Springer, Wolfdieter

Abstract P2x purinoreceptor 7 (P2RX7), an ATP-gated ion channel, is known to play pivotal roles in the progression of Alzheimer’s disease (AD), although its cell type-specific pathological mechanisms have yet to be elucidated. Here, we show that genetic deletion of P2rx7 mitigates brain atrophy, tau accumulation and cognitive impairment in PS19 tauopathy mice. Specific deletion of P2rx7 in microglia, but not astrocytes, significantly suppresses tau propagation from the entorhinal cortex to CA1 in the hippocampus, an early event in AD pathology. Single-cell (sc)-RNA sequencing of mouse brains revealed specific P2rx7 expression in microglia, inducing inflammatory changes accompanied by elevated extracellular vesicles (EVs) secretion in PS19 mice. Brain-derived EVs (BDEVs) proteome demonstrated that P2RX7 increases EV cargo loading of tau and mitochondrial molecules in BDEVs from PS19 mice, which was further validated by single-molecule super-resolution. Notably, following the injection of BDEVs isolated from PS19 mice with or without P2rx7 deficiency, the microglial transcriptome of recipient mice revealed enriched DNA-sensing and type II interferon signaling in response to BDEVs from PS19 mice, which was diminished in the group injected with P2rx7-deficient BDEVs. Thus, our results indicate that P2RX7 regulates EV-mediated tau and mitochondrial transfer and inflammatory activation in microglia with increased EV secretion, thereby contributing to tauopathy and neurodegeneration, highlighting the therapeutic potential of targeting the P2RX7-EV axis in AD.

AbstractINTRODUCTIONPhosphorylated ubiquitin (p‐S65‐Ub) is generated during PINK1‐PRKN mitophagy as a specific marker of mitochondrial damage. Despite the widespread deposition of p‐S65‐Ub in aged and diseased human brain, the genetic contribution to its accumulation remains unclear.METHODSTo identify novel mitophagy regulators, we performed a genome‐wide association study using p‐S65‐Ub level as a quantitative trait in 1012 autopsy‐confirmed Lewy body disease (LBD) samples.RESULTSWe identified a significant genome‐wide association with p‐S65‐Ub for rs429358 (apolipoprotein E ε4 [APOE4]) and a suggestive association for rs6480922 (ZMIZ1). APOE4 was associated with higher p‐S65‐Ub levels and greater neuropathological burden. Functional validation in mouse and human induced pluripotent stem cell (iPSC) models confirmed APOE4‐mediated mitophagy alterations. Intriguingly, ZMIZ1 rs6480922 was associated with lower p‐S65‐Ub levels, reduced neuropathological load, and increased brain weight, indicating a potential protective role.DISCUSSIONOur findings underscore the importance of mitochondrial quality control in LBD pathogenesis and nominate regulators that may contribute to disease risk or resilience.Highlights p‐S65‐Ub levels were used as a quantitative marker of mitochondrial damage. A GWAS identified two genetic variants that modify mitophagy in LBD autopsy brain. APOE4 was associated with increased p‐S65‐Ub accumulation and neuropathology. APOE4 altered mitophagy via pathology‐dependent and pathology‐independent mechanisms. ZMIZ1 was linked to reduced p‐S65‐Ub and neuropathology indicative of protection.

Abstract Studies assessing genetic associations with neuropathological features in Lewy body disease (LBD) have been limited to candidate gene investigations, and therefore, information is lacking regarding the genetic architecture of the neuropathology of LBD. In the current study, we examined a large series of neuropathologically confirmed LBD cases (n = 980 in the discovery series, n = 503 in the replication series) and performed genome-wide association studies of 11 different neuropathological outcome measures. The 11 neuropathological outcomes included Braak neurofibrillary tangle (NFT) stage, Thal amyloid phase, LBD subtype, Lewy body (LB) counts in five different brain regions, dorsolateral and ventromedial putaminal tyrosine hydroxylase immunoreactivity and neuronal loss in the ventrolateral part of the substantia nigra. Associations between variants and outcomes were assessed using regression models appropriate for the nature of the given neuropathological outcome and that were adjusted for age at death, sex and top principal components of genetic data. In the discovery series, APOE rs429358 (i.e. APOE ε4) was associated with a greater severity of each of Braak NFT stage [odds ratio (OR) = 3.07, P = 2.34 × 10−32], Thal amyloid phase (OR = 3.57, P = 3.28 × 10−29) and LBD subtype (OR = 1.78, P = 9.85 × 10−9), with similar findings observed in the independent replication series (Braak NFT stage, OR = 2.30, P = 2.70 × 10−11; Thal amyloid phase, OR = 3.17, P = 6.39 × 10−18; LBD subtype, OR = 2.68, P = 3.85 × 10−10). In the subgroup of cases with lower levels of Alzheimer's disease pathology (Braak NFT stage ≤ III and Thal amyloid phase ≤2), there was a strong association between APOE rs429358 and LBD subtype even when adjusting for Braak stage and Thal phase in the discovery series (n = 218, OR = 2.47, P = 0.007) and the replication series (n = 141, OR = 3.60, P = 0.006). Although additional genome-wide significant associations were identified in the discovery series between LINC01581/MCTP2 rs547411734 and lower middle frontal LB counts, between TLE3 rs3743309 and lower cingulate LB counts, and between GRIN2A/ATF7IP2 rs1097915 and lower parahippocampal LB counts, these findings were not observed in the replication series. Our results indicate that the APOE ε4 allele is the most prominent genetic determinant of severity of neuropathology in LBD. These findings represent a key step forward in our understanding of genetic drivers of neuropathological features in LBD. Future studies utilizing meta-analytical approaches will be important to more precisely assess other associations that were not quite genome-wide significant in the discovery series.

