Recent studies have identified increasing levels of nanoplastic pollution in the environment. Here, we find that anionic nanoplastic contaminants potently precipitate the formation and propagation of α-synuclein protein fibrils through a high-affinity interaction with the amphipathic and non-amyloid component (NAC) domains in α-synuclein. Nanoplastics can internalize in neurons through clathrin-dependent endocytosis, causing a mild lysosomal impairment that slows the degradation of aggregated α-synuclein. In mice, nanoplastics combine with α-synuclein fibrils to exacerbate the spread of α-synuclein pathology across interconnected vulnerable brain regions, including the strong induction of α-synuclein inclusions in dopaminergic neurons in the substantia nigra. These results highlight a potential link for further exploration between nanoplastic pollution and α-synuclein aggregation associated with Parkinson’s disease and related dementias.

Antiestrogen compounds exhibit a variety of different effects in different tissues and are widely used for the treatment of osteoporosis, breast cancer, and other diseases. Upon examining the molecular mechanisms, we found that Smad4, a common signal transducer in the bone morphogenetic protein (BMP)/transforming growth factor-β (TGF-β) signaling pathway, functions as a transcription corepressor for human estrogen receptor α (ERα). Endogenous ERα was co-immunoprecipitated with Smad4, and the interaction was induced by antiestrogen ligands such as tamoxifen, raloxifene, and droloxifen, which was confirmed in chromatin immunoprecipitation assays. Smad4 and ERα form a complex when ERα binds to the estrogen-responsive element within the estrogen target gene promoter. Importantly, the expression of Smad4 inhibits both antiestrogen-induced luciferase activity and estrogen downstream target gene transcription in breast cancer cells. Mapping of the interaction domains indicates that the activation function 1 (AF1) domain of ERα is essential for its interaction with Smad4, while the MH1 domain and linker region of Smad4 are essential for the interaction. Our findings represent a novel mechanism that TGF-β may regulate cell fate through Smad4-mediated cross-talk with estrogen.

Pathogenic missense variants in the leucine-rich repeat kinase 2 (LRRK2) gene have been identified through linkage analysis in familial Parkinson disease (PD). Subsequently, other missense variants with lower effect sizes on PD risk have emerged, as well as non-coding polymorphisms (e.g. rs76904798) enriched in PD cases in genome-wide association studies. Here we leverage recent whole-genome sequences from the Accelerating Medicines Partnership-Parkinson’s Disease (AMP-PD) and the Genome Aggregation (gnomAD) databases to characterize novel missense variants in LRRK2 and explore their relationships with known pathogenic and PD-linked missense variants. Using a computational prediction tool that successfully classifies known pathogenic LRRK2 missense variants, we describe an online web-based resource that catalogs characteristics of over 1200 LRRK2 missense variants of unknown significance. Novel high-pathogenicity scoring variants, some identified exclusively in PD cases, tightly cluster within the ROC-COR-Kinase domains. Structure–function predictions support that some of these variants exert gain-of-function effects with respect to LRRK2 kinase activity. In AMP-PD participants, all p.R1441G carriers (N = 89) are also carriers of the more common PD-linked variant p.M1646T. In addition, nearly all carriers of the PD-linked p.N2081D missense variant are also carriers of the LRRK2 PD-risk variant rs76904798. These results provide a compendium of LRRK2 missense variants and how they associate with one another. While the pathogenic p.G2019S variant is by far the most frequent high-pathogenicity scoring variant, our results suggest that ultra-rare missense variants may have an important cumulative impact in increasing the number of individuals with LRRK2-linked PD.

LRRK2 is implicated in lysosomal functions, but the physiological upstream cues that engage endogenous LRRK2 activity are incompletely defined. Here we show that lysosomal swelling serves as a selective and reversible trigger for LRRK2-mediated Rab phosphorylation, without requiring membrane damage. Acute inhibition of PIKfyve, but not the general disruption of phosphoinositide signaling, induces the robust accumulation of phosphorylated Rabs across endolysosomal membranes. Rescue of swelling through pharmacological restoration of lysosomal ionic imbalances from PIKfyve inhibition suppresses LRRK2 activation without restoring lysosomal function. Mechanical lysosomal swelling from indigestible osmolyte uptake causes a dose-dependent increase in LRRK2-mediated Rab phosphorylation on both swollen and non-swollen lysosomes. Together, these findings identify LRRK2 as a sensor of lysosomal volume and mechanical stress, not specifically membrane damage or PIKfyve inhibition. As lysosomal swelling is a shared pathological feature across LRRK2-linked diseases, these results reframe LRRK2 as part of an endolysosomal surveillance system responsive to lysosomal distension.

Corrigendum: The Mechanisms of Cucurbitacin E as a Neuroprotective and Memory-Enhancing Agent in a Cerebral Hypoperfusion Rat Model: Attenuation of Oxidative Stress, Inflammation, and Excitotoxicity

Summary: Background: Parkinson’s disease (PD) is a progressive neurodegenerative disorder. Mendelian forms have revealed multiple genes, with a notable emphasis on membrane trafficking; RAB GTPases play an important role in PD as a subset are both regulators and substrates of LRRK2 protein kinase. To explore the role of RAB GTPases in PD, we undertook a comprehensive examination of their genetic variability in familial PD. Methods: Affected probands from 130 multi-incident PD families underwent whole-exome sequencing and genotyping, Potential pathogenic variants in 61 RAB GTPases were genotyped in relatives to assess disease segregation. These variants were also genotyped in a larger case-control series, totaling 3,078 individuals (2,734 with PD). The single most significant finding was subsequently validated within genetic data (6,043 with PD). Clinical and pathologic findings were summarized for gene-identified patients, and haplotypes were constructed. In parallel, wild-type and mutant RAB GTPase structural variation, protein interactions, and resultant enzyme activities were assessed. Findings: We found RAB32 c.213C>G (Ser71Arg) to co-segregate with autosomal dominant parkinsonism in three multi-incident families. RAB32 Ser71Arg was also significantly associated with PD in case-control samples: genotyping and database searches identified thirteen more patients with the same variant that was absent in unaffected controls. Notably, RAB32 Ser71Arg heterozygotes share a common haplotype. At autopsy, one patient had sparse neurofibrillary tangle pathology in the midbrain and thalamus, without Lewy body pathology. In transfected cells the RAB32 Arg71 was twice as potent as Ser71 wild type to activate LRRK2 kinase. Interpretation: Our study provides unequivocal evidence to implicate RAB32 Ser71Arg in PD. Functional analysis demonstrates LRRK2 kinase activation. We provide a mechanistic explanation to expand and unify the etiopathogenesis of monogenic PD. Funding: National Institutes of Health, the Canada Excellence Research Chairs program, Aligning Science Across Parkinson’s, the Michael J. Fox Foundation for Parkinson’s Research, and the UK Medical Research Council.