Isabella Irrcher

Loss of the Parkinson’s Disease-linked gene DJ-1 perturbs mitochondrial dynamics

Growing evidence highlights a role for mitochondrial dysfunction and oxidative stress as underlying contributors to Parkinsons disease (PD) pathogenesis. DJ-1 (PARK7) is a recently identified recessive familial PD gene. Its loss leads to increased susceptibility of neurons to oxidative stress and death. However, its mechanism of action is not fully understood. Presently, we report that DJ-1 deficiency in cell lines, cultured neurons, mouse brain and lymphoblast cells derived from DJ-1 patients display aberrant mitochondrial morphology. We also show that these DJ-1-dependent mitochondrial defects contribute to oxidative stress-induced sensitivity to cell death since reversal of this fragmented mitochondrial phenotype abrogates neuronal cell death. Reactive oxygen species (ROS) appear to play a critical role in the observed defects, as ROS scavengers rescue the phenotype and mitochondria isolated from DJ-1 deficient animals produce more ROS compared with control. Importantly, the aberrant mitochondrial phenotype can be rescued by the expression of Pink1 and Parkin, two PD-linked genes involved in regulating mitochondrial dynamics and quality control. Finally, we show that DJ-1 deficiency leads to altered autophagy in murine and human cells. Our findings define a mechanism by which the DJ-1-dependent mitochondrial defects contribute to the increased sensitivity to oxidative stress-induced cell death that has been previously reported.

Parkin is transcriptionally regulated by ATF4: evidence for an interconnection between mitochondrial stress and ER stress

Loss of parkin function is responsible for the majority of autosomal recessive parkinsonism. Here, we show that parkin is not only a stress-protective, but also a stress-inducible protein. Both mitochondrial and endoplasmic reticulum (ER) stress induce an increase in parkin-specific mRNA and protein levels. The stress-induced upregulation of parkin is mediated by ATF4, a transcription factor of the unfolded protein response (UPR) that binds to a specific CREB/ATF site within the parkin promoter. Interestingly, c-Jun can bind to the same site, but acts as a transcriptional repressor of parkin gene expression. We also present evidence that mitochondrial damage can induce ER stress, leading to the activation of the UPR, and thereby to an upregulation of parkin expression. Vice versa, ER stress results in mitochondrial damage, which can be prevented by parkin. Notably, the activity of parkin to protect cells from stress-induced cell death is independent of the proteasome, indicating that proteasomal degradation of parkin substrates cannot explain the cytoprotective activity of parkin. Our study supports the notion that parkin has a role in the interorganellar crosstalk between the ER and mitochondria to promote cell survival under stress, suggesting that both ER and mitochondrial stress can contribute to the pathogenesis of Parkinsons disease.

DJ-1 protects the nigrostriatal axis from the neurotoxin MPTP by modulation of the AKT pathway

Loss-of-function DJ-1 (PARK7) mutations have been linked with a familial form of early onset Parkinson disease. Numerous studies have supported the role of DJ-1 in neuronal survival and function. Our initial studies using DJ-1-deficient neurons indicated that DJ-1 specifically protects the neurons against the damage induced by oxidative injury in multiple neuronal types and degenerative experimental paradigms, both in vitro and in vivo. However, the manner by which oxidative stress-induced death is ameliorated by DJ-1 is not completely clear. We now present data that show the involvement of DJ-1 in modulation of AKT, a major neuronal prosurvival pathway induced upon oxidative stress. We provide evidence that DJ-1 promotes AKT phosphorylation in response to oxidative stress induced by H2O2 in vitro and in vivo following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment. Moreover, we show that DJ-1 is necessary for normal AKT-mediated protective effects, which can be bypassed by expression of a constitutively active form of AKT. Taken together, these data suggest that DJ-1 is crucial for full activation of AKT upon oxidative injury, which serves as one explanation for the protective effects of DJ-1.

