The extracellular fragment of GPNMB (Glycoprotein nonmelanosoma protein B, osteoactivin) improves memory and increases hippocampal GluA1 levels in mice

Glycoprotein Non-metastatic Melanoma Protein B (GPNMB) Protects Against Neuroinflammation and Neuronal Loss in Pilocarpine-induced Epilepsy via the Regulation of Microglial Polarization

Epilepsy is a progressive neurodegenerative disease highlighted by recurrent seizures, neuroinflammation, and the loss of neurons. Microglial dysfunction is commonly found in epileptic foci and contributes to neuroinflammation in the initiation and progression of epilepsy. Glycoprotein non-metastatic melanoma protein B (GPNMB), a transmembrane glycoprotein, has been involved in the microglial activation and neuroinflammation response. The present study investigated the functional significance of GPNMB in epilepsy. A proven model of epilepsy was established by intraperitoneal injection of pilocarpine to male Sprague Dawley rats. Lentivirus vectors carrying GPNMB or GPNMB short hairpin RNA (shGPNMB) were injected into the hippocampus to induce overexpression or knockdown of GPNMB. GPNMB expression was significantly upregulated and overexpression of GPNMB in the hippocampus reduced seizure activity and neuronal loss after status epilepticus (SE). We here focused on the effects of GPNMB deficiency on neuronal injury and microglia polarization 28 days after SE. GPNMB knockdown accelerated neuronal damage in the hippocampus, evidenced by increased neuron loss and neuronal cell apoptosis. Following GPNMB knockdown, M1 polarization (iNOS) and secretion of pro-inflammatory cytokines IL-6, IL-1β, and TNF-α were increased, and M2 polarization (Arg1) and secretion of anti-inflammatory cytokines IL-4, IL-10, and TGF-β were decreased. BV2 cells were used to further confirm the regulatory role of GPNMB in modulating phenotypic transformations and inflammatory cytokine expressions in microglia. In conclusion, these results indicated that GPNMB suppressed epilepsy through repression of hippocampal neuroinflammation, suggesting that GPNMB might be considered the potential neurotherapeutic target for epilepsy management and play a protective role against epilepsy by modulating the polarization of microglia.

The association between plasma GPNMB and Parkinson's disease and multiple system atrophy

AIMS

Parkinson's disease (PD), as the second most common neurodegenerative disorder, often presents diagnostic challenges in differentiation from other forms of Parkinsonism. Recent studies have reported an association between plasma glycoprotein nonmetastatic melanoma protein B (pGPNMB) and PD.

METHODS

A retrospective study was conducted, comprising 401 PD patients, 111 multiple system atrophy (MSA) patients, 13 progressive supranuclear palsy (PSP) patients and 461 healthy controls from the Chinese Han population, with an assessment of pGPNMB levels.

RESULTS

The study revealed that pGPNMB concentrations were significantly lower in PD and MSA patients compared to controls (area under the receiver operating characteristics curve (AUC) 0.62 and 0.74, respectively, P < 0.0001 for both), but no difference was found in PSP patients compared to controls (P > 0.05). Interestingly, the level of pGPNMB was significantly higher in PD patients than in MSA patients (AUC = 0.63, P < 0.0001). Furthermore, the study explored the association between pGPNMB levels and disease severity in PD and MSA patients, revealing a positive correlation in PD patients but not in MSA patients with both disease severity and cognitive impairment.

CONCLUSION

This study successfully replicated prior findings, demonstrating an association between pGPNMB levels and disease severity, and also identified a correlation with cognitive impairment in PD patients of the Chinese Han population. Additionally, this study is the first to identify a significant difference in pGPNMB levels between MSA, PD, and normal controls. The data provide new evidence supporting the potential role of pGPNMB in the diagnosis and differential diagnosis of Parkinsonism.

