Up-regulation of microglial cathepsin C expression and activity in lipopolysaccharide-induced neuroinflammation

Cathepsin C exacerbates EAE by promoting the expansion of Tfh cells and the formation of TLSs in the CNS

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS) mediated by CD4+ T helper (Th) cells, and characterized by immune cell infiltration, demyelination and neurodegeneration, with no definitive cure available. Thus, it is pivotal and imperative to acquire more profound comprehension of the underlying mechanisms implicated in MS. Dysregulated immune responses are widely believed to play a primary role in the pathogenesis of MS. Recently, a plethora of studies have demonstrated the involvement of T follicular helper (Tfh) cells and tertiary lymphoid-like structures (TLSs) in the pathogenesis and progression of MS. Cathepsin C (CatC) is a cysteine exopeptidase which is crucial for the activation of immune-cell-associated serine proteinases in many inflammatory diseases in peripheral system, such as rheumatoid arthritis and septicemia. We have previously demonstrated that CatC is involved in neuroinflammation and exacerbates demyelination in both cuprizone-induced and experimental autoimmune encephalomyelitis (EAE) mouse models. However, the underlying immunopathological mechanism remains elusive. In the present study, we established a recombinant myelin oligodendrocyte glycoprotein 35-55 peptide-induced EAE model using conditional CatC overexpression mice to investigate the effects of CatC on the alteration of CD4+ Th subsets, including Th1, Th2, Th17, Tfh and T regulatory cells. Our findings demonstrated that CatC particularly enhanced the population of Tfh cell in the brain, resulting in the earlier onset and more severe chronic syndrome of EAE. Furthermore, CatC promoted the formation of TLSs in the brain, leading to persistent neuroinflammation and exacerbating the severity of EAE in the chronic phase. Conversely, treatment with AZD7986, a specific inhibitor of CatC, effectively attenuated the syndrome of EAE and its effects caused by CatC both in vivo and in vitro. These findings provide a novel insight into the critical role of CatC in innate and adaptive immunity in EAE, and specific inhibitor of CatC, AZD7986, may contribute to potential therapeutic strategies for MS.

Morin Ameliorates Lipopolysaccharides-Induced Sepsis-Associated Encephalopathy and Cognitive Impairment in Albino Mice

Sepsis-associated encephalopathy is a common neurological complication of sepsis that is characterized by neuroinflammation, oxidative stress and apoptosis, which results in cognitive impairments in septic survivors. Despite numerous treatment options for this condition, none of them are definite. Therefore, this study aimed to investigate the impact of morin, a flavone known for its neuroprotective and anti-inflammatory effects, against lipopolysaccharides-induced sepsis-associated encephalopathy in albino mice for 7 days. Mice were divided into 4 groups: Negative control, morin, septic, and septic morin-treated mice. Sepsis was induced by a single injection of lipopolysaccharides (5 mg/kg, intraperitoneally), morin (50 mg/kg b. wt.) was given orally, starting from 5 h after sepsis induction, then daily for 4 other days. Morin ameliorated septic structural and functional alternations as manifested by improving the survival rate, the behavioral functions, in addition to preserving and protecting the brain tissue. This was accompanied with the augmentation of the total antioxidant capacity, as well as the suppression of tissue levels of the lipid peroxidation marker malondialdehyde, apoptosis (cleaved-caspase-3), glial fibrillary acidic protein, and the proinflammatory cytokine tumor necrosis factor. In conclusion, morin has a promising ameliorative effect to counteract the sepsis-associated encephalopathy via its anti-inflammatory and antioxidant effects and to prevent the associated cognitive impairments.

Broadening Horizons: Exploring the Cathepsin Family as Therapeutic Targets for Alzheimer's Disease

Alzheimer's disease (AD) is an intricate neurodegenerative disorder characterized by the accumulation of misfolded proteins, including beta-amyloid (Aβ) and tau, leading to cognitive decline. Despite decades of research, the precise mechanisms underlying its onset and progression remain elusive. Cathepsins are a family of lysosomal enzymes that play vital roles in cellular processes, including protein degradation and regulation of immune responses. Emerging evidence suggests that cathepsins may be involved in AD pathogenesis. Cathepsins can influence the activation of microglia and astrocytes, the resident immune cells in the brain. However, cathepsin dysfunction may lead to the accumulation of misfolded proteins, notably Aβ and tau. In addition, dysregulated cathepsin activity may induce an exaggerated immune response, promoting chronic inflammation and neuronal dysfunction in patients with AD. By unraveling the classification, functions, and roles of cathepsins in AD's pathogenesis, this review sheds light on their intricate involvement in this devastating disease. Targeting cathepsin activity could be a promising and novel approach for mitigating the pathological processes that contribute to AD, providing new avenues for its treatment and prevention.

Cystatin F attenuates neuroinflammation and demyelination following murine coronavirus infection of the central nervous system

BACKGROUND

Cystatin F is a secreted lysosomal cysteine protease inhibitor that has been implicated in affecting the severity of demyelination and enhancing remyelination in pre-clinical models of immune-mediated demyelination. How cystatin F impacts neurologic disease severity following viral infection of the central nervous system (CNS) has not been well characterized and was the focus of this study. We used cystatin F null-mutant mice (Cst7-/-) with a well-established model of murine coronavirus-induced neurologic disease to evaluate the contributions of cystatin F in host defense, demyelination and remyelination.

METHODS

Wildtype controls and Cst7-/- mice were intracranially (i.c.) infected with a sublethal dose of the neurotropic JHM strain of mouse hepatitis virus (JHMV), with disease progression and survival monitored daily. Viral plaque assays and qPCR were used to assess viral levels in CNS. Immune cell infiltration into the CNS and immune cell activation were determined by flow cytometry and 10X genomics chromium 3' single cell RNA sequencing (scRNA-seq). Spinal cord demyelination was determined by luxol fast blue (LFB) and Hematoxylin/Eosin (H&E) staining and axonal damage assessed by immunohistochemical staining for SMI-32. Remyelination was evaluated by electron microscopy (EM) and calculation of g-ratios.

RESULTS

JHMV-infected Cst7-/- mice were able to control viral replication within the CNS, indicating that cystatin F is not essential for an effective Th1 anti-viral immune response. Infiltration of T cells into the spinal cords of JHMV-infected Cst7-/- mice was increased compared to infected controls, and this correlated with increased axonal damage and demyelination associated with impaired remyelination. Single-cell RNA-seq of CD45 + cells enriched from spinal cords of infected Cst7-/- and control mice revealed enhanced expression of transcripts encoding T cell chemoattractants, Cxcl9 and Cxcl10, combined with elevated expression of interferon-g (Ifng) and perforin (Prf1) transcripts in CD8 + T cells from Cst7-/- mice compared to controls.

