Ataxia with giant axonopathy in Acbd5-deficient mice halted by adeno-associated virus gene therapy

Acyl-CoA binding domain containing 5 (ACBD5) is a critical player in handling very long chain fatty acids (VLCFA) en route for peroxisomal β-oxidation. Mutations in ACBD5 lead to the accumulation of VLCFA and patients present retinal dystrophy, ataxia, psychomotor delay and a severe leukodystrophy. Using CRISPR/Cas9, we generated and characterized an Acbd5 Gly357* mutant allele. Gly357* mutant mice recapitulated key features of the human disorder, including reduced survival, impaired locomotion and reflexes, loss of photoreceptors, and demyelination. The ataxic presentation of Gly357* mice involved the loss of cerebellar Purkinje cells and a giant axonopathy throughout the CNS. Lipidomic studies provided evidence for the extensive lipid dysregulation caused by VLCFA accumulation. Following a proteomic survey, functional studies in neurons treated with VLCFA unravelled a deregulated cytoskeleton with reduced actin dynamics and increased neuronal filopodia. We also show that an adeno-associated virus-mediated gene delivery ameliorated the gait phenotypes and the giant axonopathy, also improving myelination and astrocyte reactivity. Collectively, we established a mouse model with significance for VLCFA-related disorders. The development of relevant neuropathological outcomes enabled the understanding of mechanisms modulated by VLCFA and the evaluation of the efficacy of preclinical therapeutic interventions.

The pathology of X-linked adrenoleukodystrophy: tissue specific changes as a clue to pathophysiology

Although the pathology of X-linked adrenoleukodystrophy (ALD) is well described, it represents the end-stage of neurodegeneration. It is still unclear what cell types are initially involved and what their role is in the disease process. Revisiting the seminal post-mortem studies from the 1970s can generate new hypotheses on pathophysiology. This review describes (histo)pathological changes of the brain and spinal cord in ALD. It aims at integrating older works with current insights and at providing an overarching theory on the pathophysiology of ALD. The data point to an important role for axons and glia in the pathology of both the myelopathy and leukodystrophy of ALD. In-depth pathological analyses with new techniques could help further unravel the sequence of events behind the pathology of ALD.

Biomarker-based risk prediction for the onset of neuroinflammation in X-linked adrenoleukodystrophy

BACKGROUND

X-linked adrenoleukodystrophy (X-ALD) is highly variable, ranging from slowly progressive adrenomyeloneuropathy to severe brain demyelination and inflammation (cerebral ALD, CALD) affecting males with childhood peak onset. Risk models integrating blood-based biomarkers to indicate CALD onset, enabling timely interventions, are lacking. Therefore, we evaluated the prognostic value of blood biomarkers in addition to current neuroimaging predictors for early detection of CALD.

METHODS

We measured blood biomarkers in a retrospective, male CALD risk-assessment cohort consisting of 134 X-ALD patients and 66 controls and in a phenotype-blinded validation set (25 X-ALD boys, 4-13 years) using Simoa®and Luminex® technologies.

FINDINGS

Among 25 biomarkers indicating axonal damage, astrocye/microglia activation, or immune-cell recruitment, neurofilament light chain (NfL) had the highest prognostic value for early indication of childhood/adolescent CALD. A plasma NfL cut-off level of 8.33 pg/mL, determined in the assessment cohort, correctly discriminated CALD with an accuracy of 96% [95% CI: 80-100] in the validation group. Multivariable logistic regression models revealed that combining NfL with GFAP or cytokines/chemokines (IL-15, IL-12p40, CXCL8, CCL11, CCL22, and IL-4) that were significantly elevated in CALD vs healthy controls had no additional benefit for detecting neuroinflammation. Some cytokines/chemokines were elevated only in childhood/adolescent CALD and already upregulated in asymptomatic X-ALD children (IL-15, IL-12p40, and CCL7). In adults, NfL levels distinguished CALD but were lower than in childhood/adolescent CALD patients with similar (MRI) lesion severity. Blood GFAP did not differentiate CALD from non-inflammatory X-ALD.

