Activity-dependent extracellular proteolytic cascade cleaves the ECM component brevican to promote structural plasticity

The actin-based dynamics of dendritic spines play a key role in synaptic plasticity, which underlies learning and memory. Although it is becoming increasingly clear that modulation of actin is critical for spine dynamics, the upstream molecular signals that regulate the formation and plasticity of spines are poorly understood. In non-neuronal cells, integrins are critical modulators of the actin cytoskeleton, but their function in the nervous system is not well characterized. Here we show that alpha5 integrin regulates spine morphogenesis and synapse formation in hippocampal neurons. Knockdown of alpha5 integrin expression using small interfering RNA decreased the number of dendritic protrusions, spines, and synapses. Expression of constitutively active or dominant negative alpha5 integrin also resulted in alterations in the number of dendritic protrusions, spines, and synapses. alpha5 integrin signaling regulates spine morphogenesis and synapse formation by a mechanism that is dependent on Src kinase, Rac, and the signaling adaptor GIT1. Alterations in the activity or localization of these molecules result in a significant decrease in the number of spines and synapses. Thus, our results point to a critical role for integrin signaling in regulating the formation of dendritic spines and synapses in hippocampal neurons.

Subthreshold repetitive transcranial magnetic stimulation drives structural synaptic plasticity in the young and aged motor cortex

Background: Pregnancy and lactation are governed by hormones and neurophysiological processes, including differential expression of trophic factors, functional and structural synaptic plasticity, and neurogenesis in different brain areas. Objectives: The aim of the study was to evaluate the number of neurotrophic factors, synaptic plasticity, and neurogenesis in the hippocampus of rats during pregnancy, lactation, as well as in dams that were deprived of their pups one week after birth or treated with Finasteride or Clomiphene. Methods: Adult female Sprague Dawley CD rats were treated with finasteride (25 mg/kg, subcutaneously) or clomiphene (5 mg/kg, intragastrically) from day 12 to 18 of pregnancy. Dams during pregnancy, lactation, and those deprived of their pups, which were sacrificed 7 days after delivery, were used to study Brain-Derived Neurotrophic Factor (BDNF) and Activity-regulated Cytoskeletal (Arc) protein expression, dendritic spine density (DSD), and cell proliferation in the hippocampus. Results: BDNF, Arc, and DSD markedly increased after 21 days of pregnancy (the time of delivery), an effect that lasted for 21 days during lactation and was abolished by physiological weaning (21 days after delivery). The modifications in the mentioned parameters were associated with a dramatic reduction of neurosteroid content when compared to estrus females. In contrast, after 21 days of pregnancy, an increase in cell proliferation and a decrease during the first three weeks of postpartum were observed. Finasteride and clomifene failed to modify the changes in BDNF and Arc content elicited by pregnancy and delivery. Pups deprivation induced a rapid reduction in the amount of BDNF, Arc, and DSD while increasing cell proliferation. Conclusion: In rats, the changes in plastic properties of hippocampal neurons during pregnancy, lactation, and pups deprivation may play a crucial role in the modulation of maternal care.

Infusion of BDNF into the nucleus accumbens of aged rats improves cognition and structural synaptic plasticity through PI3K-ILK-Akt signaling

BackgroundIn central nervous system, all components are enveloped by the extracellular matrix (ECM), regulating microenvironmental homeostasis and neuronal development. The condensed cartilage‐like ECM called perineuronal nets (PNNs), mainly surrounding parvalbumin‐expressing (PV+) fast‐firing GABAergic interneurons, are crucial to synaptic plasticity and memory modulation.MethodPNNs are developed in the vital periods of synaptic maturation and play a critical role in synaptogenesis, synaptic stability, neuroprotection and ionic buffering. In addition, ECM includes basement membranes (BM) and neural interstitial matrix (NIM). All types of ECM are composed of chondroitin sulphate proteoglycans (CSPGs), heparan sulphate proteoglycans (HSPGs), hyaluronan, glycoproteins and other molecules secreted by neurons and glial cells.ResultIn Alzheimer's disease (AD), ECM acts as a physical and chemical barrier to interact with pathological hallmarks such as β‐amyloid (Aβ), hyperphosphorylated tau protein, synaptic alternation and excitatory toxicity. These components of ECM are dynamically changed to modulate neuronal functions and cellular interactions.ConclusionWe highlight ECM, especially the perineuronal ECM, and its components in AD, and elaborate the potential therapeutic targets in AD.