CONCLUSIONS

Cystatin F is not required for immune-mediated control of JHMV replication within the CNS. However, JHMV-infected Cst7-/- mice exhibited more severe clinical disease associated with increased demyelination and impaired remyelination. The increase in disease severity was associated with elevated expression of T cell chemoattractant chemokines, concurrent with increased neuroinflammation. These findings support the idea that cystatin F influences expression of proinflammatory gene expression impacting neuroinflammation, T cell activation and/or glia cell responses ultimately impacting neuroinflammation and neurologic disease.

Polyphyllin I alleviates neuroinflammation after cerebral ischemia-reperfusion injury via facilitating autophagy-mediated M2 microglial polarization

Microglial activation and polarization play a central role in poststroke inflammation and neuronal damage. Modulating microglial polarization from pro-inflammatory to anti-inflammatory phenotype is a promising therapeutic strategy for the treatment of cerebral ischemia. Polyphyllin I (PPI), a steroidal saponin, shows multiple bioactivities in various diseases, but the potential function of PPI in cerebral ischemia is not elucidated yet. In our study, the influence of PPI on cerebral ischemia-reperfusion injury was evaluated. Mouse middle cerebral artery occlusion (MCAO) model and oxygen-glucose deprivation and reoxygenation (OGD/R) model were constructed to mimic cerebral ischemia-reperfusion injury in vivo and in vitro. TTC staining, TUNEL staining, RT-qPCR, ELISA, flow cytometry, western blot, immunofluorescence, hanging wire test, rotarod test and foot-fault test, open-field test and Morris water maze test were performed in our study. We found that PPI alleviated cerebral ischemia-reperfusion injury and neuroinflammation, and improved functional recovery of mice after MCAO. PPI modulated microglial polarization towards anti-inflammatory M2 phenotype in MCAO mice in vivo and post OGD/R in vitro. Besides, PPI promoted autophagy via suppressing Akt/mTOR signaling in microglia, while inhibition of autophagy abrogated the effect of PPI on M2 microglial polarization after OGD/R. Furthermore, PPI facilitated autophagy-mediated ROS clearance to inhibit NLRP3 inflammasome activation in microglia, and NLRP3 inflammasome reactivation by nigericin abolished the effect of PPI on M2 microglia polarization. In conclusion, PPI alleviated post-stroke neuroinflammation and tissue damage via increasing autophagy-mediated M2 microglial polarization. Our data suggested that PPI had potential for ischemic stroke treatment.

Assessing Cannabidiol as a Therapeutic Agent for Preventing and Alleviating Alzheimer's Disease Neurodegeneration

Alzheimer's disease (AD) is a leading neurodegenerative condition causing cognitive and memory decline. With small-molecule drugs targeting Aβ proving ineffective, alternative targets are urgently needed. Neuroinflammation, which is central to AD's pathology, results in synaptic and neuronal damage, highlighting the importance of addressing inflammation and conserving neuronal integrity. Cannabidiol (CBD), derived from cannabis, is noted for its neuroprotective and anti-inflammatory properties, having shown efficacy in neuropathic pain management for epilepsy. To investigate the therapeutic efficacy of CBD in AD and to elucidate its underlying mechanisms, we aimed to contribute valuable insights for incorporating AD prevention recommendations into future CBD nutritional guidelines. Aβ1-42 was employed for in vivo or in vitro model establishment, CBD treatment was utilized to assess the therapeutic efficacy of CBD, and RNA-seq analysis was conducted to elucidate the underlying therapeutic mechanism. CBD mitigates Aβ-induced cognitive deficits by modulating microglial activity, promoting neurotrophic factor release, and regulating inflammatory genes. The administration of CBD demonstrated a protective effect against Aβ toxicity both in vitro and in vivo, along with an amelioration of cognitive impairment in mice. These findings support the potential inclusion of CBD in future nutritional guidelines for Alzheimer's disease prevention.

The Role of Cysteine Protease Cathepsins B, H, C, and X/Z in Neurodegenerative Diseases and Cancer

Papain-like cysteine proteases are composed of 11 human cysteine cathepsins, originally located in the lysosomes. They exhibit broad specificity and act as endopeptidases and/or exopeptidases. Among them, only cathepsins B, H, C, and X/Z exhibit exopeptidase activity. Recently, cysteine cathepsins have been found to be present outside the lysosomes and often participate in various pathological processes. Hence, they have been considered key signalling molecules. Their potentially hazardous proteolytic activities are tightly regulated. This review aims to discuss recent advances in understanding the structural aspects of these four cathepsins, mechanisms of their zymogen activation, regulation of their activities, and functional aspects of these enzymes in neurodegeneration and cancer. Neurodegenerative effects have been evaluated, particularly in Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, multiple sclerosis, and neuropsychiatric disorders. Cysteine cathepsins also participate in tumour progression and metastasis through the overexpression and secretion of proteases, which trigger extracellular matrix degradation. To our knowledge, this is the first review to provide an in-depth analysis regarding the roles of cysteine cathepsins B, H, C, and X in neurodegenerative diseases and cancer. Further advances in understanding the functions of cysteine cathepsins in these conditions will result in the development of novel, targeted therapeutic strategies.

Axonal Transport of Lysosomes Is Unaffected in Glucocerebrosidase-Inhibited iPSC-Derived Forebrain Neurons

Lysosomes are acidic organelles that traffic throughout neurons delivering catabolic enzymes to distal regions of the cell and maintaining degradative demands. Loss of function mutations in the gene GBA encoding the lysosomal enzyme glucocerebrosidase (GCase) cause the lysosomal storage disorder Gaucher's disease (GD) and are the most common genetic risk factor for synucleinopathies like Parkinson's disease (PD) and dementia with Lewy bodies (DLB). GCase degrades the membrane lipid glucosylceramide (GlcCer) and mutations in GBA, or inhibiting its activity, results in the accumulation of GlcCer and disturbs the composition of the lysosomal membrane. The lysosomal membrane serves as the platform to which intracellular trafficking complexes are recruited and activated. Here, we investigated whether lysosomal trafficking in axons was altered by inhibition of GCase with the pharmacological agent Conduritol B Epoxide (CBE). Using live cell imaging in human male induced pluripotent human stem cell (iPSC)-derived forebrain neurons, we demonstrated that lysosomal transport was similar in both control and CBE-treated neurons. Furthermore, we tested whether lysosomal rupture, a process implicated in various neurodegenerative disorders, was affected by inhibition of GCase. Using L-leucyl-L-leucine methyl ester (LLoME) to induce lysosomal membrane damage and immunocytochemical staining for markers of lysosomal rupture, we found no difference in susceptibility to rupture between control and CBE-treated neurons. These results suggest the loss of GCase activity does not contribute to neurodegenerative disease by disrupting either lysosomal transport or rupture.

