Measurement of LRRK2 Kinase Activity by Proximity Ligation Assay.

Missense mutations in leucine rich-repeat kinase 2 (LRRK2) cause forms of familial Parkinson's disease and have been linked to 'idiopathic' Parkinson's disease. Assessment of LRRK2 kinase activity has been very challenging due to its size, complex structure, and relatively low abundance. A standard in the field to assess LRRK2 kinase activity is to measure the level of substrate phosphorylation (pThr73-Rab10) or autophosphorylation of serine 1292 (i.e., phosphoserine 1292; pS1292). The levels of pS1292 have typically been assessed by western blotting, which limits cellular and anatomical resolution. Here, we describe the method for a novel proximity ligation assay (PLA) that can detect endogenous LRRK2 kinase activity (PLA LRRK2) in situ at cellular and subcellular resolutions. PLA is a fluorescence- or chromogen-based assay that can be used to either (1) detect protein-protein interactions or (2) detect and amplify post-translational modifications on proteins. We used PLA for in situ detection and amplification of LRRK2 autophosphorylation levels at serine 1292. Our findings demonstrate that PLA LRRK2 is a highly sensitive and specific assay that can be used for assessing kinase activity in cultured cells and postmortem tissues.

Phospholipase iPLA2ß averts ferroptosis by eliminating a redox lipid death signal.

Ferroptosis, triggered by discoordination of iron, thiols and lipids, leads to the accumulation of 15-hydroperoxy (Hp)-arachidonoyl-phosphatidylethanolamine (15-HpETE-PE), generated by complexes of 15-lipoxygenase (15-LOX) and a scaffold protein, phosphatidylethanolamine (PE)-binding protein (PEBP)1. As the Ca2+-independent phospholipase A2ß (iPLA2ß, PLA2G6 or PNPLA9 gene) can preferentially hydrolyze peroxidized phospholipids, it may eliminate the ferroptotic 15-HpETE-PE death signal. Here, we demonstrate that by hydrolyzing 15-HpETE-PE, iPLA2ß averts ferroptosis, whereas its genetic or pharmacological inactivation sensitizes cells to ferroptosis. Given that PLA2G6 mutations relate to neurodegeneration, we examined fibroblasts from a patient with a Parkinson's disease (PD)-associated mutation (fPDR747W) and found selectively decreased 15-HpETE-PE-hydrolyzing activity, 15-HpETE-PE accumulation and elevated sensitivity to ferroptosis. CRISPR-Cas9-engineered Pnpla9R748W/R748W mice exhibited progressive parkinsonian motor deficits and 15-HpETE-PE accumulation. Elevated 15-HpETE-PE levels were also detected in midbrains of rotenone-infused parkinsonian rats and α-synuclein-mutant SncaA53T mice, with decreased iPLA2ß expression and a PD-relevant phenotype. Thus, iPLA2ß is a new ferroptosis regulator, and its mutations may be implicated in PD pathogenesis.

Clinical-Genetic Associations in the Prospective Huntington at Risk Observational Study (PHAROS): Implications for Clinical Trials.

IMPORTANCE: Identifying measures that are associated with the cytosine-adenine-guanine (CAG) expansion in individuals before diagnosis of Huntington disease (HD) has implications for designing clinical trials. OBJECTIVE: To identify the earliest features associated with the motor diagnosis of HD in the Prospective Huntington at Risk Observational Study (PHAROS). DESIGN, SETTING, AND PARTICIPANTS: A prospective, multicenter, longitudinal cohort study was conducted at 43 US and Canadian Huntington Study Group research sites from July 9, 1999, through December 17, 2009. Participants included 983 unaffected adults at risk for HD who had chosen to remain unaware of their mutation status. Baseline comparability between CAG expansion (≥37 repeats) and nonexpansion (<37 repeats) groups was assessed. All participants and investigators were blinded to individual CAG analysis. A repeated-measures analysis adjusting for age and sex was used to assess the divergence of the linear trend between the expanded and nonexpanded groups. Data were analyzed from April 27, 2010, to September 3, 2013. EXPOSURE: Huntington disease mutation status in individuals with CAG expansion vs without CAG expansion. MAIN OUTCOMES AND MEASURES: Unified Huntington's Disease Rating Scale motor (score range, 0-124; higher scores indicate greater impairment), cognitive (symbol digits modality is the total number of correct responses in 90 seconds; lower scores indicate greater impairment), behavioral (score range, 0-176; higher scores indicate greater behavioral symptoms), and functional (Total Functional Capacity score range, 0-13; lower scores indicate reduced functional ability) domains were assessed at baseline and every 9 months up to a maximum of 10 years. RESULTS: Among the 983 research participants at risk for HD in the longitudinal cohort, 345 (35.1%) carried the CAG expansion and 638 (64.9%) did not. The mean (SD) duration of follow-up was 5.8 (3.0) years. At baseline, participants with expansions had more impaired motor (3.0 [4.2] vs 1.9 [2.8]; P < .001), cognitive (P < .05 for all measures except Verbal Fluency, P = .52), and behavioral domain scores (9.4 [11.4] vs 6.5 [8.5]; P < .001) but not significantly different measures of functional capacity (12.9 [0.3] vs 13.0 [0.2]; P = .23). With findings reported as mean slope (95% CI), in the longitudinal analyses, participants with CAG expansions showed significant worsening in motor (0.84 [0.73 to 0.95] vs 0.03 [-0.05 to 0.11]), cognitive (-0.54 [-0.67 to -0.40] vs 0.22 [0.12 to 0.32]), and functional (-0.08 [-0.09 to -0.06] vs -0.01 [-0.02 to 0]) measures compared with those without expansion (P < .001 for all); behavioral domain scores did not diverge significantly between groups. CONCLUSIONS AND RELEVANCE: Using these prospectively accrued clinical data, relatively large treatment effects would be required to mount a randomized, placebo-controlled clinical trial involving premanifest HD individuals who carry the CAG expansion.