Brain networks store new memories using functional and structural synaptic plasticity. Memory formation is generally attributed to Hebbian plasticity, while homeostatic plasticity is thought to have an ancillary role in stabilizing network dynamics. Here we report that homeostatic plasticity alone can also lead to the formation of stable memories. We analyze this phenomenon using a new theory of network remodeling, combined with numerical simulations of recurrent spiking neural networks that exhibit structural plasticity based on firing rate homeostasis. These networks are able to store repeatedly presented patterns and recall them upon the presentation of incomplete cues. Storage is fast, governed by the homeostatic drift. In contrast, forgetting is slow, driven by a diffusion process. Joint stimulation of neurons induces the growth of associative connections between them, leading to the formation of memory engrams. These memories are stored in a distributed fashion throughout connectivity matrix, and individual synaptic connections have only a small influence. Although memory-specific connections are increased in number, the total number of inputs and outputs of neurons undergo only small changes during stimulation. We find that homeostatic structural plasticity induces a specific type of “silent memories”, different from conventional attractor states.

Exposure to the microgravity conditions of spaceflight alleviates the load normally imposed by the Earth's gravitational field on the inner ear utricular epithelia. Previous ultrastructural investigations have shown that spaceflight induces an increase in synapse density within hair cells of the rat utricle. However, the utricle exhibits broad physiological heterogeneity across different epithelial regions, and it is unknown whether capabilities for synaptic plasticity generalize to hair cells across its topography. To achieve systematic and broader sampling of the epithelium than was previously conducted, we used immunohistochemistry and volumetric image analyses to quantify synapse distributions across representative utricular regions in specimens from mice exposed to spaceflight (a 15-day mission of the space shuttle Discovery). These measures were compared with similarly sampled Earth-bound controls. Following paraformaldehyde fixation and microdissection, immunohistochemistry was performed on intact specimens to label presynaptic ribbons (anti-CtBP2) and postsynaptic receptor complexes (anti-Shank1A). Synapses were identified as closely apposed pre- and postsynaptic puncta. Epithelia from horizontal semicircular canal cristae served as "within-specimen" controls, whereas utricles and cristae from Earth-bound cohorts served as experimental controls. We found that synapse densities decreased in the medial extrastriolae of microgravity specimens compared with experimental controls, whereas they were unchanged in the striolae and horizontal cristae from the two conditions. These data demonstrate that structural plasticity was topographically localized to the utricular region that encodes very low frequency and static changes in linear acceleration, and illuminates the remarkable capabilities of utricular hair cells for synaptic plasticity in adapting to novel gravitational environments.NEW & NOTEWORTHY Spaceflight imposes a radically different sensory environment from that in which the inner ear utricle normally operates. We investigated synaptic modifications in utricles from mice flown aboard a space shuttle mission. Structural synaptic plasticity was detected in the medial extrastriola, a region associated with encoding static head position, as decreased synapse density. These results are remarkably congruent with a recent report of decreased utricular function in astronauts immediately after returning from the International Space Station.

Angiotensin II, oxidative stress, and extracellular matrix degradation during transition to LV failure in rats with hypertension

Knee osteoarthritis (KOA) is currently indicated to be characterized by destruction of articular cartilage. The destruction can be described as an imbalance between synthesis and degradation of extracellular matrix (ECM) components. It is accompanied with changes of pro-inflammatory cytokines and degradation enzymes dominated by matrix metalloproteinase (MMP) and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS). Recent studies have revealed that microRNAs (miRNAs) are associated with synthesis and degradation of extracellular matrix (ECM). They play an important role in articular cartilage homeostasis of knee osteoarthritis (KOA). The related mechanisms include mediating the relevant enzymes and pro-inflammatory cytokines. The aim of this study is to reveal the potential microRNAs (miRNAs) and their corresponding upstream or downstream targeting on cartilage extracellular matrix (ECM) degradation in knee osteoarthritis (KOA). 7 databases were extensively searched with a theme of MicroRNAs (miRNAs) and knee osteoarthritis (KOA). The articles were searched regardless of publication status and language. The databases include PubMed, Cochrane Library, EMbase, China Biology Medicine (CBM), China National Knowledge Infrastructre (CNKI), WanFang Data and Chinese Scientific Journal Database (VIP). This article reviews the microRNAs (miR-140, miR-146a, miR-25, miR-543, miR-19, miR-125b, miR-92a, miR-27b, miR-448, miR-558, miR-155) and their corresponding upstream or downstream in mediating cartilage extracellular matrix (ECM) degradation. MicroRNAs (miRNAs) have been involved in the pathogenesis of KOA. They can directly regulate cartilage homeostasis by targeting on ECM degradation via corresponding upstream/downstream.

