Cathepsin S contributes to microglia-mediated olfactory dysfunction through the regulation of Cx3cl1-Cx3cr1 axis in a Niemann-Pick disease type C1 model

Elevated circulating cathepsin S levels are associated with cognitive decline and neurodegeneration in a cohort of patients reporting memory complaints

BackgroundAs a member of the cysteine protease family, cathepsin S has been implicated in the pathogenesis of various diseases, including Alzheimer's disease (AD), primarily by promoting inflammation.ObjectiveCurrent evidence regarding the role of cathepsin S primarily comes from animal studies. This study aims to explore the clinical relevance of cathepsin S in AD.MethodsIn a cohort of older adults aged 60 or above with memory complaints, we examined baseline plasma levels of cathepsin S and assessed their association with cognitive decline and biomarkers of neurodegeneration during a 36-month follow-up.ResultsPlasma levels of cathepsin S were significantly higher in individuals experiencing longitudinal cognitive decline compared to those without cognitive decline. Furthermore, plasma levels of cathepsin S were associated with declines in Mini-Mental State Examination (MMSE) scores and increases in neurofilament light and pTau181 levels. Higher plasma cathepsin S levels were linked to an increased risk of longitudinal cognitive decline (decrease in MMSE scores of 3 or more), adjusting for age, sex, education, APOE genotype, alcohol consumption, smoking, and comorbidities.ConclusionsThis study provides additional evidence supporting the potential role of cathepsin S in the pathogenesis of AD from a clinical perspective.

Olfactory bulb microglia activation mediates neuronal pyroptosis in ozone-exposed mice with olfactory and cognitive dysfunction

In recent years, there has been a notable increase in the concentration of air pollutants in the troposphere, especially ozone. However, limited research has gone beyond examining histopathological alterations in the olfactory bulb (OB) to explore the effects of ozone exposure on olfactory and cognitive functions. In our study, we exposed nine-month-old C57BL/6 mice to ozone at a concentration of 1.0 ppm for 13 weeks to examine the effects of ozone on the OB. The results indicated that ozone exposure induces olfactory and cognitive impairments in the mice. Subsequently, microglia in the OB are activated, leading to neuroinflammation. Ozone-induced downregulation of PSD95 and Synaptophysin, which was accompanied by a decrease in dendritic length and spine density. Simultaneously, increasing in the co-labeling of C1q, Iba1, and PSD95 after ozone exposure indicated that C1q-mediated synaptic phagocytosis by microglia might play a role in synaptic damage. Furthermore, the co-labeling of GSDMD-N and NEUN results suggests that ozone exposure triggers pyroptosis in neurons. Additionally, minocycline administration can alleviate ozone-induced olfactory and cognitive impairments by suppressing microglial activation. This study illustrates that prolonged ozone exposure leads to microglial activation in the OB, causing synaptic damage, neuronal pyroptosis, and subsequent deficits in olfactory and cognitive functions.

Neuronal cathepsin S increases neuroinflammation and causes cognitive decline via CX3CL1-CX3CR1 axis and JAK2-STAT3 pathway in aging and Alzheimer's disease

Aging is an intricate process involving interactions among multiple factors, which is one of the main risks for chronic diseases, including Alzheimer's disease (AD). As a member of cysteine protease, cathepsin S (CTSS) has been implicated in inflammation across various diseases. Here, we investigated the role of neuronal CTSS in aging and AD started by examining CTSS expression in hippocampus neurons of aging mice and identified a significant increase, which was negatively correlated with recognition abilities. Concurrently, we observed an elevation of CTSS concentration in the serum of elderly people. Transcriptome and fluorescence-activated cell sorting (FACS) results revealed that CTSS overexpression in neurons aggravated brain inflammatory milieu with microglia activation to M1 pro-inflammatory phenotype, activation of chemokine C-X3-C-motif ligand 1 (CX3CL1)-chemokine C-X3-C-motif receptor 1 (CX3CR1) axis and janus kinase 2 (JAK2)-signal transducer and activator of transcription 3 (STAT3) pathway. As CX3CL1 is secreted by neurons and acts on the CX3CR1 in microglia, our results revealed for the first time the role of neuron CTSS in neuron-microglia "crosstalk." Besides, we observed elevated CTSS expression in multiple brain regions of AD patients, including the hippocampus. Utilizing CTSS selective inhibitor, LY3000328, rescued AD-related pathological features in APP/PS1 mice. We further noticed that neuronal CTSS overexpression increased cathepsin B (CTSB) activity, but decreased cathepsin L (CTSL) activity in microglia. Overall, we provide evidence that CTSS can be used as an aging biomarker and plays regulatory roles through modulating neuroinflammation and recognition in aging and AD process.

Soluble Epoxide Hydrolase Inhibitor Ameliorates Olfactory Dysfunction, Modulates Microglia Polarization, and Attenuates Neuroinflammation after Ischemic Brain Injury

Olfactory bulb (OB) microglia activation and inflammation can lead to olfactory dysfunction, which often occurs after an ischemic stroke. Inhibition of soluble epoxide hydrolase (sEH) attenuates neuroinflammation in brain injuries by reducing the degradation of anti-inflammatory epoxyeicosatrienoic acids. However, whether sEH inhibitors can ameliorate olfactory dysfunction after an ischemic stroke remains unknown. Ischemic brain injury and olfactory dysfunction were induced by middle cerebral artery occlusion (MCAO) in Wistar Kyoto rats. The rats were administered 12-(3-adamantan-1-yl-ureido)-dodecanoic acid (AUDA), a selective sEH inhibitor. Olfactory function, cerebral infarct volume, and the degree of degeneration, microglial polarization and neuroinflammation in OB were evaluated. Following treatment with AUDA, rats subjected to MCAO displayed mild cerebral infarction and OB degeneration, as well as better olfactory performance. In OB, AUDA triggered a modulation of microglial polarization toward the M2 anti-inflammatory type, reduction in proinflammatory mediators, and enhancement of the antioxidant process. The effectiveness of AUDA in terms of anti-inflammatory, neuroprotection and anti-oxidative properties suggests that it may have clinical therapeutic implication for ischemic stroke related olfactory dysfunction.