Cysteine Cathepsins as Therapeutic Targets in Immune Regulation and Immune Disorders

Cysteine cathepsins, as the most abundant proteases found in the lysosomes, play a vital role in several processes-such as protein degradation, changes in cell signaling, cell morphology, migration and proliferation, and energy metabolism. In addition to their lysosomal function, they are also secreted and may remain functional in the extracellular space. Upregulation of cathepsin expression is associated with several pathological conditions including cancer, neurodegeneration, and immune-system dysregulation. In this review, we present an overview of cysteine-cathepsin involvement and possible targeting options for mitigation of aberrant function in immune disorders such as inflammation, autoimmune diseases, and immune response in cancer.

Cathepsin C (CTSC) contributes to the antibacterial immunity in golden pompano (Trachinotus ovatus)

Cathepsins, as a class of protein hydrolases, are widely found in the lysosomes of many tissues and play an essential role in various physiological activities. Cathepsin C (CTSC), a lysosomal cysteine protease, is an essential component of the lysosomal hydrolase family. In this study, we identified a CTSC from Trachinotus ovatus (TroCTSC) and analyzed its function. TroCTSC contained an ORF of 1368 bp and encoded 455 amino acids, which included three conserved catalytically active sites (Cys²⁵¹, His³⁹⁷, and Asn⁴¹⁹). It shares high homology (69.47%-90.77%) with the other known CTSC sequences of teleosts, which was most closely related to Seriola dumerili. TroCTSC was most abundant in the muscle, liver, and head kidney. After Vibrio harveyi infection, the expression levels of TroCTSC in liver, spleen, and head kidney were significantly up-regulated. TroCTSC was found in the cytoplasm with some of which were co-located with the lysosome. After V. harveyi stimulation, TroCTSC was translocated to nucleus in golden pompano snout (GPS) cells. In vitro, results revealed that the optimal hydrolase activity of the recombinant protein, rTroCTSC, was at 40 °C and pH 5.5. The activity of rTroCTSC was promoted by Zn²⁺ and Ca²⁺ but inhibited by Fe²⁺ and Cu²⁺. However, three mutant proteins, rTroCTSC-C251A, rTroCTSC-H397A, rTroCTSC-N419A, were dramatically reduced the proteolytic activity. Furthermore, in vivo results showed that overexpression of TroCTSC could significantly enhance body's ability to resist V. harveyi and promote the expression of proinflammatory cytokines, including interleukin 1-beta (IL-1β), IL-6, IL-8, interferon-gamma (IFN-γ), and tumor necrosis factor-alpha (TNF-α). In contrast, the interference of TroCTSC expression induced a significant increase in the number of bacteria after V. harveyi infection. Our results suggested that TroCTSC was an essential effector of the innate immune system and played a pivotal role in antibacterial immunity.

Chitotriosidase 1 in the cerebrospinal fluid as a putative biomarker for HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) progression

Human T-lymphotropic virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is an inflammatory neurodegenerative disease that affects motor, urinary, intestinal, and sensory functions. Typically, HAM/TSP is slowly progressive, but it may vary from limited motor disability after decades (very slow progression) to loss of motor function in a few years from disease onset (rapid). In this study, we aimed to identify prognostic biomarkers for HAM/TSP to support patient management. Thus, proteomic analysis of the cerebrospinal fluid (CSF) was performed with samples from HTLV-1 asymptomatic carriers (AC) (n=13) and HAM/TSP patients (n=21) with rapid, typical, and very slow progression using quantitative label-free liquid chromatography/tandem mass spectrometry. Enrichment analyses were also carried out to identify key biological processes associated with distinct neurological conditions in HTLV-1 infection. Candidate biomarkers were validated by ELISA in paired CSF and serum samples, and samples from HTLV-1-seronegative individuals (n=9) were used as controls. CSF analysis identified 602 proteins. Leukocyte/cell activation, immune response processes and neurodegeneration pathways were enriched in rapid progressors. Conversely, HTLV-1 AC and HAM/TSP patients with typical and very slow progression had enriched processes for nervous system development. Differential expression analysis showed that soluble vascular cell adhesion molecule 1 (sVCAM-1), chitotriosidase 1 (CHIT1), and cathepsin C (CTSC) were upregulated in HAM/TSP. However, only CHIT1 was significantly elevated after validation, particularly in HAM/TSP rapid progressors. In contrast, none of these biomarkers were altered in serum. Additionally, CSF CHIT1 levels in HAM/TSP patients positively correlated with the speed of HAM/TSP progression, defined as points in the IPEC-2 HAM/TSP disability scale per year of disease, and with CSF levels of phosphorylated neurofilament heavy chain, neopterin, CXCL5, CXCL10, and CXCL11. In conclusion, higher CSF levels of CHIT1 were associated with HAM/TSP rapid progression and correlated with other biomarkers of neuroinflammation and neurodegeneration. Therefore, we propose CHIT1 as an additional or alternative CSF biomarker to identify HAM/TSP patients with a worse prognosis.

Lysosomal peptidases – Intriguing roles in cancer progression and neurodegeneration

Lysosomal peptidases are hydrolytic enzymes capable of digesting waste proteins that are targeted to lysosomes via endocytosis and autophagy. Besides intracellular protein catabolism, they play more specific roles in several other cellular processes and pathologies, either within lysosomes, upon secretion into the cell cytoplasm or extracellular space, or bound to the plasma membrane. In cancer, lysosomal peptidases are generally associated with disease progression, as they participate in crucial processes leading to changes in cell morphology, signaling, migration, and invasion, and finally metastasis. However, they can also enhance the mechanisms resulting in cancer regression, such as apoptosis of tumor cells or antitumor immune responses. Lysosomal peptidases have also been identified as hallmarks of aging and neurodegeneration, playing roles in oxidative stress, mitochondrial dysfunction, abnormal intercellular communication, dysregulated trafficking, and the deposition of protein aggregates in neuronal cells. Furthermore, deficiencies in lysosomal peptidases may result in other pathological states, such as lysosomal storage disease. The aim of this review was to highlight the role of lysosomal peptidases in particular pathological processes of cancer and neurodegeneration and to address the potential of lysosomal peptidases in diagnosing and treating patients.

Cysteine Peptidase Cathepsin X as a Therapeutic Target for Simultaneous TLR3/4-mediated Microglia Activation

Microglia are resident macrophages in the central nervous system that are involved in immune responses driven by Toll-like receptors (TLRs). Microglia-mediated inflammation can lead to central nervous system disorders, and more than one TLR might be involved in these pathological processes. The cysteine peptidase cathepsin X has been recognized as a pathogenic factor for inflammation-induced neurodegeneration. Here, we hypothesized that simultaneous TLR3 and TLR4 activation induces synergized microglia responses and that these phenotype changes affect cathepsin X expression and activity. Murine microglia BV2 cells and primary murine microglia were exposed to the TLR3 ligand polyinosinic-polycytidylic acid (poly(I:C)) and the TLR4 ligand lipopolysaccharide (LPS), individually and simultaneously. TLR3 and TLR4 co-activation resulted in increased inflammatory responses compared to individual TLR activation, where poly(I:C) and LPS induced distinct patterns of proinflammatory factors together with different patterns of cathepsin X expression and activity. TLR co-activation decreased intracellular cathepsin X activity and increased cathepsin X localization at the plasma membrane with concomitant increased extracellular cathepsin X protein levels and activity. Inhibition of cathepsin X in BV2 cells by AMS36, cathepsin X inhibitor, significantly reduced the poly(I:C)- and LPS-induced production of proinflammatory cytokines as well as apoptosis. Additionally, inhibiting the TLR3 and TLR4 common signaling pathway, PI3K, with LY294002 reduced the inflammatory responses of the poly(I:C)- and LPS-activated microglia and recovered cathepsin X activity. We here provide evidence that microglial cathepsin X strengthens microglia activation and leads to subsequent inflammation-induced neurodegeneration. As such, cathepsin X represents a therapeutic target for treating neurodegenerative diseases related to excess inflammation.