Potential Utility of Cerebrospinal Fluid Glycoprotein Nonmetastatic Melanoma Protein B as a Neuroinflammatory Diagnostic Biomarker in Mild Cognitive Impairment and Alzheimer's Disease

Alzheimer's disease (AD) is a very common neurodegenerative disorder characterized by the gradual loss of neurons and extracellular amyloid-peptide buildup. There is compelling evidence that the disease process depends on neuroinflammatory alterations, such as the activation of astrocytes and microglia cells. A transmembrane glycoprotein known as glycoprotein nonmetastatic melanoma protein B (GPNMB) plays a neuroprotective role during the development of neurodegeneration. To the best of our knowledge, this is the first investigation discussing the potential clinical usefulness of this protein in the AD continuum, especially in the MCI (mild cognitive impairment) stage. A total of 71 patients with AD or MCI as well as controls were enrolled in this study. The concentrations of GPNMB, YKL-40, Aβ1-42 (amyloid beta 1-42), Tau, and pTau and the Aβ1-42/1-40 ratio in the CSF (cerebrospinal fluid) were tested using immunological methods. The concentrations of both GPNMB and YKL-40 in the cerebrospinal fluid were significantly higher in patients with AD and MCI compared to the controls. Moreover, both proteins were biochemically associated with classical biomarkers of AD and were especially associated with the Aβ1-42/1-40 ratio and Tau and pTau levels in the whole study group. Elevated concentrations of GPNMB were observed in the Aβ(+) group of AD patients compared to the Aβ(-) subjects. Additionally, the diagnostic performance (AUC value) of GPNMB was higher than that of amyloid β1-42 in MCI patients compared with controls. Our study indicates that GPNMB might be a promising neuroinflammatory biomarker for the early diagnosis and prognosis of the AD continuum, with potential utility as a therapeutic target.

Ameliorative effect of the oil components derived from sweet potato shochu on impaired short-term memory in mice after amyloid β25-35 injection

Sweet potato shochu oil is a by-product of shochu production and usually discarded although some physiological functions are considered. In this study, we investigated the effects of shochu oil on short-term memory using a murine model of spontaneous alternating behavior induced by the intracerebroventricular (ICV) administration of amyloid β_25-35 (Aβ_25-35). Mice were orally administered shochu oil for 15 days. Experiments with a Y-maze model revealed that the Aβ_25-35 caused a significant decrease in spontaneous alternation behavior, and supplementation with shochu oil significantly improved this behavior. DNA microarray analysis revealed that the administration of shochu oil downregulated the expression of S100a9 and Ptgs2, which reportedly exacerbate amyloid β deposition in Alzheimer's disease. The administration of shochu oil upregulated the expression of Dnaja1 and PP2A, which is typically downregulated in Alzheimer's disease. These data suggest that shochu oil possible ameliorates on impaired short-term memory in mice after amyloid β_25-35 injection, as indicated by its effects on improving spontaneous alternation behavior and modulating the expressions of related genes.

Inflammation in the CNS - understanding various aspects of the pathogenesis of Alzheimer's disease

Alzheimer's disease is a progressive and deadly neurodegenerative disorder, and one of the most common causes of dementia in the world. Current, insufficiently sensitive and specific methods of early diagnosis and monitoring of this disease prompt a search for new tools. Numerous literature data indicate that the pathogenesis of Alzheimer's disease (AD) is not limited to the neuronal compartment, but involves various immunological mechanisms. Neuroinflammation has been recognized as a very important process in AD pathology. It seems to play pleiotropic roles, both neuroprotective as well as neurodegenerative, in the development of cognitive impairment depending on the stage of the disease. Mounting evidence demonstrates that inflammatory proteins could be considered biomarkers of disease progression. Therefore, the present review summarizes the role of some inflammatory molecules and their potential utility in the detection and monitoring of dementia severity. The paper also provides a valuable insight into new mechanisms leading to the development of dementia, which might be useful in discovering possible anti-inflammatory treatment.

