Fiesel, Fabienne C

Abstract Genetic loss of the mitochondrial control enzyme PINK1 leads to Parkinson’s disease, characterized by dopaminergic neuron degeneration and neuroinflammation, yet its role in glia remains poorly understood. To address this gap, we investigated how the function of astrocytes and their ability to support neurons is influenced by PINK1 deficiency. For the first time, we demonstrate that human astrocytes exhibit robust PINK1 activity. Next, the first bulk transcriptomic study of human PINK1 mutant astrocytes was performed followed by biochemical validation at the protein level, uncovering homeostatic collapse. Co-culture experiments demonstrated that this astrocyte dysfunction drives neuronal damage through non-cell-autonomous mechanisms. Notably, pharmacological enhancement of autophagy successfully mitigated this inflammatory secretome, indicating that mitochondrial quality control deficits are reversible. These findings establish an unexpected role for PINK1 in glial biology, reveal that astrocytes are vulnerable to mitophagy deficits, and highlight a novel mechanistic link connecting mitochondrial dysfunction, neuroinflammation, and neurodegeneration.

Abstract Parkinson’s disease (PD) is commonly associated with dysfunctional mitochondrial homeostasis. PINK1, a S/T kinase mutated in early-onset PD, generates phosphoserine 65 ubiquitin (pS65Ub) on damaged mitochondria facilitating their removal. Here, we show that pS65Ub translocates into the nucleus after generation at damaged mitochondria and is directly attached to substrates by resident E3 ligases. Histone H2A is a major substrate and is modified at lysine 119 (H2AK119) by the polycomb silencer, E3 ligase RING1B. At nucleosomes, pS65Ub simultaneously suppresses RING1B and potentiates H2A deubiquitinases USP16 and USP21. Epigenetic profiling and RNA sequencing reveal that pS65Ub is enriched at the promoters of poorly expressed yet dynamically regulated genes and is associated with H2AK119ub depletion. Functionally, we show that pS65Ub enrichment drives polycomb target gene expression, which accelerates the maturation of dopaminergic neurons. Importantly, post-mortem PD brains exhibit elevated nuclear pS65Ub, potentially linking nuclear pS65Ub accumulation with disease pathogenesis. Together, these data indicate that pS65Ub generated at damaged mitochondria regulates fundamental cellular processes at distant sites.

Objective Lewy body disease (LBD) is a complex neurodegenerative disorder characterized by the accumulation of misfolded α‐synuclein in the brain. Neuroinflammation has long been implicated in LBD pathogenesis, and recent genetic studies in Parkinson's disease (a clinical manifestation of LBD) have shown consistent association with the human leukocyte antigen (HLA) gene complex. Here, we assessed whether variation in HLA alleles influences neuropathological burden in a neuropathologically‐defined series of LBD cases. Methods We conducted a comprehensive analysis of HLA allelic variants in a cohort of 539 LBD cases of European descent from the Mayo Clinic brain bank. High‐resolution whole‐genome sequencing was used, and the HLA alleles of each sample were called using the HLA*LA tool and assessed for association with neuropathological outcomes. Results Our analysis identified 1 significant ( P < 3.43 × 10 −5 ) and 4 suggestive ( P < 0.001) associations between certain HLA alleles and specific neuropathological outcomes in LBD, suggesting a potential role for HLA‐mediated immune mechanisms in disease progression and subtype differentiation. Specifically, HLA‐DPB1*06:01 was significantly associated with lower Lewy body counts in the parahippocampal gyrus ( P = 3.30 × 10 −5 ), with weaker and suggestive associations observed in the middle frontal ( P = 1.80 × 10 −4 ) and inferior parietal gyrus ( P = 6.33 × 10 −4 ). Additionally, although only suggestive, HLA‐DRB1*11:01 correlated with a lower Thal amyloid phase ( P = 1.56 x 10 −4 ), and HLA‐B*15:01 correlated with an increased risk of diffuse LBD ( P = 7.58 x 10 −4 ). Interpretation This study provides a detailed evaluation of the relationship between HLA alleles and LBD pathology, highlighting the importance of immune‐related genetic factors in the etiology of LBD. ANN NEUROL 2026;99:492–501

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.

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.

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.