Endogenous macrophage migration inhibitory factor reduces the accumulation and toxicity of misfolded SOD1 in a mouse model of ALS

Targeting low levels of MIF expression as a potential therapeutic strategy for ALS

Mutations in SOD1 cause amyotrophic lateral sclerosis (ALS), a neurodegenerative disease characterized by motor neuron (MN) loss. We previously discovered that macrophage migration inhibitory factor (MIF), whose levels are extremely low in spinal MNs, inhibits mutant SOD1 misfolding and toxicity. In this study, we show that a single peripheral injection of adeno-associated virus (AAV) delivering MIF into adult SOD1G37R mice significantly improves their motor function, delays disease progression, and extends survival. Moreover, MIF treatment reduces neuroinflammation and misfolded SOD1 accumulation, rescues MNs, and corrects dysregulated pathways as observed by proteomics and transcriptomics. Furthermore, we reveal low MIF levels in human induced pluripotent stem cell-derived MNs from familial ALS patients with different genetic mutations, as well as in post mortem tissues of sporadic ALS patients. Our findings indicate that peripheral MIF administration may provide a potential therapeutic mechanism for modulating misfolded SOD1 in vivo and disease outcome in ALS patients.

Genetic background variation impacts microglial heterogeneity and disease progression in amyotrophic lateral sclerosis model mice

Recent single-cell analyses have revealed the complexity of microglial heterogeneity in brain development, aging, and neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS). Disease-associated microglia (DAMs) have been identified in ALS mice model, but their role in ALS pathology remains unclear. The effect of genetic background variations on microglial heterogeneity and functions remains unknown. Herein, we established and analyzed two mice models of ALS with distinct genetic backgrounds of C57BL/6 and BALB/c. We observed that the change in genetic background from C57BL/6 to BALB/c affected microglial heterogeneity and ALS pathology and its progression, likely due to the defective induction of neurotrophic factor-secreting DAMs and impaired microglial survival. Single-cell analyses of ALS mice revealed new markers for each microglial subtype and a possible association between microglial heterogeneity and systemic immune environments. Thus, we highlighted the role of microglia in ALS pathology and importance of genetic background variations in modulating microglial functions.

Blocking an epitope of misfolded SOD1 ameliorates disease phenotype in a model of amyotrophic lateral sclerosis

The current strategies to mitigate the toxicity of misfolded superoxide dismutase 1 (SOD1) in familial amyotrophic lateral sclerosis via blocking SOD1 expression in the CNS are indiscriminative for misfolded and intact proteins, and as such, entail a risk of depriving CNS cells of their essential antioxidant potential. As an alternative approach to neutralize misfolded and spare unaffected SOD1 species, we developed scFv-SE21 antibody that blocks the β6/β7 loop epitope exposed exclusively in misfolded SOD1. The β6/β7 loop epitope has previously been proposed to initiate amyloid-like aggregation of misfolded SOD1 and mediate its prion-like activity. The adeno-associated virus-mediated expression of scFv-SE21 in the CNS of hSOD1G37R mice rescued spinal motor neurons, reduced the accumulation of misfolded SOD1, decreased gliosis and thus delayed disease onset and extended survival by 90 days. The results provide evidence for the role of the exposed β6/β7 loop epitope in the mechanism of neurotoxic gain-of-function of misfolded SOD1 and open avenues for the development of mechanism-based anti-SOD1 therapeutics, whose selective targeting of misfolded SOD1 species may entail a reduced risk of collateral oxidative damage to the CNS.

The inhibitory effects of MIF on accumulation of canine degenerative myelopathy-associated mutant SOD1 aggregation

Canine degenerative myelopathy (DM) is a progressive neurodegenerative disorder, which is commonly associated with c.118G > A (p. E40K) missense mutation in the superoxide dismutase 1 (SOD1) gene. Mutant SOD1 protein (SOD1E40K) is likely to be misfolded, acquire insolubility, aggregate in the cytoplasm of neural cells, and lead to degeneration of the nervous tissues. Along with a chaperone activity, macrophage migration inhibitory factor (MIF) is a multifunctional protein that has been shown to directly inhibit human mutant SOD1 misfolding and enhance survival of mutant SOD1-expressing motor neurons. The purpose of this study was to determine whether MIF also inhibits DM-related SOD1E40K misfolding and accumulation of SOD1 aggregates. Human embryonic kidney 293A cells were transfected SOD1cWT or SOD1E40K with or without MIF. The percentages of cells containing transfected SOD1 aggregates were measured by immunocytochemistry, and the amount of SOD1E40K in the insoluble fraction was evaluated by immunoblotting. The percentage of cells with SOD1E40K aggregates and the amount of insoluble SOD1E40K protein decreased in the presence of MIF. Because the chaperone activity of MIF assists in SOD1E40K folding and enhances the refolding and degradation of misfolded SOD1E40K, the results of this study suggests that MIF regulates the accumulation of SOD1 aggregates by its chaperone activity. We propose that enhancing intracellular MIF chaperone activity could be an effective therapeutic strategy for DM.

