Takeshi Iwatsubo

LRRK2 is a Parkinson’s disease–associated kinase that phosphorylates Rab GTPases. Hyperactivation of LRRK2, which is thought to cause Parkinson’s disease, occurs on stressed endolysosomal membranes via conjugation of ATG8 to single membranes (CASM) and Rab, whereas the involvement of specific membrane lipids remained unclear. Here, we found that the inhibition of PIKfyve that metabolizes phosphatidylinositol 3-phosphate (PI3P) induces hyperactivation of LRRK2 and that additional inhibition of the class III phosphoinositide 3-kinase that generates PI3P suppressed LRRK2 hyperactivation. Cellular PI3P levels were indeed elevated when LRRK2 was activated. CASM-induced activation of LRRK2, but not CASM itself, was suppressed by phosphoinositide 3-kinase inhibitors, whereas inhibition of CASM or Rab12/Rab29 suppressed LRRK2 activation induced by PIKfyve inhibitors. LRRK2 and phospho-Rab10 were colocalized with PI3P on LAMP1-positive enlarged vacuoles, and LRRK2 directly bound PI3P in vitro via its N-terminal positively charged amino acids. Together, we propose an updated mechanism of LRRK2 hyperactivation that simultaneously requires CASM, Rab, and PI3P-rich membranes.

The cGAS-STING pathway is an innate immune system that responds to cytoplasmic double-stranded DNA, but recent studies have highlighted its noncanonical role in facilitating lysosomal stress responses. Specifically, STING activation has been shown to trigger V-ATPase-ATG16L1-induced LC3 lipidation (VAIL) and to activate LRRK2, a Parkinson disease-associated kinase, but the detailed molecular mechanism and the physiological roles of the activation have remained unclear. Here, we found that STING activation in microglia induces the translocation of LRRK2 to the pericentrosomal area, where lysosomes and recycling endosomes (REs) concentrate. This process was VAIL-dependent, and LRRK2 was found to be localized to the organelles. The translocation of LRRK2 required intact microtubule structures and was mediated by LRRK2 kinase activity, its substrate Rab35 and the motor adaptor proteins including JIP4. All these proteins were concentrated at the pericentrosomal area upon STING stimulation. The hyperactivating G2019S mutation of LRRK2 promoted the pericentrosomal translocation of these proteins. Overall, we propose a novel STING-induced noncanonical pathway that involves LRRK2 to facilitate pericentrosomal organelle positioning.

Summary: LRRK2, the Parkinson’s disease-associated kinase, phosphorylates a subset of Rab GTPases and regulates membrane dynamics. We previously reported that lysosomal stress activates LRRK2 and thereby induces the exocytic secretion of lysosomal contents, but the detailed secretion mechanism remained unclear. Here we found that, under lysosomal stress, endolysosomal luminal and membrane components were secreted with extracellular vesicles (EVs) via LRRK2. Bis(monoacylglycerol)phosphate, an endolysosomal lipid and a urinary marker of LRRK2 activity, was similarly secreted via LRRK2, whereas CD9-positive EVs were not involved. Further dissection of the secreted EVs revealed that Alix-positive EVs were secreted via Rab8a as well as the ESCRT component VPS4, whereas LAMP1/cathepsin B-positive EVs were secreted via Rab10/Rab35, and SNARE proteins syntaxin 2 and VAMP8 regulated the secretion of both EV subtypes. These findings suggest a distinctive stress-induced secretory mechanism whereby LRRK2 facilitates the secretion of multiple EV subtypes by controlling Rab GTPases involved in each pathway.

INTRODUCTION: This study aimed to identify demographic and cognitive differences based on amyloid status in older Japanese adults without dementia, addressing the lack of data in East Asian populations for early Alzheimer's disease (AD) detection. METHODS: Analyzed baseline data from 630 participants from the Japanese Trial‐Ready Cohort (J‐TRC) study, all with a Clinical Dementia Rating‐Global Score (CDR‐GS) of 0 or 0.5. Amyloid status (Aβ+ or Aβ−) was determined by amyloid positron emission tomography (PET) scans. RESULTS: Among participants, 24.8% were Aβ+. In the cognitively unimpaired (CDR‐GS 0) group, Aβ+ individuals reported slightly greater self‐perceived cognitive concerns (Cognitive Function Instrument [CFI‐self]). For those with mild impairment (CDR‐GS 0.5), Aβ+ status was associated with worse clinical scores, greater cognitive complaints, more depressive symptoms, and poorer memory and global cognition. DISCUSSION: These findings align with major Western studies, emphasizing that CFI‐self is a valuable tool for identifying early AD pathology across diverse populations. Highlights: Comparing characteristics by amyloid status in Japanese non‐demented older adults. Positron emission tomography–positive (PET+) scans in cognitively unimpaired individuals were associated with Cognitive Function Instrument–negative (CFI‐) participants. PET+ in mild cognitive impairment (MCI) was linked to functional, cognitive, and affective decline. CFI‐ participants will aid early Alzheimer's pathology detection in diverse groups.

