A Potential Boron Neutron Capture Therapy Agent Selectively Suppresses High-Grade Glioma: In Vitro and in Vivo Exploration.

Glioblastoma (GBM), as the most central nervous system (CNS) intractable disease, has spoiled millions of lives due to its high mortality. Even though several efforts have been made, the existing treatments have had limited success. In this sense, we studied a lead compound, the boron-rich selective epidermal growth factor receptor (EGFR)-inhibitor hybrid 1, as a potential drug for GBM treatment. For this end, we analyzed the in vitro activity of hybrid 1 in a glioma/primary astrocytes coculture, studying cellular death types triggered by treatment with this compound and its cellular localizations. Additionally, hybrid 1 concentrated boron in glioma cells selectively and more effectively than the boron neutron capture therapy (BNCT)-clinical agent 10B-l-boronophenylalanine and thus displayed a better in vitro-BNCT effect. This encouraged us to analyze hybrid 1 in vivo. Therefore, immunosuppressed mice bearing U87 MG human GBM were treated with both 1 and 1 encapsulated in a modified liposome (recognized by brain-blood barrier peptide transporters), and we observed a potent in vivo per se antitumor activity (tumor size decrease and animal survival increase). These data demonstrate that 1 could be a promising new targeted therapy for GBM.

Schwann cells orchestrate peripheral nerve inflammation through the expression of CSF1, IL-34, and SCF in amyotrophic lateral sclerosis.

Distal axonopathy is a recognized pathological feature of amyotrophic lateral sclerosis (ALS). In the peripheral nerves of ALS patients, motor axon loss elicits a Wallerian-like degeneration characterized by denervated Schwann cells (SCs) together with immune cell infiltration. However, the pathogenic significance of denervated SCs accumulating following impaired axonal growth in ALS remains unclear. Here, we analyze SC phenotypes in sciatic nerves of ALS patients and paralytic SOD1G93A rats, and identify remarkably similar and specific reactive SC phenotypes based on the pattern of S100ß, GFAP, isolectin and/or p75NTR immunoreactivity. Different subsets of reactive SCs expressed colony-stimulating factor-1 (CSF1) and Interleukin-34 (IL-34) and closely interacted with numerous endoneurial CSF-1R-expressing monocyte/macrophages, suggesting a paracrine mechanism of myeloid cell expansion and activation. SCs bearing phagocytic phenotypes as well as endoneurial macrophages expressed stem cell factor (SCF), a trophic factor that attracts and activates mast cells through the c-Kit receptor. Notably, a subpopulation of Ki67+ SCs expressed c-Kit in the sciatic nerves of SOD1G93A rats, suggesting a signaling pathway that fuels SC proliferation in ALS. c-Kit+ mast cells were also abundant in the sciatic nerve from ALS donors but not in controls. Pharmacological inhibition of CSF-1R and c-Kit with masitinib in SOD1G93A rats potently reduced SC reactivity and immune cell infiltration in the sciatic nerve and ventral roots, suggesting a mechanism by which the drug ameliorates peripheral nerve pathology. These findings provide strong evidence for a previously unknown inflammatory mechanism triggered by SCs in ALS peripheral nerves that has broad application in developing novel therapies.

CD34 Identifies a Subset of Proliferating Microglial Cells Associated with Degenerating Motor Neurons in ALS.