4-Phenylbutyric Acid (4-PBA) Derivatives Prevent SOD1 Amyloid Aggregation In Vitro with No Effect on Disease Progression in SOD1-ALS Mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the degeneration of motor neurons. Mutations in the superoxide dismutase (SOD1) gene, causing protein misfolding and aggregation, were suggested as the pathogenic mechanisms involved in familial ALS cases. In the present study, we investigated the potential therapeutic effect of C4 and C5, two derivatives of the chemical chaperone 4-phenylbutyric acid (4-PBA). By combining in vivo and in vitro techniques, we show that, although C4 and C5 successfully inhibited amyloid aggregation of recombinant mutant SOD1 in a dose-dependent manner, they failed to suppress the accumulation of misfolded SOD1. Moreover, C4 or C5 daily injections to SOD1^G93A mice following onset had no effect on either the accumulation of misfolded SOD1 or the neuroinflammatory response in the spinal cord and, consequently, failed to extend the survival of SOD1^G93A mice or to improve their motor symptoms. Finally, pharmacokinetic (PK) studies demonstrated that high concentrations of C4 and C5 reached the brain and spinal cord but only for a short period of time. Thus, our findings suggest that use of such chemical chaperones for ALS drug development may need to be optimized for more effective results.

MIF homolog d-dopachrome tautomerase (D-DT/MIF-2) does not inhibit accumulation and toxicity of misfolded SOD1

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by loss of upper and lower motor neurons. About 20% of familial ALS cases are caused by dominant mutations in SOD1. It has been suggested that toxicity of mutant SOD1 results from its misfolding, however, it is unclear why misfolded SOD1 accumulates within specific tissues. We have demonstrated that macrophage migration inhibitory factor (MIF), a multifunctional protein with cytokine/chemokine and chaperone-like activity, inhibits the accumulation and aggregation of misfolded SOD1. Although MIF homolog, D-dopachrome tautomerase (D-DT/MIF-2), shares structural and genetic similarities with MIF, its biological function is not well understood. In the current study, we investigated, for the first time, the mechanism of action of D-DT in a model of ALS. We show that D-DT inhibits mutant SOD1 amyloid aggregation in vitro, promoting the formation of amorphous aggregates. Moreover, we report that D-DT interacts with mutant SOD1, but does not inhibit misfolded mutant SOD1 accumulation and toxicity in neuronal cells. Finally, we show that D-DT is expressed mainly in liver and kidney, with extremely low expression in brain and spinal cord of adult mice. Our findings contribute to better understanding of D-DT versus MIF function in the context of ALS.

Macrophage migration inhibitory factor (MIF) acetylation protects neurons from ischemic injury

Ischemia-induced neuronal death leads to serious lifelong neurological deficits in ischemic stroke patients. Histone deacetylase 6 (HDAC6) is a promising target for neuroprotection in many neurological disorders, including ischemic stroke. However, the mechanism by which HDAC6 inhibition protects neurons after ischemic stroke remains unclear. Here, we discovered that genetic ablation or pharmacological inhibition of HDAC6 reduced brain injury after ischemic stroke by increasing macrophage migration inhibitory factor (MIF) acetylation. Mass spectrum analysis and biochemical results revealed that HDAC6 inhibitor or aspirin treatment promoted MIF acetylation on the K78 residue. MIF K78 acetylation suppressed the interaction between MIF and AIF, which impaired MIF translocation to the nucleus in ischemic cortical neurons. Moreover, neuronal DNA fragmentation and neuronal death were impaired in the cortex after ischemia in MIF K78Q mutant mice. Our results indicate that the neuroprotective effect of HDAC6 inhibition and aspirin treatment results from MIF K78 acetylation; thus, MIF K78 acetylation may be a therapeutic target for ischemic stroke and other neurological diseases.

Macrophage migration inhibitory factor family proteins are multitasking cytokines in tissue injury

The family of macrophage migration inhibitory factor (MIF) proteins in humans consist of MIF, its functional homolog D-dopachrome tautomerase (D-DT, also known as MIF-2) and the relatively unknown protein named DDT-like (DDTL). MIF is a pleiotropic cytokine with multiple properties in tissue homeostasis and pathology. MIF was initially found to associate with inflammatory responses and therefore established a reputation as a pro-inflammatory cytokine. However, increasing evidence demonstrates that MIF influences many different intra- and extracellular molecular processes important for the maintenance of cellular homeostasis, such as promotion of cellular survival, antioxidant signaling, and wound repair. In contrast, studies on D-DT are scarce and on DDTL almost nonexistent and their functions remain to be further investigated as it is yet unclear how similar they are compared to MIF. Importantly, the many and sometimes opposing functions of MIF suggest that targeting MIF therapeutically should be considered carefully, taking into account timing and severity of tissue injury. In this review, we focus on the latest discoveries regarding the role of MIF family members in tissue injury, inflammation and repair, and highlight the possibilities of interventions with therapeutics targeting or mimicking MIF family proteins.

Early upregulation of cytosolic phospholipase A2α in motor neurons is induced by misfolded SOD1 in a mouse model of amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal multifactorial neurodegenerative disease characterized by the selective death of motor neurons. Cytosolic phospholipase A₂ alpha (cPLA₂α) upregulation and activation in the spinal cord of ALS patients has been reported. We have previously shown that cPLA₂α upregulation in the spinal cord of mutant SOD1 transgenic mice (SOD1^G93A) was detected long before the development of the disease, and inhibition of cPLA₂α upregulation delayed the disease's onset. The aim of the present study was to determine the mechanism for cPLA₂α upregulation.

