Matrix Metalloproteinase-9, Its Tissue Inhibitor(TIMP)-1 and CRP in Alzheimer’s Disease

Plasma MMP-9/TIMP-1 ratio serves as a novel potential biomarker in Alzheimer's disease

This study aimed to explore the diagnostic potential of plasma MMP-9, TIMP-1 and MMP-9/TIMP-1 ratio for Alzheimer's disease (AD). This retrospective study was performed in a cohort consisting of patients with AD (AD group) and cognitive normal subjects (HC group). Cerebrospinal fluid (CSF) classic biomarkers including Aβ42, Aβ40, total tau (t-tau), and phosphorylated tau (p-tau) levels, and plasma MMP-9 and TIMP-1 levels were measured by commercially available ELISA kits, respectively. The differential diagnostic potential of plasma MMP-9, TIMP-1 and MMP-9/TIMP-1 ratio was evaluated using the receiver operating characteristic curve analysis. It was observed that significantly elevated levels of plasma MMP-9 and MMP-9/TIMP-1 ratio in patients with AD than HC. Both MMP-9 and MMP-9/TIMP-1 ratios were negatively correlated with CSF Aβ42/Aβ40 ratio and positively correlated with CSF p-tau in AD group. ROC curve analysis showed better diagnostic accuracy of MMP-9/TIMP-1 ratio than MMP-9 for AD at a cutoff value of 1.35 with an area under the curve of 0.906 and sensitivity and specificity of 95.8% and 75%, respectively. Our findings encourage the use of plasma MMP-9/TIMP-1 ratio as a biomarker in the diagnosis of AD.

Multifaceted Role of Matrix Metalloproteinases in Neurodegenerative Diseases: Pathophysiological and Therapeutic Perspectives

Neurodegeneration is the pathological condition, in which the nervous system or neuron loses its structure, function, or both, leading to progressive degeneration or the death of neurons, and well-defined associations of tissue system, resulting in clinical manifestations. Neuroinflammation has been shown to precede neurodegeneration in several neurodegenerative diseases (NDs). No drug is yet known to delay or treat neurodegeneration. Although the etiology and potential causes of NDs remain widely indefinable, matrix metalloproteinases (MMPs) evidently have a crucial role in the progression of NDs. MMPs, a protein family of zinc (Zn²⁺)-containing endopeptidases, are pivotal agents that are involved in various biological and pathological processes in the central nervous system (CNS). The current review delineates the several emerging evidence demonstrating the effects of MMPs in the progression of NDs, wherein they regulate several processes, such as (neuro)inflammation, microglial activation, amyloid peptide degradation, blood brain barrier (BBB) disruption, dopaminergic apoptosis, and α-synuclein modulation, leading to neurotoxicity and neuron death. Published papers to date were searched via PubMed, MEDLINE, etc., while using selective keywords highlighted in our manuscript. We also aim to shed a light on pathophysiological effect of MMPs in the CNS and focus our attention on its detrimental and beneficial effects in NDs, with a special focus on Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), multiple sclerosis (MS), and Huntington's disease (HD), and discussed various therapeutic strategies targeting MMPs, which could serve as potential modulators in NDs. Over time, several agents have been developed in order to overcome challenges and open up the possibilities for making selective modulators of MMPs to decipher the multifaceted functions of MMPs in NDs. There is still a greater need to explore them in clinics.

Neutrophil activation in Alzheimer's disease and mild cognitive impairment: A systematic review and meta-analysis of protein markers in blood and cerebrospinal fluid