Amyotrophic lateral sclerosis (ALS) is characterized by degeneration of upper and lower motor neurons accompanied by proliferation of reactive microglia in affected regions. However, it is unknown whether the hematopoietic marker CD34 can identify a subpopulation of proliferating microglial cells in the ALS degenerating spinal cord. Immunohistochemistry for CD34 and microglia markers was performed in lumbar spinal cords of ALS rats bearing the SOD1G93A mutation and autopsied ALS and control human subjects. Characterization of CD34-positive cells was also performed in primary cell cultures of the rat spinal cords. CD34 was expressed in a large number of cells that closely interacted with degenerating lumbar spinal cord motor neurons in symptomatic SOD1G93A rats, but not in controls. Most CD34+ cells co-expressed the myeloid marker CD11b, while only a subpopulation was stained for Iba1 or CD68. Notably, CD34+ cells actively proliferated and formed clusters adjacent to damaged motor neurons bearing misfolded SOD1. CD34+ cells were identified in the proximity of motor neurons in autopsied spinal cord from sporadic ALS subjects but not in controls. Cell culture of symptomatic SOD1G93A rat spinal cords yielded a large number of CD34+ cells exclusively in the non-adherent phase, which generated microglia after successive passaging. A yet unrecognized CD34+ cells, expressing or not the microglial marker Iba1, proliferate and accumulate adjacent to degenerating spinal motor neurons, representing an intriguing cell target for approaching ALS pathogenesis and therapeutics.

Neuroimmune and Inflammatory Signals in Complex Disorders of the Central Nervous System.

An extensive microglial-astrocyte-monocyte-neuronal cross talk seems to be crucial for normal brain function, development, and recovery. However, under certain conditions neuroinflammatory interactions between brain cells and neuroimmune cells influence disease outcome and brain pathology. Microglial cells express a range of functional states with dynamically pleomorphic profiles from a surveilling status of synaptic transmission to an active player in major events of development such as synaptic elimination, regeneration, and repair. Also, inflammation mediates a series of neurotoxic roles in neuropsychiatric conditions and neurodegenerative diseases. The present review discusses data on the involvement of neuroinflammatory conditions that alter neuroimmune interactions in four different pathologies. In the first section of this review, we discuss the ability of the early developing brain to respond to a focal lesion with a rapid compensatory plasticity of intact axons and the role of microglial activation and proinflammatory cytokines in brain repair. In the second section, we present data of neuroinflammation and neurodegenerative disorders and discuss the role of reactive astrocytes in motor neuron toxicity and the progression of amyotrophic lateral sclerosis. In the third section, we discuss major depressive disorders as the consequence of dysfunctional interactions between neural and immune signals that result in increased peripheral immune responses and increase proinflammatory cytokines. In the last section, we discuss autism spectrum disorders and altered brain circuitries that emerge from abnormal long-term responses of innate inflammatory cytokines and microglial phenotypic dysfunctions.

Striatal neuronal death mediated by astrocytes from the Gcdh-/- mouse model of glutaric acidemia type I.

Glutaric acidemia type I (GA-I) is an inherited neurometabolic childhood disorder caused by defective activity of glutaryl CoA dehydrogenase (GCDH) which disturb lysine (Lys) and tryptophan catabolism leading to neurotoxic accumulation of glutaric acid (GA) and related metabolites. However, it remains unknown whether GA toxicity is due to direct effects on vulnerable neurons or mediated by GA-intoxicated astrocytes that fail to support neuron function and survival. As damaged astrocytes can also contribute to sustain high GA levels, we explored the ability of Gcdh-/- mouse astrocytes to produce GA and induce neuronal death when challenged with Lys. Upon Lys treatment, Gcdh-/- astrocytes synthetized and released GA and 3-hydroxyglutaric acid (3HGA). Lys and GA treatments also increased oxidative stress and proliferation in Gcdh-/- astrocytes, both prevented by antioxidants. Pretreatment with Lys also caused Gcdh-/- astrocytes to induce extensive death of striatal and cortical neurons when compared with milder effect in WT astrocytes. Antioxidants abrogated the neuronal death induced by astrocytes exposed to Lys or GA. In contrast, Lys or GA direct exposure on Gcdh-/- or WT striatal neurons cultured in the absence of astrocytes was not toxic, indicating that neuronal death is mediated by astrocytes. In summary, GCDH-defective astrocytes actively contribute to produce and accumulate GA and 3HGA when Lys catabolism is stressed. In turn, astrocytic GA production induces a neurotoxic phenotype that kills striatal and cortical neurons by an oxidative stress-dependent mechanism. Targeting astrocytes in GA-I may prompt the development of new antioxidant-based therapeutical approaches.