INTERPRETATION

Biomarker-based risk prediction with a plasma NfL cut-off value of 8.33 pg/mL, determined by ROC analysis, indicates CALD onset with high sensitivity and specificity in childhood X-ALD patients. A specific pro-inflammatory cytokine/chemokine profile in asymptomatic X-ALD boys may indicate a primed, immanent inflammatory state aligning with peak onset of CALD. Age-related differences in biomarker levels in adult vs childhood CALD patients warrants caution in predicting onset and progression of CALD in adults. Further evaluations are needed to assess clinical utility of the NfL cut-off for risk prognosis of CALD onset.

FUNDING

Austrian Science Fund, European Leukodystrophy Association.

Abcd1 deficiency accelerates cuprizone-induced oligodendrocyte loss and axonopathy in a demyelinating mouse model of X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD), the most frequent, inherited peroxisomal disease, is caused by mutations in the ABCD1 gene encoding a peroxisomal lipid transporter importing very long-chain fatty acids (VLCFAs) from the cytosol into peroxisomes for degradation via β-oxidation. ABCD1 deficiency results in accumulation of VLCFAs in tissues and body fluids of X-ALD patients with a wide range of phenotypic manifestations. The most severe variant, cerebral X-ALD (CALD) is characterized by progressive inflammation, loss of the myelin-producing oligodendrocytes and demyelination of the cerebral white matter. Whether the oligodendrocyte loss and demyelination in CALD are caused by a primary cell autonomous defect or injury to oligodendrocytes or by a secondary effect of the inflammatory reaction remains unresolved. To address the role of X-ALD oligodendrocytes in demyelinating pathophysiology, we combined the Abcd1 deficient X-ALD mouse model, in which VLCFAs accumulate without spontaneous demyelination, with the cuprizone model of toxic demyelination. In mice, the copper chelator cuprizone induces reproducible demyelination in the corpus callosum, followed by remyelination upon cuprizone removal. By immunohistochemical analyses of oligodendrocytes, myelin, axonal damage and microglia activation during de-and remyelination, we found that the mature oligodendrocytes of Abcd1 KO mice are more susceptible to cuprizone-induced cell death compared to WT mice in the early demyelinating phase. Furthermore, this effect was mirrored by a greater extent of acute axonal damage during demyelination in the KO mice. Abcd1 deficiency did not affect the function of microglia in either phase of the treatment. Also, the proliferation and differentiation of oligodendrocyte precursor cells and remyelination progressed at similar rates in both genotypes. Taken together, our findings point to an effect of Abcd1 deficiency on mature oligodendrocytes and the oligodendrocyte-axon unit, leading to increased vulnerability in the context of a demyelinating insult.

The Role of Small Heat Shock Proteins in Protein Misfolding Associated Motoneuron Diseases

Motoneuron diseases (MNDs) are neurodegenerative conditions associated with death of upper and/or lower motoneurons (MNs). Proteostasis alteration is a pathogenic mechanism involved in many MNDs and is due to the excessive presence of misfolded and aggregated proteins. Protein misfolding may be the product of gene mutations, or due to defects in the translation process, or to stress agents; all these conditions may alter the native conformation of proteins making them prone to aggregate. Alternatively, mutations in members of the protein quality control (PQC) system may determine a loss of function of the proteostasis network. This causes an impairment in the capability to handle and remove aberrant or damaged proteins. The PQC system consists of the degradative pathways, which are the autophagy and the proteasome, and a network of chaperones and co-chaperones. Among these components, Heat Shock Protein 70 represents the main factor in substrate triage to folding, refolding, or degradation, and it is assisted in this task by a subclass of the chaperone network, the small heat shock protein (sHSPs/HSPBs) family. HSPBs take part in proteostasis by bridging misfolded and aggregated proteins to the HSP70 machinery and to the degradative pathways, facilitating refolding or clearance of the potentially toxic proteins. Because of its activity against proteostasis alteration, the chaperone system plays a relevant role in the protection against proteotoxicity in MNDs. Here, we discuss the role of HSPBs in MNDs and which HSPBs may represent a valid target for therapeutic purposes.