Inflammation is involved in the pathophysiology of Alzheimer's disease (AD), with multiple inflammatory processes implicated in its risk and progression. This review included original peer-reviewed studies measuring the cerebrospinal fluid or peripheral blood concentrations of protein markers specifically related to neutrophil activity in healthy controls (HC) and in patients with AD or mild cognitive impairment (MCI). A total of 35 studies (N_HC = 3095, N_AD = 2596, N_MCI = 1203) were included. Random-effects meta-analyses were used to estimate between-groups standardized mean differences (SMD) and 95 % confidence intervals. In blood, concentrations of myeloperoxidase (MPO; N_AD/N_HC = 271/209, SMD = 0.41 [0.20, 0.62]; I² = 15.7 %) and neutrophil gelatinase associated lipocalin (NGAL; N_AD/N_HC = 273/185, SMD = 0.30 [0.11, 0.49]; I² < 0.005 %) were significantly higher in AD relative to HC. Peripheral blood concentrations of NGAL were also higher in MCI compared to HC (N_MCI/N_HC = 489/145, SMD = 0.39 [0.11, 0.67]; I² = 38.6 %). None of the protein markers exhibited a significant difference between HC, MCI, or AD groups in the cerebrospinal fluid. The evidence suggests that peripheral neutrophil activation, as indicated by blood concentrations of NGAL and MPO, may be a pathological feature of cognitive impairment due to AD, evident at stages of MCI and AD dementia.

TIMP-1: A key cytokine released from activated astrocytes protects neurons and ameliorates cognitive behaviours in a rodent model of Alzheimer's disease

Alzheimer's disease (AD) is characterized by two pathologic species, extracellular amyloid-β (Aβ) plaques and intracellular neurofibrillary tangles. Astrocytes that maintain normal homeostasis in the brain undergo a set of molecular, cellular and functional changes called reactive astrogliosis in various neurological diseases including AD. It is hypothesized that reactive astrocytes initially tend to protect neurons by reducing Aβ load and by secreting a plethora of cytokines, however, their functions have only been poorly investigated. Our studies on the kinetics of activation of cortical astrocytes following Aβ-exposure revealed significant level of activation as early as in 6 h. The astrocyte conditioned medium (ACM) from 6 h Aβ-treated astrocytes (Aβ-ACM) provided significant neuroprotection of cultured cortical neurons against Aβ insults. Analysis of the secreted proteins in Aβ-ACM revealed a marked increase of Tissue inhibitor of Metalloproteinase-1 (TIMP-1) within 6 h. Interestingly, we found that neutralization of TIMP-1 with antibody or knockdown with siRNA in astrocytes abolished most of the neuroprotective ability of the 6 h Aβ-ACM on Aβ-treated cultured neurons. Furthermore addition of exogenous rat recombinant TIMP-1 protein protects primary neurons from Aβ mediated toxicity. In a well characterized Aβ-infused rodent model of AD, intra-cerebroventricular administration of TIMP-1 revealed a reduction in Aβ load and apoptosis in hippocampal and cortical regions. Finally, we found that TIMP-1 can ameliorate Aβ-induced cognitive dysfunctions through restoration of Akt and its downstream pathway and maintenance of synaptic integrity. Thus, our results not only provide a functional clarity for TIMP-1, secreted by activated astrocytes, but also support it as a major candidate in cytokine-mediated therapy of AD especially at the early phase of disease progression.

Friends or Foes: Matrix Metalloproteinases and Their Multifaceted Roles in Neurodegenerative Diseases

Neurodegeneration is a chronic progressive loss of neuronal cells leading to deterioration of central nervous system (CNS) functionality. It has been shown that neuroinflammation precedes neurodegeneration in various neurodegenerative diseases. Matrix metalloproteinases (MMPs), a protein family of zinc-containing endopeptidases, are essential in (neuro)inflammation and might be involved in neurodegeneration. Although MMPs are indispensable for physiological development and functioning of the organism, they are often referred to as double-edged swords due to their ability to also inflict substantial damage in various pathological conditions. MMP activity is strictly controlled, and its dysregulation leads to a variety of pathologies. Investigation of their potential use as therapeutic targets requires a better understanding of their contributions to the development of neurodegenerative diseases. Here, we review MMPs and their roles in neurodegenerative diseases: Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), and multiple sclerosis (MS). We also discuss MMP inhibition as a possible therapeutic strategy to treat neurodegenerative diseases.