Cathepsin S (CTSS) in IgA nephropathy: an exploratory study on its role as a potential diagnostic biomarker and therapeutic target

Introduction

IgA nephropathy (IgAN), a prevalent form of glomerulonephritis globally, exhibits complex pathogenesis. Cathepsins, cysteine proteases within lysosomes, are implicated in various physiological and pathological processes, including renal conditions. Prior observational studies have suggested a potential link between cathepsins and IgAN, yet the precise causal relationship remains unclear.

Methods

We conducted a comprehensive bidirectional and multivariable Mendelian randomization (MR) study using publicly available genetic data to explore the causal association between cathepsins and IgAN systematically. Additionally, immunohistochemical (IHC) staining and enzyme-linked immunosorbent assay (ELISA) were employed to evaluate cathepsin expression levels in renal tissues and serum of IgAN patients. We investigated the underlying mechanisms via gene set variation analysis (GSVA), gene set enrichment analysis (GSEA), and immune cell infiltration analysis. Molecular docking and virtual screening were also performed to identify potential drug candidates through drug repositioning.

Results

Univariate MR analyses demonstrated a significant link between increased cathepsin S (CTSS) levels and a heightened risk of IgAN. This was evidenced by an odds ratio (OR) of 1.041 (95% CI=1.009-1.073, P=0.012) as estimated using the inverse variance weighting (IVW) method. In multivariable MR analysis, even after adjusting for other cathepsins, elevated CTSS levels continued to show a strong correlation with an increased risk of IgAN (IVW P=0.020, OR=1.037, 95% CI=1.006-1.069). However, reverse MR analyses did not establish a causal relationship between IgAN and various cathepsins. IHC and ELISA findings revealed significant overexpression of CTSS in both renal tissues and serum of IgAN patients compared to controls, and this high expression was unique to IgAN compared with several other primary kidney diseases such as membranous nephropathy, minimal change disease and focal segmental glomerulosclerosis. Investigations into immune cell infiltration, GSEA, and GSVA highlighted the role of CTSS expression in the immune dysregulation observed in IgAN. Molecular docking and virtual screening pinpointed Camostat mesylate, c-Kit-IN-1, and Mocetinostat as the top drug candidates for targeting CTSS.

Conclusion

Elevated CTSS levels are associated with an increased risk of IgAN, and this enzyme is notably overexpressed in IgAN patients' serum and renal tissues. CTSS could potentially act as a diagnostic biomarker, providing new avenues for diagnosing and treating IgAN.

Triptolide alleviates cerebral ischemia/reperfusion injury via regulating the Fractalkine/CX3CR1 signaling pathway

PURPOSE

To evaluate the potential efficacy of Triptolide (TP) on cerebral ischemia/reperfusion injury (CIRI) and to uncover the underlying mechanism through which TP regulates CIRI.

METHODS

We constructed a middle cerebral artery occlusion/reperfusion (MCAO/R) mouse model to simulate CIRI, and established a lipopolysaccharide (LPS)-stimulated BV-2 cell model to mimic the inflammatory state during CIRI. The neurological deficits score (NS) of mice were measured for assessment of neurologic functions. Both the severity of cerebral infarction and the apoptosis level in mouse brain tissues or cells were respectively evaluated using corresponding techniques. The expression levels of Ionized calcium binding adapter molecule 1 (IBA-1), Inductible Nitric Oxide Synthase (iNOS), Arginase 1 (Arg-1), Tumor necrosis factor-α (TNF-α), Interleukin 1β (IL-1β), Cysteine histoproteinase S (CTSS), Fractalkine, chemokine C-X3-C motif receptor 1 (CX3CR1), BCL-2-associated X protein (BAX), and antiapoptotic proteins (Bcl-2) were detected using immunofluorescence, qRT-PCR as well as Western blot, respectively.

RESULTS

Relative to the Sham group, treatment with TP attenuated the increased NS, infarct area and apoptosis levels observed in MCAO/R mice. Upregulated expression levels of IBA-1, iNOS, Arg-1, TNF-α and IL-1β were found in MCAO/R mice, while TP suppressed iNOS, TNF-α and IL-1β expression, and enhanced Arg-1 expression in both MCAO/R mice and LPS-stimulated BV-2 cells. Besides, TP inhibited the CTSS/Fractalkine/CX3CR1 pathway activation in both MCAO/R mice and LPS-induced BV-2 cells, while overexpression of CTSS reversed such effect. Co-culturing HT-22 cells with TP+LPS-treated BV-2 cells led to enhanced cell viability and decreased apoptosis levels. However, overexpression of CTSS further aggravated HT-22 cell injury.

