Neuroprotection induced by dexpramipexole delays disease progression in a mouse model of progressive multiple sclerosis

The mitochondriogenic but not the immunosuppressant effects of mTOR inhibitors prompt neuroprotection and delay disease evolution in a mouse model of progressive multiple sclerosis

INTRODUCTION

Purportedly, the progression of multiple sclerosis (MS) occurs when neurodegenerative processes due to derangement of axonal bioenergetics take over the autoimmune response. However, a clear picture of the causative interrelationship between autoimmunity and axonal mitochondrial dysfunction in progressive MS (PMS) pathogenesis waits to be provided.

METHODS

In the present study, by adopting the NOD mouse model of PMS, we compared the pharmacological effects of the immunosuppressants dexamethasone and fingolimod with those of mTOR inhibitors rapamycin and everolimus that, in addition to immunosuppression, also regulate mitochondrial functioning. Female Non-Obese Diabetic (NOD) mice were immunized with MOG35-55 and treated with drugs to evaluate functional, immune and mitochondrial parameters during disease evolution.

RESULTS

We found that dexamethasone and fingolimod did not affect the pattern of progression as well as survival. Conversely, mTOR inhibitors rapamycin and everolimus delayed disease progression and robustly extended survival of immunized mice. The same effects were obtained when treatment was delayed by 30 days after immunization. Remarkably, dexamethasone and fingolimod prompted the same degree of immunosuppression of rapamycin within both spleen and spinal cord of mice. However, only rapamycin prompted mitochondriogenesis by increasing mitochondrial content, and expression of several mitochondrial respiratory complex subunits, thereby preventing mtDNA reduction in the spinal cords of immunized mice. These pharmacodynamic effects were not reproduced in healthy NOD mice, suggesting a disease context-dependent pharmacodynamic effect.

DISCUSSION

Data corroborate the key role of mitochondriogenesis to treatment of MS progression, and for the first time disclose the translational potential of mTOR inhibitors in PMS therapy.

Early derangement of axonal mitochondria occurs in a mouse model of progressive but not relapsing-remitting multiple sclerosis

INTRODUCTION

Derangement of axonal mitochondrial bioenergetics occurs during progressive multiple sclerosis (PMS). However, whether this is a delayed epiphenomenon or an early causative event of disease progression waits to be understood. Answering this question might further our knowledge of mechanisms underlying neurobiology of PMS and related therapy.

METHODS

MOG_35-55-immunized NOD and PLP_139-151-immunized SJL female mice were adopted as models of progressive or relapsing-remitting experimental autoimmune encephalomyelitis (EAE), respectively. Multiple parameters of mitochondrial homeostasis were analyzed in the mouse spinal cord during the early asymptomatic stage, also evaluating the effects of scavenging mitochondrial reactive oxygen species with Mito-TEMPO.

RESULTS

Almost identical lumbar spinal cord immune infiltrates consisting of Th1 cells and neutrophils without B and Th17 lymphocytes occurred early upon immunization in both mouse strains. Still, only NOD mice showed axon-restricted dysregulation of mitochondrial homeostasis, with reduced mtDNA contents and increased cristae area. Increased expression of mitochondrial respiratory complex subunits Nd2, Cox1, Atp5d, Sdha also exclusively occurred in lumbar spinal cord of NOD and not SJL mice. Accordingly, in this region genes regulating mitochondrial morphology (Opa1, Mfn1, Mfn2 and Atp5j2) and mitochondriogenesis (Pgc1α, Foxo, Hif-1α and Nrf2) were induced early upon immunization. A reduced extent of mitochondrial derangement occurred in the thoracic spinal cord. Notably, the mitochondrial radical scavenger Mito-TEMPO reduced H₂O₂ content and prevented both mtDNA depletion and cristae remodeling, having no effects on dysregulation of mitochondrial transcriptome.

DISCUSSION

We provide here the first evidence that axonal-restricted derangement of mitochondrial homeostasis already occurs during the asymptomatic state exclusively in a mouse model of PMS. Data further our understanding of mechanisms related to EAE progression, and point to very early axonal mitochondrial dysfunction as central to the neuropathogenesis of MS evolution.

