PART 2: Mouse models for multiple sclerosis research

A preclinical mice model of multiple sclerosis based on the toxin-induced double-site demyelination of callosal and cerebellar fibers

BACKGROUND

Multiple sclerosis (MS) is an irreversible progressive CNS pathology characterized by the loss of myelin (i.e. demyelination). The lack of myelin is followed by a progressive neurodegeneration triggering symptoms as diverse as fatigue, motor, locomotor and sensory impairments and/or bladder, cardiac and respiratory dysfunction. Even though there are more than fourteen approved treatments for reducing MS progression, there are still no cure for the disease. Thus, MS research is a very active field and therefore we count with different experimental animal models for studying mechanisms of demyelination and myelin repair, however, we still lack a preclinical MS model assembling demyelination mechanisms with relevant clinical-like signs.

RESULTS

Here, by inducing the simultaneous demyelination of both callosal and cerebellar white matter fibers by the double-site injection of lysolecithin (LPC), we were able to reproduce CNS demyelination, astrocyte recruitment and increases levels of proinflammatory cytokines levels along with motor, locomotor and urinary impairment, as well as cardiac and respiratory dysfunction, in the same animal model. Single site LPC-injections either in corpus callosum or cerebellum only, fails in to reproduce such a complete range of MS-like signs.

CONCLUSION

We here report that the double-site LPC injections treatment evoke a complex MS-like mice model. We hope that this experimental approach will help to deepen our knowledge about the mechanisms of demyelinated diseases such as MS.

Differential transcriptomic changes in the central nervous system and urinary bladders of mice infected with a coronavirus

Multiple sclerosis (MS) often leads to the development of neurogenic lower urinary tract symptoms (LUTS). We previously characterized neurogenic bladder dysfunction in a mouse model of MS induced by a coronavirus, mouse hepatitis virus (MHV). The aim of the study was to identify genes and pathways linking neuroinflammation in the central nervous system with urinary bladder (UB) dysfunction to enhance our understanding of the mechanisms underlying LUTS in demyelinating diseases. Adult C57BL/6 male mice (N = 12) received either an intracranial injection of MHV (coronavirus-induced encephalomyelitis, CIE group), or sterile saline (control group). Spinal cord (SC) and urinary bladders (UB) were collected from CIE mice at 1 wk and 4 wks, followed by RNA isolation and NanoString nCounter Neuroinflammation assay. Transcriptome analysis of SC identified a significantly changed expression of >150 genes in CIE mice known to regulate astrocyte, microglia and oligodendrocyte functions, neuroinflammation and immune responses. Two genes were significantly upregulated (Ttr and Ms4a4a), and two were downregulated (Asb2 and Myct1) only in the UB of CIE mice. Siglec1 and Zbp1 were the only genes significantly upregulated in both tissues, suggesting a common transcriptomic link between neuroinflammation in the CNS and neurogenic changes in the UB of CIE mice.

Cuprizone-mediated demyelination reversibly degrades voiding behavior in mice while sparing brainstem reflex

Multiple sclerosis (MS) is a chronic, progressively debilitating demyelinating disease of the central nervous system (CNS). Nearly 80% of MS patients experience lower urinary tract dysfunction early in their diagnosis. This significantly affects the quality of life, and in latter stages of disease is a leading cause of hospitalization. Previously, animal models have shown that inflammatory demyelination in the CNS causes profound bladder dysfunction, but the confounding influence of systemic inflammation limits the potential interpretation of the contribution of CNS demyelination to bladder dysfunction. Since the micturition circuit has myelinated neuronal connections in the cortex, brainstem, and spinal cord, we examined alterations in bladder function in the cuprizone model characterized by demyelinating lesions in the cortex and corpus callosum that are independent of T-cell-mediated autoimmunity. Herein, we report that a 4-week dietary cuprizone treatment in C57Bl/6J mice induced alterations in voiding behavior with increased micturition frequency and reduced volume voided, similar to human MS bladder dysfunction. Subsequently, recovery from cuprizone treatment restored normal bladder function. Demyelination and remyelination were confirmed by Luxol Fast Blue staining of the corpus callosum. Additionally, we also determined that an 8-week cuprizone treatment, resulting in chronic demyelination lacking spontaneous remyelination potential, is associated with an exacerbated voiding phenotype. Interestingly, while cuprizone-induced CNS demyelination severely affected conscious (cortical) urinary behavior, the brainstem and spinal cord reflex remained unchanged, as confirmed by urethane-anesthetized cystometry. This is the first study to show that cortical demyelination independent of inflammation can negatively impact urinary function.