CONCLUSION

TP inhibits not only microglia polarization towards the M1 phenotype by suppressing the CTSS/Fractalkine/CX3CR1 pathway activation, but also HT-22 apoptosis by crosstalk with BV-2 cells, thereby ameliorating CIRI. These findings reveal a novel mechanism of TP in improving CIRI, and offer potential implications for addressing the preventive and therapeutic strategies of CIRI.

An update on new-age potential biomarkers for Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder that deals with dopaminergic deficiency in Substantia nigra pars compact (SNpc) region of the brain. Dopaminergic deficiency manifests into motor dysfunction. Alpha-synuclein protein aggregation is the source for inception of the pathology. Motor symptoms include rigidity, akinesia, tremor and gait dysfunction. Pre-motor symptoms are also seen in early stage of the disease; however, they are not distinguishable. Lack of early diagnosis in PD pathology poses a major challenge for development of disease modifying therapeutics. Substantial neuronal loss has already been occurred before the clinical manifestations appear and hence, it becomes impossible to halt the disease progression. Current diagnostics are majorly based on the clinical symptoms and thus fail to detect early progression of the disease. Thus, there is need for early diagnosis of PD, for detection of the disease at its inception. This will facilitate the effective use of therapies that halt the progression and will make remission possible. Many novel biomarkers are being developed that include blood-based biomarker, CSF biomarker. Other than that, there are non-invasive techniques that can detect biomarkers. We aim to discuss potential role of these new age biomarkers and their association with PD pathogenesis in this review.

Traumatic brain injury-induced inflammatory changes in the olfactory bulb disrupt neuronal networks leading to olfactory dysfunction

Approximately 20-68% of traumatic brain injury (TBI) patients exhibit trauma-associated olfactory deficits (OD) which can compromise not only the quality of life but also cognitive and neuropsychiatric functions. However, few studies to date have examined the impact of experimental TBI on OD. The present study examined inflammation and neuronal dysfunction in the olfactory bulb (OB) and the underlying mechanisms associated with OD in male mice using a controlled cortical impact (CCI) model. TBI caused a rapid inflammatory response in the OB as early as 24 h post-injury, including elevated mRNA levels of proinflammatory cytokines, increased numbers of microglia and infiltrating myeloid cells, and increased IL1β and IL6 production in these cells. These changes were sustained for up to 90 days after TBI. Moreover, we observed significant upregulation of the voltage-gated proton channel Hv1 and NOX2 expression levels, which were predominantly localized in microglia/macrophages and accompanied by increased reactive oxygen species production. In vivo OB neuronal firing activities showed early neuronal hyperexcitation and later hypo-neuronal activity in both glomerular layer and mitral cell layer after TBI, which were improved in the absence of Hv1. In a battery of olfactory behavioral tests, WT/TBI mice displayed significant OD. In contrast, neither Hv1 KO/TBI nor NOX2 KO/TBI mice showed robust OD. Finally, seven days of intranasal delivery of a NOX2 inhibitor (NOX2ds-tat) ameliorated post-traumatic OD. Collectively, these findings highlight the importance of OB neuronal networks and its role in TBI-mediated OD. Thus, targeting Hv1/NOX2 may be a potential intervention for improving post-traumatic anosmia.

SARS-CoV-2 envelope protein triggers depression-like behaviors and dysosmia via TLR2-mediated neuroinflammation in mice

BACKGROUND

Depression and dysosmia have been regarded as primary neurological symptoms in COVID-19 patients, the mechanism of which remains unclear. Current studies have demonstrated that the SARS-CoV-2 envelope (E) protein is a pro-inflammatory factor sensed by Toll-like receptor 2 (TLR2), suggesting the pathological feature of E protein is independent of viral infection. In this study, we aim to ascertain the role of E protein in depression, dysosmia and associated neuroinflammation in the central nervous system (CNS).

METHODS

Depression-like behaviors and olfactory function were observed in both female and male mice receiving intracisternal injection of E protein. Immunohistochemistry was applied in conjunction with RT-PCR to evaluate glial activation, blood-brain barrier status and mediators synthesis in the cortex, hippocampus and olfactory bulb. TLR2 was pharmacologically blocked to determine its role in E protein-related depression-like behaviors and dysosmia in mice.

RESULTS

Intracisternal injection of E protein evoked depression-like behaviors and dysosmia in both female and male mice. Immunohistochemistry suggested that the E protein upregulated IBA1 and GFAP in the cortex, hippocampus and olfactory bulb, while ZO-1 was downregulated. Moreover, IL-1β, TNF-α, IL-6, CCL2, MMP2 and CSF1 were upregulated in both cortex and hippocampus, whereas IL-1β, IL-6 and CCL2 were upregulated in the olfactory bulb. Furtherly, inhibiting microglia, rather than astrocytes, alleviated depression-like behaviors and dysosmia induced by E protein. Finally, RT-PCR and immunohistochemistry suggested that TLR2 was upregulated in the cortex, hippocampus and olfactory bulb, the blocking of which mitigated depression-like behaviors and dysosmia induced by E protein.

CONCLUSIONS

Our study demonstrates that envelope protein could directly induce depression-like behaviors, dysosmia, and obvious neuroinflammation in CNS. TLR2 mediated depression-like behaviors and dysosmia induced by envelope protein, which could serve as a promising therapeutic target for neurological manifestation in COVID-19 patients.