Dexpramipexole ameliorates cognitive deficits in sepsis-associated encephalopathy through suppressing mitochondria-mediated pyroptosis and apoptosis

OBJECTIVES

This study was aimed at evaluating the effects of dexpramipexole (DPX) - a mitochondrial protectant that sustains mitochondrial function and energy production - on cognitive function in a mouse model of sepsis-associated encephalopathy (SAE) induced by peripheral administration of lipopolysaccharide (LPS) and examining the potential mechanisms.

METHODS

C57BL/6 male mice were randomized into one of four treatment protocols: Con+Sal, Con+DPX, LPS+Sal or LPS+DPX. The mice were intraperitoneally (i.p.) injected with LPS or equivalent volumes of normal saline once daily for 3 consecutive days. To evaluate the protective effects of DPX, we administered DPX or normal saline i.p. to the mice once daily for 6 consecutive days. Six mice in each group were decapitated on day 7, and each brain was rapidly removed and separated into two halves for biochemical and histochemical analysis. The remaining surviving mice in each group were subjected to behavioral tests from days 7 to 10.

RESULTS

Peripheral administration of LPS to mice led to learning and memory deficits in behavioral tests, which were associated with mitochondrial impairment and ATP depletion in the hippocampus. Repeated DPX treatment protected the mitochondria against LPS-induced morphological and functional impairment; inhibited the activation of the Nod-like receptor pyrin domain-containing 3 (NLRP3) inflammasome-caspase-1-dependent pyroptosis pathway and cytochrome c (Cyt-c)-caspase-3-dependent apoptosis pathway; and attenuated LPS-induced neuroinflammation and cell death in the hippocampus in SAE mice.

CONCLUSIONS

Mitochondria-mediated pyroptosis and apoptosis are involved in the pathogenesis of cognitive deficits in a mouse model of SAE and DPX protects mitochondria and suppresses the mitochondria-medicated pyroptosis and apoptosis pathways, and ameliorates LPS-induced neuroinflammation and cognitive deficits. This study provides theoretical evidence supporting DPX for the treatment of SAE.

Dexpramipexole Attenuates White Matter Injury to Facilitate Locomotion and Motor Coordination Recovery via Reducing Ferroptosis after Intracerebral Hemorrhage

Deciphering the factors causing damage to white matter fiber bundles and exploring new strategies to alleviate white matter injury (WMI) is a promising treatment to improve neurological impairments after intracerebral hemorrhage (ICH). Ferroptosis usually occurs at perihematomal region and contributes to neuronal death due to reactive oxygen species (ROS) production. Dexpramipexole (DPX) easily crosses the blood brain barrier (BBB) and exerts antioxidative properties by reducing ROS production, while the role of DPX in ferroptosis after ICH remains elusive. Here, our results indicated that ferroptosis played a significant role in WMI resulting from iron and ROS accumulation around hematoma. Further evidence demonstrated that the administration of DPX decreased iron and ROS deposition to inhibit ferroptosis at perihematomal site. With the inhibition of ferroptosis, WMI was alleviated at perihematomal site, thereafter promoting locomotion and motor coordination recovery in mice after ICH. Subsequently, the results showcased that the expression of glutathione peroxidase 4 (GPX4) and ferroptosis suppressing protein 1 (FSP1) was upregulated with the administration of DPX. Collectively, the present study uncovers the underlying mechanism and elucidates the therapeutic effect of DPX on ICH, and even in other central nervous system (CNS) diseases with the presence of ferroptosis.

Treatment with Non-specific HDAC Inhibitors Administered after Disease Onset does not Delay Evolution in a Mouse Model of Progressive Multiple Sclerosis