METHODS

Immunofluorescence analysis and western blot analysis of misfolded SOD1, cPLA₂α and inflammatory markers were performed in the spinal cord sections of SOD1^G93A transgenic mice and in primary motor neurons. Over expression of mutant SOD1 was performed by induction or transfection in primary motor neurons and in differentiated NSC34 motor neuron like cells.

RESULTS

Misfolded SOD1 was detected in the spinal cord of 3 weeks old mutant SOD1^G93A mice before cPLA₂α upregulation. Elevated expression of both misfolded SOD1 and cPLA₂α was specifically detected in the motor neurons at 6 weeks with a high correlation between them. Elevated TNFα levels were detected in the spinal cord lysates of 6 weeks old mutant SOD1^G93A mice. Elevated TNFα was specifically detected in the motor neurons and its expression was highly correlated with cPLA₂α expression at 6 weeks. Induction of mutant SOD1 in primary motor neurons induced cPLA₂α and TNFα upregulation. Over expression of mutant SOD1 in NSC34 cells caused cPLA₂α upregulation which was prevented by antibodies against TNFα. The addition of TNFα to NSC34 cells caused cPLA₂α upregulation in a dose dependent manner.

CONCLUSIONS

Motor neurons expressing elevated cPLA₂α and TNFα are in an inflammatory state as early as at 6 weeks old mutant SOD1^G93A mice long before the development of the disease. Accumulated misfolded SOD1 in the motor neurons induced cPLA₂α upregulation via induction of TNFα.

Macrophage migration inhibitory factor in Nodding syndrome

Nodding syndrome (NS) is a catastrophic and enigmatic childhood epilepsy, accompanied by multiple neurological impairments and neuroinflammation. Of all the infectious, environmental and psychological factors associated with NS, the major culprit is Onchocerca Volvulus (Ov)-a parasitic worm transmitted to human by blackflies. NS seems to be an 'Autoimmune Epilepsy' in light of the recent findings of deleterious autoimmune antibodies to Glutamate receptors and to Leiomodin-I in NS patients. Moreover, we recently found immunogenetic fingerprints in HLA peptide-binding grooves associate with protection or susceptibility to NS. Macrophage migration inhibitory factor (MIF) is an immune-regulatory cytokine playing a central role in modulating innate and adaptive immunity. MIF is also involved in various pathologies: infectious, autoimmune and neurodegenerative diseases, epilepsy and others. Herein, two functional polymorphisms in the MIF gene, a -794 CATT5-8 microsatellite repeat and a -173 G/C single-nucleotide polymorphism, were assessed in 49 NS patients and 51 healthy controls from South Sudan. We also measured MIF plasma levels in established NS patients and healthy controls. We discovered that the frequency of the high-expression MIF -173C containing genotype was significantly lower in NS patients compared to healthy controls. Interestingly however, MIF plasma levels were significantly elevated in NS patients than in healthy controls. We further demonstrated that the HLA protective and susceptibility associations are dominant over the MIF association with NS. Our findings suggest that MIF might have a dual role in NS. Genetically controlled high-expression MIF genotype is associated with disease protection. However, elevated MIF in the plasma may contribute to the detrimental autoimmunity, neuroinflammation and epilepsy.

Macrophage migration inhibitory factor (MIF): A multifaceted cytokine regulated by genetic and physiological strategies

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine encoded within a functionally polymorphic genetic locus. MIF was initially recognized as a cytokine generated by activated T cells, but in recent days it has been identified as a multipotent key cytokine secreted by many other cell types involved in immune response and physiological processes. MIF is a highly conserved 12.5 kDa secretory protein that is involved in numerous biological processes. The expression and secretion profile of MIF suggests that MIF to be ubiquitously and constitutively expressed in almost all mammalian cells and is vital for numerous physiological processes. MIF is a critical upstream mediator of host innate and adaptive immunity and survival pathways resulting in the clearance of pathogens thus playing a protective role during infectious diseases. On the other hand, MIF being an immune modulator accelerates detrimental inflammation, promotes cancer metastasis and progression, thus worsening disease conditions. Several reports demonstrated that genetic and physiological factors, including MIF gene polymorphisms, posttranslational regulations, and receptor binding control the functional activities of MIF. Taking into consideration the multi-faceted role of MIF both in physiology and pathology, we thought it is timely to review and summarize the expressional and functional regulation of MIF, its functional mechanisms associated with its beneficial and pathological roles, and MIF-targeting therapies. Thus, our review will provide an overview on how MIF is regulated, its response, and the potency of the therapies that target MIF.

The Potential Role of Cytokines and Growth Factors in the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is one of the most prominent neurodegenerative diseases, which impairs cognitive function in afflicted individuals. AD results in gradual decay of neuronal function as a consequence of diverse degenerating events. Several neuroimmune players (such as cytokines and growth factors that are key players in maintaining CNS homeostasis) turn aberrant during crosstalk between the innate and adaptive immunities. This aberrance underlies neuroinflammation and drives neuronal cells toward apoptotic decline. Neuroinflammation involves microglial activation and has been shown to exacerbate AD. This review attempted to elucidate the role of cytokines, growth factors, and associated mechanisms implicated in the course of AD, especially with neuroinflammation. We also evaluated the propensities and specific mechanism(s) of cytokines and growth factors impacting neuron upon apoptotic decline and further shed light on the availability and accessibility of cytokines across the blood-brain barrier and choroid plexus in AD pathophysiology. The pathogenic and the protective roles of macrophage migration and inhibitory factors, neurotrophic factors, hematopoietic-related growth factors, TAU phosphorylation, advanced glycation end products, complement system, and glial cells in AD and neuropsychiatric pathology were also discussed. Taken together, the emerging roles of these factors in AD pathology emphasize the importance of building novel strategies for an effective therapeutic/neuropsychiatric management of AD in clinics.