DJ-1 Interacts with and Regulates Paraoxonase-2, an Enzyme Critical for Neuronal Survival in Response to Oxidative Stress

Loss-of-function mutations in DJ-1 (PARK7) gene account for about 1% of all familial Parkinsons disease (PD). While its physiological function(s) are not completely clear, DJ-1 protects neurons against oxidative stress in both in vitro and in vivo models of PD. The molecular mechanism(s) through which DJ-1 alleviates oxidative stress-mediated damage remains elusive. In this study, we identified Paraoxonase-2 (PON2) as an interacting target of DJ-1. PON2 activity is elevated in response to oxidative stress and DJ-1 is crucial for this response. Importantly, we showed that PON2 deficiency hypersensitizes neurons to oxidative stress induced by MPP+ (1-methyl-4-phenylpyridinium). Conversely, over-expression of PON2 protects neurons in this death paradigm. Interestingly, PON2 effectively rescues DJ-1 deficiency-mediated hypersensitivity to oxidative stress. Taken together, our data suggest a model by which DJ-1 exerts its antioxidant activities, at least partly through regulation of PON2.

Regulation of the VHL/HIF-1 Pathway by DJ-1

DJ-1 (PARK7) is a gene linked to autosomal recessive Parkinson disease (PD). We showed previously that DJ-1 loss sensitizes neurons in models of PD and stroke. However, the biochemical mechanisms underlying this protective role are not completely clear. Here, we identify Von Hippel Lindau (VHL) protein as a critical DJ-1-interacting protein. We provide evidence that DJ-1 negatively regulates VHL ubiquitination activity of the α-subunit of hypoxia-inducible factor-1 (HIF-1α) by inhibiting HIF–VHL interaction. Consistent with this observation, DJ-1 deficiency leads to lowered HIF-1α levels in models of both hypoxia and oxidative stress, two stresses known to stabilize HIF-1α. We also demonstrate that HIF-1α accumulation rescues DJ-1-deficient neurons against 1-methyl-4-phenylpyridinium-induced toxicity. Interestingly, lymphoblast cells extracted from DJ-1-related PD patients show impaired HIF-1α stabilization when compared with normal individuals, indicating that the DJ-1–VHL link may also be relevant to a human context. Together, our findings delineate a model by which DJ-1 mediates neuronal survival by regulation of the VHL–HIF-1α pathway.

Anti-inflammatory therapy after selective laser trabeculoplasty: a randomized, double-masked, placebo-controlled clinical trial.

PURPOSEnTo investigate the effect of anti-inflammatory therapy on selective laser trabeculoplasty (SLT) outcomes.nnnDESIGNnRandomized, double-masked, placebo-controlled trial.nnnPARTICIPANTSnPatients with primary open-angle or pseudo-exfoliation glaucoma.nnnMETHODSnPatients undergoing SLT were randomized to receive placebo (artificial tears), prednisolone acetate 1%, or ketorolac tromethamine 0.5% eye drops 4 times per day for 5 days commencing immediately after SLT.nnnMAIN OUTCOME MEASURESnChange in intraocular pressure (IOP) from baseline to the 1-month post-SLT visit.nnnRESULTSnMean change in IOP at the 1-month primary outcome time point, as well as all other time points, was not significantly different among groups (P = 0.99). Likewise, a repeated-measures, mixed-effects model did not find significant differences in IOP outcome at the 1-month time point (P = 0.95). The IOP was reduced in all groups at the 1-month post-SLT time point and all other time points, and no significant differences were found between groups using separate unadjusted cross-sectional analyses of variance (P > 0.15 for analyses at all time points). Treatment failure rates were not different among groups (P = 0.75), and at 1 year after SLT, the percentage of patients maintaining a 20% IOP reduction ranged from 18% to 22% in the 3 study groups.nnnCONCLUSIONSnAnti-inflammatory therapy after SLT does not seem to substantially influence the IOP-lowering effect of SLT. In this study of patients with low baseline IOP, SLT showed limited efficacy in achieving a sustained reduction in IOP.