Cathepsin C inhibitors as anti-inflammatory drug discovery: Challenges and opportunities

Cathepsin C, an important lysosomal cysteine protease, mediates the maturation process of neutrophil serine proteases, and participates in the inflammation and immune regulation process associated with polymorphonuclear neutrophils. Therefore, cathepsin C is considered to be an attractive target for treating inflammatory diseases. With INS1007 (trade name: brensocatib) being granted a breakthrough drug designation by FDA for the treatment of Adult Non-cystic Fibrosis Bronchiectasis and Coronavirus Disease 2019, the development of cathepsin C inhibitor will attract attentions from medicinal chemists in the future soon. Here, we summarized the research results of cathepsin C as a therapeutic target, focusing on the development of cathepsin C inhibitor, and provided guidance and reference opinions for the upcoming development boom of cathepsin C inhibitor.

New Insights into the Role of Cysteine Cathepsins in Neuroinflammation

Neuroinflammation, which is mediated by microglia and astrocytes, is associated with the progression of neurodegenerative diseases. Increasing evidence shows that activated microglia induce the expression and secretion of various lysosomal cathepsins, particularly during the early stage of neuroinflammation. This trigger signaling cascade that aggravate neurodegeneration. To date, most research on neuroinflammation has focused on the role of cysteine cathepsins, the largest cathepsin family. Cysteine cathepsins are primarily responsible for protein degradation in lysosomes; however, they also play a role in regulating a number of other important physiological and pathological processes. This review focuses on the functional roles of cysteine cathepsins in the central nervous system during neuroinflammation, with an emphasis on their roles in the polarization of microglia and neuroinflammation signaling, which in turn causes neuronal death and thus neurodegeneration.

Cathepsin C aggravates neuroinflammation via promoting production of CCL2 and CXCL2 in glial cells and neurons in a cryogenic brain lesion

OBJECTIVE

Chemokines regulate infiltration of immune cells to brain in inflammation. Cathepsin C (CatC), a lysosomal protease, has been found to participate in neuroinflammation. However, how CatC affects chemokines expression in neuroinflammation triggered by traumatic brain injury (TBI) remains unclear. Here, we investigated the effects of CatC on chemokines and neuroinflammation in TBI.

METHODS

The present study used CatC knockdown (KD) and overexpression (OE) mice to generate cryogenic brain lesion model and determined effects of CatC on expression of chemokines CCL2, CCL5 and CXCL2 and infiltration of immune cells in acute and chronic phases of the lesion. Further, cellular sources of various chemokines were demonstrated in vitro. Values were compared with wild type (WT) mice.

RESULTS

The results found that 6 h after lesion, CatC expression,IL-1β and TNF-α mRNA and protein expression were strongly induced in the lesions; CCL2 and CXCL2 mRNA and protein expression were increased in CatC OE mice, while decreased in CatC KD mice. On the 3rd day after lesion, macrophages and neutrophils were mainly infiltrated to the lesions. Simultaneously, Iba-1+ cells in CatC OE mice were increased, while MPO + cells in CatC KD mice were decreased. In contrast, on the 28th day after lesion, a few lymphocytes were infiltrated surrounding new blood vessels. CatC OE mice showed larger volumes of scar areas, higher expression of CCL2,CXCL2,IL-1β,TNF-α,IL-6 and iNOS, as well as stronger GFAP+ and Iba-1+ signals, while CatC KD mice had reversed effects. No significant differences of CCL5 expression were found in various genotype mice. Further, in vitro study demonstrated CatC-induced expression of CCL2 were mainly derived from microglia and neurons, while CXCL2 derived from microglia and astrocytes.

CONCLUSION

Our data indicate that CatC aggravates neuroinflammation via promoting production of CCL2 and CXCL2 in glial cells and neurons in a cryogenic brain lesion, providing potential cellular and molecular targets for future intervention of TBI and other neuroinflammatory diseases.

Neuroinflammation-Induced Upregulation of Glial Cathepsin X Expression and Activity in vivo

Neuroinflammation is an important factor in the pathogenesis of neurodegenerative diseases. Microglia-derived lysosomal cathepsins have been increasingly recognized as important inflammatory mediators that trigger signaling pathways that aggravate neuroinflammation. In vitro, a contribution to neuroinflammation processes has been shown for cathepsin X: however, the expression patterns and functional role of cathepsin X in neuroinflammatory brain pathology remain elusive. In this study we analyzed the expression, activity, regional distribution and cellular localization of cathepsin X in the rat brain with neuroinflammation-induced neurodegeneration. The unilateral injection of lipopolysaccharide (LPS) induced a strong upregulation of cathepsin X expression and its activity in the ipsilateral striatum. In addition to the striatum, cathepsin X overexpression was detected in other brain areas such as the cerebral cortex, corpus callosum, subventricular zone and external globus pallidus, whereas the upregulation was mainly restricted to activated microglia and reactive astrocytes. Continuous administration of the cathepsin X inhibitor AMS36 indicated protective effects against LPS-induced striatal degeneration, as seen by the attenuated LPS-mediated dilation of the lateral ventricles and partial decreased extent of striatal lesion. Taken together, our results indicate that cathepsin X plays a role as a pathogenic factor in neuroinflammation-induced neurodegeneration and represents a potential therapeutic target for neurodegenerative diseases associated with neuroinflammation.

Whole-Genome Sequencing of Inbred Mouse Strains Selected for High and Low Open-Field Activity

We conducted whole-genome sequencing of four inbred mouse strains initially selected for high (H1, H2) or low (L1, L2) open-field activity (OFA), and then examined strain distribution patterns for all DNA variants that differed between their BALB/cJ and C57BL/6J parental strains. Next, we assessed genome-wide sharing (3,678,826 variants) both between and within the High and Low Activity strains. Results suggested that about 10% of these DNA variants may be associated with OFA, and clearly demonstrated its polygenic nature. Finally, we conducted bioinformatic analyses of functional genomics data from mouse, rat, and human to refine previously identified quantitative trait loci (QTL) for anxiety-related measures. This combination of sequence analysis and genomic-data integration facilitated refinement of previously intractable QTL findings, and identified possible genes for functional follow-up studies.