Focal Transplantation of Aberrant Glial Cells Carrying the SOD1G93A Mutation into Rat Spinal Cord Induces Extensive Gliosis.

OBJECTIVE: We aimed to determine the potential of aberrant glial cells (AbAs) isolated from the spinal cord of adult SOD1G93A symptomatic rats to induce gliosis and neuronal damage following focal transplantation into the lumbar spinal cord of wild-type rats. METHODS: AbAs were obtained from the spinal cords of SOD1G93A symptomatic rats. One hundred thousand cells were injected using a glass micropipette into the lumbar spinal cords (L3-L5) of syngeneic wild-type adult rats. Equal volumes of culture medium or wild-type neonatal microglia were used as controls. Seven days after transplantation, immunohistochemistry analysis was carried out using astrocytic and microglia cell markers. Transplanted SOD1G93A AbAs were recognized by specific antibodies to human SOD1 (hSOD1) or misfolded human SOD1. RESULTS: Seven days after transplantation, AbAs were mainly detected in the medial region of the lumbar ventral horn as a well-limited cell cluster formed at the site of injection by their immunoreactivity to either misfolded SOD1 or normally folded hSOD1. Compared with controls, transplanted AbAs were surrounded by marked microgliosis and reactive astrocytes. Marked microgliosis was observed to extend bilaterally up to the cervical cord. Motor neurons close to AbA transplants were surrounded by activated glial cells and displayed ubiquitin aggregation. CONCLUSIONS: AbAs bearing mutant SOD1G93A have the potential to induce neuroinflammation along the spinal cord and incipient damage to the motor neurons. The emergence of AbAs during amyotrophic lateral sclerosis pathogenesis may therefore be a mechanism to boost neuroinflammation and spread motor neuron damage along the neuroaxis.

Copper delivery to the CNS by CuATSM effectively treats motor neuron disease in SOD(G93A) mice co-expressing the Copper-Chaperone-for-SOD.

Over-expression of mutant copper, zinc superoxide dismutase (SOD) in mice induces ALS and has become the most widely used model of neurodegeneration. However, no pharmaceutical agent in 20 years has extended lifespan by more than a few weeks. The Copper-Chaperone-for-SOD (CCS) protein completes the maturation of SOD by inserting copper, but paradoxically human CCS causes mice co-expressing mutant SOD to die within two weeks of birth. Hypothesizing that co-expression of CCS created copper deficiency in spinal cord, we treated these pups with the PET-imaging agent CuATSM, which is known to deliver copper into the CNS within minutes. CuATSM prevented the early mortality of CCSxSOD mice, while markedly increasing Cu, Zn SOD protein in their ventral spinal cord. Remarkably, continued treatment with CuATSM extended the survival of these mice by an average of 18 months. When CuATSM treatment was stopped, these mice developed ALS-related symptoms and died within 3 months. Restoring CuATSM treatment could rescue these mice after they became symptomatic, providing a means to start and stop disease progression. All ALS patients also express human CCS, raising the hope that familial SOD ALS patients could respond to CuATSM treatment similarly to the CCSxSOD mice.

Post-paralysis tyrosine kinase inhibition with masitinib abrogates neuroinflammation and slows disease progression in inherited amyotrophic lateral sclerosis.

