Imaging Axonal Degeneration and Repair in Preclinical Animal Models of Multiple Sclerosis

Neuronal DAMPs exacerbate neurodegeneration via astrocytic RIPK3 signaling

Astrocyte activation is a common feature of neurodegenerative diseases. However, the ways in which dying neurons influence the activity of astrocytes is poorly understood. Receptor interacting protein kinase-3 (RIPK3) signaling has recently been described as a key regulator of neuroinflammation, but whether this kinase mediates astrocytic responsiveness to neuronal death has not yet been studied. Here, we used the 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine model of Parkinson's disease to show that activation of astrocytic RIPK3 drives dopaminergic cell death and axon damage. Transcriptomic profiling revealed that astrocytic RIPK3 promoted gene expression associated with neuroinflammation and movement disorders, and this coincided with significant engagement of damage-associated molecular pattern signaling. In mechanistic experiments, we showed that factors released from dying neurons signaled through receptor for advanced glycation endproducts to induce astrocytic RIPK3 signaling, which conferred inflammatory and neurotoxic functional activity. These findings highlight a mechanism of neuron-glia crosstalk in which neuronal death perpetuates further neurodegeneration by engaging inflammatory astrocyte activation via RIPK3.

TREM2 alleviates white matter injury after traumatic brain injury in mice might be mediated by regulation of DHCR24/LXR pathway in microglia

BACKGROUND

White matter injury (WMI) is an important pathological process after traumatic brain injury (TBI). The correlation between white matter functions and the myeloid cells expressing triggering receptor-2 (TREM2) has been convincingly demonstrated. Moreover, a recent study revealed that microglial sterol metabolism is crucial for early remyelination after demyelinating diseases. However, the potential roles of TREM2 expression and microglial sterol metabolism in WMI after TBI have not yet been explored.

METHODS

Controlled cortical injury was induced in both wild-type (WT) and TREM2 depletion (TREM2 KO) mice to simulate clinical TBI. COG1410 was used to upregulate TREM2, while PLX5622 and GSK2033 were used to deplete microglia and inhibit the liver X receptor (LXR), respectively. Immunofluorescence, Luxol fast blue staining, magnetic resonance imaging, transmission electron microscopy, and oil red O staining were employed to assess WMI after TBI. Neurological behaviour tests and electrophysiological recordings were utilized to evaluate cognitive functions following TBI. Microglial cell sorting and transcriptomic sequencing were utilized to identify alterations in microglial sterol metabolism-related genes, while western blot was conducted to validate the findings.

RESULTS

TREM2 expressed highest at 3 days post-TBI and was predominantly localized to microglial cells within the white matter. Depletion of TREM2 worsened aberrant neurological behaviours, and this phenomenon was mediated by the exacerbation of WMI, reduced renewal of oligodendrocytes, and impaired phagocytosis ability of microglia after TBI. Subsequently, the upregulation of TREM2 alleviated WMI, promoted oligodendrocyte regeneration, and ultimately facilitated the recovery of neurological behaviours after TBI. Finally, the expression of DHCR24 increased in TREM2 KO mice after TBI. Interestingly, TREM2 inhibited DHCR24 and upregulated members of the LXR pathway. Moreover, LXR inhibition could partially reverse the effects of TREM2 upregulation on electrophysiological activities.

CONCLUSIONS

We demonstrate that TREM2 has the potential to alleviate WMI following TBI, possibly through the DHCR24/LXR pathway in microglia.

Delimiting MOGAD as a disease entity using translational imaging

The first formal consensus diagnostic criteria for myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) were recently proposed. Yet, the distinction of MOGAD-defining characteristics from characteristics of its important differential diagnoses such as multiple sclerosis (MS) and aquaporin-4 antibody seropositive neuromyelitis optica spectrum disorder (NMOSD) is still obstructed. In preclinical research, MOG antibody-based animal models were used for decades to derive knowledge about MS. In clinical research, people with MOGAD have been combined into cohorts with other diagnoses. Thus, it remains unclear to which extent the generated knowledge is specifically applicable to MOGAD. Translational research can contribute to identifying MOGAD characteristic features by establishing imaging methods and outcome parameters on proven pathophysiological grounds. This article reviews suitable animal models for translational MOGAD research and the current state and prospect of translational imaging in MOGAD.

