MT5-MMP promotes neuroinflammation, neuronal excitability and Aβ production in primary neuron/astrocyte cultures from the 5xFAD mouse model of Alzheimer’s disease

The Effects of Pb on TNF-R1-RIPK1/RIPK3 Signaling Pathway in the Hippocampus of Mice

Lead (Pb), a dense, soft, blue-gray metal, is widely used in metallurgy, cables, storage batteries, pigments, and other industrial applications. Pb has been shown to cause degenerative changes in the nervous system. Necroptosis, a form of non-apoptotic programmed cell death modality, is closely associated with neurodegenerative diseases. Whether the TNF-R1-RIPK1/RIPK3 pathway is involved in the neurodegeneration induced by Pb has yet to be determined. Here, we explored the role of the TNF-R1-RIPK1/RIPK3 signaling pathway in the Pb-induced necroptosis by using HT-22 cells, primary mouse hippocampal neurons, and C57BL/6 mice models, demonstrating that Pb exposure elevated lead levels in murine whole blood and hippocampal tissue in a dose-response relationship. Protein expression levels of PARP, c-PARP, RIPK1, p-RIPK1, RIPK3, MLKL, and p-MLKL in the hippocampal tissues were elevated, while the protein expression of caspase-8 was decreased. Furthermore, Pb exposure reduced the survival rates in HT-22 cells and primary mouse hippocampal neurons, while increasing the protein expressions of RIPK1 and p-MLKL. Collectively, these novel findings suggest that the TNF-R1/RIPK1/RIPK3 signaling pathway is associated with Pb-induced neurotoxicity in hippocampal neurons in mice.

Secretase promotes AD progression: simultaneously cleave Notch and APP

Alzheimer's disease (AD) involves complex pathological mechanisms. Secretases include membrane protein extracellular structural domain proteases and intramembrane proteases that cleave the topology to type I or type II. Secretases can effectively regulate the activation of Notch and amyloid precursor protein (APP), key factors in the progression of AD and cancer. This article systematically summarizes the intracellular localization, cleavage sites and products, and biological functions of six subtypes of secretases (α-secretase, β-secretase, γ-secretase, δ-secretase, ε-secretase, and η-secretase), and for the first time, elucidates the commonalities and differences between these subtypes of secretases. We found that each subtype of secretase primarily cleaves APP and Notch as substrates, regulating Aβ levels through APP cleavage to impact the progression of AD, while also cleaving Notch receptors to affect cancer progression. Finally, we review the chemical structures, indications, and research stages of various secretase inhibitors, emphasizing the promising development of secretase inhibitors in the fields of cancer and AD.

The Link Between Matrix Metalloproteinases and Alzheimer's Disease Pathophysiology

Alzheimer's disease (AD) is a major contributor to dementia and the most common neurodegenerative disorder. In AD pathophysiology, matrix metalloproteinases (MMPs)-proteolytic enzymes, best known to be responsible for remodeling and degradation of the extracellular matrix-were suggested to play an important role. Due to the diverse nature of the published data and frequent inconsistent results presented in available papers, it was considered essential to analyze all aspects of MMP literature with respect to AD pathophysiology and attempt to outline a unifying concept for understanding their role in AD. Thus, the main contribution of this review article is to summarize the most recent research on the participation of MMP in AD pathophysiology obtained using the cell cultures to understand the molecular principles of their action. Furthermore, an updated comprehensive view regarding this topic based exclusively on papers from human studies is provided as well. It can be concluded that determining the exact role of any particular MMPs in the AD pathophysiology holds promise for establishing their role as potential biomarkers reflecting the severity or progression of this disease or for developing new therapeutic agents targeting the processes that lead to AD.

