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Hedi Raizer

Journal 7 min read

How does the extracellular matrix work?

The extracellular matrix is the non-cellular protein scaffold that surrounds cells, and it works by presenting adhesion ligands, storing and releasing growth factors, and transmitting mechanical tension into intracellula

peptides-pro Editorial

The extracellular matrix (ECM) is the non-cellular, protein-and-glycoconjugate network deposited by cells into the space around them; it is also referred to in the literature as the extracellular matrix, the interstitial matrix, or, for its basement-membrane subset, the basal lamina. It is not a single molecule but a class of assembled supramolecular structures, principally fibrillar fibronectin, collagens, proteoglycans and associated matricellular proteins. Because it is an assembled material rather than a defined compound, the evidence base does not supply a single sequence, formula or molecular weight for "the ECM"; individual constituents are characterised separately, and fibrillar fibronectin matrix is described as the predominant ECM in most tissues, while in neural tissue it is limited to sites of tissue damage and disease [12].

Mechanistically, the work summarised here centres on integrin-mediated adhesion: matrix proteins engage integrin receptors at the cell surface, and the resulting signals are transduced through kinase cascades including JNK, with downstream transcriptional effectors such as ETS2 and RIP3-MLKL necroptotic machinery [2].

Research Studies

Fibronectin and matrix assembly in astrocytes versus fibroblasts

Fibrillar fibronectin is the main ECM component of most tissues, but in neural tissue it appears only at sites of damage and disease. In primary cortical astrocytes, fibronectin was produced and assembled into fibrils through a process that differed from the assembly behaviour of fibroblasts, and the effects of TGFβ on fibronectin matrix assembly also differed between the two cell types [12]. This is an in vitro cell-culture finding and does not establish astrocyte matrix behaviour in intact tissue.

Fibronectin tensional state and fibrotic matrix in idiopathic pulmonary fibrosis models

An in vitro fibrosis assay was established using patient-derived fibroblasts together with the tension-sensitive fibronectin-binding peptide FnBPA5, whose multivalent binding to fibronectin is impaired by fibre strain. The system was validated against known fibrosis biomarkers at the protein and mRNA levels, and the work reported a direct relationship between ECM fibre tension and fibrosis progression in idiopathic pulmonary fibrosis models [8]. The readout is a peptide-binding proxy for fibre tension in cultured cells, not a clinical measurement.

Periostin, integrin-JNK signalling and cardiac fibrosis in arrhythmogenic cardiomyopathy

Periostin (POSTN) is a multifunctional ECM protein. In myocardium from arrhythmogenic cardiomyopathy (ACM) mice and from patients with ACM, POSTN was significantly elevated. POSTN deficiency alleviated heart dysfunction, reduced cardiac fibrosis and improved survival rates in ACM mice. POSTN was mainly derived from cardiac myofibroblasts and promoted cardiomyocyte necroptosis both in vivo and in vitro, acting through integrin-JNK-RIP3-MLKL signalling, and induced CCL3 expression via an integrin-JNK-ETS2 pathway; CCL3 in turn activated cardiac myofibroblasts, forming a feedforward loop [2]. The human data here are descriptive tissue-level observations; the causal and survival findings are from the mouse model.

Apabetalone and fibrotic activation of cardiac fibroblasts

Accumulation of ECM causes tissue fibrosis that contributes to myocardial dysfunction and heart failure, and no approved anti-fibrotic therapeutics target it. BET protein inhibitors reduced fibrosis in preclinical heart failure models, and the clinical-stage BET inhibitor apabetalone reduced hospitalisations for heart failure in a phase 3 trial. Apabetalone was tested for anti-fibrotic activity in cell models recapitulating cardiac fibrosis, using human immortalised cardiac fibroblasts, cryopreserved cardiac fibroblasts, and ex vivo cultured fibroblasts from patients undergoing bypass grafting [3]. These are cell-model results; they do not demonstrate an effect on fibrosis in patients.

MAFF and contraction-induced transcription in skeletal muscle

Skeletal muscle adapts to exercise through rapid transcriptional remodelling. MAFF, a small MAF transcription factor, was consistently induced by acute exercise in both human and mouse skeletal muscle, with induction restricted to muscles recruited by the exercise modality. In C2C12 cells, Maff was induced by an in vitro electrical pulse stimulation model, and CRISPR/Cas9-mediated Maff knockout reduced myogenic fusion with accumulation of unfused nuclei; RNA sequencing showed broad reprogramming in Maff-deficient myotubes [4]. The human component is an acute exercise-induction observation; the fusion and transcriptomic findings are from the C2C12 line.

BDNF, disc degeneration and intradiscal neoinnervation

BDNF is a neurotrophin family protein involved in neuronal survival, growth and synaptic plasticity, and its expression has been confirmed within intervertebral disc tissue, with degenerated discs showing increased BDNF expression compared with normal discs and further increases reported with degeneration severity. Intervertebral disc degeneration is closely associated with intradiscal nerve ingrowth [5]. This is a registered clinical study of serum BDNF correlation with Pfirrmann grading and IL-1β, and the tissue-level expression statements are background to that study rather than its results.

Graphene oxide-hydroxyapatite coatings and ECM protein interactions at the implant interface

Graphene oxide (GO) has strong protein-binding ability attributed to its high surface area and oxygen functional groups, but is limited by dose-dependent cytotoxicity; hydroxyapatite (HA) is highly biocompatible but shows relatively weak protein-protein interactions at the molecular scale. Molecular docking, pharmacophore modelling and molecular dynamics simulations were used to explore interactions of GO, HA and GO-HA nanocomposites with ECM proteins for osseointegration at dental implant interfaces [6]. These are computational and materials-characterisation results, not in vivo osseointegration outcomes.

Matrix metalloproteinases and other molecular targets in skin biology

A review of molecular targets in cosmetic research focused on telomerase, histone deacetylases (particularly sirtuins), matrix metalloproteinases, antioxidant enzymes, the CD44 receptor, tyrosinase, microphthalmia-associated transcription factor and melanocortin receptors, all of which regulate processes including DNA repair, gene expression and extracellular matrix turnover in skin ageing, pigmentation, inflammation and tissue regeneration [7]. This is a review-level synthesis of target biology, not primary experimental data.

Bone ageing as multiscale matrix degeneration

Bone ageing is described not merely as bone mass loss but as a multi-level, networked degenerative phenomenon spanning molecular, cellular, tissue and system levels. At the macroscopic level, bone ageing is characterised by declines in bone mass, microstructure and biomechanical properties [1]. This is a review-level framework; it does not report a single interventional result.

Matrix protein or targetModel or populationReported mechanism
FibronectinPrimary cortical astrocytes vs fibroblasts, in vitro [12]Fibril assembly; TGFβ response differs by cell type
Fibronectin fibre tensionPatient-derived fibroblasts, in vitro IPF assay [8]Tension-sensitive FnBPA5 binding tracks fibrosis progression
Periostin (POSTN)ACM mice and human ACM myocardium [2]Integrin-JNK-RIP3-MLKL necroptosis; integrin-JNK-ETS2-CCL3 feedforward loop
BET proteins (apabetalone)Human cardiac fibroblasts, cell models [3]Suppression of fibrotic activation
MAFFHuman and mouse skeletal muscle; C2C12 cells [4]Contraction-induced transcription; myogenic fusion
BDNFIntervertebral disc tissue; registered clinical study [5]Increased expression with degeneration severity; intradiscal neoinnervation
GO-HA nanocompositeMolecular docking and dynamics simulations [6]ECM protein binding at implant interface

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