Neuronal DAMPs exacerbate neurodegeneration via astrocytic RIPK3 signaling

Astrocyte activation is a common feature of neurodegenerative diseases. However, the ways in which dying neurons influence the activity of astrocytes is poorly understood. RIPK3 signaling has recently been described as a key regulator of neuroinflammation, but whether this kinase mediates astrocytic responsiveness to neuronal death has not yet been studied. Here, we used the MPTP model of Parkinson's disease to show that activation of astrocytic RIPK3 drives dopaminergic cell death and axon damage. Transcriptomic profiling revealed that astrocytic RIPK3 promoted gene expression associated with neuroinflammation and movement disorders, and this coincided with significant engagement of DAMP signaling. Using human cell culture systems, we show that factors released from dying neurons signal through RAGE to induce RIPK3-dependent astrocyte activation. These findings highlight a mechanism of neuron-glia crosstalk in which neuronal death perpetuates further neurodegeneration by engaging inflammatory astrocyte activation via RIPK3.

Cerebral Creatine Deficiency Affects the Timing of Oligodendrocyte Myelination

Cerebral creatine deficiency syndrome (CCDS) is an inborn error of metabolism characterized by intellectual delays, seizures, and autistic-like behavior. However, the role of endogenously synthesized creatine on CNS development and function remains poorly understood. Here, magnetic resonance spectroscopy of adult mouse brains from both sexes revealed creatine synthesis is dependent on the expression of the enzyme, guanidinoacetate methyltransferase (GAMT). To identify Gamt-expressed cells, and how Gamt affects postnatal CNS development, we generated a mouse line by knocking-in a GFP, which is expressed on excision of Gamt We found that Gamt is expressed in mature oligodendrocytes during active myelination in the developing postnatal CNS. Homozygous deletion of Gamt resulted in significantly reduced mature oligodendrocytes and delayed myelination in the corpus callosum. Moreover, the absence of endogenous creatine resulted in altered AMPK signaling in the brain, reduced brain creatine kinase expression in cortical neurons, and signs of axonal damage. Experimental demyelination in mice after tamoxifen-induced conditional deletion of Gamt in oligodendrocyte lineage cells resulted in delayed maturation of oligodendrocytes and myelin coverage in lesions. Moreover, creatine and cyclocreatine supplementation can enhance remyelination after demyelination. Our results suggest endogenously synthesized creatine controls the bioenergetic demand required for the timely maturation of oligodendrocytes during postnatal CNS development, and that delayed myelination and altered CNS energetics through the disruption of creatine synthesis might contribute to conditions, such as CCDS.SIGNIFICANCE STATEMENT Cerebral creatine deficiency syndrome is a rare disease of inborn errors in metabolism, which is characterized by intellectual delays, seizures, and autism-like behavior. We found that oligodendrocytes are the main source of endogenously synthesized creatine in the adult CNS, and the loss of endogenous creatine synthesis led to delayed myelination. Our study suggests impaired cerebral creatine synthesis affects the timing of myelination and may impact brain bioenergetics.

Modulation of the proteoglycan receptor PTPσ promotes white matter integrity and functional recovery after intracerebral hemorrhage stroke in mice

Background

Intracerebral hemorrhage (ICH) is associated with high morbidity and mortality rates. However, extant investigations have mainly focused on gray matter injury within the primary injury site after ICH rather than on white matter (WM) injury in the brain and spinal cord. This focus partly accounts for the diminished therapeutic discovery. Recent evidence suggests that chondroitin sulphate proteoglycans (CSPG), which can bind to the neural transmembrane protein tyrosine phosphatase-sigma (PTPσ), may facilitate axonal regrowth and remyelination by ameliorating neuroinflammation.