Human iPSC-derived astrocytes generated from donors with globoid cell leukodystrophy display phenotypes associated with disease

Globoid cell leukodystrophy (Krabbe disease) is a fatal neurodegenerative, demyelinating disease caused by dysfunctional activity of galactosylceramidase (GALC), leading to the accumulation of glycosphingolipids including psychosine. While oligodendrocytes have been extensively studied due to their high levels of GALC, the contribution of astrocytes to disease pathogenesis remains to be fully elucidated. In the current study, we generated induced pluripotent stem cells (iPSCs) from two donors with infantile onset Krabbe disease and differentiated them into cultures of astrocytes. Krabbe astrocytes recapitulated many key findings observed in humans and rodent models of the disease, including the accumulation of psychosine and elevated expression of the pro-inflammatory cytokine IL-6. Unexpectedly, Krabbe astrocytes had higher levels of glucosylceramide and ceramide, and displayed compensatory changes in genes encoding glycosphingolipid biosynthetic enzymes, suggesting a shunting away from the galactosylceramide and psychosine pathway. In co-culture, Krabbe astrocytes negatively impacted the survival of iPSC-derived human neurons while enhancing survival of iPSC-derived human microglia. Substrate reduction approaches targeting either glucosylceramide synthase or serine palmitoyltransferase to reduce the sphingolipids elevated in Krabbe astrocytes failed to rescue their detrimental impact on neuron survival. Our results suggest that astrocytes may contribute to the progression of Krabbe disease and warrant further exploration into their role as therapeutic targets.

Beneficial Effects of the Direct AMP-Kinase Activator PXL770 in In Vitro and In Vivo Models of X-Linked Adrenoleukodystrophy

X-linked adrenoleukodystrophy (ALD) is a severe orphan disease caused by mutations in the peroxisomal ABCD1 transporter gene, leading to toxic accumulation of Very Long-Chain Fatty Acids (VLCFA - in particular C26:0) resulting in inflammation, mitochondrial dysfunction and demyelination. AMP-activated protein kinase (AMPK) is downregulated in ALD, and its activation is implicated as a therapeutic target. PXL770 is the first direct allosteric AMPK activator with established clinical efficacy and tolerability. Methods: We investigated its effects in ALD patient-derived fibroblasts/lymphocytes and Abcd1 KO mouse glial cells. Readouts included VLCFA levels, mitochondrial function and mRNA levels of proinflammatory genes and compensatory transporters (ABCD2-3). After PXL770 treatment in Abcd1 KO mice, we assessed VLCFA levels in tissues, sciatic nerve axonal morphology by electronic microscopy and locomotor function by open-field/balance-beam tests. Results: In patients' cells and Abcd1 KO glial cells, PXL770 substantially decreased C26:0 levels (by ∼90%), improved mitochondrial respiration, reduced expression of multiple inflammatory genes and induced expression of ABCD2-3 In Abcd1 KO mice, PXL770 treatment normalized VLCFA in plasma and significantly reduced elevated levels in brain (-25%) and spinal cord (-32%) versus untreated (P < 0.001). Abnormal sciatic nerve axonal morphology was also improved along with amelioration of locomotor function. Conclusion: Direct AMPK activation exerts beneficial effects on several hallmarks of pathology in multiple ALD models in vitro and in vivo, supporting clinical development of PXL770 for this disease. Further studies would be needed to overcome limitations including small sample size for some parameters, lack of additional in vivo biomarkers and incomplete pharmacokinetic characterization. SIGNIFICANCE STATEMENT: Adrenoleukodystrophy is a rare and debilitating condition with no approved therapies, caused by accumulation of very long-chain fatty acids. AMPK is downregulated in the disease and has been implicated as a potential therapeutic target. PXL770 is a novel clinical stage direct AMPK activator. In these studies, we used PXL770 to achieve preclinical validation of direct AMPK activation for this disease - based on correction of key biochemical and functional readouts in vitro and in vivo, thus supporting clinical development.