BACKGROUND: In the SOD1(G93A) mutant rat model of amyotrophic lateral sclerosis (ALS), neuronal death and rapid paralysis progression are associated with the emergence of activated aberrant glial cells that proliferate in the degenerating spinal cord. Whether pharmacological downregulation of such aberrant glial cells will decrease motor neuron death and prolong survival is unknown. We hypothesized that proliferation of aberrant glial cells is dependent on kinase receptor activation, and therefore, the tyrosine kinase inhibitor masitinib (AB1010) could potentially control neuroinflammation in the rat model of ALS. METHODS: The cellular effects of pharmacological inhibition of tyrosine kinases with masitinib were analyzed in cell cultures of microglia isolated from aged symptomatic SOD1(G93A) rats. To determine whether masitinib prevented the appearance of aberrant glial cells or modified post-paralysis survival, the drug was orally administered at 30 mg/kg/day starting after paralysis onset. RESULTS: We found that masitinib selectively inhibited the tyrosine kinase receptor colony-stimulating factor 1R (CSF-1R) at nanomolar concentrations. In microglia cultures from symptomatic SOD1(G93A) spinal cords, masitinib prevented CSF-induced proliferation, cell migration, and the expression of inflammatory mediators. Oral administration of masitinib to SOD1(G93A) rats starting after paralysis onset decreased the number of aberrant glial cells, microgliosis, and motor neuron pathology in the degenerating spinal cord, relative to vehicle-treated rats. Masitinib treatment initiated 7 days after paralysis onset prolonged post-paralysis survival by 40 %. CONCLUSIONS: These data show that masitinib is capable of controlling microgliosis and the emergence/expansion of aberrant glial cells, thus providing a strong biological rationale for its use to control neuroinflammation in ALS. Remarkably, masitinib significantly prolonged survival when delivered after paralysis onset, an unprecedented effect in preclinical models of ALS, and therefore appears well-suited for treating ALS.

Phenotypically aberrant astrocytes that promote motoneuron damage in a model of inherited amyotrophic lateral sclerosis.

Motoneuron loss and reactive astrocytosis are pathological hallmarks of amyotrophic lateral sclerosis (ALS), a paralytic neurodegenerative disease that can be triggered by mutations in Cu-Zn superoxide dismutase (SOD1). Dysfunctional astrocytes contribute to ALS pathogenesis, inducing motoneuron damage and accelerating disease progression. However, it is unknown whether ALS progression is associated with the appearance of a specific astrocytic phenotype with neurotoxic potential. Here, we report the isolation of astrocytes with aberrant phenotype (referred as "AbA cells") from primary spinal cord cultures of symptomatic rats expressing the SOD1(G93A) mutation. Isolation was based on AbA cells' marked proliferative capacity and lack of replicative senescence, which allowed oligoclonal cell expansion for 1 y. AbA cells displayed astrocytic markers including glial fibrillary acidic protein, S100ß protein, glutamine synthase, and connexin 43 but lacked glutamate transporter 1 and the glial progenitor marker NG2 glycoprotein. Notably, AbA cells secreted soluble factors that induced motoneuron death with a 10-fold higher potency than neonatal SOD1(G93A) astrocytes. AbA-like aberrant astrocytes expressing S100ß and connexin 43 but lacking NG2 were identified in nearby motoneurons, and their number increased sharply after disease onset. Thus, AbA cells appear to be an as-yet unknown astrocyte population arising during ALS progression with unprecedented proliferative and neurotoxic capacity and may be potential cellular targets for slowing ALS progression.

Impact of Plant-Derived Compounds on Amyotrophic Lateral Sclerosis.

Amyotrophic lateral sclerosis (ALS) is a fatal illness characterized by progressive motor neuron degeneration. Conventional therapies for ALS are based on treatment of symptoms, and the disease remains incurable. Molecular mechanisms are unclear, but studies have been pointing to involvement of glia, neuroinflammation, oxidative stress, and glutamate excitotoxicity as a key factor. Nowadays, we have few treatments for this disease that only delays death, but also does not stop the neurodegenerative process. These treatments are based on glutamate blockage (riluzole), tyrosine kinase inhibition (masitinib), and antioxidant activity (edaravone). In the past few years, plant-derived compounds have been studied for neurodegenerative disorder therapies based on neuroprotection and glial cell response. In this review, we describe mechanisms of action of natural compounds associated with neuroprotective effects, and the possibilities for new therapeutic strategies in ALS.