Anaesthetic plus dilating gel improves pupil dilation for cataract surgery

OBJECTIVEnTo evaluate the efficacy of a combination anaesthetic plus dilating gel (ADG) on pupil dilation (PD) and corneal anaesthesia (KA) compared to traditional preoperative pharmacotherapy for cataract surgery.nnnDESIGNnProspective, noninferiority study.nnnMETHODSnWe studied 20 consenting adults who experienced unilateral cataracts and underwent routine cataract surgery, receiving the traditional preoperative pharmacologic regimen in the operated eye (control eye): diclofenac 0.1%, gentamicin 0.3%, cyclopentolate 1%, phenylephrine 2.5%, and tropicamide 1% 60 and 20 minutes prior to surgery. They then received tetracaine 0.5% and povidone-iodine 5% 10 minutes prior to surgery; and were given tetracaine 0.5%, povidone-iodine 5%, and lidocaine 2% gel 1 minute prior to surgery. Epinephrine 0.1%, 1 cc per 500 mL bag of balanced saline salt solution was administered during surgery. The nonoperated eye (study eye) received tetracaine 0.5%, povidone-iodine 5%, and 0.35 cc ADG gel (phenylephrine 10%, tropicamide 1%, diclofenac 0.1%, and lidocaine 2%) 60 and 10 minutes prior to surgery. PD and KA were measured at baseline, at 30 minutes, and at 5 minutes prior to surgery, and at 5 minutes after surgery.nnnRESULTSnThere was no difference in PD (p = 0.2634) or KA (p = 0.6058) between the study eyes and the control eyes at baseline. Preoperatively, greater mydriasis was achieved in the study eye (7.95 ± 0.91 mm vs 7.17 ± 1.25 mm; p < 0.0001). There was no significant difference in preoperative KA between the study and control eyes (1.5 ± 2.2 mm vs 1.4 ± 2.1 mm; p = 0.77).nnnCONCLUSIONSnThe combination ADG for preoperative preparation of cataract patients achieves at least equivalent dilation and corneal anaesthesia as the current preoperative pharmacologic regimen.

Assessing a narrated white board animation as part of the consent process for intravenous fluorescein angiography: a randomized educational study

OBJECTIVEnTo determine if a narrated white board animation (nWBA) video as part of the consent process for intravenous fluorescein angiography (IVFA) improves patient comprehension compared with a standard consent process.nnnDESIGNnProspective, randomized study.nnnPARTICIPANTSnPatients undergoing an initial IVFA investigation.nnnMETHODSnThree groups of 26 patients (N = 78) naïve to the IVFA procedure were included. Groups 1 and 2 consisted of patients undergoing IVFA for diagnostic purposes. Group 1 received the IVFA information via standard physician-patient interaction to obtain standard consent. Group 2 received IVFA information by watching an nWBA explaining the purpose, method, and risks of the diagnostic test to obtain informed consent. Group 3 comprised patients who were not scheduled to undergo IVFA. This group was exposed to both the standard and nWBA consent. All groups completed a 6-question knowledge quiz to assess retained information and a survey to reflect on the consent experience.nnnRESULTSnParticipants receiving information via standard physician-patient interaction to obtain informed consent had a lower mean knowledge score (4.38 out of 6; 73%) than participants receiving the information to obtain consent via nWBA (5.04 out of 6, 84%; P = 0.023). Of participants receiving both forms of information (group 3) to obtain informed consent, 73% preferred the nWBA to the standard consent process.nnnCONCLUSIONSnParticipants receiving consent information for an IVFA diagnostic test via nWBA have better knowledge retention regarding the IVFA procedure and preferred this medium compared with participants receiving the standard physician-patient interaction for obtaining consent. Incorporation of multimedia into the informed consent process should be explored for other diagnostic tests.