The Niemann-Pick type diseases – A synopsis of inborn errors in sphingolipid and cholesterol metabolism

Disturbances of lipid homeostasis in cells provoke human diseases. The elucidation of the underlying mechanisms and the development of efficient therapies represent formidable challenges for biomedical research. Exemplary cases are two rare, autosomal recessive, and ultimately fatal lysosomal diseases historically named "Niemann-Pick" honoring the physicians, whose pioneering observations led to their discovery. Acid sphingomyelinase deficiency (ASMD) and Niemann-Pick type C disease (NPCD) are caused by specific variants of the sphingomyelin phosphodiesterase 1 (SMPD1) and NPC intracellular cholesterol transporter 1 (NPC1) or NPC intracellular cholesterol transporter 2 (NPC2) genes that perturb homeostasis of two key membrane components, sphingomyelin and cholesterol, respectively. Patients with severe forms of these diseases present visceral and neurologic symptoms and succumb to premature death. This synopsis traces the tortuous discovery of the Niemann-Pick diseases, highlights important advances with respect to genetic culprits and cellular mechanisms, and exposes efforts to improve diagnosis and to explore new therapeutic approaches.

Fractalkine/CX3CR1-Dependent Modulation of Synaptic and Network Plasticity in Health and Disease

CX3CR1 is a G protein-coupled receptor that is expressed exclusively by microglia within the brain parenchyma. The only known physiological CX3CR1 ligand is the chemokine fractalkine (FKN), which is constitutively expressed in neuronal cell membranes and tonically released by them. Through its key role in microglia-neuron communication, the FKN/CX3CR1 axis regulates microglial state, neuronal survival, synaptic plasticity, and a variety of synaptic functions, as well as neuronal excitability via cytokine release modulation, chemotaxis, and phagocytosis. Thus, the absence of CX3CR1 or any failure in the FKN/CX3CR1 axis has been linked to alterations in different brain functions, including changes in synaptic and network plasticity in structures such as the hippocampus, cortex, brainstem, and spinal cord. Since synaptic plasticity is a basic phenomenon in neural circuit integration and adjustment, here, we will review its modulation by the FKN/CX3CR1 axis in diverse brain circuits and its impact on brain function and adaptation in health and disease.

Single-cell RNA sequencing of peripheral blood reveals that monocytes with high cathepsin S expression aggravate cerebral ischemia-reperfusion injury

BACKGROUND

Stroke is a major cause of morbidity and mortality worldwide. After cerebral ischemia, peripheral immune cells infiltrate the brain and elicit an inflammatory response. However, it is not clear when and how these peripheral immune cells affect the central inflammatory response, and whether interventions that target these processes can alleviate ischemia-reperfusion (I/R) injury.

METHODS

Single-cell transcriptomic sequencing and bioinformatics analysis were performed on peripheral blood of mice at different times after I/R to analyze the key molecule of cell subsets. Then, the expression pattern of this molecule was determined through various biological experiments, including quantitative RT-PCR, western blot, ELISA, and in situ hybridization. Next, the function of this molecule was assessed using knockout mice and the corresponding inhibitor.

RESULTS

Single-cell transcriptomic sequencing revealed that peripheral monocyte subpopulations increased significantly after I/R. Cathepsin S (Ctss)was identified as a key molecule regulating monocyte activation by pseudotime trajectory analysis and gene function analysis. Next, Cathepsin S was confirmed to be expressed in monocytes with the highest expression level 3 days after I/R. Infarct size (p < 0.05), neurological function scores (p < 0.05), and apoptosis and vascular leakage rates were significantly reduced after Ctss knockout. In addition, CTSS destroyed the blood-brain barrier (BBB) by binding to junctional adhesion molecule (JAM) family proteins to cause their degradation.

CONCLUSIONS

Cathepsin S inhibition attenuated cerebral I/R injury; therefore, cathepsin S can be used as a novel target for drug intervention after stroke.

Cathepsin S (CTSS) activity in health and disease - A treasure trove of untapped clinical potential

Amongst the lysosomal cysteine cathepsin family of proteases, cathepsin S (CTSS) holds particular interest due to distinctive properties including a normal restricted expression profile, inducible upregulation and activity at a broad pH range. Consequently, while CTSS is well-established as a member of the proteolytic cocktail within the lysosome, degrading unwanted and damaged proteins, it has increasingly been shown to mediate a number of distinct, more selective roles including antigen processing and antigen presentation, and cleavage of substrates both intra and extracellularly. Increasingly, aberrant CTSS expression has been demonstrated in a variety of conditions and disease states, marking it out as both a biomarker and potential therapeutic target. This review seeks to contextualise CTSS within the cysteine cathepsin family before providing an overview of the broad range of pathologies in which roles for CTSS have been identified. Additionally, current clinical progress towards specific inhibitors is detailed, updating the position of the field in exploiting this most unique of proteases.

Potential significance of CX3CR1 dynamics in stress resilience against neuronal disorders

Recent findings have implicated inflammatory responses in the central nervous system in a variety of neuropsychiatric and neurodegenerative diseases, and the understanding and control of immunological responses could be a major factor of future therapeutic strategies for neurological disorders. Microglia, derived from myelogenous cells, respond to a number of stimuli and make immune responses, resulting in a prominent role as cells that act on inflammation in the central nervous system. Fractalkine (FKN or CX3CL1) signaling is an important factor that influences the inflammatory response of microglia. The receptor for FKN, CX3CR1, is usually expressed in microglia in the brain, and therefore the inflammatory response of microglia is modified by FKN. Reportedly, FKN often suppresses inflammatory responses in microglia and activation of its receptor may be effective in the treatment of inflammatory neurological disorders. However, it has also been suggested that inflammatory responses facilitated by FKN signaling aggravate neurological disorders. Thus, further studies are still required to resolve the conflicting interpretation of the protective or deleterious contribution of microglial FKN signaling. Yet notably, regulation of FKN signaling has recently been shown to be beneficial in the treatment of human diseases, although not neurological diseases. In addition, a CX3CR1 inhibitor has been developed and successfully tested in animal models, and it is expected to be in human clinical trials in the future. In this review, I describe the potential therapeutic consideration of microglial CX3CR1 dynamics through altered FKN signaling.