All Roads Lead to Rome: Different Molecular Players Converge to Common Toxic Pathways in Neurodegeneration

Multiple neurodegenerative diseases (NDDs) such as Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS) and Huntington’s disease (HD) are being suggested to have common cellular and molecular pathological mechanisms, characterized mainly by protein misfolding and aggregation. These large inclusions, most likely, represent an end stage of a molecular cascade; however, the soluble misfolded proteins, which take part in earlier steps of this cascade, are the more toxic players. These pathological proteins, which characterize each specific disease, lead to the selective vulnerability of different neurons, likely resulting from a combination of different intracellular mechanisms, including mitochondrial dysfunction, ER stress, proteasome inhibition, excitotoxicity, oxidative damage, defects in nucleocytoplasmic transport, defective axonal transport and neuroinflammation. Damage within these neurons is enhanced by damage from the nonneuronal cells, via inflammatory processes that accelerate the progression of these diseases. In this review, while acknowledging the hallmark proteins which characterize the most common NDDs; we place specific focus on the common overlapping mechanisms leading to disease pathology despite these different molecular players and discuss how this convergence may occur, with the ultimate hope that therapies effective in one disease may successfully translate to another.

Prolonged NCX activation prevents SOD1 accumulation, reduces neuroinflammation, ameliorates motor behavior and prolongs survival in a ALS mouse model

Imbalance in cellular ionic homeostasis is a hallmark of several neurodegenerative diseases including Amyotrophic Lateral Sclerosis (ALS). Sodium-calcium exchanger (NCX) is a membrane antiporter that, operating in a bidirectional way, couples the exchange of Ca²⁺ and Na ⁺ ions in neurons and glial cells, thus controlling the intracellular homeostasis of these ions. Among the three NCX genes, NCX1 and NCX2 are widely expressed within the CNS, while NCX3 is present only in skeletal muscles and at lower levels of expression in selected brain regions. ALS mice showed a reduction in the expression and activity of NCX1 and NCX2 consistent with disease progression, therefore we aimed to investigate their role in ALS pathophysiology. Notably, we demonstrated that the pharmacological activation of NCX1 and NCX2 by the prolonged treatment of SOD1^G93A mice with the newly synthesized compound neurounina: (1) prevented the reduction in NCX activity observed in spinal cord; (2) preserved motor neurons survival in the ventral spinal horn of SOD1^G93A mice; (3) prevented the spinal cord accumulation of misfolded SOD1; (4) reduced astroglia and microglia activation and spared the resident microglia cells in the spinal cord; (5) improved the lifespan and mitigated motor symptoms of ALS mice. The present study highlights the significant role of NCX1 and NCX2 in the pathophysiology of this neurodegenerative disorder and paves the way for the design of a new pharmacological approach for ALS.

Molecular and pharmacological chaperones for SOD1

The efficacy of superoxide dismutase-1 (SOD1) folding impacts neuronal loss in motor system neurodegenerative diseases. Mutations can prevent SOD1 post-translational processing leading to misfolding and cytoplasmic aggregation in familial amyotrophic lateral sclerosis (ALS). Evidence of immature, wild-type SOD1 misfolding has also been observed in sporadic ALS, non-SOD1 familial ALS and Parkinson's disease. The copper chaperone for SOD1 (hCCS) is a dedicated and specific chaperone that assists SOD1 folding and maturation to produce the active enzyme. Misfolded or misfolding prone SOD1 also interacts with heat shock proteins and macrophage migration inhibitory factor to aid folding, refolding or degradation. Recognition of specific SOD1 structures by the molecular chaperone network and timely dissociation of SOD1-chaperone complexes are, therefore, important steps in SOD1 processing. Harnessing these interactions for therapeutic benefit is actively pursued as is the modulation of SOD1 behaviour with pharmacological and peptide chaperones. This review highlights the structural and mechanistic aspects of a selection of SOD1-chaperone interactions together with their impact on disease models.