Methods

A clinically relevant ICH model was established using adult C57BL/6 mice. The mice were then treated systemically with intracellular sigma peptide (ISP), which specifically targets PTPσ. Sensorimotor function was assessed by various behavioral tests and electrophysiological assessment. Western blot was used to verify the expression levels of Iba-1 and different inflammatory cytokines. The morphology of white matter tracts of brain and spinal cord was evaluated by immunofluorescence staining and transmission electron microscopy (TEM). Adeno-associated virus (AAV) 2/9 injection was used to assess the ipsilateral axonal compensation after injury. Parallel in vitro studies on the effects of CSPG interference on oligodendrocyte–DRG neuron co-culture explored the molecular mechanism through which ISP treatment promoted myelination capability.

Results

ISP, by targeting PTPσ, improved WM integrity and sensorimotor recovery via immunomodulation. In addition, ISP administration significantly decreased WM injury in the peri-hematomal region as well as cervical spinal cord, enhanced axonal myelination and facilitated neurological restoration, including electrophysiologically assessed sensorimotor functions. Parallel in vitro studies showed that inhibition of PTPσ by ISP fosters myelination by modulating the Erk/CREB signaling pathway.

Conclusions

Our findings revealed for the first time that manipulation of PTPσ signaling by ISP can promote prolonged neurological recovery by restoration of the integrity of neural circuits in the CNS through modulation of Erk/CREB signaling pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02561-4.

Elevated microglial oxidative phosphorylation and phagocytosis stimulate post-stroke brain remodeling and cognitive function recovery in mice

New research shows that disease-associated microglia in neurodegenerative brains present features of elevated phagocytosis, lysosomal functions, and lipid metabolism, which benefit brain repair. The underlying mechanisms remain poorly understood. Intracellular pH (pH_i) is important for regulating aerobic glycolysis in microglia, where Na/H exchanger (NHE1) is a key pH regulator by extruding H⁺ in exchange of Na⁺ influx. We report here that post-stroke Cx3cr1-Cre^ER+/-;Nhe1^flox/flox (Nhe1 cKO) brains displayed stimulation of microglial transcriptomes of rate-limiting enzyme genes for glycolysis, tricarboxylic acid cycle, and oxidative phosphorylation. The other upregulated genes included genes for phagocytosis and LXR/RXR pathway activation as well as the disease-associated microglia hallmark genes (Apoe, Trem2, Spp1). The cKO microglia exhibited increased oxidative phosphorylation capacity, and higher phagocytic activity, which likely played a role in enhanced synaptic stripping and remodeling, oligodendrogenesis, and remyelination. This study reveals that genetic blockade of microglial NHE1 stimulated oxidative phosphorylation immunometabolism, and boosted phagocytosis function which is associated with tissue remodeling and post-stroke cognitive function recovery.

Dysregulation of Blood-Brain Barrier and Exacerbated Inflammatory Response in Cx47-Deficient Mice after Induction of EAE

Induction of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS), in connexin 32 (Cx32) or Cx47 knockout (KO) mice with deficiency in oligodendrocyte gap junctions (GJs) results in a more severe disease course. In particular, Cx47 KO EAE mice experience an earlier EAE onset and more pronounced disease severity, accompanied by dysregulated pro-inflammatory responses preceding the disease manifestations. In this study, analysis of relevant pro-inflammatory cytokines in wild type EAE, Cx32 KO EAE, and Cx47 KO EAE mice revealed altered expression of Vcam-1 preceding EAE [7 days post injection (dpi)], of Ccl2 at the onset of EAE (12 dpi), and of Gm-csf at the peak of EAE (24 dpi) in Cx47 KO EAE mice. Moreover, Cx47 KO EAE mice exhibited more severe blood-spinal cord barrier (BSCB) disruption, enhanced astrogliosis with defects in tight junction formation at the glia limitans, and increased T-cell infiltration prior to disease onset. Thus, Cx47 deficiency appears to cause dysregulation of the inflammatory profile and BSCB integrity, promoting early astrocyte responses in Cx47 KO EAE mice that lead to a more severe EAE outcome. Further investigation into the role of oligodendrocytic Cx47 in EAE and multiple sclerosis pathology is warranted.