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.

Understanding and Treating Niemann-Pick Type C Disease: Models Matter

Biomedical research aims to understand the molecular mechanisms causing human diseases and to develop curative therapies. So far, these goals have been achieved for a small fraction of diseases, limiting factors being the availability, validity, and use of experimental models. Niemann–Pick type C (NPC) is a prime example for a disease that lacks a curative therapy despite substantial breakthroughs. This rare, fatal, and autosomal-recessive disorder is caused by defects in NPC1 or NPC2. These ubiquitously expressed proteins help cholesterol exit from the endosomal–lysosomal system. The dysfunction of either causes an aberrant accumulation of lipids with patients presenting a large range of disease onset, neurovisceral symptoms, and life span. Here, we note general aspects of experimental models, we describe the line-up used for NPC-related research and therapy development, and we provide an outlook on future topics.

Single Cell Transcriptome Analysis of Niemann-Pick Disease, Type C1 Cerebella

Niemann-Pick disease, type C1 (NPC1) is a lysosomal disease characterized by endolysosomal storage of unesterified cholesterol and decreased cellular cholesterol bioavailability. A cardinal symptom of NPC1 is cerebellar ataxia due to Purkinje neuron loss. To gain an understanding of the cerebellar neuropathology we obtained single cell transcriptome data from control (Npc1^+/+) and both three-week-old presymptomatic and seven-week-old symptomatic mutant (Npc1^-/-) mice. In seven-week-old Npc1^-/- mice, differential expression data was obtained for neuronal, glial, vascular, and myeloid cells. As anticipated, we observed microglial activation and increased expression of innate immunity genes. We also observed increased expression of innate immunity genes by other cerebellar cell types, including Purkinje neurons. Whereas neuroinflammation mediated by microglia may have both neuroprotective and neurotoxic components, the contribution of increased expression of these genes by non-immune cells to NPC1 pathology is not known. It is possible that dysregulated expression of innate immunity genes by non-immune cells is neurotoxic. We did not anticipate a general lack of transcriptomic changes in cells other than microglia from presymptomatic three-week-old Npc1^-/- mice. This observation suggests that microglia activation precedes neuronal dysfunction. The data presented in this paper will be useful for generating testable hypotheses related to disease progression and Purkinje neurons loss as well as providing insight into potential novel therapeutic interventions.

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.

Candesartan Neuroprotection in Rat Primary Neurons Negatively Correlates with Aging and Senescence: a Transcriptomic Analysis

Preclinical experiments and clinical trials demonstrated that angiotensin II AT₁ receptor overactivity associates with aging and cellular senescence and that AT₁ receptor blockers (ARBs) protect from age-related brain disorders. In a primary neuronal culture submitted to glutamate excitotoxicity, gene set enrichment analysis (GSEA) revealed expression of several hundred genes altered by glutamate and normalized by candesartan correlated with changes in expression in Alzheimer's patient's hippocampus. To further establish whether our data correlated with gene expression alterations associated with aging and senescence, we compared our global transcriptional data with additional published datasets, including alterations in gene expression in the neocortex and cerebellum of old mice, human frontal cortex after age of 40, gene alterations in the Werner syndrome, rodent caloric restriction, Ras and oncogene-induced senescence in fibroblasts, and to tissues besides the brain such as the muscle and kidney. The most significant and enriched pathways associated with aging and senescence were positively correlated with alterations in gene expression in glutamate-injured neurons and, conversely, negatively correlated when the injured neurons were treated with candesartan. Our results involve multiple genes and pathways, including CAV1, CCND1, CDKN1A, CHEK1, ICAM1, IL-1B, IL-6, MAPK14, PTGS2, SERPINE1, and TP53, encoding proteins associated with aging and senescence hallmarks, such as inflammation, oxidative stress, cell cycle and mitochondrial function alterations, insulin resistance, genomic instability including telomere shortening and DNA damage, and the senescent-associated secretory phenotype. Our results demonstrate that AT₁ receptor blockade ameliorates central mechanisms of aging and senescence. Using ARBs for prevention and treatment of age-related disorders has important translational value.