PD-1/PD-L1 blockade abrogates a dysfunctional innate-adaptive immune axis in critical ß-coronavirus disease.

Severe COVID-19 is associated with hyperinflammation and weak T cell responses against SARS-CoV-2. However, the links between those processes remain partially characterized. Moreover, whether and how therapeutically manipulating T cells may benefit patients are unknown. Our genetic and pharmacological evidence demonstrates that the ion channel TMEM176B inhibited inflammasome activation triggered by SARS-CoV-2 and SARS-CoV-2-related murine ß-coronavirus. Tmem176b-/- mice infected with murine ß-coronavirus developed inflammasome-dependent T cell dysfunction and critical disease, which was controlled by modulating dysfunctional T cells with PD-1 blockers. In critical COVID-19, inflammasome activation correlated with dysfunctional T cells and low monocytic TMEM176B expression, whereas PD-L1 blockade rescued T cell functionality. Here, we mechanistically link T cell dysfunction and inflammation, supporting a cancer immunotherapy to reinforce T cell immunity in critical ß-coronavirus disease.

Olive oil-derived nitro-fatty acids: protection of mitochondrial function in non-alcoholic fatty liver disease.

Non-alcoholic fatty liver disease (NAFLD) is characterized by excessive liver fat deposition in the absence of significant alcohol intake. Since extra virgin olive oil (EVOO) reduces fat accumulation, we analyzed the involvement of nitro-fatty acids (NO2-FA) on the beneficial effects of EVOO consumption on NAFLD. Nitro-fatty acids formation was observed during digestion in mice supplemented with EVOO and nitrite. Mice fed with a high-fat diet (HF) presented lower plasma NO2-FA levels than normal chow, and circulating concentrations recovered when the HF diet was supplemented with 10% EVOO plus nitrite. Under NO2-FA formation conditions, liver hemoxygenase-1 expression significantly increased while decreased body weight and fat liver accumulation. Mitochondrial dysfunction plays a central role in the pathogenesis of NAFLD while NO2-FA has been shown to protect from mitochondrial oxidative damage. Accordingly, an improvement of respiratory indexes was observed when mice were supplemented with both EVOO plus nitrite. Liver mitochondrial complexes II and V activities were greater in mice with EVOO supplementation and further improved in the presence of nitrite. Overall, our results strongly suggest a positive correlation between NO2-OA formation from EVOO and the observed improvement of mitochondrial function in NAFLD. The formation of NO2-FA can account for the health benefits associated with EVOO consumption.

The pathogenic role of c-Kit+ mast cells in the spinal motor neuron-vascular niche in ALS.

Degeneration of motor neurons, glial cell reactivity, and vascular alterations in the CNS are important neuropathological features of amyotrophic lateral sclerosis (ALS). Immune cells trafficking from the blood also infiltrate the affected CNS parenchyma and contribute to neuroinflammation. Mast cells (MCs) are hematopoietic-derived immune cells whose precursors differentiate upon migration into tissues. Upon activation, MCs undergo degranulation with the ability to increase vascular permeability, orchestrate neuroinflammation and modulate the neuroimmune response. However, the prevalence, pathological significance, and pharmacology of MCs in the CNS of ALS patients remain largely unknown. In autopsy ALS spinal cords, we identified for the first time that MCs express c-Kit together with chymase, tryptase, and Cox-2 and display granular or degranulating morphology, as compared with scarce MCs in control cords. In ALS, MCs were mainly found in the niche between spinal motor neuron somas and nearby microvascular elements, and they displayed remarkable pathological abnormalities. Similarly, MCs accumulated in the motor neuron-vascular niche of ALS murine models, in the vicinity of astrocytes and motor neurons expressing the c-Kit ligand stem cell factor (SCF), suggesting an SCF/c-Kit-dependent mechanism of MC differentiation from precursors. Mechanistically, we provide evidence that fully differentiated MCs in cell cultures can be generated from the murine ALS spinal cord tissue, further supporting the presence of c-Kit+ MC precursors. Moreover, intravenous administration of bone marrow-derived c-Kit+ MC precursors infiltrated the spinal cord in ALS mice but not in controls, consistent with aberrant trafficking through a defective microvasculature. Pharmacological inhibition of c-Kit with masitinib in ALS mice reduced the MC number and the influx of MC precursors from the periphery. Our results suggest a previously unknown pathogenic mechanism triggered by MCs in the ALS motor neuron-vascular niche that might be targeted pharmacologically.