Background: Mechanical stress along with inflammation play causative roles in the development of osteoarthritis (OA), which decreases the quality of life and causes economic loss. Inflammation and extracellular matrix (ECM) degradation have been identified as key factors in the development of OA. As the main active component in frankincense, acetyl-11-keto-β-boswellic acid (AKBA) has been shown to have positive effects on inflammation. However, the effects of AKBA in cartilage inflammation and ECM degradation are currently elusive. Methods: Micro-CT, Histologic analysis, and Immunohistochemical (IHC) analysis were conducted in vivo on Hulth-Telhag OA rat with or without AKBA treatment. The effects of AKBA on inflammation and ECM degradation of rat articular chondrocytes were evaluated by CCK-8, Western Blot, quantitative real-time polymerase chain reaction (qRT-PCR), and immunofluorescence (IF) assay. We demonstrated the role of inflammation and ECM degradation in the pathogenesis of OA and determined the protective effect of AKBA on both Hulth-Telhag rat OA model and lipopolysaccharide (LPS)-induced rat chondrocytes. Findings: We found increased inflammatory expression and decreased ECM expression in OA model cartilage and LPS-induced chondrocytes. Meanwhile, the protective effect of AKBA and its inhibitory effects on inflammation as well as ECM-related markers were also observed in the rat Hulth-Telhag model. Furthermore, activation of NF-κB attenuated nuclear p65 protein levels in chondrocytes upon LPS stimulation. In addition, AKBA was found to subsequently reversed the LPS-induced activation of NF- κB signal and inflammation-related ECM degradation in chondrocytes. Interpretation: Suppression of NF-κB pathway activation by AKBA restrains OA development via inhibition of inflammation and ECM degradation. AKBA is a promising therapeutic agent for the treatment of OA. Funding Information: Financial supports from National Natural Science Foundation of China (Nos. 82072425, 81873991 and 81672238), the Natural Science Foundation of Jiangsu Province (Nos. BK20180001), Jiangsu Commission of Health (No. H2018027); the Young Medical Talents of Jiangsu Province (No. QNRC2016751), Suzhou Jiangsu Commission of Health (No. SYS2019100 and SYS2019101), Suzhou Science and Technology Foundation (No. SYSD2017170, SYSD2018207 and SS201805), Project of Suzhou Sports Research Bureau (No. TY2019-204), and Special Project of Diagnosis and Treatment Technology for Key Clinical Diseases in Suzhou (LCZX202003). Declaration of Interests: There are no declarations of interest. Ethics Approval Statement: Animal welfare and experimental procedures were carried out in accordance with the Declaration of Helsinki, and were approved by the Ethics Committee of the First Affiliated Hospital of Soochow University.

In neurons, transport of a subset of mRNAs to subcellular regions and their translation has a role in synaptic plasticity. Recent studies have suggested a control mechanism of this local translation through mRNA compartmentalization or degradation. Here we report that processing bodies (P-bodies), which are involved in mRNA degradation or storage, are transported to dendrites by conventional kinesin (KIF5A) as a motor protein. Neuronal activation induced by depolarization increased the colocalization of P-bodies with PSD-95 in dendrites. This neuronal activity increased the release of Nd1 and Arp2 mRNA from the P-bodies and, consequently, reversed the decrease of F-actin (induced by overexpression of Dcp1a) in the dendrites. Our data suggest that the activity-induced redistribution of P-bodies and mRNA release from P-bodies might have a role in synaptic structural plasticity by altering levels of mRNAs that are involved in the dynamics of the actin cytoskeleton in dendrites.

Tumour growth and invasiveness require extracellular matrix (ECM) degradation and are stimulated by the GALA pathway, which induces protein O-glycosylation in the endoplasmic reticulum (ER). ECM degradation requires metalloproteases, but whether other enzymes are required is unclear. Here, we show that GALA induces the glycosylation of the ER-resident calnexin (Cnx) in breast and liver cancer. Glycosylated Cnx and its partner ERp57 are trafficked to invadosomes, which are sites of ECM degradation. We find that disulfide bridges are abundant in connective and liver ECM. Cell surface Cnx-ERp57 complexes reduce these extracellular disulfide bonds and are essential for ECM degradation. In vivo, liver cancer cells but not hepatocytes display cell surface Cnx. Liver tumour growth and lung metastasis of breast and liver cancer cells are inhibited by anti-Cnx antibodies. These findings uncover a moonlighting function of Cnx-ERp57 at the cell surface that is essential for ECM breakdown and tumour development.