c-Jun N-terminal kinase 1 (JNK1) modulates oligodendrocyte progenitor cell architecture, proliferation and myelination

During Central Nervous System ontogenesis, myelinating oligodendrocytes (OLs) arise from highly ramified and proliferative precursors called oligodendrocyte progenitor cells (OPCs). OPC architecture, proliferation and oligodendro-/myelino-genesis are finely regulated by the interplay of cell-intrinsic and extrinsic factors. A variety of extrinsic cues converge on the extracellular signal-regulated kinase/mitogen activated protein kinase (ERK/MAPK) pathway. Here we found that the germinal ablation of the MAPK c-Jun N-Terminal Kinase isoform 1 (JNK1) results in a significant reduction of myelin in the cerebral cortex and corpus callosum at both postnatal and adult stages. Myelin alterations are accompanied by higher OPC density and proliferation during the first weeks of life, consistent with a transient alteration of mechanisms regulating OPC self-renewal and differentiation. JNK1 KO OPCs also show smaller occupancy territories and a less complex branching architecture in vivo. Notably, these latter phenotypes are recapitulated in pure cultures of JNK1 KO OPCs and of WT OPCs treated with the JNK inhibitor D-JNKI-1. Moreover, JNK1 KO and WT D-JNKI-1 treated OLs, while not showing overt alterations of differentiation in vitro, display a reduced surface compared to controls. Our results unveil a novel player in the complex regulation of OPC biology, on the one hand showing that JNK1 ablation cell-autonomously determines alterations of OPC proliferation and branching architecture and, on the other hand, suggesting that JNK1 signaling in OLs participates in myelination in vivo.

An optimized animal model of lysolecithin induced demyelination in optic nerve; more feasible, more reproducible, promising for studying the progressive forms of multiple sclerosis

BACKGROUND

Multiple Sclerosis (MS) is a demyelinating disease leading to long-term neurological deficit due to unsuccessful remyelination and axonal loss. Currently, there are no satisfactory treatments for progressive MS somewhat due to the lack of an adequate animal model for studying the mechanisms of disease progression and screening new drugs.

NEW METHOD

Lysolecithin (LPC) or agarose-gel loaded LPC (AL-LPC) were applied to mouse optic nerve behind the globe via a minor surgery. Agarose loading was used to achieve longer time of LPC exposure and subsequently long-lasting demyelination.

RESULTS

The lesion sites characterized by luxol fast blue (LFB), FluoroMyelin, Bielschowsky's staining, and immunostaining showed extensive demyelination and axonal damage. The loss of Retinal ganglion cells (RGCs) in the corresponding retinal layer was shown by immunostaining and H&E staining. Visual evoked potential (VEP) recordings showed a significant increase in the latency of the P1 wave and a decrease in the amplitude of the P1N1 wave.

COMPARISON WITH EXISTING METHODS

The new approach with a very minor surgery seems to be more feasible and reproducible compared to stereotaxic LPC injection to optic chiasm. Our data revealed prolonged demyelination, axonal degeneration and RGCs loss in both AL-LPC and LPC groups; however, these pathologies were more extensive in the AL-LPC group.

CONCLUSION

The optimized model provides a longer demyelination time frame and axonal damage followed by RGC degeneration; which is of exceptional interest in investigating axonal degeneration mechanisms and screening the new drugs for progressive MS.