Decreased neural stem cell proliferation and olfaction in mouse models of Niemann-Pick C1 disease and the response to hydroxypropyl-β-cyclodextrin

The Npc1^nih/nih-null model and the Npc1^{nmf164/nmf164} hypomorph models of Niemann-Pick C1 (NPC1) disease show defects in olfaction. We have tested the effects of the life-prolonging treatment hydroxypropyl-beta-cyclodextrin (HPBCD) on olfaction and neural stem cell numbers when delivered either systemically or by nasal inhalation. Using the paradigm of finding a hidden cube of food after overnight food deprivation, Npc1^nih/nih homozygous mice showed a highly significant delay in finding the food compared with wild-type mice. Npc1^{nmf164/nmf164} homozygous mice showed an early loss of olfaction which was mildly corrected by somatic delivery of HPBCD which also increased the number of neural stem cells in the mutant but did not change the number in wild-type mice. In contrast, nasal delivery of this drug, at 1/5 the dosage used for somatic delivery, to Npc1^{nmf164/nmf164} mutant mice delayed loss of olfaction but the control of nasal delivered saline did so as well. The nasal delivery of HPBCD to wild-type mice caused loss of olfaction but nasal delivery of saline did not. Neural stem cell counts were not improved by nasal therapy with HPBCD. We credit the delay in olfaction found with the treatment, a delay which was also found for time of death, to a large amount of stimulation the mice received with handling during the nasal delivery.

The pathogenesis of lysosomal storage disorders: beyond the engorgement of lysosomes to abnormal development and neuroinflammation

There is growing evidence that the complex clinical manifestations of lysosomal storage diseases (LSDs) are not fully explained by the engorgement of the endosomal-autophagic-lysosomal system. In this review, we explore current knowledge of common pathogenetic mechanisms responsible for the early onset of tissue abnormalities of two LSDs, Mucopolysaccharidosis type II (MPSII) and Niemann-Pick type C (NPC) diseases. In particular, perturbations of the homeostasis of glycosaminoglycans (GAGs) and cholesterol (Chol) in MPSII and NPC diseases, respectively, affect key biological processes, including morphogen signaling. Both GAGs and Chol finely regulate the release, reception and tissue distribution of Shh. Hence, not surprisingly, developmental processes depending on correct Shh signaling have been found altered in both diseases. Besides abnormal signaling, exaggerated activation of microglia and impairment of autophagy and mitophagy occur in both diseases, largely before the appearance of typical pathological signs.

Human umbilical cord blood plasma alleviates age-related olfactory dysfunction by attenuating peripheral TNF-α expression

Social requirements are needed for living in an aging society and individual longevity. Among them, improved health and medical cares, appropriate for an aging society are strongly demanded. Human cord blood-derived plasma (hUCP) has recently emerged for its unique anti-aging effects. In this study, we investigated brain rejuvenation, particularly olfactory function, that could be achieved by a systemic administration of young blood and its underlying mechanisms. Older than 24-month-old mice were used as an aged group and administered with intravenous injection of hUCP repetitively, eight times. Anti-aging effect of hUCP on olfactory function was evaluated by buried food finding test. To investigate the mode of action of hUCP, brain, serum and spleen of mice were collected for further ex vivo analyses. Systemic injection of hUCP improved aging-associated olfactory deficits, reducing time for finding food. In the brain, although an infiltration of activated microglia and its expression of cathepsin S remarkably decreased, significant changes of proinflammatory factors were not detected. Conversely, peripheral immune balance distinctly switched from predominance of Type 1 helper T (Th1) cells to alternative regulatory T cells (Tregs). These findings indicate that systemic administration of hUCP attenuates age-related neuroinflammation and subsequent olfactory dysfunction by modulating peripheral immune balance toward Treg cells, suggesting another therapeutic function and mechanism of hUCP administration.

Gene Expression Profile of Olfactory Transduction Signaling in an Animal Model of Human Multiple Sclerosis

Olfactory dysfunction occurs in multiple sclerosis in humans, as well as in an animal model of experimental autoimmune encephalomyelitis (EAE). The aim of this study was to analyze differentially expressed genes (DEGs) in olfactory bulb of EAE-affected mice by next generation sequencing, with a particular focus on changes in olfaction-related signals. EAE was induced in C57BL/6 mice following immunization with myelin oligodendrocyte glycoprotein and adjuvant. Inflammatory lesions were identified in the olfactory bulbs as well as in the spinal cord of immunized mice. Analysis of DEGs in the olfactory bulb of EAE-affected mice revealed that 44 genes were upregulated (and which were primarily related to inflammatory mediators), while 519 genes were downregulated; among the latter, olfactory marker protein and stomatin-like 3, which have been linked to olfactory signal transduction, were significantly downregulated (log2 [fold change] >1 and p-value <0.05). These findings suggest that inflammation in the olfactory bulb of EAE-affected mice is associated with the downregulation of some olfactory signal transduction genes, particularly olfactory marker protein and stomatin-like 3, which may lead to olfactory dysfunction in an animal model of human multiple sclerosis.

Congenital Cytomegalovirus Infection Alters Olfaction Before Hearing Deterioration In Mice