MIF as a biomarker and therapeutic target for overcoming resistance to proteasome inhibitors in human myeloma

Multiple myeloma (MM) remains largely incurable despite significant advances in biotherapy and chemotherapy. The development of drug resistance is a major problem in MM management. Macrophage migration inhibitory factor (MIF) expression was significantly higher in purified MM cells from relapsed patients than those with sustained response, and MM patients with high MIF had significantly shorter progression-free survival (PFS) and overall survival (OS). MM cell lines also express high levels of MIF, and knocking out MIF made them more sensitive to proteasome inhibitor (PI)-induced apoptosis not observed with other chemotherapy drugs. Mechanistic studies showed that MIF protects MM cells from PI-induced apoptosis by maintaining mitochondrial function via suppression of superoxide production in response to PIs. Specifically, MIF, in the form of a homotrimer, acts as a chaperone for superoxide dismutase 1 (SOD1) to suppress PI-induced SOD1 misfolding and to maintain SOD1 activity. MIF inhibitor 4-iodo-6-phenylpyrimidine and homotrimer disrupter ebselen, which do not kill MM cells, enhanced PI-induced SOD1 misfolding and loss of function, resulting in significantly more cell death in both cell lines and primary MM cells. More importantly, inhibiting MIF activity in vivo displayed synergistic antitumor activity with PIs and resensitized PI-resistant MM cells to treatment. In support of these findings, gene-profiling data showed a significantly negative correlation between MIF and SOD1 expression and response to PI treatment in patients with MM. This study shows that MIF plays a crucial role in MM sensitivity to PIs and suggests that targeting MIF may be a promising strategy to (re)sensitize MM to the treatment.

ALS-Related Mutant SOD1 Aggregates Interfere with Mitophagy by Sequestering the Autophagy Receptor Optineurin

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the progressive demise of motor neurons. One of the causes of familial ALS is the mutation of the gene encoding superoxide dismutase 1 (SOD1), which leads to abnormal protein aggregates. How SOD1 aggregation drives ALS is still poorly understood. Recently, ALS pathogenesis has been functionally implicated in mitophagy, specifically the clearance of damaged mitochondria. Here, to understand this mechanism, we investigated the relationship between the mitophagy receptor optineurin and SOD1 aggregates. We found that mutant SOD1 (mSOD1) proteins associate with and then sequester optineurin, which is required to form the mitophagosomes, to aggregates in N2a cells. Optineurin recruitment into mSOD1 aggregates resulted in a reduced mitophagy flux. Furthermore, we observed that an exogenous augmentation of optineurin alleviated the cellular cytotoxicity induced by mSOD1. Taken together, these studies demonstrate that ALS-linked mutations in SOD1 interfere with the mitophagy process through optineurin sequestration, suggesting that the accumulation of damaged mitochondria may play a crucial role in the pathophysiological mechanisms contributing to ALS.

The Dichotomic Role of Macrophage Migration Inhibitory Factor in Neurodegeneration

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine expressed by different cell types and exerting multiple biological functions. It has been shown that MIF may be involved in several disorders, including neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS), Parkinson disease (PD), and Huntington disease (HD), that represent an unmet medical need. Therefore, further studies are needed to identify novel pathogenetic mechanisms that may translate into tailored therapeutic approaches so to improve patients’ survival and quality of life. Here, we reviewed the preclinical and clinical studies investigating the role of MIF in ALS, PD, and HD. The emerging results suggest that MIF might play a dichotomic role in these disorders, exerting a protective action in ALS, a pathogenetic action in HD, and a yet undefined and debated role in PD. The better understanding of the role of MIF in these diseases could allow its use as a novel diagnostic and therapeutic tool for the monitoring and treatment of the patients and for eventual biomarker-driven therapeutic approaches.

Pathogenic contribution of the Macrophage migration inhibitory factor family to major depressive disorder and emerging tailored therapeutic approaches

BACKGROUND

Immunoinflammatory disorders are often accompanied by depression. Here, we review the available preclinical and clinical studies suggesting a role for the pro-inflammatory cytokine Macrophage migration inhibitory factor (MIF) and the second member of the MIF family, D-dopachrome tautomerase (D-DT; DDT), in the pathogenesis of Major Depressive Disorders (MDD).

METHODS

We prepared a narrative review from a search on PubMed of studies pertaining to MDD and MIF, as for October 2019. Both humans and animal studies haves been considered.

RESULTS

Preclinical data show conflicting results on the role of endogenous MIF and DDT in depression. In contrast, several human studies show that circulating MIF levels tend to increase during the course of MDD. Higher levels of inflammatory biomarkers have also been associated with poorer responses to antidepressants and the levels of MIF significantly decrease after treatment, despite this may not be necessarily associated to an improvement in psychiatric symptoms.

LIMITATIONS

This is a narrative and not a systematic review of the literature on the involvement of MIF in MDD. We have highlighted studies performed in humans and in animal models, irrespective of population size and methodological approach.

CONCLUSIONS

This review highlights a role of MIF, and possibly DDT, in the pathogenesis of MDD. Whilst studies in animal models are discordant, the studies in patients with MDD convergently suggest that MIF plays a role in induction and maintenance of the disease. Additional studies are also needed on DDT that often displays synergistic function with MIF and their receptors.

The Role of Macrophage Migration Inhibitory Factor in Alzheimer's Disease: Conventionally Pathogenetic or Unconventionally Protective?

Recent preclinical and clinical observations have offered relevant insights on the etiopathogenesis of late onset Alzheimer′s disease (AD) and upregulated immunoinflammatory events have been described as underlying mechanisms involved in the development of AD. Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine produced by several cells of the innate and adaptive immune system, as well as non-immune cells. In the present review, we highlight experimental, genetic, and clinical studies on MIF in rodent models of AD and AD patients, and we discuss emerging therapeutic opportunities for tailored modulation of the activity of MIF, that may potentially be applied to AD patients. Dismantling the exact role of MIF and its receptors in AD may offer novel diagnostic and therapeutic opportunities in AD.