The Role of Oxidative Stress and Inflammation in X-Link Adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is an inherited disease caused by a mutation in the ABCD1 gene encoding a peroxisomal transmembrane protein. It is characterized by the accumulation of very-long-chain fatty acids (VLCFAs) in body fluids and tissues, leading to progressive demyelination and adrenal insufficiency. ALD has various phenotypes, among which the most common and severe is childhood cerebral adrenoleukodystrophy (CCALD). The pathophysiological mechanisms of ALD remain unclear, but some in vitro/in vivo research showed that VLCFA could induce oxidative stress and inflammation, leading to damage. In addition, the evidence that oxidative stress and inflammation are increased in patients with X-ALD also proves that it is a potential mechanism of brain and adrenal damage. Therefore, normalizing the redox balance becomes a critical therapeutic target. This study focuses on the possible predictors of the severity and progression of X-ALD, the potential mechanisms of pathogenesis, and the promising targeted drugs involved in oxidative stress and inflammation.

Insights on Human Small Heat Shock Proteins and Their Alterations in Diseases

The family of the human small Heat Shock Proteins (HSPBs) consists of ten members of chaperones (HSPB1-HSPB10), characterized by a low molecular weight and capable of dimerization and oligomerization forming large homo- or hetero-complexes. All HSPBs possess a highly conserved centrally located α-crystallin domain and poorly conserved N- and C-terminal domains. The main feature of HSPBs is to exert cytoprotective functions by preserving proteostasis, assuring the structural maintenance of the cytoskeleton and acting in response to cellular stresses and apoptosis. HSPBs take part in cell homeostasis by acting as holdases, which is the ability to interact with a substrate preventing its aggregation. In addition, HSPBs cooperate in substrates refolding driven by other chaperones or, alternatively, promote substrate routing to degradation. Notably, while some HSPBs are ubiquitously expressed, others show peculiar tissue-specific expression. Cardiac muscle, skeletal muscle and neurons show high expression levels for a wide variety of HSPBs. Indeed, most of the mutations identified in HSPBs are associated to cardiomyopathies, myopathies, and motor neuropathies. Instead, mutations in HSPB4 and HSPB5, which are also expressed in lens, have been associated with cataract. Mutations of HSPBs family members encompass base substitutions, insertions, and deletions, resulting in single amino acid substitutions or in the generation of truncated or elongated proteins. This review will provide an updated overview of disease-related mutations in HSPBs focusing on the structural and biochemical effects of mutations and their functional consequences.

Management of adrenoleukodystrophy: From pre-clinical studies to the development of new therapies

X-linked adrenoleukodystrophy (X-ALD) is an inherited neurodegenerative disorder associated with mutations of the ABCD1 gene that encodes a peroxisomal transmembrane protein. It results in accumulation of very long chain fatty acids in tissues and body fluid. Along with other factors such as epigenetic and environmental involvement, ABCD1 mutation-provoked disorders can present different phenotypes including cerebral adrenoleukodystrophy (cALD), adrenomyeloneuropathy (AMN), and peripheral neuropathy. cALD is the most severe form that causes death in young childhood. Bone marrow transplantation and hematopoietic stem cell gene therapy are only effective when performed at an early stage of onsets in cALD. Nonetheless, current research and development of novel therapies are hampered by a lack of in-depth understanding disease pathophysiology and a lack of reliable cALD models. The Abcd1 and Abcd1/Abcd2 knock-out mouse models as well as the deficiency of Abcd1 rabbit models created in our lab, do not develop cALD phenotypes observed in human beings. In this review, we summarize the clinical and biochemical features of X-ALD, the progress of pre-clinical and clinical studies. Challenges and perspectives for future X-ALD studies are also discussed.