GPNMB mitigates Alzheimer's disease and enhances autophagy via suppressing the mTOR signal

Alzheimer's disease (AD) is a common neurodegenerative disease which is characterized by amyloid beta (Aβ) accumulation. We found that glycoprotein NMB (GPNMB) was highly expressed in the brain of APP/PS1 mice, a mouse model of AD. However, its role in AD remains unclear. In this study, we aimed to explore the function of GPNMB in AD. The expression of GPNMB in the brain was detected by immunofluorescence and western blot. In addition, the role of GPNMB in AD was explored through gain-of-function. Autophagy, which is beneficial to Aβ clearance, was evaluated by transmission electron microscope and immunofluorescence with beclin-1. Furthermore, 3-MA, an autophagy inhibitor, was employed to evidence whether GPNMB reduced the level of Aβ through autophagy. We found that over-expression of GPNMB improved AD-like behaviors in APP/PS1 mice and reduced Aβ deposition. Further study showed that GPNMB enhanced autophagy, reduced microglial cells and inhibited the activation of the mTOR signal. Additionally, treatment with 3-MA abolished the beneficial effect of GPNMB on Aβ clearance. This study revealed that the high level of GPNMB in AD brain may help Aβ clearance and improve AD-like behaviors through enhancing autophagy via suppressing the mTOR signal. This beneficial role of GPNMB provides us novel strategies for the prevention and treatment of AD.

Functional Domains and Evolutionary History of the PMEL and GPNMB Family Proteins

The ancient paralogs premelanosome protein (PMEL) and glycoprotein nonmetastatic melanoma protein B (GPNMB) have independently emerged as intriguing disease loci in recent years. Both proteins possess common functional domains and variants that cause a shared spectrum of overlapping phenotypes and disease associations: melanin-based pigmentation, cancer, neurodegenerative disease and glaucoma. Surprisingly, these proteins have yet to be shown to physically or genetically interact within the same cellular pathway. This juxtaposition inspired us to compare and contrast this family across a breadth of species to better understand the divergent evolutionary trajectories of two related, but distinct, genes. In this study, we investigated the evolutionary history of PMEL and GPNMB in clade-representative species and identified TMEM130 as the most ancient paralog of the family. By curating the functional domains in each paralog, we identified many commonalities dating back to the emergence of the gene family in basal metazoans. PMEL and GPNMB have gained functional domains since their divergence from TMEM130, including the core amyloid fragment (CAF) that is critical for the amyloid potential of PMEL. Additionally, the PMEL gene has acquired the enigmatic repeat domain (RPT), composed of a variable number of imperfect tandem repeats; this domain acts in an accessory role to control amyloid formation. Our analyses revealed the vast variability in sequence, length and repeat number in homologous RPT domains between craniates, even within the same taxonomic class. We hope that these analyses inspire further investigation into a gene family that is remarkable from the evolutionary, pathological and cell biology perspectives.

Glycoprotein nonmetastatic melanoma protein B: A key mediator and an emerging therapeutic target in autoimmune diseases

The glycoprotein nonmetastatic melanoma protein B (GPNMB, also known as osteoactivin) is highly expressed in many cell types and regulates the homeostasis in various tissues. In different physiological contexts, it functions as a melanosome-associated protein, membrane-bound surface receptor, soluble ligand, or adhesion molecule. Therefore, GPNMB is involved in cell differentiation, migration, inflammation, metabolism, and neuroprotection. Because of its various involvement in different physiological conditions, GPNMB has been implicated in many diseases, including cancer, neurological disorders, and more recently immune-mediated diseases. This review summarizes the regulation and function of GPNMB in normal physiology, and discusses the involvement of GPNMB in disease conditions with a particular focus on its potential role and therapeutic implications in autoimmunity.

Microglia express GPNMB in the brains of Alzheimer's disease and Nasu-Hakola disease