A VDAC1-Derived N-Terminal Peptide Inhibits Mutant SOD1-VDAC1 Interactions and Toxicity in the SOD1 Model of ALS

Mutations in superoxide dismutase (SOD1) are the second most common cause of familial amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease caused by the death of motor neurons in the brain and spinal cord. SOD1 neurotoxicity has been attributed to aberrant accumulation of misfolded SOD1, which in its soluble form binds to intracellular organelles, such as mitochondria and ER, disrupting their functions. Here, we demonstrate that mutant SOD1 binds specifically to the N-terminal domain of the voltage-dependent anion channel (VDAC1), an outer mitochondrial membrane protein controlling cell energy, metabolic and survival pathways. Mutant SOD1^G93A and SOD1^G85R, but not wild type SOD1, directly interact with VDAC1 and reduce its channel conductance. No such interaction with N-terminal-truncated VDAC1 occurs. Moreover, a VDAC1-derived N-terminal peptide inhibited mutant SOD1-induced toxicity. Incubation of motor neuron-like NSC-34 cells expressing mutant SOD1 or mouse embryonic stem cell-derived motor neurons with different VDAC1 N-terminal peptides resulted in enhanced cell survival. Taken together, our results establish a direct link between mutant SOD1 toxicity and the VDAC1 N-terminal domain and suggest that VDAC1 N-terminal peptides targeting mutant SOD1 provide potential new therapeutic strategies for ALS.

AAV2/9-mediated overexpression of MIF inhibits SOD1 misfolding, delays disease onset, and extends survival in mouse models of ALS

Mutations in superoxide dismutase (SOD1) cause amyotrophic lateral sclerosis (ALS), a neurodegenerative disease characterized by the loss of upper and lower motor neurons. Transgenic mice that overexpress mutant SOD1 develop paralysis and accumulate misfolded SOD1 onto the cytoplasmic faces of intracellular organelles, including mitochondria and endoplasmic reticulum (ER). Recently, macrophage migration inhibitory factor (MIF) was shown to directly inhibit mutant SOD1 misfolding and binding to intracellular membranes. In addition, complete elimination of endogenous MIF accelerated disease onset and late disease progression, as well as shortened the lifespan of mutant SOD1 mice with higher amounts of misfolded SOD1 detected within the spinal cord. Based on these findings, we used adeno-associated viral (AAV) vectors to overexpress MIF in the spinal cord of mutant SOD1^G93A and loxSOD1^G37R mice. Our data show that MIF mRNA and protein levels were increased in the spinal cords of AAV2/9-MIF-injected mice. Furthermore, mutant SOD1^G93A and loxSOD1^G37R mice injected with AAV2/9-MIF demonstrated a significant delay in disease onset and prolonged survival compared with their AAV2/9-GFP-injected or noninjected littermates. Moreover, these mice accumulated reduced amounts of misfolded SOD1 in their spinal cords, with no observed effect on glial overactivation as a result of MIF up-regulation. Our findings indicate that MIF plays a significant role in SOD1 folding and misfolding mechanisms and strengthen the hypothesis that MIF acts as a chaperone for misfolded SOD1 in vivo and may have further implications regarding the therapeutic potential role of up-regulation of MIF in modulating the specific accumulation of misfolded SOD1.

Structural Properties and Interaction Partners of Familial ALS-Associated SOD1 Mutants

Amyotrophic lateral sclerosis (ALS) is the most common motor neuron degenerative disease in adults and has also been proven to be a type of conformational disease associated with protein misfolding and dysfunction. To date, more than 150 distinct genes have been found to be associated with ALS, among which Superoxide Dismutase 1 (SOD1) is the first and the most extensively studied gene. It has been well-established that SOD1 mutants-mediated toxicity is caused by a gain-of-function rather than the loss of the detoxifying activity of SOD1. Compared with the clear autosomal dominant inheritance of SOD1 mutants in ALS, the potential toxic mechanisms of SOD1 mutants in motor neurons remain incompletely understood. A large body of evidence has shown that SOD1 mutants may adopt a complex profile of conformations and interact with a wide range of client proteins. Here, in this review, we summarize the fundamental conformational properties and the gained interaction partners of the soluble forms of the SOD1 mutants which have been published in the past decades. Our goal is to find clues to the possible internal links between structural and functional anomalies of SOD1 mutants, as well as the relationships between their exposed epitopes and interaction partners, in order to help reveal and determine potential diagnostic and therapeutic targets.

MAP4K4 Activation Mediates Motor Neuron Degeneration in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting both upper and lower motor neurons (MNs). To date, its underlying mechanisms have yet to be clarified completely, and there are no truly effective treatments. Here, we show that MAP4K4, a MAP kinase family member, regulates MN death, with its suppression not only promoting survival but preventing neurite degeneration and decreasing mutant SOD1 levels through autophagy activation. Moreover, we report that MAP4K4 signaling specifically modulates MN viability via phosphorylated JNK3 and activation of the canonical c-Jun apoptotic pathway. Finally, we show the feasibility of MAP4K4 as a drug target by using an available MAP4K4-specific inhibitor, which improves survival of ESC and/or iPSC-derived MNs and MNs cultured from mouse spinal cords. In summary, our studies highlight a MAP4K4-initiated signaling cascade that induces MN degeneration, shedding light on the mechanism underlying MN degeneration and providing a druggable target for ALS therapeutics.