The brain penetrant PPARγ agonist leriglitazone restores multiple altered pathways in models of X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD), a potentially fatal neurometabolic disorder with no effective pharmacological treatment, is characterized by clinical manifestations ranging from progressive spinal cord axonopathy [adrenomyeloneuropathy (AMN)] to severe demyelination and neuroinflammation (cerebral ALD-cALD), for which molecular mechanisms are not well known. Leriglitazone is a recently developed brain penetrant full PPARγ agonist that could modulate multiple biological pathways relevant for neuroinflammatory and neurodegenerative diseases, and particularly for X-ALD. We found that leriglitazone decreased oxidative stress, increased adenosine 5'-triphosphate concentration, and exerted neuroprotective effects in primary rodent neurons and astrocytes after very long chain fatty acid-induced toxicity simulating X-ALD. In addition, leriglitazone improved motor function; restored markers of oxidative stress, mitochondrial function, and inflammation in spinal cord tissues from AMN mouse models; and decreased the neurological disability in the EAE neuroinflammatory mouse model. X-ALD monocyte-derived patient macrophages treated with leriglitazone were less skewed toward an inflammatory phenotype, and the adhesion of human X-ALD monocytes to brain endothelial cells decreased after treatment, suggesting the potential of leriglitazone to prevent the progression to pathologically disrupted blood-brain barrier. Leriglitazone increased myelin debris clearance in vitro and increased myelination and oligodendrocyte survival in demyelination-remyelination in vivo models, thus promoting remyelination. Last, leriglitazone was clinically tested in a phase 1 study showing central nervous system target engagement (adiponectin increase) and changes on inflammatory biomarkers in plasma and cerebrospinal fluid. The results of our study support the use of leriglitazone in X-ALD and, more generally, in other neuroinflammatory and neurodegenerative conditions.

Concurrent axon and myelin destruction differentiates X-linked adrenoleukodystrophy from multiple sclerosis

Cerebral disease manifestation occurs in about two thirds of males with X-linked adrenoleukodystrophy (CALD) and is fatally progressive if left untreated. Early histopathologic studies categorized CALD as an inflammatory demyelinating disease, which led to repeated comparisons to multiple sclerosis (MS). The aim of this study was to revisit the relationship between axonal damage and myelin loss in CALD. We applied novel immunohistochemical tools to investigate axonal damage, myelin loss and myelin repair in autopsy brain tissue of eight CALD and 25 MS patients. We found extensive and severe acute axonal damage in CALD already in prelesional areas defined by microglia loss and relative myelin preservation. In contrast to MS, we did not observe selective phagocytosis of myelin, but a concomitant decay of the entire axon-myelin unit in all CALD lesion stages. Using a novel marker protein for actively remyelinating oligodendrocytes, breast carcinoma-amplified sequence (BCAS) 1, we show that repair pathways are activated in oligodendrocytes in CALD. Regenerating cells, however, were affected by the ongoing disease process. We provide evidence that-in contrast to MS-selective myelin phagocytosis is not characteristic of CALD. On the contrary, our data indicate that acute axonal injury and permanent axonal loss are thus far underestimated features of the disease that must come into focus in our search for biomarkers and novel therapeutic approaches.