Identification of binding partners that facilitate membrane-type 5 matrix metalloproteinase (MT5-MMP) processing of amyloid precursor protein

One of the pathological hallmarks of Alzheimer's disease (AD) is the presence of extracellular deposits of amyloid beta (Aβ) peptide. In addition to Aβ as the core component of the amyloid plaque, the amyloid precursor protein (APP) processing fragment Aβ was also found accumulated around the plaque. The APPη pathway, mainly mediated by membrane-type 5 matrix metalloproteinase (MT5-MMP), represents an important factor in AD pathogenesis. The proamyloidogenic features of MT5-MMP could result from interactions with APP when trafficking between organelles, so determination of the location within the cell of APPη cleavage and interacting proteins of MT5-MMP affecting this process will be of priority in understanding the role of MT5-MMP in AD. In the present study, MT5-MMP was found to be located in the nucleus, cytosol, and cytosolic subcellular granules of CHO cells that stably expressed wild-type human APP751. MT5-MMP fusion proteins were constructed that could localize enzyme production in the Golgi apparatus, endosome, ER, mitochondria, or plasma membrane. The fusion proteins significantly increased sAPPη when directed to the endosome, Golgi apparatus, plasma membrane, or mitochondria. Since the C-terminal region of MT5-MMP is responsible for its intracellular location and trafficking, this domain was used as the bait in a yeast two-hybrid screen to identify MT5-MMP protein partners in a human brain cDNA library. Identified binding partners included N4BP2L1, TMX3, EIG121, bridging Integrator 1 (BIN1), RUFY4, HTRA1, and TMEM199. The binding of N4BP2L1, EIG121, BIN1, or TMX3 to MT5-MMP resulted in the most significant increase in sAPPη production. Thus, the action of MT5-MMP on APP occurs in multiple locations within the cell and is facilitated by site-specific binding partners.

PCSK6 exacerbates Alzheimer's disease pathogenesis by promoting MT5-MMP maturation

Proprotein convertase subtilisin/kexin type 6 (PCSK6) is a calcium-dependent serine proteinase that regulates the proteolytic activity of various precursor proteins and facilitates protein maturation. Dysregulation of PCSK6 expression or function has been implicated in several pathological processes including nervous system diseases. However, whether and how PCSK6 is involved in the pathogenesis of Alzheimer's disease (AD) remains unclear. In this study, we reported that the expression of PCSK6 was significantly increased in the brain tissues of postmortem AD patients and APP23/PS45 transgenic AD model mice, as well as N2AAPP cells. Genetic knockdown of PCSK6 reduced amyloidogenic processing of APP in N2AAPP cells by suppressing the activation of membrane-type 5-matrix metalloproteinase (MT5-MMP), referred to as η-secretase. We further found that PCSK6 cleaved and activated MT5-MMP by recognizing the RRRNKR sequence in its N-terminal propeptide domain in N2A cells. The mutation or knockout of this cleavage motif prevented PCSK6 from interacting with MT5-MMP and performing cleavage. Importantly, genetic knockdown of PCSK6 with adeno-associated virus (AAV) reduced Aβ production and ameliorated hippocampal long-term potentiation (LTP) and long-term spatial learning and memory in APP23/PS45 transgenic mice. Taken together, these results demonstrate that genetic knockdown of PCSK6 effectively alleviate AD-related pathology and cognitive impairments by inactivating MT5-MMP, highlighting its potential as a novel therapeutic target for AD treatment.

Amyloid Precursor Protein: A Regulatory Hub in Alzheimer's Disease

Decades of research have demonstrated an incontrovertible role of amyloid-β (Aβ) in the etiology of Alzheimer's disease (AD). However, the overemphasis on the pathological impacts of Aβ may obscure the role of its metabolic precursor, amyloid precursor protein (APP), as a significant hub in the occurrence and progression of AD. The complicated enzymatic processing, ubiquitous receptor-like properties, and abundant expression of APP in the brain, as well as its close links with systemic metabolism, mitochondrial function and neuroinflammation, imply that APP plays multifaceted roles in AD. In this review, we briefly describe the evolutionarily conserved biological characteristics of APP, including its structure, functions and enzymatic processing. We also discuss the possible involvement of APP and its enzymatic metabolites in AD, both detrimental and beneficial. Finally, we describe pharmacological agents or genetic approaches with the capability to reduce APP expression or inhibit its cellular internalization, which can ameliorate multiple aspects of AD pathologies and halt disease progression. These approaches provide a basis for further drug development to combat this terrible disease.