Mutations in Leucine-rich repeat kinase 2 (LRRK2) and PTEN-induced kinase 1 (PINK1) are associated with familial Parkinson’s disease (PD). LRRK2 phosphorylates Rab guanosine triphosphatase (GTPases) within the Switch II domain while PINK1 directly phosphorylates Parkin and ubiquitin (Ub) and indirectly induces phosphorylation of a subset of Rab GTPases. Herein we have crossed LRRK2 [R1441C] mutant knock-in mice with PINK1 knock-out (KO) mice and report that loss of PINK1 does not impact endogenous LRRK2-mediated Rab phosphorylation nor do we see significant effect of mutant LRRK2 on PINK1-mediated Rab and Ub phosphorylation. In addition, we observe that a pool of the Rab-specific, protein phosphatase family member 1H phosphatase, is transcriptionally up-regulated and recruited to damaged mitochondria, independent of PINK1 or LRRK2 activity. Parallel signaling of LRRK2 and PINK1 pathways is supported by assessment of motor behavioral studies that show no evidence of genetic interaction in crossed mouse lines. Previously we showed loss of cilia in LRRK2 R1441C mice and herein we show that PINK1 KO mice exhibit a ciliogenesis defect in striatal cholinergic interneurons and astrocytes that interferes with Hedgehog induction of glial derived-neurotrophic factor transcription. This is not exacerbated in double-mutant LRRK2 and PINK1 mice. Overall, our analysis indicates that LRRK2 activation and/or loss of PINK1 function along parallel pathways to impair ciliogenesis, suggesting a convergent mechanism toward PD. Our data suggest that reversal of defects downstream of ciliogenesis offers a common therapeutic strategy for LRRK2 or PINK1 PD patients, whereas LRRK2 inhibitors that are currently in clinical trials are unlikely to benefit PINK1 PD patients.

AbstractBackgroundDirected by the enzyme pair PINK1 and PRKN, mitophagy is a crucial mitochondrial quality control mechanism that selectively decorates damaged mitochondria with phosphorylated ubiquitin (pS65‐Ub), facilitating their lysosomal degradation. The dynamic pS65‐Ub signal accumulates upon enhanced activation from increased mitochondrial damage or upon reduced autophagic‐lysosomal flux. Previous studies including ours demonstrated altered mitophagy and elevated pS65‐Ub levels in Parkinson’s and Alzheimer’s disease brains that also independently associated with α‐synuclein, tau, or amyloid pathology. However, their combined impact on mitophagy and organelle function remains unclear. Notably these three pathologies often coexist in susceptible brain areas of a neurodegenerative condition named dementia with Lewy bodies (DLB). We herein investigated the interactions of α‐synuclein, tau, and amyloid pathology to uncover their combined effects on mitophagy in a large DLB cohort.MethodThis study included 371 DLB autopsy brains with neurologically normal cases as controls. Immunohistochemistry for the mitophagy marker pS65‐Ub in the hippocampus and amygdala was performed and associations of pS65‐Ub levels with neuropathological measures from the same region were evaluated. Immunofluorescence co‐staining of pS65‐Ub, phospho‐α‐synuclein, and phospho‐tau was conducted to study their interactions at single‐cell level.ResultpS65‐Ub positive cells were significantly more abundant in the hippocampus and amygdala of DLB cases compared to controls. Significant associations were observed between pS65‐Ub levels with age, brain weight, Braak stage, Thal phase as well as counts of Lewy body (LB), neurofibrillary tangle (NFT), and senile plaque (SP) in both regions. Strong synergistic effects of LB and NFT pathologies on pS65‐Ub accumulation were found in the amygdala, while only additive effects of LB and SP pathologies were observed. Single‐cell analysis in the amygdala showed that most affected cells contained either LB or NFT inclusion rather than co‐residing two pathologies within the same cell. Notably, cells harboring LB pathology exhibited mainly smaller, granular pS65‐Ub deposits (type G), possibly associated with increased mitochondrial dysfunction. Conversely, those containing NFT showed larger, vacuolar pS65‐Ub deposits (type V), likely resulting from reduced lysosomal degradation.ConclusionOur study revealed complex interactions of α‐synuclein, tau, and amyloid pathology on mitophagy alteration in DLB brains, highlighting different molecular mechanisms underlying α‐synuclein‐ and tau‐associated mitophagy alterations.