Background: There is an urgent need to determine the utility of plasma biomarkers, particularly tau phosphorylated at threonine 217 ( p ‐tau217), in predicting amyloid PET positivity and monitoring the efficacy of disease‐modifying therapies (DMT) in the early stages of Alzheimer's disease (AD). Method: Participants in the Japanese trial‐ready cohort for preclinical/prodromal AD (J‐TRC), which included 474 non‐demented individuals (CDR 0: 331, CDR 0.5: 143), were assessed by amyloid PET (florbetapir or flutemetamol) and plasma biomarker assays. Plasma Aβ42 and Aβ40 were measured by IP mass spectrometry (Shimadzu), and p ‐tau217 was measured by immunoassay on the Meso Scale Discovery platform (Eli Lilly). The study was conducted by collaborative groups from the J‐TRC and the AD DMT Registry. Result: Aβ‐PET was abnormal in 81 participants. High accuracy in detecting an abnormal Aβ‐PET scan was achieved by plasma p ‐tau217 (AUC = 0.913) or Aβ42/40 (AUC = 0.856), which was improved by combining plasma biomarkers and by including clinical information in the models. The highest AUCs were observed for the models combining p ‐tau217/Aβ42 ratio, APOE, age, sex in the whole cohort (AUC = 0.936), p ‐tau217, Aβ42/Aβ40 ratio, APOE, age, sex in the CDR 0 group (AUC = 0.948), and p ‐tau217/Aβ42 ratio, APOE, age, sex in the CDR 0.5 group (AUC = 0.955), respectively. Conclusion: These results indicate that plasma p ‐tau217 alone, or combinations of plasma Aβ biomarkers and p ‐tau217, are effective in predicting Aβ‐PET positivity in preclinical and prodromal AD. The ability of the p ‐tau217 plasma assays to prescreen eligible patients and monitor the efficacy of anti‐Aβ antibodies and other DMTs is also being tested in a real‐world setting in the Japanese early symptomatic AD patient registry.

LRRK2 is a Parkinson's disease (PD)-associated kinase that phosphorylates Rab GTPases. Hyperactivation of LRRK2, which is thought to cause PD, occurs on stressed endolysosomal membranes via CASM (conjugation of ATG8 to single membranes) and Rab, whereas the involvement of specific membrane lipids remained unclear. Here, we found that the inhibition of PIKfyve that metabolizes phosphatidylinositol 3-phosphate (PI3P) induces hyperactivation of LRRK2, and that additional inhibition of the class III phosphoinositide 3-kinase (PI3K) that generates PI3P suppressed LRRK2 hyperactivation. Cellular PI3P levels were indeed elevated when LRRK2 was activated. CASM-induced activation of LRRK2, but not CASM itself, was suppressed by PI3K inhibitors, whereas inhibition of CASM or Rab12/Rab29 suppressed LRRK2 activation induced by PIKfyve inhibitors. LRRK2 and phospho-Rab10 were co-localized with PI3P on LAMP1-positive enlarged vacuoles, and LRRK2 directly bound PI3P in vitro via its N-terminal positively charged amino acids. Together, we propose an updated mechanism of LRRK2 hyperactivation that simultaneously requires CASM, Rab and PI3P-rich membranes.

INTRODUCTION: Lecanemab was approved for early Alzheimer's disease in Japan, with ≈ 6000 patients treated in the first year post approval. This study explores real‐world practices, challenges, and potential solutions. METHODS: We conducted an anonymized online survey of clinical specialists authorized to prescribe lecanemab, obtaining responses from 311 specialists who collectively treated 3259 patients with lecanemab. RESULTS: A majority of respondents (79%) reported wait times of ≤ 3 months from first consultation to initial infusion. One fourth reported tight outpatient space and staffing and significantly lower capacity of treatment than anticipated. Safety concerns were limited, with amyloid imaging‐related abnormality–related interruptions in 3.5%. More than half highly supported additional reimbursement for infusion‐related services and insurance coverage for apolipoprotein E ( APOE ) testing. DISCUSSION: Early access to lecanemab appears feasible, yet infrastructure and financial hurdles remain. Dedicated reimbursement and insurance coverage for APOE testing may be essential for ensuring safer, more accessible, and sustainable use of this therapy in Japan. Highlights: Results from an online survey of 311 Japanese specialists prescribing lecanemab in its first year are reported. Majority of wait times from first consultation to initial infusion were 1 to 3 months. Tight affordability of infusion space and staffing was reported by one quarter. Establishing additional medical fee for infusion management was highly expected. Reimbursement of apolipoprotein E test in Japanese health insurance system was also demanded.