The Function Role Of Cathepsin C In Remyelination Process

Background: In the central nervous system,oligodendrocytes extend the myelin sheath to wrap up the axons closely.Unmyelinated axonal regions between myelin segments are termed nodes of Ranvier,which greatly speeds up the conduction of the action potential on the axon.In addition,the myelin sheath also provides physical protection and nutritional support for axons.Multiple Sclerosis(MS)is the most common demyelinating disease of the central nervous system,which is difficult to cure for the lack of effective treatment.Pathological features of MS include inflammation,destruction of the blood-brain barrier,demyelination and axonal degeneration.In the majority of MS patients,the myelin sheath can be regenerated in the early stage of disease.However,the process of remyelination gradually fails while demyelination continues.This leads to the degeneration of the axon,which eventually results in the loss of neurons.The loss of neurons may be the fundamental reason of disability in patients with chronic demyelination.Therefore,the promotion of remyelination is an effective strategy to improve and cure MS,and it is very important to study its mechanism for searching a new therapeutic target.In our previous study,we found that cathepsin C(Cat C)is significantly increased in neuroinflammation and demyelinating disease in the central nervous system.Moreover,Cat C overexpression increases inflammatory cell infiltration in the central nervous system in murine demyelinating models,thereby aggravating myelin damage.However,the effect of Cat C on remyelination is unclear.Objective: Investigate the effect and its mechanisms of Cat C on remyelination in demyelinating diseases.Methods: C57BL/6J wild type(WT)?Cat C over expression(Cat C OE)and Cat C knock down(Cat C KD)were used for this reaserch.For the focal demyelination model,mice were placed in a stereotaxic frame(Stoelting)and 2 ?l of 1% lysolecithin(LPC)solution was injected into the forceps minor of the corpus callosum(fmi)using Hamilton microliter syringe,and controls were injected with 2 ?l of saline.Mice were analysed at 7 and 14 days post-injection after LPC injection.Immunohistochemical staining were preformed to detect the activation of microglia(Iba-1)and the number of oligodendrocyte(CC1)in the demyelinating zone.The thickness of myelin regeneration in demyelinating region was observed by electron microscopy,and analyzed by comparing the G-ratio(axon diameter/total myelin diameter).Real-time PCR was used to analyze the expression of TNF-? and IL-1? mRNA in the demyelinating zone.Immunofluorescence and 5-Ethynyl-2-deoxyuridine(EdU)staining was used to detect oligodendrocyte precursor cells(PDGFR-?)proliferation.The experimental data were analyzed with one-way ANOVA.When P <0.05,the statistical results were significantly different.The results were expressed as mean ± standard deviation.Results:1.In 14 day after LPC injection,the number of oligodendrocytes in the demyelinating area in Cat C OE mice was significantly lower than the number of oligodendrocytes in wild-type and Cat C KD mice.2.In 14 day after LPC injection,the G-ratio in the demyelinating area in Cat C OE mice was significantly higher than that in wild type and Cat C KD mice.3.The number of microglia in the demyelinating area in Cat C OE mice was significantly higher than that in wild type and Cat C KD mice both in 7 and 14 day after LPC injection.4.The expression of pro-inflammatory cytokines TNF-? and IL-1? in the demyelinating area in Cat C OE mice was significantly higher than that in wild type and Cat C KD mice both in 7 and 14 day after LPC injection.5.In 14 day after LPC injection,the number of proliferating oligodendrocyte precursor cells in the demyelinating area in Cat C OE mice was significantly lower than that in wild type and Cat C KD mice.Conclusions:Cat C gene overexpression enhances the activation of microglia and the expression of pro-inflammatory cytokines TNF-? and IL-1? in the demyelinating region by LPC-induced demyelination,,thus delaying the process of remyelination.