AbstractBackgroundUFMylation is an understudied ubiquitin‐like post‐translational modification (PTM). Like ubiquitin, UFM1 is conjugated to substrates via a catalytic cascade involving a UFM1‐specific E1 (UBA5), E2 (UFC1), and an E3 ligase complex (UFL1, DDRGK1 and CDK5RAP3). UFMylation is reversible, and this is mediated by UFSP2. UFMylation plays essential roles in several biological processes including the DNA damage response, endoplasmic reticulum homeostasis, unfolded protein response, autophagic functions, and immune response. Importantly, UFMylation is also crucial for healthy brain development. Alzheimer’s disease (AD), a complex neurodegenerative disorder, is characterized by the accumulation of pathologic tau and beta‐amyloid proteins and has been associated with abnormalities in the aforementioned processes. Intriguingly, the potential link between AD and UFMylation has not been investigated yet. Considering that pathological tau plays a critical role in AD, and tau also plays an important role for the DNA damage response in neurons under physiological conditions, we speculated that tau itself could be modified with UFM1.MethodWe performed Western blot and Meso Scale Discovery based ELISA to measure the protein level of UFM1, UFSP2 and other UFMylation pathway components in RIPA‐soluble and insoluble fraction in human post‐mortem frontal cortex. To test whether tau can be modified by UFM1, we performed co‐immunoprecipitation (Co‐IP), Proximity Ligation Assays (PLA) and liquid chromatography‐tandem mass spectrometry (LC‐MS/MS).ResultWe found a significant reduction of soluble UFSP2, but an increase of soluble total UFM1 in AD compared to controls. We found that tau interacts with UFL1 and DDRGK1. In addition, using immunoprecipitation of denaturing lysates we found that tau can indeed be covalently modified by UFM1 when overexpressed. We detected strong signal of HA‐UFM1‐tau in neurons but not in negative controls using PLA. Furthermore, we immunoprecipitated denatured UFM1 from human autopsy brain, and detected two specific UFM1‐tau bands with tau antibodies. Together, this data strongly indicates that tau is UFMylated under endogenous conditions. Using LC‐MS/MS, we identified 17 UFMylation sites in tau proteins.ConclusionUFMylation is dysregulated in AD; tau protein can be modified by UFM1 both in vitro and in vivo, which enables a more comprehensive understanding of tau PTMs.

ABSTRACT Background Inclusion body myositis (IBM) is the most prevalent muscle disease in adults for which no current treatment exists. The pathogenesis of IBM remains poorly defined. In this study, we aimed to explore the interplay between inflammation and mitochondrial dysfunction in IBM. Methods The study population consisted of 38 IBM patients and 22 age‐ and sex‐matched controls without a myopathy. Mean age was 62.9 years (SD = 9) in IBM group and 59.7 (10) in controls. Bulk RNA sequencing, Meso Scale Discovery electrochemiluminescence (ECL), western blotting, histochemistry and immunohistochemistry were performed on frozen muscle samples from the study participants. Results We demonstrated activation of the NLRP3 inflammasome in IBM muscle samples, with the NLRP3 inflammasome being the most upregulated pathway on RNA sequencing, along with increased expression of NLRP3 and ASC proteins in IBM group. NLRP3 RNA levels most strongly correlated with TLR7 (correlation coefficient ρ = 0.91) and complement activation‐related genes, and inversely correlated with several mitochondria‐related genes among others. On muscle histopathology, there was increased NRLP3 immunoreactivity in both inflammatory cells and muscle fibres. Mitophagy is critical for removing damaged mitochondria and preventing the formation of a vicious cycle of mitochondrial dysfunction—NLRP3 inflammasome activation. Herein, we showed altered mitophagy, as witnessed by the elevated levels of p‐S65‐Ubiquitin, a mitophagy marker, in muscle lysates from IBM patients compared to controls (median of 114.3 vs. 81.25 ECL units, p = 0.005). The p‐S65‐Ubiquitin levels were most significantly elevated in IBM males compared to male controls (136 vs. 83.5 ECL units; p = 0.013), whereas IBM females had milder nonsignificant elevation compared to female controls (97.25 vs. 69 ECL units, p = 0.31). On muscle histopathology, p‐S65‐Ubiquitin aggregates accumulated in muscle fibres that were mostly Type 2 and devoid of cytochrome‐c‐oxidase reactivity. NLRP3 RNA levels correlated with p‐S65‐Ubiquitin levels in both sexes (males: ρ = 0.48, females: ρ = 0.54) but with loss of muscle strength, as reflected by the manual motor test score, only in males (males: ρ = 0.62, females: ρ = −0.14). Lastly, we identified sex‐specific molecular pathways in IBM. Females had upregulation of pathways related to response to stress, which could conceivably offset some of the pathomechanisms of IBM, while males had upregulation of pathways related to cell adhesion and migration. Conclusions There is activation of the NLRP3 inflammasome in IBM, along with altered mitophagy, particularly in males, which is of potential therapeutic significance. These findings suggest sex‐specific mechanisms in IBM that warrant further investigation.