PD-1 Blockade Reverses Obesity-Mediated T Cell Priming Impairment

Despite obesity reaching pandemic proportions, its impact on antigen-specific T cell responses is still unclear. We have recently demonstrated that obesity results in increased expression of PD-1 on T cells, and checkpoint blockade targeting PD-1/PD-L1 surprisingly resulted in greater clinical efficacy in cancer therapy. Adverse events associated with this therapy center around autoimmune reactions. In this study, we examined the impact of obesity on T cell priming and on autoimmune pathogenesis using the mouse model experimental autoimmune encephalomyelitis (EAE), which is mediated by autoreactive myelin-specific T cells generated after immunization. We observed that diet-induced obese (DIO) mice had a markedly delayed EAE onset and developed milder clinical symptoms compared to mice on control diet (CD). This delay was associated with impaired generation of myelin-specific T cell numbers and concurrently correlated with increased PD-L1 upregulation on antigen-presenting cells in secondary lymphoid organs. PD-1 blockade during the priming stage of EAE restored disease onset and severity and increased numbers of pathogenic CD4+ T cells in the central nervous system (CNS) of DIO mice to similar levels to those of CD mice. Administration of anti-PD-1 after onset of clinical symptoms did not increase EAE pathogenesis demonstrating that initial priming is the critical juncture affected by obesity. These findings demonstrate that obesity impairs antigen-specific T cell priming, but this can be reversed with PD-1 blockade. Our results further suggest that PD-1 blockade may increase the risk of autoimmune toxicities, particularly in obesity.

Transdiagnostic treatment of emotional disorders for women with multiple sclerosis: a randomized controlled trial

BACKGROUND

Multiple sclerosis (MS) is a chronic, unpredictable, neurodegenerative disease, significantly associated with psychological, behavioral, cognitive, and emotional consequences. MS is more common in females than males and frequently affects women during their reproductive years. Despite the frequent mental disorders, comorbidities, and emotional problems in People with MS (PwMS), these conditions are too often underdiagnosed and undertreated.

OBJECTIVE

This study aimed to examine the efficacy of a group format of the Unified Protocol (UP) for the Transdiagnostic treatment of depression and anxiety disorders in females with MS.

METHODS

In the present study, Sixty-four adult females diagnosed with MS were randomized to either the UP (n = 32) or treatment-as-usual conditions. The assessment protocol included semi-structured clinical interviews and self-reports evaluating diagnostic criteria, depression, anxiety and worry symptoms, emotional regulation, and affectivity.

RESULTS

Repeated measure analysis of variance (ANOVA) revealed that the UP significantly improved depression scores [Cohen's d = - 2.11, 95% CI (- 2.72, - 1.50)], anxiety scores [Cohen's d = - 3.34, 95% CI (- 4.01, - 2.58)], positive and negative affect scale (PANAS)-positive affect scores [Cohen's d = 1.46, 95% CI (1.46, 2.01)], PANAS-negative affect scores [Coen's d = - 2.21, 95% CI (- 2.84, - 1.60)], difficulties emotion regulation scale scores [Cohen's d = 1.40, 95% CI (- 0.87, - 0.03)], and Worry scale scores [Cohen's d = - 0.45, 95% CI (- 0.95, - 0.04)] at the end of treatment relative to compared to the control condition. Also, treatment gains were maintained at the three-month follow-up (p < 0.001).

CONCLUSION

The findings provide the support that the UP could be an additional efficient psychological treatment for females with MS. ISRCTN Number: ISRCTN95459505.

Involvement of Indoleamine-2,3-Dioxygenase and Kynurenine Pathway in Experimental Autoimmune Encephalomyelitis in Mice

The experimental autoimmune encephalomyelitis (EAE) is a model that mimics multiple sclerosis in rodents. Evidence has suggested that the activation of indoleamine-2,3-dioxygenase (IDO), the rate-limiting enzyme in the kynurenine pathway (KP), plays a crucial role in inflammation-related diseases. The present study aimed to investigate the involvement of the inflammatory process and KP components in a model of EAE in mice. To identify the role of KP in EAE pathogenesis, mice received IDO inhibitor (INCB024360) at a dose of 200 mg/kg (per oral) for 25 days. We demonstrated that IDO inhibitor mitigated the clinical signs of EAE, in parallel with the reduction of cytokine levels (brain, spinal cord, spleen and lymph node) and ionized calcium-binding adaptor protein-1 (Iba-1) gene expression in the central nervous system of EAE mice. Besides, IDO inhibitor causes a significant decrease in the levels of tryptophan, kynurenine and neurotoxic metabolites of KP, such as 3-hydroxykynurenine (3-HK) and quinolinic acid (QUIN) in the prefrontal cortex, hippocampus, spinal cord, spleen and lymph node of EAE mice. The mRNA expression and enzyme activity of IDO and kynurenine 3-monooxygenase (KMO) were also reduced by IDO inhibitor. These findings indicate that the inflammatory process concomitant with the activation of IDO/KP is involved in the pathogenic mechanisms of EAE. The modulation of KP is a promising target for novel pharmacological treatment of MS.