Matrix metalloproteinases and their multiple roles in Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent type of dementia. Pathological changes in the AD brain include amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs), as well as neuronal death and synaptic loss. Matrix metalloproteinases (MMPs) play an important role as inflammatory components in the pathogenesis of AD. MMP-2 might be assumed to have a protective role in AD and is the major MMP which is directly linked to Aβ in the brain. Synthesis of MMP-9 can be induced by Aβ, and the enzymes appear to exert multiple effects in AD in senile plaque homoeostasis. The proaggregatory influence on tau oligomer formation in strategic brain regions may be a potential neurotoxic side effect of MMP-9. MMP-3 levels are correlated to the duration of AD and correlate with the CSF T-tau and P-tau levels in the elderly controls. Elevated brain levels of MMP-3 might result in increased MMP-9 activity and indirectly facilitate tau aggregation. At present, the clinical utility of these proteins, particularly in plasma or serum, as potential early diagnostic biomarkers for AD remains to be established. More research is needed to understand the diverse roles of these proteases to design specific drugs and devise therapeutic strategies for AD.

A meta-analysis of cytokines in Alzheimer's disease

BACKGROUND

Studies suggest that inflammation is involved in the neurodegenerative cascade leading to Alzheimer's disease (AD) pathology and symptoms. This study sought to quantitatively summarize the clinical cytokine data.

METHODS

Original English language peer-reviewed studies measuring cytokine concentrations in AD and healthy control subjects were included. Mean (± standard deviation) cytokine concentrations for AD and control subjects were extracted.

RESULTS

Forty studies measuring peripheral blood cytokine concentrations and 14 measuring cerebrospinal fluid (CSF) cytokine concentrations were included. In peripheral blood, there were significantly higher concentrations (weighted mean difference [95% confidence interval]) of interleukin (IL)-6 (2.86 [1.68, 4.04] pg/mL, p < .00001, N[AD/control subjects] = 985/680, 14 studies), tumor necrosis factor (TNF)-α (3.25 [.76, 5.74] pg/mL, p = .01, N = 680/447, 14 studies), IL-1β (.55 [.32, .78] pg/mL, p < .00001, N = 574/370, 10 studies), transforming growth factor (TGF)-β (67.23 [28.62, 105.83] pg/mL, p = .0006, N = 190/158, 5 studies), IL-12 (7.60 [5.58, 9.62] pg/mL, p < .00001, N = 148/106, 5 studies), and IL-18 (15.82 [1.98, 29.66] pg/mL, p = .03, N = 131/94, 4 studies) but not of IL-4, IL-8, IL-10, interferon-γ, or C-reactive protein in AD subjects compared with control subjects. There were significantly higher concentrations of TGF-β (7.81 [2.27, 13.35] pg/mL, p =.006, N = 113/114, 5 studies) but not IL-6, TNF-α, and IL-1β in the CSF of AD subjects compared with control subjects.

CONCLUSIONS

These results strengthen the clinical evidence that AD is accompanied by an inflammatory response, particularly higher peripheral concentrations of IL-6, TNF-α, IL-1β, TGF-β, IL-12 and IL-18 and higher CSF concentrations of TGF-β.

Matrix metalloproteinases in cerebral ischemia

Matrix metalloproteinases (MMPs) are involved in the pathophysiology of several central nervous system diseases that share common pathogeneses, such as disruption of the blood-brain barrier (BBB), neuroinflammation, oxidative stress, and remodeling of the extracellular matrix (ECM). In early ischemic injury, MMPs participate in disruption of the BBB by digesting the basal lamina of capillaries and ECM, leading to vasogenic edema and hemorrhagic transformation. However, ECM degradation and remodeling are essential for tissue recovery, with MMPs having a key role as modulators of homeostasis between neuronal death and tissue regeneration. Thus, MMPs may be a double-edged sword that has a deleterious or beneficial role depending on the stage of brain injury.