The Multitasking Potential of Alarmins and Atypical Chemokines

When the human genome was sequenced, it came as a surprise that it contains “only” 21,306 protein-coding genes. However, complexity and diversity are multiplied by alternative splicing, non-protein-coding transcripts, or post-translational modifications (PTMs) on proteome level. Here, we discuss how the multi-tasking potential of proteins can substantially enhance the complexity of the proteome further, while at the same time offering mechanisms for the fine-regulation of cell responses. Discoveries over the past two decades have led to the identification of “surprising” and previously unrecognized functionalities of long known cytokines, inflammatory mediators, and intracellular proteins that have established novel molecular networks in physiology, inflammation, and cardiovascular disease. In this mini-review, we focus on alarmins and atypical chemokines such as high-mobility group box protein-1 (HMGB-1) and macrophage migration-inhibitory factor (MIF)-type proteins that are prototypical examples of these classes, featuring a remarkable multitasking potential that allows for an elaborate fine-tuning of molecular networks in the extra- and intracellular space that may eventually give rise to novel “task”-based precision medicine intervention strategies.

Increased serum levels and promoter polymorphisms of macrophage migration inhibitory factor in schizophrenia

BACKGROUND

Numerous studies have suggested that an immune system imbalance plays an important role in schizophrenia. Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine. It plays multiple roles in various biological processes, including inflammation and neurogenesis. Furthermore, several exhaustive serum proteomic profiling studies have identified MIF as a potential biomarker of schizophrenia. Here, we investigate MIF protein levels in serum and postmortem prefrontal cortex in patients with schizophrenia and controls. Moreover, we investigate the association of two functional polymorphisms in the MIF gene promoter region (MIF-794CATT_5-8 microsatellite and MIF-173G/C single-nucleotide polymorphism [SNP]) with schizophrenia.

METHODS

We measured serum MIF levels with an enzyme-linked immunosorbent assay (ELISA) (51 patients vs. 86 controls) and postmortem brain MIF levels with a western blotting assay (18 patients vs. 22 controls). Subsequently, we genotyped the MIF-794CATT_5-8 microsatellite with a fluorescence-based fragment assay and the MIF-173G/C SNP with a TaqMan SNP genotyping assay (1483 patients vs. 1454 controls).

RESULTS

Serum MIF levels were significantly higher in patients with schizophrenia than in controls (p=0.00118), and were positively correlated with antipsychotic dose (Spearman's r=0.222, p=0.0402). In addition, an earlier age of onset was observed in patients with a high serum MIF level (≥40ng/mL) than those with a low serum MIF level (<40ng/mL) (p=0.0392). However, postmortem brain MIF levels did not differ between patients with schizophrenia and controls. The association study revealed that the CATT₆-G haplotype was nominally significantly associated with schizophrenia (p=0.0338), and that the CATT₆ allele and CATT₆-G haplotype were significantly associated with female adolescent-onset schizophrenia (AsOS) (corrected p=0.0222 and p=0.0147, respectively).

CONCLUSIONS

These results suggest that serum MIF level is a potential pharmacodynamic and/or monitoring marker of schizophrenia, and is related to a novel antipsychotic effect beyond dopamine antagonism. Furthermore, the MIF gene polymorphisms are associated with the risk for schizophrenia especially in adolescent females, and are potential stratification markers of schizophrenia. Further studies of MIF are warranted to elucidate the pathophysiology of schizophrenia and the effects of antipsychotics.

MIF inhibits the formation and toxicity of misfolded SOD1 amyloid aggregates: implications for familial ALS

Mutations in superoxide dismutase (SOD1) cause amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease caused by the progressive loss of motor neurons in the brain and spinal cord. It has been suggested that toxicity of mutant SOD1 results from its misfolding, however, it is yet unclear why misfolded SOD1 accumulates specifically within motor neurons. We recently demonstrated that macrophage migration inhibitory factor (MIF)-a multifunctional protein with cytokine/chemokine activity and cytosolic chaperone-like properties-inhibits the accumulation of misfolded SOD1. Here, we show that MIF inhibits mutant SOD1 nuclear clearance when overexpressed in motor neuron-like NSC-34 cells. In addition, MIF alters the typical SOD1 amyloid aggregation pathway in vitro, and, instead, promotes the formation of disordered aggregates, as measured by Thioflavin T (ThT) assay and transmission electron microscopy (TEM) imaging. Moreover, we report that MIF reduces the toxicity of misfolded SOD1 by directly interacting with it, and that the chaperone function and protective effect of MIF in neuronal cultures do not require its intrinsic catalytic activities. Importantly, we report that the locked-trimeric MIF^N110C mutant, which exhibits strongly impaired CD74-mediated cytokine functions, has strong chaperone activity, dissociating, for the first time, these two cellular functions. Altogether, our study implicates MIF as a potential therapeutic candidate in the treatment of ALS.