Cathepsin C promotes the progression of periapical periodontitis

Although the role of cathepsin C (Cat C) in inflammation is gradually being elucidated, its function in periapical periodontitis, which is one of the most common infectious diseases worldwide, has not been studied. This study evaluated a surgically-induced model of periapical periodontitis in cathepsin C (Cat C) knock-down (KD) mice, which was constructed with a tetracycline operator, to evaluate the role of Cat C in the pathogenesis and progression of periapical periodontitis. Our results showed, for the first time, that there was a statistically significant increase in the expression of Cat C as periapical periodontitis progressed; this increase started from 1 week after surgery and reached a peak at 3 weeks after surgery, before gradually decreasing. The volume of periapical bone resorption in Cat C KD mice was significantly smaller than that in wild-type mice at 3 and 4 weeks after surgery (P<0.05). Inflammatory cell infiltration into the apical tissues of wild-type mice was also significantly higher than that of Cat C KD mice. The expression of receptor activator of nuclear factor-κB ligand (RANKL) in wild-type mice was also higher than that in Cat C KD mice. The difference in the number of osteoclasts in the apical area between the two groups was statistically significant after 2 weeks. Correlation analysis showed that there was a significant correlation between Cat C and RANKL expression (r= 0.835). Therefore, our data indicated that Cat C promoted the apical inflammation and bone destruction in mice.

Upregulation of Cathepsins in Olfactory Bulbs Is Associated with Transient Olfactory Dysfunction in Mice with Experimental Autoimmune Encephalomyelitis

Cathepsins are a family of lysosomal/endosomal proteolytic enzymes that include serine, aspartate, and cysteine proteases. The role of cathepsin in neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease, remains elusive. We evaluated the expression level and localization of different cathepsins in the olfactory bulbs of mice with experimental autoimmune encephalomyelitis (EAE), a model of human multiple sclerosis. Quantitative real-time PCR results and Western blotting analyses revealed that serine, aspartate, and cysteine cathepsins are expressed at significantly higher levels in the olfactory bulbs of mice with EAE in the paralytic stage compared with those of control mice. Immunohistochemical analyses indicated that cathepsin A, D, and S were expressed in the glomerulus layer, external plexiform layer, and mitral cell layer. Furthermore, cathepsins were detected in astrocytes, microglia, inflammatory cells, and vascular cells in the olfactory bulb of EAE mice at the paralytic stage. Collectively, these results suggest that the upregulation of cathepsins in the olfactory bulb of mice with EAE is associated with transient olfactory dysfunction in autoimmune encephalomyelitis.

Pioglitazone Attenuates Lipopolysaccharide-Induced Oxidative Stress, Dopaminergic Neuronal Loss and Neurobehavioral Impairment by Activating Nrf2/ARE/HO-1

The aim of the present study was to examine the neuroprotective potential of pioglitazone via activation of Nrf2/ARE-dependent HO-1 signaling pathway in chronic neuroinflammation and progressive neurodegeneration mouse model induced by lipopolysaccharide (LPS). After assessing spatial memory, anxiety and motor-coordination, TH+ neurons in substantia nigra (SN) were counted. The oxidative stress marker carbonyl protein levels and HO-1 enzyme activity were also evaluated. RT-qPCR was conducted to detect HO-1, Nrf2 and NF-κp65 mRNA expression levels and Nrf2 transcriptional activation of antioxidant response element (ARE) of HO-1 was investigated. Pioglitazone ameliorated LPS-induced dopaminergic neuronal loss, as well as mitigated neurobehavioral impairments. It enhanced Nrf2 mRNA expression, and augmented Nrf2/ARE-dependent HO-1 pathway activation by amplifying HO-1 mRNA expression. Moreover, it induced a significant decrease in NF-κB p65 mRNA expression, while reducing carbonyl protein levels and restoring the HO-1 enzyme activity. Interestingly, LPS induced Nrf2/antioxidant response element (ARE) of HO-1 activation, ultimately resulting in slight enhanced HO-1 mRNA expression. However, LPS elicited decrease in HO-1 enzyme activity. Zinc protoporphyrin-IX (ZnPPIX) administrated with pioglitazone abolished its effects in the LPS mouse model. The study results demonstrate that coordinated activation of Nrf2/ARE-dependent HO-1 pathway defense mechanism by the PPARγ agonist pioglitazone mediated its neuroprotective effects.

Up-regulated cathepsin C induces macrophage M1 polarization through FAK-triggered p38 MAPK/NF-κB pathway

Increasing evidence indicates that in response to environmental changes, macrophages can dynamically change into two main functional phenotypes, namely M1 and M2. Depending on these different phenotypes, macrophages can produce either pro-inflammatory or anti-inflammatory factors which may affect the outcome of inflammation. Mastering the switching of M1/M2 phenotypes may provide therapeutic approaches to chronic inflammatory disease, such as atherosclerosis, rheumatoid arthritis, even the metabolic disorders. Cathepsin C (CTSC), as a member of the papain family of cysteine proteases, is a key enzyme in the activation of granule serine proteases thereby involved in modulating the inflammatory responses. Moreover, abundant expression of CTSC has been found in M1 macrophages in plaques of atherosclerosis and related to the progression of disease. However, whether CTSC can regulate macrophage activation status in inflammatory responses has not been fully investigated. In the present study, using peritoneal macrophages (PMs) and mouse macrophage cell line RAW264.7 treated with LPS and active monomer of CTSC, we found that CTSC was not only expressed in macrophages in M1 activation status, but also facilitated macrophages towards M1 phenotype, suggesting a self-activation mechanism involved in this process which may lead to a vicious circle in chronic inflammation. Then we attempted to explore the underlying molecular mechanisms of CTSC resulting in M1 activation. Focal adhesion kinase (FAK) is one of the non-receptor cytoplasmic protein tyrosine kinases, serving as an upstream mediator that leads to transcription of many pro-inflammatory factors. We found FAK expression was up-regulated at both mRNA and protein levels following CTSC stimulation, and FAK phosphorylation level was also significantly increased. The p38MAPK/NF-κB pathway, as the downstream of FAK, were also found activated in CTSC-treated macrophages, suggesting that CTSC may promote macrophage towards M1 activation status through FAK-induced p38MAPK/NF-κB signaling pathway activation. Our study provides a new therapeutic target in the treatment of chronic inflammatory diseases.

Cathepsin C promotes microglia M1 polarization and aggravates neuroinflammation via activation of Ca2+-dependent PKC/p38MAPK/NF-κB pathway

Background

Microglia-derived lysosomal cathepsins are important inflammatory mediators to trigger signaling pathways in inflammation-related cascades. Our previous study showed that the expression of cathepsin C (CatC) in the brain is induced predominantly in activated microglia in neuroinflammation. Moreover, CatC can induce chemokine production in brain inflammatory processes. In vitro studies further confirmed that CatC is secreted extracellularly from LPS-treated microglia. However, the mechanisms of CatC affecting neuroinflammatory responses are not known yet.

