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WDR45 plays an essential role in the early stage of autophagy. De novo heterozygous mutations in WDR45 have been known to cause β-propeller protein-associated neurodegeneration (BPAN), a subtype of neurodegeneration with brain iron accumulation (NBIA). Although BPAN patients display global developmental delay with intellectual disability, the neurodevelopmental pathophysiology of BPAN remains largely unknown. In the present study, we analyzed the physiological role of Wdr45 and pathophysiological significance of the gene abnormality during mouse brain development. Morphological and biochemical analyses revealed that Wdr45 is expressed in a developmental stage-dependent manner in mouse brain. Wdr45 was also found to be located in excitatory synapses by biochemical fractionation. Since WDR45 mutations are thought to cause protein degradation, we conducted acute knockdown experiments by in utero electroporation in mice to recapitulate the pathophysiological conditions of BPAN. Knockdown of Wdr45 caused abnormal dendritic development and synaptogenesis during corticogenesis, both of which were significantly rescued by co-expression with RNAi-resistant version of Wdr45. In addition, terminal arbors of callosal axons were less developed in Wdr45-deficient cortical neurons of adult mouse when compared to control cells. These results strongly suggest a pathophysiological significance of WDR45 gene abnormalities in neurodevelopmental aspects of BPAN.

Neurodegeneration with brain iron accumulation (NBIA) involves a group of rare neurogenetic disorders often linked with iron overload in the basal nuclei of the brain presenting with spasticity, dystonia, muscle rigidity, neuropsychiatric symptoms, and retinal degeneration. Among NBIA subtypes, beta-propeller-protein-associated neurodegeneration (BPAN) is associated with mutations in the autophagy gene WDR45 (WD repeat domain 45). Previously, we demonstrated that WDR45 mutations in BPAN cellular models impaired autophagy, iron metabolism, and cell bioenergetics. In addition, antioxidant supplementation partially improved cell physiopathology; however, autophagy and cell bioenergetics remained affected. In this work, we explored the possibility of expressing the normal WDR45 allele present in the inactive chromosome X (Xi) of BPAN cells through treatment with epigenetic modulators. The aim of this study was to demonstrate whether biotin, an epigenetic nutrient, was able to restore the expression levels of WDR45 by a mechanism involving Xi reactivation and, consequently, correct BPAN defects. Our study demonstrated that biotin supplementation increases histone biotinylation and allows for the transcription of the WDR45 allele in Xi. Consequently, all physiopathological alterations in BPAN cells were notably corrected. The reactivation of Xi by epigenetic modulators can be a promising approach for the treatment of BPAN and other X-linked diseases.

Contrary to previous findings, this study finds that ablation of microglia, the resident macrophages of the brain, does not affect amyloid plaque or neuritic pathology in two mouse models of Alzheimer's disease. In Alzheimer's disease, microglia cluster around β-amyloid deposits, suggesting that these cells are important for amyloid plaque formation, maintenance and/or clearance. We crossed two distinct APP transgenic mouse strains with CD11b - HSVTK mice, in which nearly complete ablation of microglia was achieved for up to 4 weeks after ganciclovir application. Neither amyloid plaque formation and maintenance nor amyloid-associated neuritic dystrophy depended on the presence of microglia.

Increased iron levels, common in neurodegenerative diseases, correlate with disease severity, suggesting a role in the pathological process. Recently, efforts have been made to understand the role of iron in cerebral inflammatory processes. Employing astrocyte cell models of genetic neurodegenerative pathologies characterized by iron imbalance, such as the neurodegeneration with brain iron accumulation disorders, can provide valuable insights into astrocytes reactivity, a pivotal process in brain inflammation. Specifically, we employed human-induced pluripotent stem cell-derived astrocytes from Neuroferritinopathy, where iron accumulation is primary. After confirming iron accumulation and the deregulation of proteins involved in iron management, we observed that at 35 days since the beginning of differentiation, the elevated iron levels not only trigger ferroptosis but also place the astrocytes in a reactive state. This is evident in the higher extracellular concentrations of IL-6, IL-1β, and glutamate, along with changes in morphology, genes, and proteins involved in astrocyte reactivity. Interestingly, by day 60, IL-6 and IL-1β levels drop below those of the controls, and we observe a reversal in most of the factors considered. Moreover, at day 60, it is possible to observe not only increased senescence but also ferroptosis. These findings demonstrate that iron plays a primary role in inducing astrocyte reactivity.