In developed countries, cytomegalovirus (CMV)-infected newborns are at high risk of developing sensorineural handicaps such as hearing loss, requiring extensive follow-up. However, early prognostic tools for auditory damage in children are not yet available. In the fetus, CMV infection leads to early olfactory bulb (OB) damage, suggesting that olfaction might represent a valuable prognosis for neurological outcome of this viral infection. Here, we demonstrate that in utero CMV inoculation causes fetal infection and growth retardation in mice of both sexes. It disrupts OB normal development, leading to disproportionate OB cell layers and rapid major olfactory deficits. Olfaction is impaired as early as day 6 after birth in both sexes, long before the emergence of auditory deficits. Olfactometry in males reveals a long-lasting alteration in olfactory perception and discrimination, particularly in binary mixtures of monomolecular odorants. Although sensory inputs to the OB remain unchanged, hallmarks of autophagy are increased in the OB of 3-postnatal week-old mice, leading to local neuroinflammation and loss of neurons expressing tyrosine hydroxylase and calbindin. At the cellular level, we found CMV-infected cells and an increased number of apoptotic cells scattered throughout the OB layers, whereas cell proliferation in the neurogenic subventricular zone was decreased. These cellular observations were long-lasting, persisting up to 16 weeks after birth in both males and females and thus providing a mechanism supporting olfactory loss. Despite obvious differences in neurogenesis between human and mouse, these findings offer new strategies aimed at early detection of neurological dysfunctions caused by congenital infections.SIGNIFICANCE STATEMENT In developed countries, congenital cytomegalovirus (CMV)-infected newborns are at high risk of developing sensory handicaps such as hearing loss, thus requiring prolonged follow-up. In this study, we describe for the first time the functional impact of congenital CMV infection on the olfactory system and its associated sense of smell. We demonstrate that a mouse model of congenital CMV infection shows defects in olfactory bulb (OB) normal development and pronounced olfactory deficits affecting acuity and discrimination of odorants. These major olfactory deficits occur long before the emergence of auditory deficits through the upregulation of OB autophagy inducing local neuroinflammation and altered neuron content. Our findings provide new opportunities for designing olfactory means to monitor the possible neurological outcome during congenital CMV infection.

Pleiotropic Impacts of Macrophage and Microglial Deficiency on Development in Rats with Targeted Mutation of the Csf1r Locus

We have produced Csf1r-deficient rats by homologous recombination in embryonic stem cells. Consistent with the role of Csf1r in macrophage differentiation, there was a loss of peripheral blood monocytes, microglia in the brain, epidermal Langerhans cells, splenic marginal zone macrophages, bone-associated macrophages and osteoclasts, and peritoneal macrophages. Macrophages of splenic red pulp, liver, lung, and gut were less affected. The pleiotropic impacts of the loss of macrophages on development of multiple organ systems in rats were distinct from those reported in mice. Csf1r^-/- rats survived well into adulthood with postnatal growth retardation, distinct skeletal and bone marrow abnormalities, infertility, and loss of visceral adipose tissue. Gene expression analysis in spleen revealed selective loss of transcripts associated with the marginal zone and, in brain regions, the loss of known and candidate novel microglia-associated transcripts. Despite the complete absence of microglia, there was little overt phenotype in brain, aside from reduced myelination and increased expression of dopamine receptor-associated transcripts in striatum. The results highlight the redundant and nonredundant functions of CSF1R signaling and of macrophages in development, organogenesis, and homeostasis.

Microglial involvement in the development of olfactory dysfunction

Olfactory impairment is the most common clinical manifestation among the elderly, and its prevalence increases sharply with age. Notably, growing evidence has shown that olfactory dysfunction is the first sign of neurodegeneration, indicating the importance of olfactory assessment as an early marker in the diagnosis of neurological disorders. In this review, we describe the nature of olfactory dysfunction and the advantage of using animal models in olfaction study, and we include a brief introduction to olfactory behavior tests widely used in this field. The contribution of microglia in the neurodegenerative processes including olfactory impairment is then discussed to provide a comprehensive description of the physiopathological role of interactions between neurons and microglia within the olfactory system.

Olfactory Dysfunction in CNS Neuroimmunological Disorders: a Review

Olfactory dysfunction is deeply associated with quality of human life in the aging population. Olfactory dysfunction is an occasional presymptomatic sign of neuroimmunological multiple sclerosis, neuromyelitis optica, and systemic lupus erythematosus. Olfaction is initially processed by olfactory receptor cells that capture odor molecules, and the signals are transmitted to the glomeruli in the olfactory bulbs via olfactory nerves and processed in the primary olfactory cortex in the brain. Damage to either the olfactory receptor cells or the olfactory bulb and primary olfactory cortex may influence olfactory functioning. A close link between neuroimmunological disorders and olfactory dysfunction has been reported in patients and animal models. This review summarizes the literature data concerning olfactory dysfunction in autoimmune diseases including multiple sclerosis, neuromyelitis optica, and systemic lupus erythematosus; animal models thereof; and inflammation in the olfactory bulb.

Olfactory Performance as an Indicator for Protective Treatment Effects in an Animal Model of Neurodegeneration

Background: Neurodegenerative diseases are often accompanied by olfactory deficits. Here we use a rare neurovisceral lipid storage disorder, Niemann–Pick disease C1 (NPC1), to illustrate disease-specific dynamics of olfactory dysfunction and its reaction upon therapy. Previous findings in a transgenic mouse model (NPC1^-/-) showed severe morphological and electrophysiological alterations of the olfactory epithelium (OE) and the olfactory bulb (OB) that ameliorated under therapy with combined 2-hydroxypropyl-ß-cyclodextrin (HPßCD)/allopregnanolone/miglustat or HPßCD alone.

Methods: A buried pellet test was conducted to assess olfactory performance. qPCR for olfactory key markers and several olfactory receptors was applied to determine if their expression was changed under treatment conditions. In order to investigate the cell dynamics of the OB, we determined proliferative and apoptotic activities using a bromodeoxyuridine (BrdU) protocol and caspase-3 (cas-3) activity. Further, we performed immunohistochemistry and western blotting for microglia (Iba1), astroglia (GFAP) and tyrosine hydroxylase (TH).