Methods

CatC over-expression (CatCOE) and knock-down (CatCKD) mice were treated with intraperitoneal and intracerebroventricular LPS injection. Morris water maze (MWM) test was used to assess the ability of learning and memory. Cytokine expression in vivo was detected by in situ hybridization, quantitative PCR, and ELISA. In vitro, microglia M1 polarization was determined by quantitative PCR. Intracellular Ca²⁺ concentration was determined by flow cytometry, and the expression of NR2B, PKC, p38, IkBα, and p65 was determined by western blotting.

Results

The LPS-treated CatCOE mice exhibited significantly increased escape latency compared with similarly treated wild-type or CatCKD mice. The highest levels of TNF-α, IL-1β, and other M1 markers (IL-6, CD86, CD16, and CD32) were found in the brain or serum of LPS-treated CatCOE mice, and the lowest levels were detected in CatCKD mice. Similar results were found in LPS-treated microglia derived from CatC differentially expressing mice or in CatC-treated microglia from wild-type mice. Furthermore, the expression of NR2B mRNA, phosphorylation of NR2B, Ca²⁺ concentration, phosphorylation of PKC, p38, IκBα, and p65 were all increased in CatC-treated microglia, while addition of E-64 and MK-801 reversed the phosphorylation of above molecules.

Conclusion

The data suggest that CatC promotes microglia M1 polarization and aggravates neuroinflammation via activation of Ca²⁺-dependent PKC/p38MAPK/NF-κB pathway. CatC may be one of key molecular targets for alleviating and controlling neuroinflammation in neurological diseases.

Characterization of cathepsin C from orange-spotted grouper, Epinephelus coioides involved in SGIV infection

The lysosomal cysteine protease cathepsin C plays a pivotal role in regulation of inflammatory and immune responses. However, the function of fish cathepsin C in virus replication remains largely unknown. In this study, cathepsin C gene (Ec-CC) was cloned and characterized from orange-spotted grouper, Epinephelus coioides. The full-length Ec-CC cDNA was composed of 2077 bp. It contained an open reading frame (ORF) of 1374 bp and encoded a 458-amino acid protein which shared 89% identity to cathepsin C from bicolor damselfish (Stegastes partitus). Amino acid alignment analysis showed that Ec-CC contained an N-terminal signal peptide, the propeptide region and the mature peptide. RT-PCR analysis showed that Ec-CC transcript was expressed in all the examined tissues which abundant in spleen and head kidney. After challenged with Singapore grouper iridovirus (SGIV) stimulation, the relative expression of EC-CC was significantly increased at 24 h post-infection. Subcellular localization analysis revealed that Ec-CC was distributed mainly in the cytoplasm. Further studies showed that overexpression of Ec-CC in vitro significantly delayed the cytopathic effect (CPE) progression evoked by SGIV and inhibited the viral genes transcription. Moreover, overexpression of Ec-CC significantly increased the expression of proinflammatory cytokines during SGIV infection. Taken together, our results demonstrated that Ec-CC might play a functional role in SGIV infection by regulating the inflammation response.

Upregulation of Cysteine Protease Cathepsin X in the 6-Hydroxydopamine Model of Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative disorder characterized by loss of midbrain dopaminergic neurons in the substantia nigra pars compacta (SNc). In vitro, a contribution to neuroinflammation and neurotoxicity has been shown for the lysosomal protease cathepsin X; however, its expression and its role in PD remain unknown. Therefore, the current study was designed to address the regional, cellular, and subcellular localization and activity of cathepsin X in hemi-parkinsonian rats with 6-hydroxydopamine (6-OHDA)-induced excitotoxicity in the unilateral medial forebrain bundle (MFB) lesion. We report for the first time that cathepsin X expression and activity are rapidly increased in the ipsilateral SNc after injection of 6-OHDA into the MFB reaching a maximum after 12 h but seem to stay strongly upregulated after 4 weeks after injection. At early time points of 6-OHDA injection into the MFB, the increased cathepsin X is localized in the lysosomes in the neuronal, predominantly tyrosine hydroxylase-positive dopaminergic cells. After 12 h of 6-OHDA induced lesion, only a few activated microglial cells are positive for cathepsin X whereas, in 4 weeks post-lesion accompanied with complete loss of dopaminergic neurons, there is persistent cathepsin X upregulation restricted to activated glia cells. Taken together, our results demonstrate that cathepsin X upregulation in the lesioned dopaminergic system may play a role as a pathogenic factor in PD. Moreover, inhibition of cathepsin X expression or activity may be useful in protecting the nigrostriatal dopaminergic projection in the PD.

Porphyromonas gingivalis, a periodontitis causing bacterium, induces memory impairment and age-dependent neuroinflammation in mice

Background

A possible relationship between periodontitis and Alzheimer's disease (AD) has been reported. However, there is limited information on the association between the Porphyromonas gingivalis (P. gingivalis) periodontal infection and the pathological features of AD. The hypothesis that P. gingivalis periodontal infection may cause cognitive impairment via age-dependent neuroinflammation was tested.

Results

Thirty 4-week-old (young) female C57BL/6 J mice were randomly divided into two groups, the control group and the experimental group. Thirty 12-month-old (middle-aged) were grouped as above. The mouth of the mice in the experimental group was infected with P. gingivalis. Morris water maze(MWM) was performed to assess the learning and memory ability of mice after 6 weeks. Moreover, the expression levels of the pro-inflammatory cytokines TNF-α, IL-6, and IL-1β in the mice brain tissues were determined by Quantitative real-time polymerase chain reaction (qRT-PCR), Enzyme Linked Immunosorbent Assay(ELISA) and immunohistochemistry. Our results showed that the learning and memory abilities of the middle-aged P. gingivalis infected mice were impaired. Moreover, the expression levels of the pro-inflammatory cytokines TNF-α, IL-6, and IL-1β in the brain tissues of the middle-aged P. gingivalis infected mice were increased.

Conclusions

These results suggest that P. gingivalis periodontal infection may cause cognitive impairment via the release of the pro-inflammatory cytokines TNF-α, IL-6, and IL-1β in the brain tissues of middle-aged mice.

