells (NSCs) and astrocytes were poorly unknown.ResultsWe show that PINK1 expression increases from embryonic day 12 to postnatal day 1 in mice, which represents the main period of brain development. PINK1 expression also increases during neural stem cell (NSC) differentiation. Interestingly, expression of GFAP (a marker of astrocytes) was lower in PINK1 knockout (KO) mouse brain lysates compared to wild-type (WT) lysates at postnatal days 1-8, whereas there was little difference in the expression of markers for other brain cell types (e.g., neurons and oligodendrocytes). Further experiments showed that PINK1-KO NSCs were defective in their differentiation to astrocytes, producing fewer GFAP-positive cells compared to WT NSCs. However, the KO and WT NSCs did not differ in their self-renewal capabilities or ability to differentiate to neurons and oligodendrocytes. Interestingly, during differentiation of KO NSCs there were no defects in mitochondrial function, and there were not changes in signaling molecules such as SMAD1/5/8, STAT3, and HES1 involved in differentiation of NSCs into astrocytes. In brain sections, GFAP-positive astrocytes were more sparsely distributed in the corpus callosum and substantia nigra of KO animals compared with WT.ConclusionOur study suggests that PINK1 deficiency causes defects in GFAP-positive astrogliogenesis during brain development and NSC differentiation, which may be a factor to increase risk for PD.

PINK1 positively regulates HDAC3 to suppress dopaminergic neuronal cell death

Deciphering the molecular basis of neuronal cell death is a central issue in the etiology of neurodegenerative diseases, such as Parkinsons and Alzheimers. Dysregulation of p53 levels has been implicated in neuronal apoptosis. The role of histone deacetylase 3 (HDAC3) in suppressing p53-dependent apoptosis has been recently emphasized; however, the molecular basis of modulation of p53 function by HDAC3 remains unclear. Here we show that PTEN-induced putative kinase 1 (PINK1), which is linked to autosomal recessive early-onset familial Parkinsons disease, phosphorylates HDAC3 at Ser-424 to enhance its HDAC activity in a neural cell-specific manner. PINK1 prevents H2O2-induced C-terminal cleavage of HDAC3 via phosphorylation of HDAC3 at Ser-424, which is reversed by protein phosphatase 4c. PINK1-mediated phosphorylation of HDAC3 enhances its direct association with p53 and causes subsequent hypoacetylation of p53. Genetic deletion of PINK1 partly impaired the suppressive role of HDAC3 in regulating p53 acetylation and transcriptional activity. However, depletion of HDAC3 fully abolished the PINK1-mediated p53 inhibitory loop. Finally, ectopic expression of phosphomometic-HDAC3(S424E) substantially overcomes the defective action of PINK1 against oxidative stress in dopaminergic neuronal cells. Together, our results uncovered a mechanism by which PINK1-HDAC3 network mediates p53 inhibitory loop in response to oxidative stress-induced damage.

Interplay between Leucine-Rich Repeat Kinase 2 (LRRK2) and p62/SQSTM-1 in Selective Autophagy

The deposit of polyubiquitinated aggregates has been implicated in the pathophysiology of Parkinson’s disease (PD), and growing evidence indicates that selective autophagy plays a critical role in the clearance of ubiquitin-positive protein aggregates by autophagosomes. The selective autophagic receptor p62/SQSTM-1, which associates directly with both ubiquitin and LC3, transports ubiquitin conjugates to autophagosomes for degradation. Leucine-rich repeat kinase 2 (LRRK2), a PD-associated protein kinase, is tightly controlled by autophagy-lysosome degradation as well as by the ubiquitin-proteasome pathway. However, little is known about the degradation of ubiquitinated LRRK2 via selective autophagy. In the present study, we found that p62/SQSTM-1 physically interacts with LRRK2 as a selective autophagic receptor. The overexpression of p62 leads to the robust degradation of LRRK2 through the autophagy-lysosome pathway. In addition, LRRK2 indirectly regulates Ser351 and Ser403 phosphorylation of p62. Of particular interest, the interaction between phosphorylated p62 and Keap1 is reduced by LRRK2 overexpression. Therefore, we propose that the interplay between LRRK2 and p62 may contribute to the pathophysiological function and homeostasis of LRRK2 protein.

Erratum: PINK1 expression increases during brain development and stem cell differentiation, and affects the development of GFAPpositive astrocytes (Molecular Brain (2016) 9:5 DOI 10.1186/s13041-016-0186-6)

Author details Neuroscience Graduate Program Department of Biomedical Sciences, Ajou University School of Medicine, Suwon, Korea. Chronic Inflammatory Disease Research Center, Ajou University School of Medicine, Suwon, Korea. Department of Pharmacology, Ajou University School of Medicine san-5, Woncheon-dong, Youngtong-gu, SuwonKyunggi-do 442–721Korea. Department of Biochemistry and Molecular Biology, College of Medicine, Hanyang University, Seoul, Korea. Department of Anatomy and Division of Brain Korea 21 Plus Biomedical Science, Korea University College of Medicine, Seoul 136-705, Korea. Department of Brain Science, Ajou University School of Medicine, Suwon, Korea. Brain Disease Research Center, Ajou University School of Medicine, Suwon, Korea.

LRRK2 Inhibits FAK Activity by Promoting FERM-mediated Autoinhibition of FAK and Recruiting the Tyrosine Phosphatase, SHP-2

Mutation of leucine-rich repeat kinase 2 (LRRK2) causes an autosomal dominant and late-onset familial Parkinsons disease (PD). Recently, we reported that LRRK2 directly binds to and phosphorylates the threonine 474 (T474)-containing Thr-X-Arg(Lys) (TXR) motif of focal adhesion kinase (FAK), thereby inhibiting the phosphorylation of FAK at tyrosine (Y) 397 residue (pY397-FAK), which is a marker of its activation. Mechanistically, however, it remained unclear how T474-FAK phosphorylation suppressed FAK activation. Here, we report that T474-FAK phosphorylation could inhibit FAK activation via at least two different mechanisms. First, T474 phosphorylation appears to induce a conformational change of FAK, enabling its N-terminal FERM domain to autoinhibit Y397 phosphorylation. This is supported by the observation that the levels of pY397-FAK were increased by deletion of the FERM domain and/or mutation of the FERM domain to prevent its interaction with the kinase domain of FAK. Second, pT474-FAK appears to recruit SHP-2, which is a phosphatase responsible for dephosphorylating pY397-FAK. We found that mutation of T474 into glutamate (T474E-FAK) to mimic phosphorylation induced more strong interaction with SHP-2 than WT-FAK, and that pharmacological inhibition of SHP-2 with NSC-87877 rescued the level of pY397 in HEK293T cells. These results collectively show that LRRK2 suppresses FAK activation through diverse mechanisms that include the promotion of autoinhibition and/or the recruitment of phosphatases, such as SHP-2.