Pathology of the neurovascular unit in leukodystrophies

The blood-brain barrier is a dynamic endothelial cell barrier in the brain microvasculature that separates the blood from the brain parenchyma. Specialized brain endothelial cells, astrocytes, neurons, microglia and pericytes together compose the neurovascular unit and interact to maintain blood-brain barrier function. A disturbed brain barrier function is reported in most common neurological disorders and may play a role in disease pathogenesis. However, a comprehensive overview of how the neurovascular unit is affected in a wide range of rare disorders is lacking. Our aim was to provide further insights into the neuropathology of the neurovascular unit in leukodystrophies to unravel its potential pathogenic role in these diseases. Leukodystrophies are monogenic disorders of the white matter due to defects in any of its structural components. Single leukodystrophies are exceedingly rare, and availability of human tissue is unique. Expression of selective neurovascular unit markers such as claudin-5, zona occludens 1, laminin, PDGFRβ, aquaporin-4 and α-dystroglycan was investigated in eight different leukodystrophies using immunohistochemistry. We observed tight junction rearrangements, indicative of endothelial dysfunction, in five out of eight assessed leukodystrophies of different origin and an altered aquaporin-4 distribution in all. Aquaporin-4 redistribution indicates a general astrocytic dysfunction in leukodystrophies, even in those not directly related to astrocytic pathology or without prominent reactive astrogliosis. These findings provide further evidence for dysfunction in the orchestration of the neurovascular unit in leukodystrophies and contribute to a better understanding of the underlying disease mechanism.

Fulminating Autoimmune Demyelination with Optic Neuropathy in a Case of Pediatric Cerebral Adrenoleukodystrophy: Case Report and Review of the Literature

X-linked adrenoleukodystrophy (ALD) is a leukodystrophy characterized not only by progressive loss of myelin in the central nervous system due to dysmyelination, but also by acute, subacute, or chronic inflammatory demyelination. This results in the phenotypic variability of cerebral ALD (cerALD), which is independent of the genotype. In this article, we reported a fulminant presentation with fluctuating encephalopathy and visual loss in a patient with childhood onset cerALD. Brain MRI showed symmetric confluent occipito-temporal demyelination with severe disruption of the blood–brain barrier and prechiasmal optic neuropathy. The patient's cerebral spinal fluid (CSF) demonstrated an elevated IgG index, myelin basic proteins, and oligoclonal bands. Within 48 hours of receiving immunomodulating therapy, the patient's symptoms of psychomotor slowing, visual impairment, and areflexia partially resolved. High plasma C26:0 levels and high ratios of C24/22 and C26/22 were diagnostic of ALD. It has been shown that environmental factors play an important role in the inflammatory demyelination responsible for the severe phenotypes of cerALD.

Role of glial cells in the generation of sex differences in neurodegenerative diseases and brain aging

Diseases and aging-associated alterations of the nervous system often show sex-specific characteristics. Glial cells play a major role in the endogenous homeostatic response of neural tissue, and sex differences in the glial transcriptome and function have been described. Therefore, the possible role of these cells in the generation of sex differences in pathological alterations of the nervous system is reviewed here. Studies have shown that glia react to pathological insults with sex-specific neuroprotective and regenerative effects. At least three factors determine this sex-specific response of glia: sex chromosome genes, gonadal hormones and neuroactive steroid hormone metabolites. The sex chromosome complement determines differences in the transcriptional responses in glia after brain injury, while gonadal hormones and their metabolites activate sex-specific neuroprotective mechanisms in these cells. Since the sex-specific neuroprotective and regenerative activity of glial cells causes sex differences in the pathological alterations of the nervous system, glia may represent a relevant target for sex-specific therapeutic interventions.

