Modulation of remyelination by adaptive inflammation and electrical stimulation
by Patrik Kunz
Date of Examination:2017-06-14
Date of issue:2017-06-29
Advisor:Prof. Dr. Walter Paulus
Referee:Prof. Dr. Walter Paulus
Referee:Prof. Dr. Wolfgang Brück
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Abstract
English
Multiple sclerosis (MS) is a chronic, inflammatory demyelinating disease of the central nervous system (CNS). Typical characteristics of MS are blood-brain barrier (BBB) breakdown, invasion of peripheral immune cells, demyelinated lesions and axonal damage with functional loss. Although the brain is able to remyelinate demyelinated lesions to a certain degree during the relapsing-remitting phase, for reasons yet unknown remyelination fails in the later, chronic stages of MS. The different disease stages of MS feature different pathological mechanisms, e.g. T cell infiltration and inflammatory activity decreases during the chronic phase, accompanied by a reduced remyelination capacity of the demyelinated lesions. Therefore, in this thesis, we evaluated the impact of CNS infiltrating and auto-reactive immune cells on remyelination in a mouse model of demyelination. We demonstrated that the induction of experimental autoimmune encephalomyelitis (EAE) by immunization with MOG35-55 peptide in a model of Cuprizone-induced demyelination led to increased infiltration of inflammatory mediators like T cells, B cells, NK cells, granulocytes and inflammatory monocytes and subsequent increased axonal damage. The infiltration of the CNS by auto-reactive immune cells however, did not substantially influence the remyelination process, as indicated by the analysis of oligodendrocyte populations, myelin formation and myelinated fiber density in the corpus callosum (CC). To improve the efficacy of remyelination in demyelinating diseases like MS is of great therapeutic interest. Recent studies demonstrated neuroregenerative effects and increased (re-)myelination by electrical stimulation in mixed cortical cell cultures as well as rodent models of peripheral nerve injury and ischemic stroke. Based on these studies, we established a novel method for transcranial electrical stimulation in a rat model of focal, cortical demyelination as well as in a mouse model of chronic, Cuprizone-induced demyelination. Furthermore, we evaluated the impact of alternating current stimulation on oligodendrocyte survival, myelin production and the myelination of axonal fibers in oligodendrocyte and mixed cortical cultures. The in vitro experiments did not reveal an impact of electrical stimulation on oligodendrocyte numbers and cell viability. Also, no effects on myelin production or the amount of myelinated fibers could be determined. However, we were able to apply transcranial alternating electrical currents safely and mostly non-invasively and therefore established the foundation for further experiments. However, the lack of effects on oligodendrocyte populations and remyelination, most likely caused by insufficient stimulation of neurons, indicate the need for improved stimulation protocols in terms of intensity and directionality. Theta burst stimulation (TBS), a form of repetitive transcranial magnetic stimulation (rTMS) established by Huang et al. in 2005, showed promising results in modulating neuronal activity of healthy human subjects, demonstrated by alterations of motor responses. Since the application of rTMS can be very uncomfortable for the recipient and bears an elevated risk of inducing epileptic seizures, we translated the established TBS protocols into electrical TBS (eTBS) protocols using high frequency, high intensity transcranial alternating currents. A double-blinded, crossover clinical study on healthy human subjects was conducted, and eTBS proofed to be a safe and non-invasive way to apply high frequency, high intensity alternating currents to the human brain. However, no effects on cortical excitability were observed by analysis of muscle evoked potential (MEP) responses.
Keywords: Multiple sclerosis; remyelination; electrical stimulation; inflammation; tACS