Chronic mechanical hypersensitivity in experimental autoimmune encephalomyelitis is regulated by disease severity and neuroinflammation

Chronic pain severely affects quality of life in more than half of people living with multiple sclerosis (MS). A commonly-used model of MS, experimental autoimmune encephalomyelitis (EAE), typically presents with hindlimb paralysis, neuroinflammation and neurodegeneration. However, this paralysis may hinder the use of pain behavior tests, with no apparent hypersensitivity observed post-peak disease. We sought to adapt the classic actively-induced EAE model to optimize its pain phenotype. EAE was induced with MOG_35-55/CFA and 100-600 ng pertussis toxin (PTX), and mice were assessed for mechanical, cold and thermal sensitivity over a 28-day period. Spinal cord tissue was collected at 14 and 28 days post-injection to assess demyelination and neuroinflammation. Only mice treated with 100 ng PTX exhibited mechanical hypersensitivity. Hallmarks of disease pathology, including demyelination, immune cell recruitment, cytokine expression, glial activation, and neuronal damage were higher in EAE mice induced with moderate (200 ng) doses of pertussis toxin, compared to those treated with low (100 ng) levels. Immunostaining demonstrated activated astrocytes and myeloid/microglial cells in both EAE groups. These results indicate that a lower severity of EAE disease may allow for the study of pain behaviors while still presenting with disease pathology. By using this modified model, researchers may better study the mechanisms underlying pain.

Wallerian degeneration as a therapeutic target in traumatic brain injury

PURPOSE OF REVIEW

Diffuse or traumatic axonal injury is one of the principal pathologies encountered in traumatic brain injury (TBI) and the resulting axonal loss, disconnection, and brain atrophy contribute significantly to clinical morbidity and disability. The seminal discovery of the slow Wallerian degeneration mice (Wld) in which transected axons do not degenerate but survive and function independently for weeks has transformed concepts on axonal biology and raised hopes that axonopathies may be amenable to specific therapeutic interventions. Here we review mechanisms of axonal degeneration and also describe how these mechanisms may inform biological therapies of traumatic axonopathy in the context of TBI.

RECENT FINDINGS

In the last decade, SARM1 [sterile a and Toll/interleukin-1 receptor (TIR) motif containing 1] and the DLK (dual leucine zipper bearing kinase) and LZK (leucine zipper kinase) MAPK (mitogen-activated protein kinases) cascade have been established as the key drivers of Wallerian degeneration, a complex program of axonal self-destruction which is activated by a wide range of injurious insults, including insults that may otherwise leave axons structurally robust and potentially salvageable. Detailed studies on animal models and postmortem human brains indicate that this type of partial disruption is the main initial pathology in traumatic axonopathy. At the same time, the molecular dissection of Wallerian degeneration has revealed that the decision that commits axons to degeneration is temporally separated from the time of injury, a window that allows potentially effective pharmacological interventions.

SUMMARY

Molecular signals initiating and triggering Wallerian degeneration appear to be playing an important role in traumatic axonopathy and recent advances in understanding their nature and significance is opening up new therapeutic opportunities for TBI.

Animal models for human disease

This chapter introduces some types of animal models which are used for better understanding the disease mechanisms and its treatment. These experimental models fall into two categories: spontaneous models and induced models. Among the diseases, rheumatoid arthritis (RA) as an autoimmune disease was considered. To study the pathogenesis of RA, we explained collagen-induced arthritis as an animal model that reflects a characteristic feature of RA patients. In addition, experimental allergic encephalomyelitis (EAE) as an experimental model for multiple sclerosis (MS) was explained in detail to represent a standard method to investigate in its mechanism, finding the way for the amelioration of this incurable neurological disorder.