Matrix metalloproteinases as biomarkers and therapeutic targets in colitis-associated cancer

Colorectal cancer (CRC) remains a major cause of morbidity and mortality. Therapeutic approaches for advanced CRC are limited and rarely provide long-term benefit. Enzymes comprising the 24-member matrix metalloproteinase (MMP) family of zinc- and calcium-dependent endopeptidases are key players in extracellular matrix degradation, a requirement for colon tumor expansion, invasion, and metastasis; hence, MMPs are an important research focus. Compared to sporadic CRC, less is known regarding the molecular mechanisms and the role of MMPs in the development and progression of colitis-associated cancer (CAC) - CRC on a background of chronic inflammatory bowel disease (IBD) - primarily ulcerative colitis and Crohn's disease. Hence, the potential of MMPs as biomarkers and therapeutic targets for CAC is uncertain. Our goal was to review data regarding the role of MMPs in the development and progression of CAC. We sought to identify promising prognostic and therapeutic opportunities and novel lines of investigation. A key observation is that since MMPs may be more active in early phases of CAC, using MMPs as biomarkers of advancing neoplasia and as potential therapeutic targets for adjuvant therapy in those with advanced stage primary CAC rather than overt metastases may yield more favorable outcomes.

Attenuation of Alzheimer's brain pathology in 5XFAD mice by PTH1-34, a peptide of parathyroid hormone

BACKGROUND

Alzheimer's disease (AD) and osteoporosis are two distinct diseases but often occur in the same patient. Their relationship remains poorly understood. Studies using Tg2576 AD animal model demonstrate bone deficits, which precede the brain phenotypes by several months, arguing for the independence of bone deficits on brain degeneration and raising a question if the bone deficits contribute to the AD development. To address this question, we investigated the effects of PTH_1-34, a peptide of parathyroid hormone analog and a well-recognized effective anabolic therapy drug for patients with osteoporosis, on 5XFAD animal model.

METHODS

5XFAD mice, an early onset β-amyloid (Aβ)-based AD mouse model, were treated with PTH_1-34 intermittently [once daily injection of hPTH_1-34 (50 μg/Kg), 5 days/week, starting at 2-month old (MO) for 2-3 month]. Wild type mice (C57BL/6) were used as control. The bone phenotypes were examined by microCT and evaluated by measuring serum bone formation and resorption markers. The AD relevant brain pathology (e.g., Aβ and glial activation) and behaviors were assessed by a combination of immunohistochemical staining analysis, western blots, and behavior tests. Additionally, systemic and brain inflammation were evaluated by serum cytokine array, real-time PCR (qPCR), and RNAscope.

RESULTS

A reduced trabecular, but not cortical, bone mass, accompanied with a decrease in bone formation and an increase in bone resorption, was detected in 5XFAD mice at age of 5/6-month old (MO). Upon PTH_1-34 treatments, not only these bone deficits but also Aβ-associated brain pathologies, including Aβ and Aβ deposition levels, dystrophic neurites, glial cell activation, and brain inflammatory cytokines, were all diminished; and the cognitive function was improved. Further studies suggest that PTH_1-34 acts on not only osteoblasts in the bone but also astrocytes in the brain, suppressing astrocyte senescence and expression of inflammatory cytokines in 5XFAD mice.

CONCLUSIONS

These results suggest that PTH_1-34 may act as a senolytic-like drug, reducing systemic and brain inflammation and improving cognitive function, and implicate PTH_1-34's therapeutic potential for patients with not only osteoporosis but also AD.