Results: The buried pellet test revealed a significant olfactory deterioration in NPC1^-/- mice, which reverted to normal levels after treatment. At the OE level, mRNA for olfactory markers showed no changes; the mRNA level of classical olfactory receptor (ORs) was unaltered, that of unique ORs was reduced. In the OB of untreated NPC1^-/- mice, BrdU and cas-3 data showed increased proliferation and apoptotic activity, respectively. At the protein level, Iba1 and GFAP in the OB indicated increased microgliosis and astrogliosis, which was prevented by treatment.

Conclusion: Due to the unique plasticity especially of peripheral olfactory components the results show a successful treatment in NPC1 condition with respect to normalization of olfaction. Unchanged mRNA levels for olfactory marker protein and distinct olfactory receptors indicate no effects in the OE in NPC1^-/- mice. Olfactory deficits are thus likely due to central deficits at the level of the OB. Further studies are needed to examine if olfactory performance can also be changed at a later onset and interrupted treatment of the disease. Taken together, our results demonstrate that olfactory testing in patients with NPC1 may be successfully used as a biomarker during the monitoring of the treatment.

Olfactory Dysfunction in Autoimmune Central Nervous System Neuroinflammation

Olfactory dysfunction is an early sign of neuroinflammation of the central nervous system (CNS). Microgliosis and astrogliosis are representative pathological changes that develop during neuroinflammation of CNS tissues. Autoimmune CNS inflammation, including human multiple sclerosis, is an occasional cause of olfactory disorders. We evaluated whether gliosis and olfactory dysfunction developed in animals with experimental autoimmune encephalomyelitis (EAE), a model of human multiple sclerosis. Neuroinflammatory lesions characterized by infiltration of inflammatory cells and microglial cell activation were occasionally found in the olfactory bulbs of EAE-affected rats. Microglial activation, visualized by immunohistochemical staining of ionized calcium binding protein (Iba)-1, and astrogliosis in the olfactory bulb were also evident in the olfactory bulb of EAE rats. Inflammatory cells were found along the olfactory nerves and in the olfactory submucosa. Western blot analysis of olfactory marker protein (OMP) levels showed that OMP expression was significantly downregulated in the olfactory mucosa of EAE rats. On the buried food test, EAE-affected mice required significantly more time to find a bait pellet. Collectively, the results suggest that the olfactory dysfunction of EAE is closely linked to downregulation of OMP and the development of inflammatory foci in the olfactory system in an animal model of human multiple sclerosis.

In Niemann-Pick C1 mouse models, glial-only expression of the normal gene extends survival much further than do changes in genetic background or treatment with hydroxypropyl-beta-cyclodextrin

The Npc1^nmf164 allele of Npc1 provides a mouse model for Niemann-Pick disease type C1 (NPC1), a genetic disease known to have a widely variable phenotype. The transfer of the Npc1^nmf164 mutation from the C57BL/6J inbred strain to the BALB/cJ inbred strain increased the mean lifespan from 117.8days to 153.1days, confirming that the severity of the NPC1 phenotype is strongly influenced by genetic background. The transfer of another Npc1 allele, Npc1^nih, to this background also extended survival of the homozygotes indicating that the modifying effect of BALB/cJ is not limited to a single allele of Npc1. The increased longevity due to the BALB/cJ background did not map to a previously mapped modifier on chromosome 19, indicating the presence of additional genes impacting disease severity. The previously studied Glial Fibrillary Acidic Protein promoter-Npc1 cDNA transgene (GFAP-Npc1) which only expresses NPC1 in astrocytes further extended the lifespan of Npc1^nmf164 homozygotes on a BALB/cJ background (up to 600days). Hydroxypropyl-β-cyclodextrin (HPβCD) treatment, not previously tested in the Npc1^nmf164 mutant, extended life in the Npc1^nmf164 homozygotes but not the transgenic, Npc1^nmf164 mice on the BALB/cJ background. In all cases, lack of weight gain and early cerebellar symptoms of loss of motor control were found. At termination, the one mouse sacrificed for histological studies showed severe, diffuse pulmonary alveolar proteinosis suggesting that pulmonary abnormalities in NPC1 mouse models are not unique to the Npc1^nih allele.

The microglial fractalkine receptor is not required for activity-dependent plasticity in the mouse visual system

Microglia have recently been implicated as key regulators of activity-dependent plasticity, where they contribute to the removal of inappropriate or excess synapses. However, the molecular mechanisms that mediate this microglial function are still not well understood. Although multiple studies have implicated fractalkine signaling as a mediator of microglia-neuron communications during synaptic plasticity, it is unclear whether this is a universal signaling mechanism or whether its role is limited to specific brain regions and stages of the lifespan. Here, we examined whether fractalkine signaling mediates microglial contributions to activity-dependent plasticity in the developing and adolescent visual system. Using genetic ablation of fractalkine's cognate receptor, CX3 CR1, and both ex vivo characterization and in vivo imaging in mice, we examined whether fractalkine signaling is required for microglial dynamics and modulation of synapses, as well as activity-dependent plasticity in the visual system. We did not find a role for fractalkine signaling in mediating microglial properties during visual plasticity. Ablation of CX3 CR1 had no effect on microglial density, distribution, morphology, or motility, in either adolescent or young adult mice across brain regions that include the visual cortex. Ablation of CX3 CR1 also had no effect on baseline synaptic turnover or contact dynamics between microglia and neurons. Finally, we found that fractalkine signaling is not required for either early or late forms of activity-dependent visual system plasticity. These findings suggest that fractalkine is not a universal regulator of synaptic plasticity, but rather has heterogeneous roles in specific brain regions and life stages.