Glycoprotein non-metastatic melanoma protein B (GPNMB) is a type I transmembrane glycoprotein first identified in low-metastatic human melanoma cell lines as a regulator of tumor growth. GPNMB is widely expressed in various tissues, where it is involved in cell differentiation, migration, inflammation/anti-inflammation, tissue regeneration, and neuroprotection. GPNMB is identified in microglia of adult rat brains, neurons and astrocytes of GPNMB transgenic (Tg) mouse brains, and motor neurons of amyotrophic lateral sclerosis (ALS) patients. Nasu-Hakola disease (NHD) is a rare autosomal recessive disorder, characterized by progressive presenile dementia and formation of multifocal bone cysts, caused by genetic mutations of either TYROBP (DAP12) or TREM2. TREM2 and DAP12 constitute a receptor/adaptor signaling complex expressed exclusively on osteoclasts, dendritic cells, macrophages, and microglia. Pathologically, the brains of NHD patients exhibit leukoencephalopathy, astrogliosis, accumulation of axonal spheroids, and remarkable activation of microglia predominantly in the white matter of frontal and temporal lobes and the basal ganglia. At present, molecular mechanisms responsible for development of leukoencephaolpathy in NHD brains remain totally unknown. Recent evidence indicates that disease-associated microglia (DAM) that cluster around amyloid plaques express high levels of GPNMB in Alzheimer's disease (AD) brains. Because microglia act as a key regulator of leukoencephalopathy in NHD brains, it is proposed that GPNMB expressed on microglia might play a protective role in progression of leukoencephalopathy possibly via active phagocytosis of myelin debris. In the present study using immunohistochemistry, we have attempted to clarify the expression of GPNMB in NHD brains, compared with AD brains. We found that microglia accumulating in the white matter express an intense GPNMB immunoreactivity in both NHD and AD brains, suggesting that the accumulation of GPNMB-immunoreactive microglia is a general phenomenon in neurodegenerative brains.

The glycoprotein GPNMB is selectively elevated in the substantia nigra of Parkinson's disease patients and increases after lysosomal stress

GPNMB is a glycoprotein observed upon tissue damage and inflammation and is associated with astrocytes, microglia, and macrophages. Gene variations in GPNMB are linked with Parkinson's disease (PD) risk, and changes in protein levels of GPNMB have been found in lysosomal storage disorders, including Gaucher's disease with glucocerebrosidase (GCase) deficiency. In the current study, GPNMB increases were seen in the substantia nigra (SN) of PD patients compared to age-matched controls. Such PD patients have a decrease in GCase activity and corresponding elevation of glycosphingolipids in the SN (Rocha et al., 2015a). Interestingly, transgenic mice modelling synucleinopathy did not show GPNMB elevations or altered GCase activity levels compared to wild-type mice. However, upon CBE-induced GCase lysosomal dysfunction with elevated glycosphingolipids in wild-type mice, there were similar changes in GPNMB levels in the brain as seen in PD patient brains. These results indicate that GPNMB levels do not depend on alpha-synuclein load per se but relate directly to the lipidopathy changes induced by CBE-mediated GCase inhibition. The experimental modelling of elevating glycolipids resulted in GPNMB elevations with glial activation in several brain regions in mice. This is the first demonstration of region-specific elevations of GPNMB protein in Parkinson's disease. The presence of GPNMB in PD patient substantia nigra, the induction of GPNMB after experimental glycosphingolipid increases, but not with pure alpha-synucleinopathy, point towards the potential for primary lipid-induced degeneration in PD.

Glycoprotein NMB: an Emerging Role in Neurodegenerative Disease

Neurodegeneration is characterized by severe neuronal loss leading to the cognitive and physical impairments that define various neurodegenerative diseases. Neuroinflammation is one hallmark of neurodegenerative diseases and can ultimately contribute to disease progression. Increased inflammatory cytokines, such as interleukin-6 (IL-6), interleukin-1β (IL-1 β), and tumor necrosis factor-α (TNF-α) are associated with Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS). Unfortunately, current therapeutic options lack ability to stop or effectively slow progression of these diseases and are primarily aimed at alleviating symptoms. Thus, it is crucial to discover novel treatment candidates for neurodegenerative diseases. Glycoprotein nonmetastatic melanoma protein B (GPNMB) is a type-I transmembrane glycoprotein first identified in a melanoma cell line. GPNMB augments bone mineral deposition by stimulating osteoblast differentiation. Aside from its anabolic function in the bone, emerging evidence suggests that GPNMB has anti-inflammatory and reparative functions. GPNMB has also been demonstrated to be neuroprotective in an animal model of ALS, cerebral ischemia, and other disease models. Given these discoveries, GPNMB should be investigated as a potential therapeutic option for multiple neurodegenerative diseases.