The immunomodulatory role of matrix metalloproteinases in colitis-associated cancer

Matrix metalloproteinases (MMPs) are an important class of enzymes in the body that function through the extracellular matrix (ECM). They are involved in diverse pathophysiological processes, such as tumor invasion and metastasis, cardiovascular diseases, arthritis, periodontal disease, osteogenesis imperfecta, and diseases of the central nervous system. MMPs participate in the occurrence and development of numerous cancers and are closely related to immunity. In the present study, we review the immunomodulatory role of MMPs in colitis-associated cancer (CAC) and discuss relevant clinical applications. We analyze more than 300 pharmacological studies retrieved from PubMed and the Web of Science, related to MMPs, cancer, colitis, CAC, and immunomodulation. Key MMPs that interfere with pathological processes in CAC such as MMP-2, MMP-3, MMP-7, MMP-9, MMP-10, MMP-12, and MMP-13, as well as their corresponding mechanisms are elaborated. MMPs are involved in cell proliferation, cell differentiation, angiogenesis, ECM remodeling, and the inflammatory response in CAC. They also affect the immune system by modulating differentiation and immune activity of immune cells, recruitment of macrophages, and recruitment of neutrophils. Herein we describe the immunomodulatory role of MMPs in CAC to facilitate treatment of this special type of colon cancer, which is preceded by detectable inflammatory bowel disease in clinical populations.

The STIM1/2-Regulated Calcium Homeostasis Is Impaired in Hippocampal Neurons of the 5xFAD Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of age-related dementia. Neuronal calcium homeostasis impairment may contribute to AD. Here we demonstrated that voltage-gated calcium (VGC) entry and store-operated calcium (SOC) entry regulated by calcium sensors of intracellular calcium stores STIM proteins are affected in hippocampal neurons of the 5xFAD transgenic mouse model. We observed excessive SOC entry in 5xFAD mouse neurons, mediated by STIM1 and STIM2 proteins with increased STIM1 contribution. There were no significant changes in cytoplasmic calcium level, endoplasmic reticulum (ER) bulk calcium levels, or expression levels of STIM1 or STIM2 proteins. The potent inhibitor BTP-2 and the FDA-approved drug leflunomide reduced SOC entry in 5xFAD neurons. In turn, excessive voltage-gated calcium entry was sensitive to the inhibitor of L-type calcium channels nifedipine but not to the T-type channels inhibitor ML218. Interestingly, the depolarization-induced calcium entry mediated by VGC channels in 5xFAD neurons was dependent on STIM2 but not STIM1 protein in cells with replete Ca²⁺ stores. The result gives new evidence on the VGC channel modulation by STIM2. Overall, the data demonstrate the changes in calcium signaling of hippocampal neurons of the AD mouse model, which precede amyloid plaque accumulation or other signs of pathology manifestation.

The Role of Extracellular Matrix in Human Neurodegenerative Diseases

The dense neuropil of the central nervous system leaves only limited space for extracellular substances free. The advent of immunohistochemistry, soon followed by advanced diagnostic tools, enabled us to explore the biochemical heterogeneity and compartmentalization of the brain extracellular matrix in exploratory and clinical research alike. The composition of the extracellular matrix is critical to shape neuronal function; changes in its assembly trigger or reflect brain/spinal cord malfunction. In this study, we focus on extracellular matrix changes in neurodegenerative disorders. We summarize its phenotypic appearance and biochemical characteristics, as well as the major enzymes which regulate and remodel matrix establishment in disease. The specifically built basement membrane of the central nervous system, perineuronal nets and perisynaptic axonal coats can protect neurons from toxic agents, and biochemical analysis revealed how the individual glycosaminoglycan and proteoglycan components interact with these molecules. Depending on the site, type and progress of the disease, select matrix components can either proactively trigger the formation of disease-specific harmful products, or reactively accumulate, likely to reduce tissue breakdown and neuronal loss. We review the diagnostic use and the increasing importance of medical screening of extracellular matrix components, especially enzymes, which informs us about disease status and, better yet, allows us to forecast illness.