The ‘neurodegeneration with brain iron accumulation’ (NBIA) disease family entails movement or cognitive impairment, often with psychiatric features. To understand how iron loading affects the brain, we studied mice with disruption of two iron regulatory genes, hemochromatosis ( Hfe ) and transferrin receptor 2 ( Tfr2 ). Inductively coupled plasma atomic emission spectroscopy demonstrated increased iron in the Hfe −/− × Tfr2 mut brain ( P =0.002, n ≥5/group), primarily localized by Perls’ staining to myelinated structures. Western immunoblotting showed increases of the iron storage protein ferritin light polypeptide and microarray and real-time reverse transcription-PCR revealed decreased transcript levels ( P <0.04, n ≥5/group) for five other NBIA genes, phospholipase A2 group VI , fatty acid 2-hydroxylase , ceruloplasmin , chromosome 19 open reading frame 12 and ATPase type 13A2 . Apart from the ferroxidase ceruloplasmin, all are involved in myelin homeostasis; 16 other myelin-related genes also showed reduced expression ( P <0.05), although gross myelin structure and integrity appear unaffected ( P >0.05). Overlap ( P <0.0001) of differentially expressed genes in Hfe −/− × Tfr2 mut brain with human gene co-expression networks suggests iron loading influences expression of NBIA-related and myelin-related genes co-expressed in normal human basal ganglia. There was overlap ( P <0.0001) of genes differentially expressed in Hfe −/− × Tfr2 mut brain and post-mortem NBIA basal ganglia. Hfe −/− × Tfr2 mut mice were hyperactive ( P <0.0112) without apparent cognitive impairment by IntelliCage testing ( P >0.05). These results implicate myelin-related systems involved in NBIA neuropathogenesis in early responses to iron loading. This may contribute to behavioral symptoms in NBIA and hemochromatosis and is relevant to patients with abnormal iron status and psychiatric disorders involving myelin abnormalities or resistant to conventional treatments.

Infantile neuroaxonal dystrophy (INAD) is caused by recessive variants in PLA2G6 and is a lethal pediatric neurodegenerative disorder. Loss of the Drosophila homolog of PLA2G6 , leads to ceramide accumulation, lysosome expansion, and mitochondrial defects. Here, we report that retromer function, ceramide metabolism, the endolysosomal pathway, and mitochondrial morphology are affected in INAD patient-derived neurons. We show that in INAD mouse models, the same features are affected in Purkinje cells, arguing that the neuropathological mechanisms are evolutionary conserved and that these features can be used as biomarkers. We tested 20 drugs that target these pathways and found that Ambroxol, Desipramine, Azoramide, and Genistein alleviate neurodegenerative phenotypes in INAD flies and INAD patient-derived neural progenitor cells. We also develop an AAV-based gene therapy approach that delays neurodegeneration and prolongs lifespan in an INAD mouse model.

Neuroferritinopathy is a rare autosomal dominant inherited movement disorder caused by alteration of the L-ferritin gene that results in the production of a ferritin molecule that is unable to properly manage iron, leading to the presence of free redox-active iron in the cytosol. This form of iron has detrimental effects on cells, particularly severe for neuronal cells, which are highly sensitive to oxidative stress. Although very rare, the disorder is notable for two reasons. First, neuroferritinopathy displays features also found in a larger group of disorders named Neurodegeneration with Brain Iron Accumulation (NBIA), such as iron deposition in the basal ganglia and extrapyramidal symptoms; thus, the elucidation of its pathogenic mechanism may contribute to clarifying the incompletely understood aspects of NBIA. Second, neuroferritinopathy shows the characteristic signs of an accelerated process of aging; thus, it can be considered an interesting model to study the progress of aging. Here, we will review the clinical and neurological features of neuroferritinopathy and summarize biochemical studies and data from cellular and animal models to propose a pathogenic mechanism of the disorder.