Drugs able to efficiently counteract progression of multiple sclerosis (MS) are still an unmet need. Several lines of evidence indicate that histone deacetylase inhibitors (HDACi) are clinically-available epigenetic drugs that might be repurposed for immunosuppression in MS therapy. Here, we studied the effects of HDACi on disease evolution in myelin oligodendrocyte glycoprotein (MOG)-immunized NOD mice, an experimental model of progressive experimental autoimmune encephalomyelitis (PEAE). To obtain data of potential clinical relevance, the HDACi panobinostat, givinostat and entinostat were administered orally adopting a daily treatment protocol after disease onset. We report that the 3 drugs efficiently reduced in vitro lymphocyte proliferation in a dose-dependent manner. Notably, however, none of the drugs delayed evolution of PEAE or reduced lethality in NOD mice. In striking contrast with this, however, the lymphocyte proliferation response to MOG as well as Th1 and Th17 spinal cord infiltrates were significantly lower in animals exposed to the HDACi compared to those receiving vehicle. When put into a clinical context, for the first time data cast doubt on the relevance of HDACi to treatment of progressive MS (PMS). Also, our findings further indicate that, akin to PMS, neuropathogensis of PEAE in NOD mice becomes independent from autoimmunity, thereby corroborating the relevance of this model to experimental PMS research.

Cuprizone-Dependent De/Remyelination Responses and Functional Correlates in Mouse Strains Adopted to Model Relapsing, Chronic and Progressive Experimental Autoimmune Encephalomyelitis

NOD mice represent a unique strain that recapitulates some aspects of progressive MS when subjected to experimental autoimmune encephalomyelitis (EAE). It is unknown, however, whether a proneness to demyelination and/or defect in remyelination contribute to disease progression in NOD mice. Answering to this question might help deciphering the molecular and cellular events underpinning disease evolution in progressive MS. Here, we compared the cuprizone-dependent demyelination and remyelination responses, as well as their functional correlates, in NOD, C57BL/6, and SJL mice typically adopted to model progressive, chronic or relapsing EAE. We report that demyelination occurred to a similar extent in the three mice strains, and that in none of them there was evidence of axonal degeneration during prolonged demyelination. Moreover, immunostaining for GFAP⁺ astrocytes, Iba1⁺ microglia, and NG2⁺ oligodendrocyte precursor cells similarly increased in the 3 mouse strains after cuprizone exposure. The mice underwent concomitant and complete remyelination 2 weeks after cuprizone withdrawal. On a functional level, NOD mice showed the earliest reduction of spontaneous motility and full recovery, but no impairment of motor skill. Conversely, C57BL/6 animals showed phasic reduction of both spontaneous motility and motor skill. Lastly, SJL mice presented the most severe neurological impairment with long-lasting reduction of spontaneous motility and motor skill. Overall, data suggest that the unique feature of EAE progression in NOD mice is not due to proneness to demyelination or intrinsic defects in myelin formation. Findings also unravel important functional differences in the response of the three mouse stains to cuprizone that can be harnessed to design and interpret future experiments.

Neuroprotection induced by dexpramipexole delays disease progression in a mouse model of progressive multiple sclerosis

BACKGROUND AND PURPOSE

Drugs able to counteract progressive multiple sclerosis (MS) represent a largely unmet therapeutic need. Even though the pathogenesis of disease evolution is still obscure, accumulating evidence indicates that mitochondrial dysfunction plays a causative role in neurodegeneration and axonopathy in progressive MS patients. Here, we investigated the effects of dexpramipexole, a compound with a good safety profile in humans and able to sustain mitochondria functioning and energy production, in a mouse model of progressive MS.

EXPERIMENTAL APPROACH

Female non-obese diabetic mice were immunized with MOG_35-55 . Functional, immune and neuropathological parameters were analysed during disease evolution in animals treated or not with dexpramipexole. The compound's effects on bioenergetics and neuroprotection were also evaluated in vitro.

KEY RESULTS

We found that oral treatment with dexpramipexole at a dose consistent with that well tolerated in humans delayed disability progression, extended survival, counteracted reduction of spinal cord mitochondrial DNA content and reduced spinal cord axonal loss of mice. Accordingly, the drug sustained in vitro bioenergetics of mouse optic nerve and dorsal root ganglia and counteracted neurodegeneration of organotypic mouse cortical cultures exposed to the adenosine triphosphate-depleting agents oligomycin or veratridine. Dexpramipexole, however, was unable to affect the adaptive and innate immune responses both in vivo and in vitro.

CONCLUSION AND IMPLICATION

The present findings corroborate the hypothesis that neuroprotective agents may be of relevance to counteract MS progression and disclose the translational potential of dexpramipexole to treatment of progressive MS patients as a stand-alone or adjunctive therapy.