m6A-dependent circular RNA formation mediates tau-induced neurotoxicity.

Circular RNAs (circRNAs), covalently closed RNA molecules that form due to back-splicing of RNA transcripts, have recently been implicated in Alzheimer's disease and related tauopathies. circRNAs are regulated by N6-methyladenosine (m6A) RNA methylation, can serve as "sponges" for proteins and RNAs, and can be translated into protein via a cap-independent mechanism. Mechanisms underlying circRNA dysregulation in tauopathies and causal relationships between circRNA and neurodegeneration are currently unknown. In the current study, we aimed to determine whether pathogenic forms of tau drive circRNA dysregulation and whether such dysregulation causally mediates neurodegeneration. We identify circRNAs that are differentially expressed in the brain of a Drosophila model of tauopathy and in induced pluripotent stem cell (iPSC)-derived neurons carrying a tau mutation associated with autosomal dominant tauopathy. We leverage Drosophila to discover that depletion of circular forms of muscleblind (circMbl), a circRNA that is particularly abundant in brains of tau transgenic Drosophila, significantly suppresses tau neurotoxicity, suggesting that tau-induced circMbl elevation is neurotoxic. We detect a general elevation of m6A RNA methylation and circRNA methylation in tau transgenic Drosophila and find that tau-induced m6A methylation is a mechanistic driver of circMbl formation. Interestingly, we find that circRNA and m6A RNA accumulate within nuclear envelope invaginations of tau transgenic Drosophila and in iPSC-derived cerebral organoid models of tauopathy. Taken together, our studies add critical new insight into the mechanisms underlying circRNA dysregulation in tauopathy and identify m6A-modified circRNA as a causal factor contributing to neurodegeneration. These findings add to a growing literature implicating pathogenic forms of tau as drivers of altered RNA metabolism.

TauLUM, an in vivo Drosophila sensor of tau multimerization, identifies neuroprotective interventions in tauopathy.

Tau protein aggregates are a defining neuropathological feature of "tauopathies," a group of neurodegenerative disorders that include Alzheimer's disease. In the current study, we develop a Drosophila split-luciferase-based sensor of tau-tau interaction. This model, which we term "tauLUM," allows investigators to quantify tau multimerization at individual time points or longitudinally in adult, living animals housed in a 96-well plate. TauLUM causes cell death in the adult Drosophila brain and responds to both pharmacological and genetic interventions. We find that transgenic expression of an anti-tau intrabody or pharmacological inhibition of HSP90 reduces tau multimerization and cell death in tauLUM flies, establishing the suitability of this system for future drug and genetic modifier screening. Overall, our studies position tauLUM as a powerful in vivo discovery platform that leverages the advantages of the Drosophila model organism to better understand tau multimerization.

Genome-wide association study and functional validation implicates JADE1 in tauopathy.

Primary age-related tauopathy (PART) is a neurodegenerative pathology with features distinct from but also overlapping with Alzheimer disease (AD). While both exhibit Alzheimer-type temporal lobe neurofibrillary degeneration alongside amnestic cognitive impairment, PART develops independently of amyloid-ß (Aß) plaques. The pathogenesis of PART is not known, but evidence suggests an association with genes that promote tau pathology and others that protect from Aß toxicity. Here, we performed a genetic association study in an autopsy cohort of individuals with PART (n = 647) using Braak neurofibrillary tangle stage as a quantitative trait. We found some significant associations with candidate loci associated with AD (SLC24A4, MS4A6A, HS3ST1) and progressive supranuclear palsy (MAPT and EIF2AK3). Genome-wide association analysis revealed a novel significant association with a single nucleotide polymorphism on chromosome 4 (rs56405341) in a locus containing three genes, including JADE1 which was significantly upregulated in tangle-bearing neurons by single-soma RNA-seq. Immunohistochemical studies using antisera targeting JADE1 protein revealed localization within tau aggregates in autopsy brains with four microtubule-binding domain repeats (4R) isoforms and mixed 3R/4R, but not with 3R exclusively. Co-immunoprecipitation in post-mortem human PART brain tissue revealed a specific binding of JADE1 protein to four repeat tau lacking N-terminal inserts (0N4R). Finally, knockdown of the Drosophila JADE1 homolog rhinoceros (rno) enhanced tau-induced toxicity and apoptosis in vivo in a humanized 0N4R mutant tau knock-in model, as quantified by rough eye phenotype and terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) in the fly brain. Together, these findings indicate that PART has a genetic architecture that partially overlaps with AD and other tauopathies and suggests a novel role for JADE1 as a modifier of neurofibrillary degeneration.

Emerging roles of CCM genes during tumorigenesis with potential application as novel biomarkers across major types of cancers.

Cerebral cavernous malformations (CCMs) are microvascular anomalies in the brain that result in increased susceptibility to stroke. Three genes have been identified as causes of CCMs: cerebral cavernous malformations 1 [(CCM1) also termed Krev interaction trapped 1 (KRIT1)], cerebral cavernous malformation 2 [(CCM2) also termed MGC4607] and cerebral cavernous malformation 3 [(CCM3) also termed programmed cell death 10 (PDCD10)]. It has been demonstrated that both CCM1 and CCM3 bind to CCM2 to form a CCM signaling complex (CSC) with which to modulate multiple signaling cascades. CCM proteins have been reported to play major roles in microvascular angiogenesis in human and animal models. However, CCM proteins are ubiquitously expressed in all major tissues, suggesting an unseen broader role of the CSC in biogenesis. Recent evidence suggests the possible involvement of the CSC complex during tumorigenesis; however, studies concerning this aspect are limited. This is the first report to systematically investigate the expression patterns of CCM proteins in major human tumors using real­time quantitative PCR, RNA­fluorescence in situ hybridization, immunohistochemistry and multicolor immunofluorescence imaging. Our data demonstrated that differential expression patterns of the CSC complex are correlated with certain types and grades of major human cancers, indicating the potential application of CCM genes as molecular biomarkers for clinical oncology. Our data strongly suggest that more efforts are needed to elucidate the role of the CSC complex in tumorigenesis, which may have enormous clinical potential for cancer diagnostic, prognostic and therapeutic applications.