PLA2G6-associated neurodegeneration (PLAN) is a group of rare genetic disorders characterised by progressive neurodegeneration resulting from mutations in the PLA2G6 gene, encoding a calcium-independent phospholipase enzyme. Here, we have explored the effects of decanoic acid (DA), a medium-chain fatty acid, in the fruit fly Drosophila melanogaster models of PLAN and show that DA treatment significantly extends the lifespan, reduces bang sensitivity and improves resistance to heat shock stress. Transcriptional analysis showed that DA affects genes in key signalling pathways, including Insulin/Insulin-like Growth Factor, mTOR, heat shock response, Sirtuin, autophagy and mitochondrial function. Additionally, DA treatment alters the metabolite profiles in PLAN model flies, with the most pronounced changes observed in gut tissue. Pathway analysis of these metabolomic shifts highlights potential therapeutic effects of DA in several pathways, including ATP-binding cassette (ABC) transporters, purine metabolism, cAMP signalling and neuroactive ligand-receptor interactions. These findings suggest that DA may be a promising therapeutic agent for PLAN, offering insights into the mechanisms of the disease and paving the way for future research on medium-chain fatty acids as potential treatments for neurodegenerative diseases.

Neurodegeneration with brain iron accumulation (NBIA) is a group of rare diseases associated with genetic mutations in several genes including C19orf12. To explore the underlying mechanism of NBIA pathogenesis, we investigated a mouse homolog of human C19orf12 gene knockout mouse model. In the brains of knockout mice, an age-dependent accumulation of abundant axonal spheroids, alongside brain iron accumulation, neuroinflammation, α-synuclein and ubiquitin pathology was observed. Axonal spheroids were associated with abnormal ER and damaged mitochondria in knockout mice. These abnormal spheroids consistently contained the tubular ER protein reticulon 3 (RTN3) even at younger ages which preceded the onset of motor symptoms. The abnormal localized expansion of axonal ER underlies swollen axon terminals of dopaminergic neurons. The accumulated neuroaxonal swellings likely impair functioning of the dopaminergic system in the substantia nigra, striatum, and other brain regions, which ultimately led to motor function deficits in knockout mice. Altogether, the absence of C19orf12 in mouse brains recapitulates cardinal features of neuropathology in human NBIA, suggesting that C19orf12 is essential to maintain the tubular ER homeostasis in neuronal axon.

Iron is an essential metal ion implicated in several cellular processes. However, the reactive nature of iron renders this metal ion potentially dangerous for cells, and its levels need to be tightly controlled. Alterations in the intracellular concentration of iron are associated with different neuropathological conditions, including neurodegeneration with brain iron accumulation (NBIA). As the name suggests, NBIA encompasses a class of rare and still poorly investigated neurodegenerative disorders characterized by an abnormal accumulation of iron in the brain. NBIA is mostly a genetic pathology, and to date, 10 genes have been linked to familial forms of NBIA. In the present review, after the description of the principal mechanisms implicated in iron homeostasis, we summarize the research data concerning the pathological mechanisms underlying the genetic forms of NBIA and discuss the potential involvement of iron in such processes. The picture that emerges is that, while iron overload can contribute to the pathogenesis of NBIA, it does not seem to be the causal factor in most forms of the pathology. The onset of these pathologies is rather caused by a combination of processes involving the interplay between lipid metabolism, mitochondrial functions, and autophagic activity, eventually leading to iron dyshomeostasis.