A Nitroalkene Benzoic Acid Derivative Targets Reactive Microglia and Prolongs Survival in an Inherited Model of ALS via NF-κB Inhibition.

Motor neuron degeneration and neuroinflammation are the most striking pathological features of amyotrophic lateral sclerosis (ALS). ALS currently has no cure and approved drugs have only a modest clinically therapeutic effect in patients. Drugs targeting different deleterious inflammatory pathways in ALS appear as promising therapeutic alternatives. Here, we have assessed the potential therapeutic effect of an electrophilic nitroalkene benzoic acid derivative, (E)-4-(2-nitrovinyl) benzoic acid (BANA), to slow down paralysis progression when administered after overt disease onset in SOD1G93A rats. BANA exerted a significant inhibition of NF-κB activation in NF-κB reporter transgenic mice and microglial cell cultures. Systemic daily oral administration of BANA to SOD1G93A rats after paralysis onset significantly decreased microgliosis and astrocytosis, and significantly reduced the number of NF-κB-p65-positive microglial nuclei surrounding spinal motor neurons. Numerous microglia bearing nuclear NF-κB-p65 were observed in the surrounding of motor neurons in autopsy spinal cords from ALS patients but not in controls, suggesting ALS-associated microglia could be targeted by BANA. In addition, BANA-treated SOD1G93A rats after paralysis onset showed significantly ameliorated spinal motor neuron pathology as well as conserved neuromuscular junction innervation in the skeletal muscle, as compared to controls. Notably, BANA prolonged post-paralysis survival by ~30%, compared to vehicle-treated littermates. These data provide a rationale to therapeutically slow paralysis progression in ALS using small electrophilic compounds such as BANA, through a mechanism involving microglial NF-κB inhibition.

Closo-Carboranyl- and Metallacarboranyl [1,2,3]triazolyl-Decorated Lapatinib-Scaffold for Cancer Therapy Combining Tyrosine Kinase Inhibition and Boron Neutron Capture Therapy.

One of the driving forces of carcinogenesis in humans is the aberrant activation of receptors; consequently, one of the most promising mechanisms for cancer treatment is receptor inhibition by chemotherapy. Although a variety of cancers are initially susceptible to chemotherapy, they eventually develop multi-drug resistance. Anti-tumor agents overcoming resistance and acting through two or more ways offer greater therapeutic benefits over single-mechanism entities. In this study, we report on a new family of bifunctional compounds that, offering the possibility of dual action (drug + radiotherapy combinations), may result in significant clinical benefits. This new family of compounds combines two fragments: the drug fragment is a lapatinib group, which inhibits the tyrosine kinase receptor activity, and an icosahedral boron cluster used as agents for neutron capture therapy (BNCT). The developed compounds were evaluated in vitro against different tyrosine kinase receptors (TKRs)-expressing tumoral cells, and in vitro-BNCT experiments were performed for two of the most promising hybrids, 19 and 22. We identified hybrid 19 with excellent selectivity to inhibit cell proliferation and ability to induce necrosis/apoptosis of glioblastoma U87 MG cell line. Furthermore, derivative 22, bearing a water-solubility-enhancing moiety, showed moderate inhibition of cell proliferation in both U87 MG and colorectal HT-29 cell lines. Additionally, the HT-29 cells accumulated adequate levels of boron after hybrids 19 and 22 incubations rendering, and after neutron irradiation, higher BNCT-effects than BPA. The attractive profile of developed hybrids makes them interesting agents for combined therapy.