Osteoarthritis (OA) is histopathologically marked by extracellular matrix (ECM) degradation in joint cartilage. Abnormal mechanical stimulation on joint cartilage may result in ECM degeneration and OA development. Matrix metalloproteinase 13 (MMP-13) is one of the catabolic enzymes contributing to the degradation of ECM, and it has become the potential biomarker for the therapeutic management of OA. Xanthohumol (XH), a naturally occurring prenylflavonoid derived from hops and beer, shows the protective activity against OA development. However, the potential mechanisms still need great effort. In this article, mechanical stimulation could significantly increase the expression of MMP-13 and lncRNA GAS5 (GAS5) and promoting ECM degradation. These could be effectively reversed by XH administration. Suppressed expression GAS5 ameliorated mechanical stimulation-induced MMP-13 expression. MiR-27a was predicted and verified as a target of GAS5, and overexpression of miR-27a down regulated the expression of MMP-13. Collectively, XH exhibited protective effects against mechanical stimulation-induced ECM degradation by mediating the GAS5/miR-27a signaling pathway in OA chondrocytes.

Poor chemotherapy efficacy in pancreatic cancer is attributed to limited drug permeation caused by the dense extracellular matrix (ECM) and drug degradation induced by tumor-colonizing bacteria. Here, a tumor-targeting probiotic-nanosystem is elaborately designed to remodulate ECM and selectively regulate tumor-colonizing bacteria for improving chemo-immunotherapy against pancreatic cancer. Specifically, drug-loaded liposomes are conjugated with Clostridium Butyricum (CB) via matrix metalloproteinase-2 (MMP-2)-responsive peptide to construct a probiotic-nanosystem. Particularly, vactosertib (VAC, a transforming growth factor-β1 receptor inhibitor) is delivered by probiotic-nanosystem to silence the active pancreatic stellate cells (PSCs) for inhibiting the development of ECM, resulting in a loosened ECM and providing a golden opportunity for the deep penetration of chemotherapy drugs and immune cells. Subsequently, gemcitabine (GEM) is efficiently delivered into the core of tumors via probiotic-nanosystem, achieving an enhanced chemotherapy efficacy. Noteworthily, CB can alleviate γ-proteobacteria-mediated GEM degradation through competitively reducing the contents of γ-proteobacteria and promoting the amounts of tumor-inhibiting bacteria, thereby significantly potentiating the therapeutic effect of GEM. The engineered probiotic-nanosystem can not only enhance the GEM-induced immunogenic cell death (ICD) of a pancreatic tumor to activate antitumor immune responses but also markedly increase the tumor-infiltration of effector immune cells to heighten tumoricidal immunity, offering a promising strategy for chemo-immunotherapy of pancreatic cancer.

Osteoarthritis (OA) is characterized by an imbalance of cartilage extracellular matrix (ECM) production and degradation, due, in part, to increased cytokine production. It has been demonstrated that the cytokine, Interleukin‐1 beta (IL‐1β), is produced by OA articular chondrocytes and plays a prominent role in altering ECM metabolism by targeting the matrix metalloproteases (MMPs) that degrade the ECM. We are developing a novel, OA therapeutic, Extracellular Matrix Protection Factor‐1 (ECPF‐1) that targets MMP interaction with its ECM substrate. We have demonstrated a reduction in ECM degradation when primary, human OA chondrocyte (HOAC) cultures are treated with ECPF‐1. In this study, HOACs isolated from total knee arthroplasty were reared in three‐dimensional, serum‐free, alginate cultures. The sides of least and greatest pathology of the femoral condyles and tibial plateaus were determined by gross inspection and cells isolated were cultured separately (LP and GP). Chondrocytes were plated at 2.5×106 cells per milliliter of alginate and incubated in serum‐free medium for five days. Cells were released from the alginate and the RNA extracted from the pellet, reverse‐transcribed into cDNA and quantitative, real time PCR (qRT‐PCR) was performed with TaqMan Gene Expression assays for IL‐1β, collagen type I, collagen type II and 18s rRNA. In a previous study, IL‐1β production was detected in the conditioned media of HOAC cultures with the highest concentration of this cytokine present in the cultures established from the region of greatest pathology (GP). In this study, IL‐1β expression was detectable in mRNA produced by LP and GP HOAC cultures. The expression was reduced 2‐fold in LP cultures treated 24 hours with 2.5 uM ECPF‐1 and 1.4 fold in GP cultures. These results demonstrate the ability of ECPF‐1 to alter expression of a molecule involved in the feedback loop of ECM destruction. ECPF‐1 provides a tool with which to further define the cellular mechanisms responsible for OA chondrocyte pathology.Support or Funding InformationNew Jersey Health Foundation, Center for Chronic Disorders of Aging Small Grant, PCOM's Division of ResearchThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.