Correction: Disinhibition of Cathepsin C Caused by Cystatin F Deficiency Aggravates the Demyelination in a Cuprizone Model.

[This corrects the article on p. 152 in vol. 9, PMID: 28066178.].

Disinhibition of Cathepsin C Caused by Cystatin F Deficiency Aggravates the Demyelination in a Cuprizone Model.

Although the precise mechanism underlying initial lesion development in multiple sclerosis (MS) remains unclear, CNS inflammation has long been associated with demyelination, and axonal degeneration. The activation of microglia/macrophages, which serve as innate immune cells in the CNS, is the first reaction to even minor pathologic changes in the CNS and is considered an initial pathogenic event in MS. Microglial activation accompanies a variety of gene expressions, including cystatin F (Cys F), which belongs to the cystatin superfamily and is one of the cathepsin inhibitors. In our previous study we showed that Cys F has a unique expression pattern in microglia/macrophages in the demyelination process. Specifically, the timing of Cys F induction correlated with ongoing demyelination, and the sites of Cys F expression overlapped with areas of remyelination. Cys F induction ceased in chronic demyelination when remyelination capacity was lost, suggesting that Cys F expressed by microglia/macrophages may play an important role in demyelination and/or remyelination. The functional role of Cys F in demyelinating disease of the CNS, however, is unclear. Cys F gene knockout mice were used in the current study to clarify the functional role of Cys F in the demyelination process in a cuprizone-induced demyelination animal model. We demonstrated that absence of the Cys F gene and the resulting disinhibition of cathepsin C (Cat C) aggravates the demyelination, and this finding may be related to the increased expression of the glia-derived chemokine, CXCL2, which may attract inflammatory cells to sites of myelin sheath damage. This effect was reversed by knock down of the Cat C gene. The findings gain further insight to function of Cat C in pathophysiology of MS, which may have implications for therapeutics for the prevention of neuroinflammation-involved neurological disorders in the future.

The induction of neuronal death by up-regulated microglial cathepsin H in LPS-induced neuroinflammation.

BACKGROUND: Neuroinflammation is a hallmark that leads to selective neuronal loss and/or dysfunction in neurodegenerative disorders. Microglia-derived lysosomal cathepsins are increasingly recognized as important inflammatory mediators to trigger signaling pathways that aggravate neuroinflammation. However, cathepsin H (Cat H), a cysteine protease, has been far less studied in neuroinflammation, compared to cathepsins B, D, L, and S. The expression patterns and functional roles of Cat H in the brain in neuroinflammation remain unknown. METHODS: C57BL/6J mice were intraperitoneally injected with either 0.9% saline or lipopolysaccharide (LPS, 5 mg/kg). Immunohistochemistry (IHC) and in situ hybridization (ISH) were used to analyze expression and localization of Cat H in the brain. Nitrite assay was used to examine microglial activation in vitro; ELISA was used to determine the release of Cat H and proinflammatory cytokines (TNF-α, IL-1ß, IL-6, IFN-γ). Cat H activity was analyzed by cellular Cat H assay kit. Flow cytometry and in situ cell death detection were used to investigate neuronal death. Data were evaluated for statistical significance with one-way ANOVA and t test. RESULTS: Cat H mRNA was only present in perivascular microglia and non-parenchymal sites under normal conditions. After LPS injection, Cat H mRNA expression in activated microglia in different brain regions was increased. Twenty-four hours after LPS injection, Cat H mRNA expression was maximal in SNr; 72 h later, it peaked in cerebral cortex and hippocampus then decreased and maintained at a low level. The expression of Cat H protein exhibited the similar alterations after LPS injection. In vitro, inflammatory stimulation (LPS, TNF-α, IL-1ß, IL-6, and IFN-γ) increased the release and activity of Cat H in microglia. Conversely, addition of Cat H to microglia promoted the production and release of NO, IL-1ß, and IFN-γ which could be prevented by neutralizing antibody. Further, addition of Cat H to Neuro2a cells induced neuronal death. CONCLUSIONS: Taken together, these data indicate that the up-regulated microglial Cat H expression, release, and activity in the brain lead to neuronal death in neuroinflammation. The functional link of Cat H with microglial activation might contribute to the initiation and maintenance of microglia-driven chronic neuroinflammation.