The role of Ca2+ signaling in Parkinson's disease

Across all kingdoms in the tree of life, calcium (Ca2+) is an essential element used by cells to respond and adapt to constantly changing environments. In multicellular organisms, it plays fundamental roles during fertilization, development and adulthood. The inability of cells to regulate Ca2+ can lead to pathological conditions that ultimately culminate in cell death. One such pathological condition is manifested in Parkinson's disease, the second most common neurological disorder in humans, which is characterized by the aggregation of the protein, α-synuclein. This Review discusses current evidence that implicates Ca2+ in the pathogenesis of Parkinson's disease. Understanding the mechanisms by which Ca2+ signaling contributes to the progression of this disease will be crucial for the development of effective therapies to combat this devastating neurological condition.

GPNMB ameliorates mutant TDP-43-induced motor neuron cell death

Glycoprotein nonmetastatic melanoma protein B (GPNMB) aggregates are observed in the spinal cord of amyotrophic lateral sclerosis (ALS) patients, but the detailed localization is still unclear. Mutations of transactive response DNA binding protein 43kDa (TDP-43) are associated with neurodegenerative diseases including ALS. In this study, we evaluated the localization of GPNMB aggregates in the spinal cord of ALS patients and the effect of GPNMB against mutant TDP-43 induced motor neuron cell death. GPNMB aggregates were not localized in the glial fibrillary acidic protein (GFAP)-positive astrocyte and ionized calcium binding adaptor molecule-1 (Iba1)-positive microglia. GPNMB aggregates were localized in the microtubule-associated protein 2 (MAP-2)-positive neuron and neurofilament H non-phosphorylated (SMI-32)-positive neuron, and these were co-localized with TDP-43 aggregates in the spinal cord of ALS patients. Mock or TDP-43 (WT, M337V, and A315T) plasmids were transfected into mouse motor neuron cells (NSC34). The expression level of GPNMB was increased by transfection of mutant TDP-43 plasmids. Recombinant GPNMB ameliorated motor neuron cell death induced by transfection of mutant TDP-43 plasmids and serum-free stress. Furthermore, the expression of phosphorylated ERK1/2 and phosphorylated Akt were decreased by this stress, and these expressions were increased by recombinant GPNMB. These results indicate that GPNMB has protective effects against mutant TDP-43 stress via activating the ERK1/2 and Akt pathways, and GPNMB may be a therapeutic target for TDP-43 proteinopathy in familial and sporadic ALS. © 2016 Wiley Periodicals, Inc.

Long-term upregulation of cortical glutamatergic AMPA receptors in a mouse model of chronic visceral pain

Background

Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal disorders and it causes long-lasting visceral pain and discomfort. AMPA receptor mediated long-term potentiation (LTP) has been shown to play a critical role in animal models of neuropathic and inflammatory pain. No report is available for central changes in the ACC of mice with chronic visceral pain.

Results

In this study, we used integrative methods to investigate potential central plastic changes in the anterior cingulate cortex (ACC) of a visceral pain mouse model induced by intracolonic injection of zymosan. We found that visceral pain induced an increased expression of AMPA receptors (at the post synapses) in the ACC via an enhanced trafficking of the AMPA receptors to the membrane. Both GluA1 and GluA2/3 subunits were significantly increased. Supporting biochemical changes, excitatory synaptic transmission in the ACC were also significantly enhanced. Microinjection of AMPA receptor inhibitor IEM1460 into the ACC inhibited visceral and spontaneous pain behaviors. Furthermore, we found that the phosphorylation of GluA1 at the Ser845 site was increased, suggesting that GluA1 phosphorylation may contribute to AMPA receptor trafficking. Using genetically knockout mice lacking calcium-calmodulin stimulated adenylyl cyclase subtype 1 (AC1), we found that AMPA receptor phosphorylation and its membrane trafficking induced by zymosan injection were completely blocked.

Conclusions

Our results provide direct evidence for cortical AMPA receptors to contribute to zymosan-induced visceral and spontaneous pain and inhibition of AC1 activity may help to reduce chronic visceral pain.