Addition of thiols to the double bond of dipeptide C-terminal dehydroalanine as a source of new inhibitors of cathepsin C

Addition of thiols to double bond of glycyl-dehydroalanine and phenyl-dehydroalanine esters provided micromolar inhibitors of cathepsin C. The structure-activity studies indicated that dipeptides containing N-terminal phenylalanine exhibit higher affinity towards the enzyme. A series of C-terminal S-substituted cysteines are responsible for varying interaction with S1 binding pocket of cathepsin C. Depending on diastereomer these compounds most likely act as slowly reacting substrates or competitive inhibitors. This was proved by TLC analysis of the medium in which interaction of methyl (S)-phenylalanyl-(R,S)-(S-adamantyl)cysteinate (7i) with the enzyme was studied. Molecular modeling enabled to establish their mode of binding showed that S2 pocket is long and narrow and accommodates phenyl group of phenylalanine while significantly spacious sites located at the surface of the enzyme (one of them being S1 pocket) bind the adamantyl moiety oriented in different direction for each stereoisomer. Finally replacement of carboxymethyl moiety of methyl (S)-phenylalanyl-(R,S)-(S-phenyl)cysteinate (7c) with nitrile group provided about 650-times more potent inhibitor of cathepsin C indicating that the studied C-terminal S-substituted cysteines are good activity probes for S1 binding pocket of this enzyme.

Degradomics in Neurotrauma: Profiling Traumatic Brain Injury

Degradomics has recently emerged as a subdiscipline in the omics era with a focus on characterizing signature breakdown products implicated in various disease processes. Driven by promising experimental findings in cancer, neuroscience, and metabolomic disorders, degradomics has significantly promoted the notion of disease-specific "degradome." A degradome arises from the activation of several proteases that target specific substrates and generate signature protein fragments. Several proteases such as calpains, caspases, cathepsins, and matrix metalloproteinases (MMPs) are involved in the pathogenesis of numerous diseases that disturb the physiologic balance between protein synthesis and protein degradation. While regulated proteolytic activities are needed for development, growth, and regeneration, uncontrolled proteolysis initiated under pathological conditions ultimately culminates into apoptotic and necrotic processes. In this chapter, we aim to review the protease-substrate repertoires in neural injury concentrating on traumatic brain injury. A striking diversity of protease substrates, essential for neuronal and brain structural and functional integrity, namely, encryptic biomarker neoproteins, have been characterized in brain injury. These include cytoskeletal proteins, transcription factors, cell cycle regulatory proteins, synaptic proteins, and cell junction proteins. As these substrates are subject to proteolytic fragmentation, they are ceaselessly exposed to activated proteases. Characterization of these molecules allows for a surge of "possible" therapeutic approaches of intervention at various levels of the proteolytic cascade.

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.

PI3K signaling: A molecular pathway associated with acute hypophagic response during inflammatory challenges

Energy balance has in the hypothalamus a central component of integration of food intake and energy expenditure. An accumulating body of evidence indicates that energy homeostasis is largely affected by inflammatory challenges. Severe undernutrition caused by exacerbated inflammatory response may lead to cachexia. On the other hand, prolonged low-grade inflammation such as that observed in obesity and metabolic syndrome, raises the risk for the development of diabetes and heart diseases. Changes in circulating insulin and cytokines such as leptin, interleukins and tumor necrosis factor, as well as changes in their action in the hypothalamus drive the inhibition of food consumption during inflammation. The molecular pathways associated with these responses have only started to be unraveled. One potential candidate is the PI3K signaling, an important player in distinct hypothalamic neurons that control food intake. This study presents an overview of the current knowledge about PI3K role on cytokines and insulin signaling in the hypothalamic regulation of feeding during inflammation.

Inhibition of cathepsin X reduces the strength of microglial-mediated neuroinflammation

Inflammation plays a central role in the processes associated with neurodegeneration. The inflammatory response is mediated by activated microglia that release inflammatory mediators to the neuronal environment. Microglia-derived lysosomal cathepsins, including cathepsin X, are increasingly recognized as important mediators of the inflammation involved in lipopolysaccharide (LPS)-induced neuroinflammation. The current study was undertaken to investigate the role of cathepsin X and its molecular target, γ-enolase, in neuroinflammation and to elucidate the underlying mechanism. We determined that the exposure of activated BV2 and EOC 13.31 cells to LPS led to increased levels of cathepsin X protein and activity in the culture supernatants in a concentration- and time-dependent manner. In contrast, LPS stimulation of these two cells reduced the release of active γ-enolase in a manner regulated by the cathepsin X activity. Cathepsin X inhibitor AMS36 significantly reduced LPS-induced production of nitric oxide, reactive oxygen species and the pro-inflammatory cytokines interleukin-6 and tumor necrosis factor-α from BV2 cells. Inhibition of cathepsin X suppressed microglial activation through the reduced caspase-3 activity, together with diminished microglial cell death and apoptosis, and also through inhibition of the activity of the mitogen-activated protein kinases. Further, SH-SY5Y treatment with culture supernatants of activated microglial cells showed that cathepsin X inhibition reduces microglia-mediated neurotoxicity. These results indicate that up-regulated expression and increased release and activity of microglial cathepsin X leads to microglia activation-mediated neurodegeneration. Cathepsin X inhibitor caused neuroprotection via its inhibition of the activation of microglia. Cathepsin X could thus be a potential therapeutic target for neuroinflammatory disorders.

The opioid antagonist, β-funaltrexamine, inhibits NF-κB signaling and chemokine expression in human astrocytes and in mice

Opioid-immune crosstalk occurs when opioid drugs alter the activity of the immune system. In this study, the opioid antagonist β-funaltrexamine (β-FNA) decreases the expression and release of an inflammatory chemokine, interferon-γ inducible protein-10 (CXCL10) from normal human astrocytes stimulated by interleukin 1β (IL-1β). β-FNA decreased CXCL10 by an unknown action that did not involve the mu opioid receptor (MOR). As IL-1β acts through its receptor to activate NF-κB/MAPK signaling pathways which leads to CXCL10 expression and release, key steps in the IL-1β signaling pathways were examined following β-FNA treatment. IL-1β-induced activation of p38 mitogen-activated protein kinases (p38 MAPK) was inhibited by β-FNA as shown by decreased p38 MAPK phosphorylation in treated cells. β-FNA also decreased the levels of activated subunits of NF-κB (p50 and p65) in treated astrocytes. The impact of β-FNA was also observed in proteins that act to negatively regulate NF-κB signaling. IL-1β upregulated the expression of A20, a ubiquitin (Ub)-editing enzyme that dampens NF-κB signaling by altering ubiquination patterns on IL-1 receptor second messengers, and the increase in A20 was significantly inhibited by β-FNA treatment. Inhibition of the Ub-activating enzyme E1 by the inhibitor PYR41 also decreased CXCL10 release, like β-FNA, and concurrent treatment with both PYR41 and β-FNA inhibited CXCL10 more than did either agent alone. In mice, lipopolysaccharide-induced CXCL10 expression in the brain was inhibited by treatment with β-FNA. These findings suggest that β-FNA exerts an anti-inflammatory action in vitro and in vivo that is MOR-independent and possibly due to the alkylating ability of β-FNA.

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-1β, 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-1β, 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-1β, 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.