Generation of an immortalized astrocytic cell line from Abcd1-deficient H-2KbtsA58 mice to facilitate the study of the role of astrocytes in X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is an inherited metabolic disease characterized by inflammatory demyelination, and activated astrocytes as well as microglia are thought to be involved in its pathogenesis. Conditionally immortalized astrocytic cell clones were prepared from wild-type or Abcd1-deficient H-2K^btsA58 transgenic mice to study the involvement of astrocytes in the pathogenesis of X-ALD. The established astrocyte clones expressed astrocyte-specific molecules such as Vimentin, S100β, Aldh1L1 and Glast. The conditionally immortalized astrocytes proliferated vigorously and exhibited a compact cell body under a permissive condition at 33 °C in the presence of IFN-γ, whereas they became quiescent and exhibited substantial cell enlargement under a non-permissive condition at 37 °C in the absence of IFN-γ. An Abcd1-deficient astrocyte clone exhibited a decrease in the β-oxidation of very long chain fatty acid (VLCFA) and an increase in cellular levels of VLCFA, typical features of Abcd1-deficiency. Upon stimulation with LPS, the Abcd1-deficient astrocyte clone expressed higher levels of pro-inflammatory genes, such as Il6, Nos2, Ccl2 and Cxcl10, compared to wild-type (WT) astrocytes. Furthermore, the Abcd1-deficient astrocytes produced higher amounts of chondroitin sulfate, a marker of reactive astrocytes. These results suggest that dysfunction of Abcd1 renders astrocytes highly responsive to innate immune stimuli. Conditionally immortalized cell clones which preserve astrocyte properties are a useful tool for analyzing the cellular and molecular pathology of ALD.

Astrocytes in rare neurological conditions: Morphological and functional considerations

Astrocytes are a population of central nervous system (CNS) cells with distinctive morphological and functional characteristics that differ within specific areas of the brain and are widely distributed throughout the CNS. There are mainly two types of astrocytes, protoplasmic and fibrous, which differ in morphologic appearance and location. Astrocytes are important cells of the CNS that not only provide structural support, but also modulate synaptic activity, regulate neuroinflammatory responses, maintain the blood-brain barrier, and supply energy to neurons. As a result, astrocytic disruption can lead to widespread detrimental effects and can contribute to the pathophysiology of several neurological conditions. The characteristics of astrocytes in more common neuropathologies such as Alzheimer's and Parkinson's disease have significantly been described and continue to be widely studied. However, there still exist numerous rare neurological conditions in which astrocytic involvement is unknown and needs to be explored. Accordingly, this review will summarize functional and morphological changes of astrocytes in various rare neurological conditions based on current knowledge thus far and highlight remaining neuropathologies where astrocytic involvement has yet to be investigated.

The Role of HSPB8, a Component of the Chaperone-Assisted Selective Autophagy Machinery, in Cancer

The cellular response to cancer-induced stress is one of the major aspects regulating cancer development and progression. The Heat Shock Protein B8 (HSPB8) is a small chaperone involved in chaperone-assisted selective autophagy (CASA). CASA promotes the selective degradation of proteins to counteract cell stress such as tumor-induced stress. HSPB8 is also involved in (i) the cell division machinery regulating chromosome segregation and cell cycle arrest in the G0/G1 phase and (ii) inflammation regulating dendritic cell maturation and cytokine production. HSPB8 expression and role are tumor-specific, showing a dual and opposite role. Interestingly, HSPB8 may be involved in the acquisition of chemoresistance to drugs. Despite the fact the mechanisms of HSPB8-mediated CASA activation in tumors need further studies, HSPB8 could represent an important factor in cancer induction and progression and it may be a potential target for anticancer treatment in specific types of cancer. In this review, we will discuss the molecular mechanism underlying HSPB8 roles in normal and cancer conditions. The basic mechanisms involved in anti- and pro-tumoral activities of HSPB8 are deeply discussed together with the pathways that modulate HSPB8 expression, in order to outline molecules with a beneficial effect for cancer cell growth, migration, and death.

Astrocyte and Oligodendrocyte Cross-Talk in the Central Nervous System

Over the last decade knowledge of the role of astrocytes in central nervous system (CNS) neuroinflammatory diseases has changed dramatically. Rather than playing a merely passive role in response to damage it is clear that astrocytes actively maintain CNS homeostasis by influencing pH, ion and water balance, the plasticity of neurotransmitters and synapses, cerebral blood flow, and are important immune cells. During disease astrocytes become reactive and hypertrophic, a response that was long considered to be pathogenic. However, recent studies reveal that astrocytes also have a strong tissue regenerative role. Whilst most astrocyte research focuses on modulating neuronal function and synaptic transmission little is known about the cross-talk between astrocytes and oligodendrocytes, the myelinating cells of the CNS. This communication occurs via direct cell-cell contact as well as via secreted cytokines, chemokines, exosomes, and signalling molecules. Additionally, this cross-talk is important for glial development, triggering disease onset and progression, as well as stimulating regeneration and repair. Its critical role in homeostasis is most evident when this communication fails. Here, we review emerging evidence of astrocyte-oligodendrocyte communication in health and disease. Understanding the pathways involved in this cross-talk will reveal important insights into the pathogenesis and treatment of CNS diseases.