Misfolded SOD1 Accumulation and Mitochondrial Association Contribute to the Selective Vulnerability of Motor Neurons in Familial ALS: Correlation to Human Disease

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder, with a 10% genetic linkage, of which 20% of these cases may be attributed to mutations in superoxide dismutase (SOD1). Specific mutations in SOD1 have been associated with disease duration, which can be highly variable ranging from a life expectancy of 3 to beyond 10 years. SOD1 neurotoxicity has been attributed to aberrant accumulation of misfolded SOD1, which in its soluble form binds to intracellular organelles disrupting their function or forms insoluble toxic aggregates. To understand whether these biophysical properties of the mutant protein may influence disease onset and duration, we generated 19 point mutations in the SOD1 gene, based on available clinical data of disease onset and progression from patients. By overexpressing these mutants in motor-neuron-like NSC-34 cells, we demonstrate a variability in misfolding capacity between the different mutants with a correlation between the degree of protein misfolding and mutation severity. We also show a clear variation of the different SOD1 mutants to associate with mitochondrial-enriched fractions with a correlation between mutation severity and this association. In summary, these findings reveal a correlation between the accumulation of misfolded SOD1 species and their mitochondrial association with disease duration but not with disease onset, and they have implications for the potential therapeutic role of suppressing the accumulation of misfolded SOD1.

HSPB1 mutations causing hereditary neuropathy in humans disrupt non-cell autonomous protection of motor neurons

Heat shock protein beta-1 (HSPB1), is a ubiquitously expressed, multifunctional protein chaperone. Mutations in HSPB1 result in the development of a late-onset, distal hereditary motor neuropathy type II (dHMN) and axonal Charcot-Marie Tooth disease with sensory involvement (CMT2F). The functional consequences of HSPB1 mutations associated with hereditary neuropathy are unknown. HSPB1 also displays neuroprotective properties in many neuronal disease models, including the motor neuron disease amyotrophic lateral sclerosis (ALS). HSPB1 is upregulated in SOD1-ALS animal models during disease progression, predominately in glial cells. Glial cells are known to contribute to motor neuron loss in ALS through a non-cell autonomous mechanism. In this study, we examined the non-cell autonomous role of wild type and mutant HSPB1 in an astrocyte-motor neuron co-culture model system of ALS. Astrocyte-specific overexpression of wild type HSPB1 was sufficient to attenuate SOD1(G93A) astrocyte-mediated toxicity in motor neurons, whereas, overexpression of mutHSPB1 failed to ameliorate motor neuron toxicity. Expression of a phosphomimetic HSPB1 mutant in SOD1(G93A) astrocytes also reduced toxicity to motor neurons, suggesting that phosphorylation may contribute to HSPB1 mediated-neuroprotection. These data provide evidence that astrocytic HSPB1 expression may play a central role in motor neuron health and maintenance.

Macrophage migration inhibitory factor: A multifaceted cytokine implicated in multiple neurological diseases

Macrophage migration inhibitory factor (MIF) is a conserved cytokine found as a homotrimer protein. It is found in a wide spectrum of cell types in the body including neuronal and non-neuronal cells. MIF is implicated in several biological processes; chemo-attraction, cytokine activity, and receptor binding, among other functions. More recently, a chaperone-like activity has been added to its repertoire. In this review, we focus on the implication of MIF in the central nervous system and peripheries, its role in neurological disorders, and the mechanisms by which MIF is regulated. Numerous studies have associated MIF with various disease settings. MIF plays an important role in advocating tumorigenic processes, Alzheimer's disease, and is also upregulated in autism-spectrum disorders and spinal cord injury where it contributes to the severity of the injured area. The protective effect of MIF has been reported in amyotrophic lateral sclerosis by its reduction of aggregated misfolded SOD1, subsequently reducing the severity of this disease. Interestingly, a protective as well as pathological role for MIF has been implicated in stroke and cerebral ischemia, as well as depression. Thus, the role of MIF in neurological disorders appears to be diverse with both beneficial and adversary effects. Furthermore, its modulation is rather complex and it is regulated by different proteins, either on a molecular or protein level. This complexity might be dependent on the pathophysiological context and/or cellular microenvironment. Hence, further clarification of its diverse roles in neurological pathologies is warranted to provide new mechanistic insights which may lead in the future to the development of therapeutic strategies based on MIF, to fight some of these neurological disorders.

Superoxide Dismutase 1 (SOD1)-Derived Peptide Inhibits Amyloid Aggregation of Familial Amyotrophic Lateral Sclerosis SOD1 Mutants

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder that leads to the death of the upper and lower motor neurons. Superoxide dismutase 1 (SOD1) is an ALS pathogenic protein, whose misfolding results in the formation of amyloid aggregates. The mechanism underlying SOD1 pathogenesis in ALS remains obscure, but one possible mechanism involves gain-of-interaction, in which the misfolded soluble SOD1 forms abnormal protein-protein interactions (PPIs) with various cellular proteins, including with other SOD1 molecules, thereby interfering with their function. The structural basis of this gain-of-interaction mechanism is unknown. Here, we characterized the backbone dynamics landscape of misfolded SOD1 to pinpoint surface areas predisposed to aberrant PPIs. This analysis enabled us to formulate a working hypothesis for the mechanism of the gain-of-function of misfolded SOD1, according to which an abnormal PPI potential results from the increased mobility of the SOD1 surface backbone. Guided by the backbone dynamics landscape, we have identified a SOD1-derived peptide that can bind SOD1 proteins and divert the typical amyloid aggregation of ALS-related SOD1 mutants toward a potentially less toxic amorphous aggregation pathway.