Sunitinib-Containing Carborane Pharmacophore with the Ability to Inhibit Tyrosine Kinases Receptors FLT3, KIT and PDGFR-ß, Exhibits Powerful In Vivo Anti-Glioblastoma Activity.

Malignant gliomas are the most common malignant and aggressive primary brain tumors in adults, the prognosis being-especially for glioblastomas-extremely poor. There are no effective treatments yet. However, tyrosine kinase receptor (TKR) inhibitors and boron neutron capture therapy (BNCT), together, have been proposed as future therapeutic strategies. In this sense in our ongoing project of developing new anti-glioblastoma drugs, we identified a sunitinib-carborane hybrid agent, 1, with both in vitro selective cytotoxicity and excellent BNCT-behavior. Consequently, we studied the ability of compound 1 to inhibit TKRs, its promotion of cellular death processes, and its effects on the cell cycle. Moreover, we analyzed some relevant drug-like properties of 1, i.e., mutagenicity and ability to cross the blood-brain barrier. These results encouraged us to perform an in vivo anti-glioblastoma proof of concept assay. It turned out to be a selective FLT3, KIT, and PDGFR-ß inhibitor and increased the apoptotic glioma-cell numbers and arrested sub-G1-phase cell cycle. Its in vivo activity in immunosuppressed mice bearing U87 MG human glioblastoma evidenced excellent anti-tumor behavior.

Emergence of Microglia Bearing Senescence Markers During Paralysis Progression in a Rat Model of Inherited ALS.

Age is a recognized risk factor for amyotrophic lateral sclerosis (ALS), a paralytic disease characterized by progressive loss of motor neurons and neuroinflammation. A hallmark of aging is the accumulation of senescent cells. Yet, the pathogenic role of cellular senescence in ALS remains poorly understood. In rats bearing the ALS-linked SOD1G93A mutation, microgliosis contribute to motor neuron death, and its pharmacologic downregulation results in increased survival. Here, we have explored whether gliosis and motor neuron loss were associated with cellular senescence in the spinal cord during paralysis progression. In the lumbar spinal cord of symptomatic SOD1G93A rats, numerous cells displayed nuclear p16INK4a as well as loss of nuclear Lamin B1 expression, two recognized senescence-associated markers. The number of p16INK4a-positive nuclei increased by four-fold while Lamin B1-negative nuclei increased by 1,2-fold, respect to non-transgenic or asymptomatic transgenic rats. p16INK4a-positive nuclei and Lamin B1-negative nuclei were typically localized in a subset of hypertrophic Iba1-positive microglia, occasionally exhibiting nuclear giant multinucleated cell aggregates and abnormal nuclear morphology. Next, we analyzed senescence markers in cell cultures of microglia obtained from the spinal cord of symptomatic SOD1G93A rats. Although microglia actively proliferated in cultures, a subset of them developed senescence markers after few days in vitro and subsequent passages. Senescent SOD1G93A microglia in culture conditions were characterized by large and flat morphology, senescence-associated beta-Galactosidase (SA-ß-Gal) activity as well as positive labeling for p16INK4a, p53, matrix metalloproteinase-1 (MMP-1) and nitrotyrosine, suggesting a senescent-associated secretory phenotype (SASP). Remarkably, in the degenerating lumbar spinal cord other cell types, including ChAT-positive motor neurons and GFAP-expressing astrocytes, also displayed nuclear p16INK4a staining. These results suggest that cellular senescence is closely associated with inflammation and motor neuron loss occurring after paralysis onset in SOD1G93A rats. The emergence of senescent cells could mediate key pathogenic mechanisms in ALS.