Lipopolysaccharide-induced sepsis induces long-lasting affective changes in the mouse

Post-septic encephalopathy is a poorly understood condition in survivors of sepsis that is characterised by cognitive and affective impairments. In this study we have sought to better understand this condition by undertaking a comprehensive behavioural and cognitive assessment of mice who had previously survived sepsis. Mice were treated with lipopolysaccharide (LPS; 5mg/kg) and one month after this assessed on a battery of tests. Post-septic animals were found to display significantly more immobility in the tail suspension test and show a significantly decreased sucrose preference. Acute fluoxetine treatment reversed the increase in immobility in the tail suspension test in post-septic animals. Post-septic animals also showed less overall exploratory behaviour in the novel object recognition task and also showed increased anxiety-like behaviour in the elevated plus maze. Post-septic mice did not show signs of cognitive impairment, as assessed in the Morris watermaze, the 8-arm radial maze or on preference for the novel object in the novel object recognition task. Immunohistochemical analysis revealed significant upregulation of the microglial marker CD-11b, F4/80 and IBA-1 in the hippocampus of post-septic animals, as well as significant downregulation of the plasticity-related immediate early gene products ARC and EGR1. We also observed a decrease in neural stem cell proliferation in the dentate gyrus of post-septic animals as judged by BrdU incorporation. Co-treatment with the NF-κB pathway inhibitor PDTC attenuated the long-lasting effects of LPS on most of the affected parameters, but not on neural stem cell proliferation. These results show that LPS-induced sepsis in the mouse is followed by long-lasting increases in depressive- and anxiety-like behaviours, as well as by changes in neuroinflammatory- and neural plasticity-associated factors, and that attenuation of the severity of sepsis by PDTC attenuates many of these effects.

Impairment of autophagy in the central nervous system during lipopolysaccharide-induced inflammatory stress in mice

Background

Current evidence suggests a central role for autophagy in many neurodegenerative diseases including Alzheimer’s disease, Huntington’s disease, Parkinson’s disease and amyotrophic lateral sclerosis. Furthermore, it is well admitted that inflammation contributes to the progression of these diseases. Interestingly, crosstalks between autophagy and inflammation have been reported in vitro and at the peripheral level such as in Crohn’s disease. However, the impact of systemic inflammation on autophagic components in the brain remains to be documented. Therefore, this study monitored autophagy markers after acute and chronic lipopolysaccharide (LPS)-induced inflammatory stress in mice.

Results

We showed that acute inflammation, 24 h post-intraperitoneal 10 mg/kg LPS, substantially increased cytokine production (Interleukin(IL)-1β, Tumor necrosis factor (TNF)-α and IL-6), decreased the levels of autophagy markers (Beclin-1, p62 and LC3 II) and reduced p70S6K activation in cortex and hippocampus. In hippocampus, IL-1β levels and LC3 II expression were positively and highly correlated and a negative correlation was noted between TNF-α levels and p70S6K activation. Chronic inflammation by injection of 0.5 mg/kg LPS every three days during three months led to a moderate IL-1β production and decreased TNF-α levels. Interestingly, Beclin-1 and LC3 II levels decreased while those of p62 increased. Cortical IL-1β levels positively correlated with Beclin-1 and LC3 II and on the contrary inversely correlated with p62.

Conclusion

The present study is the first showing links between IL-1β-mediated inflammation and autophagy in the brain. It could open to new therapeutic strategies in brain diseases where regulation impairment of inflammation and autophagy progress with the severity of diseases.

The pathological changes in the spinal cord after dural tear with and without autologous fascia repair

PURPOSE

Dural tear is one of the common complications of spinal surgery leading to cerebrospinal fluid leakage followed by serial secondary symptoms. However, little is known about pathological changes of the spinal cord after dural tear. In the present study, we aimed to study the pathological changes in the spinal cord after dural tear with and without autologous fascia repair.

METHODS

Sixty Sprague-Dawley rats were used for dural tear and autologous fascia graft repair models. Three days and 1 week after surgery, the pathological changes in the spinal cord were analyzed by immunohistochemistry, Western blot, enzyme-linked immunosorbent assay and spinal somatosensory evoked potentials test.

RESULTS

Neuroinflammation was found in the parenchyma of the spinal cord characterized by gliosis, increased expression of inflammatory factors and infiltration of exogenesis immunocells in the rats without repair, which impaired the sensory conduction function of the spinal cord at the early stage of injury. Repairing with autologous fascia could attenuate neuroinflammation and help to maintain normal sensory conduction function of the spinal cord.

CONCLUSION

Dural tear could cause a series of inflammatory reactions in the spinal cord and further impair its sensory conduction function at the early stage of injury. Repairing with autologous fascia was a necessary and effective way to prevent the neuroinflammation and to maintain the normal function of the spinal cord.

Cysteine cathepsins in neurological disorders

Increased proteolytic activity is a hallmark of several pathological processes, including neurodegeneration. Increased expression and activity of cathepsins, lysosomal cysteine proteases, during degeneration of the central nervous system is frequently reported. Recent studies reveal that a disturbed balance of their enzymatic activities is the first insult in brain aging and age-related diseases. Leakage of cathepsins from lysosomes, due to their membrane permeability, and activation of pro-apoptotic factors additionally contribute to neurodegeneration. Furthermore, in inflammation-induced neurodegeneration the cathepsins expressed in activated microglia play a pivotal role in neuronal death. The proteolytic activity of cysteine cathepsins is controlled by endogenous protein inhibitors-the cystatins-which evidently fail to perform their function in neurodegenerative processes. Exogenous synthetic inhibitors, which may augment their inhibitory potential, are considered as possible therapeutic tools for the treatment of neurological disorders.

Differences in expression patterns of cathepsin C/dipeptidyl peptidase I in normal, pathological and aged mouse central nervous system

Cathepsin C (CC) (EC 3.4.14.1, dipeptidyl peptidase I) is a lysosomal cysteine protease that is required for the activation of several granule-associated serine proteases in vivo. CC has been shown to be constitutively expressed in various tissues, but the enzyme is hardly detectable in central nervous system (CNS) tissues. In the present study, we investigated the regional and cellular distribution of CC in normal, aging and pathological mouse brains. Immunoblotting failed to detect CC protein in whole brain tissues of normal mice, as previously described. However, low proteolytic activity of CC was detected in a brain region-dependent manner, and granular immunohistochemical signals were found in neuronal perikarya of particular brain regions, including the accessory olfactory bulb, the septum, CA2 of the hippocampus, a part of the cerebral cortex, the medial geniculate, and the inferior colliculus. In aged mice, the number of CC-positive neurons increased to some extent. The protein level of CC and its proteolytic activity showed significant increases in particular brain regions of mouse models with pathological conditions--the thalamus in cathepsin D-deficient mice, the hippocampus of ipsilateral brain hemispheres after hypoxic-ischemic brain injury, and peri-damaged portions of brains after penetrating injury. In such pathological conditions, the majority of the cells that were strongly immunopositive for CC were activated microglia. These lines of evidence suggest that CC is involved in normal neuronal function in certain brain regions, and also participates in inflammatory processes accompanying pathogenesis in the CNS.