Microglia damage precedes major myelin breakdown in X-linked adrenoleukodystrophy and metachromatic leukodystrophy

X-linked adrenoleukodystrophy (X-ALD) and metachromatic leukodystrophy (MLD) are two relatively common examples of hereditary demyelinating diseases caused by a dysfunction of peroxisomal or lysosomal lipid degradation. In both conditions, accumulation of nondegraded lipids leads to the destruction of cerebral white matter. Because of their high lipid content, oligodendrocytes are considered key to the pathophysiology of these leukodystrophies. However, the response to allogeneic stem cell transplantation points to the relevance of cells related to the hematopoietic lineage. In the present study, we aimed to better characterize the pathogenetic role of microglia in the above-mentioned diseases. Applying recently established microglia markers to human autopsy cases of X-ALD and MLD we were able to delineate distinct lesion stages in evolving demyelinating lesions. The immune-phenotype of microglia was altered already early in lesion evolution, and microglia loss preceded full-blown myelin degeneration both in X-ALD and MLD. DNA fragmentation indicating phagocyte death was observed in areas showing microglia loss. The morphology and dynamics of phagocyte decay differed between the diseases and between lesion stages, hinting at distinct pathways of programmed cell death. In summary, the present study shows an early and severe damage to microglia in the pathogenesis of X-ALD and MLD. This hints at a central pathophysiologic role of these cells in the diseases and provides evidence for an ongoing transfer of toxic substrates primarily enriched in myelinating cells to microglia.

Rapidly progressive amyotrophic lateral sclerosis is associated with microglial reactivity and small heat shock protein expression in reactive astrocytes

AIMS

Amyotrophic lateral sclerosis (ALS) is a chronic neurodegenerative disease characterized by progressive loss of motor neurons, muscle weakness, spasticity, paralysis and death usually within 2-5 years of onset. Neuroinflammation is a hallmark of ALS pathology characterized by activation of glial cells, which respond by upregulating small heat shock proteins (HSPBs), but the exact underlying pathological mechanisms are still largely unknown. Here, we investigated the association between ALS disease duration, lower motor neuron loss, TARDNA-binding protein 43 (TDP-43) pathology, neuroinflammation and HSPB expression.

METHODS

With immunohistochemistry, we examined HSPB1, HSPB5, HSPB6, HSPB8 and HSP16.2 expression in cervical, thoracic and sacral spinal cord regions in 12 ALS cases, seven with short disease duration (SDD), five with moderate disease duration (MDD), and ten age-matched controls. Expression was quantified using ImageJ to examine HSP expression, motor neuron numbers, microglial and astrocyte density and phosphorylated TDP-43 (pTDP-43+) inclusions.

RESULTS

SDD was associated with elevated HSPB5 and 8 expression in lateral tract astrocytes, while HSP16.2 expression was increased in astrocytes in MDD cases. SDD cases had higher numbers of motor neurons and microglial activation than MDD cases, but similar levels of motor neurons with pTDP-43+ inclusions.

CONCLUSIONS

Increased expression of several HSPBs in lateral column astrocytes suggests that astrocytes play a role in the pathogenesis of ALS. SDD is associated with increased microgliosis, HSPB5 and 8 expression in astrocytes, and only minor changes in motor neuron loss. This suggests that the interaction between motor neurons, microglia and astrocytes determines neuronal fate and functional decline in ALS.