Phenotypic heterogeneity of astrocytes in motor neuron disease.

Accumulating evidence has shown that astrocytes do not just support the function of neurons, but play key roles in maintaining the brain environment in health and disease. Contrary to the traditional understanding of astrocytes as static cells, reactive astrocytes possess more diverse functions and phenotypes than previously predicted. In the present focused review, we summarize the evidence showing that astrocytes are playing profound roles in the disease process of amyotrophic lateral sclerosis. Aberrantly activated astrocytes in amyotrophic lateral sclerosis rodents express microglial molecular markers and provoke toxicities to accelerate disease progression. In addition, TIR domain-containing adapter protein-inducing interferon-ß-dependent innate immune pathway in astrocytes also has a novel function in terminating glial activation and neuroinflammation. Furthermore, heterogeneity in phenotypes and functions of astrocytes are also observed in various disease conditions, such as other neurodegenerative diseases, ischemia, aging and acute lesions in the central nervous system. Through accumulating knowledge of the phenotypic and functional diversity of astrocytes, these cells will become more attractive therapeutic targets for neurological diseases.

Mast cells and neutrophils mediate peripheral motor pathway degeneration in ALS.

Neuroinflammation is a recognized pathogenic mechanism underlying motor neuron degeneration in amyotrophic lateral sclerosis (ALS), but the inflammatory mechanisms influencing peripheral motor axon degeneration remain largely unknown. A recent report showed a pathogenic role for c-Kit-expressing mast cells mediating inflammation and neuromuscular junction denervation in muscles from SOD1G93A rats. Here, we have explored whether mast cells infiltrate skeletal muscles in autopsied muscles from ALS patients. We report that degranulating mast cells were abundant in the quadriceps muscles from ALS subjects but not in controls. Mast cells were associated with myofibers and motor endplates and, remarkably, interacted with neutrophils forming large extracellular traps. Mast cells and neutrophils were also abundant around motor axons in the extensor digitorum longus muscle, sciatic nerve, and ventral roots of symptomatic SOD1G93A rats, indicating that immune cell infiltration extends along the entire peripheral motor pathway. Postparalysis treatment of SOD1G93A rats with the tyrosine kinase inhibitor drug masitinib prevented mast cell and neutrophil infiltration, axonal pathology, secondary demyelination, and the loss of type 2B myofibers, compared with vehicle-treated rats. These findings provide further evidence for a yet unrecognized contribution of immune cells in peripheral motor pathway degeneration that can be therapeutically targeted by tyrosine kinase inhibitors.

Significance of aberrant glial cell phenotypes in pathophysiology of amyotrophic lateral sclerosis.

Amyotrophic Lateral Sclerosis (ALS) is a paradigmatic neurodegenerative disease, characterized by progressive paralysis of skeletal muscles associated with motor neuron degeneration. It is well-established that glial cells play a key role in ALS pathogenesis. In transgenic rodent models for familial ALS reactive astrocytes, microglia and oligodendrocyte precursors accumulate in the degenerating spinal cord and appear to contribute to primary motor neuron death through a non-cell autonomous pathogenic mechanism. Furthermore in rats expressing the ALS-linked SOD1G93A mutation, rapid spread of paralysis coincides with emergence of neurotoxic and proliferating aberrant glia cells with an astrocyte-like phenotype (AbA cells) that are found surrounding damaged motor neurons. AbAs simultaneously express astrocytic markers GFAP, S100ß and Connexin-43 along with microglial markers Iba-1, CD11b and CD163. Studies with cell cultures have shown that AbAs originate from inflammatory microglial cells that undergo phenotypic transition. Because AbAs appear only after paralysis onset and exponentially increase in parallel with disease progression, they appear to actively contribute to ALS progression. While several reviews have been published on the pathogenic role of glial cells in ALS, this review focuses on emergence and pro-inflammatory activity of AbAs as part of an increasingly complex neurodegenerative microenvironment during ALS disease development.