Glycosaminoglycan Modification of Decorin Depends on MMP14 Activity and Regulates Collagen Assembly

Decorin attenuates hypertrophic scar fibrosis via TGFβ/Smad signalling

The management of hypertrophic scars (HSs), characterized by excessive collagen production, involves various nonsurgical and surgical interventions. However, the absence of a well-defined molecular mechanism governing hypertrophic scarring has led to less-than-ideal results in clinical antifibrotic treatments. Therefore, our study focused on the role of decorin (DCN) and its regulatory role in the TGF-β/Smad signalling pathway in the development of HSs. In our research, we observed a decrease in DCN expression within hypertrophic scar tissue and its derived cells (HSFc) compared to that in normal tissue. Then, the inhibitory effect of DCN on collagen synthesis was confirmed in Fc and HSFc via the detection of fibrosis markers such as COL-1 and COL-3 after the overexpression and knockdown of DCN. Moreover, functional assessments revealed that DCN suppresses the proliferation, migration and invasion of HSFc. We discovered that DCN significantly inhibits the TGF-β1/Smad3 pathway by suppressing TGF-β1 expression, as well as the formation and phosphorylation of Smad3. This finding suggested that DCN regulates the synthesis of collagen-based extracellular matrix and fibrosis through the TGF-β1/Smad3 pathway.

Matricellular Proteins in the Homeostasis, Regeneration, and Aging of Skin

Matricellular proteins are secreted extracellular proteins that bear no primary structural functions but play crucial roles in tissue remodeling during development, homeostasis, and aging. Despite their low expression after birth, matricellular proteins within skin compartments support the structural function of many extracellular matrix proteins, such as collagens. In this review, we summarize the function of matricellular proteins in skin stem cell niches that influence stem cells' fate and self-renewal ability. In the epidermal stem cell niche, fibulin 7 promotes epidermal stem cells' heterogeneity and fitness into old age, and the transforming growth factor-β-induced protein ig-h3 (TGFBI)-enhances epidermal stem cell growth and wound healing. In the hair follicle stem cell niche, matricellular proteins such as periostin, tenascin C, SPARC, fibulin 1, CCN2, and R-Spondin 2 and 3 modulate stem cell activity during the hair cycle and may stabilize arrector pili muscle attachment to the hair follicle during piloerections (goosebumps). In skin wound healing, matricellular proteins are upregulated, and their functions have been examined in various gain-and-loss-of-function studies. However, much remains unknown concerning whether these proteins modulate skin stem cell behavior, plasticity, or cell-cell communications during wound healing and aging, leaving a new avenue for future studies.

Differential MMP-14 targeting by biglycan, decorin, fibromodulin, and lumican unraveled by in silico approach

Small leucine-rich proteoglycans (SLRPs) are major regulators of extracellular matrix assembly and cell signaling. Lumican, a member of the SLRPs family, and its derived peptides were shown to possess antitumor activity by interacting directly with the catalytic domain of MMP-14 leading to the inhibition of its activity. The aim of the present report was to characterize by in silico three-dimensional (3D) modeling the structure and the dynamics of four SLRPs including their core protein and their specific polysaccharide chains to assess their capacity to bind to MMP-14 and to regulate its activity. Molecular docking experiments were performed to identify the specific amino acids of MMP-14 interacting with each of the four SLRPs. The inhibition of each SLRP (100 nM) on MMP-14 activity was measured and the constants of inhibition (K_i) were evaluated. The impact of the number of glycan chains, structures, and dynamics of lumican on the interaction with MMP-14 was assessed by molecular dynamics simulations. Molecular docking analysis showed that all SLRPs bind to MMP-14 through their concave face, but in different regions of the catalytic domain of MMP-14. Each SLRPs inhibited significantly the MMP-14 activity. Finally, molecular dynamics showed the role of glycan chains in interaction with MMP-14 and shielding effect of SLRPs. Altogether, the results demonstrated that each SLRP exhibited inhibition of MMP-14 activity. However, the differential targeting of MMP-14 by the SLRPs was shown to be related not only to the core protein conformation but also to the glycan chain structures and dynamics.

Extracellular Matrix (ECM) and Fibrosis in Adipose Tissue: Overview and Perspectives

Fibrosis in adipose tissue is a major driver of obesity-related metabolic dysregulation. It is characterized by an overaccumulation of extracellular matrix (ECM) during unhealthy expansion of adipose tissue in response to over nutrition. In obese adipose-depots, hypoxia stimulates multiple pro-fibrotic signaling pathways in different cell populations, thereby inducing the overproduction of the ECM components, including collagens, noncollagenous proteins, and additional enzymatic components of ECM synthesis. As a consequence, local fibrosis develops. The result of fibrosis-induced mechanical stress not only triggers cell necrosis and inflammation locally in adipose tissue but also leads to system-wide lipotoxicity and insulin resistance. A better understanding of the mechanisms underlying the obesity-induced fibrosis will help design therapeutic approaches to reduce or reverse the pathological changes associated with obese adipose tissue. Here, we aim to summarize the major advances in the field, which include newly identified fibrotic factors, cell populations that contribute to the fibrosis in adipose tissue, as well as novel mechanisms underlying the development of fibrosis. We further discuss the potential therapeutic strategies to target fibrosis in adipose tissue for the treatment of obesity-linked metabolic diseases and cancer. © 2023 American Physiological Society. Compr Physiol 13:4387-4407, 2023.

Single-Nucleus RNA Sequencing Reveals that Decorin Expression in the Amygdala Regulates Perineuronal Nets Expression and Fear Conditioning Response after Traumatic Brain Injury

Traumatic brain injury (TBI) is a risk factor for posttraumatic stress disorder (PTSD). Augmented fear is a defining characteristic of PTSD, and the amygdala is considered the main brain region to process fear. The mechanism by which the amygdala is involved in fear conditioning after TBI is still unclear. Using single-nucleus RNA sequencing (snRNA-seq), transcriptional changes in cells in the amygdala after TBI are investigated. In total, 72 328 nuclei are obtained from the sham and TBI groups. 7 cell types, and analysis of differentially expressed genes (DEGs) reveals widespread transcriptional changes in each cell type after TBI are identified. In in vivo experiments, it is demonstrated that Decorin (Dcn) expression in the excitatory neurons of the amygdala significantly increased after TBI, and Dcn knockout in the amygdala mitigates TBI-associated fear conditioning. Of note, this effect is caused by a Dcn-mediated decrease in the expression of perineuronal nets (PNNs), which affect the glutamate-γ-aminobutyric acid balance in the amygdala. Finally, the results suggest that Dcn functions by interacting with collagen VI α3 (Col6a3). Consequently, the findings reveal transcriptional changes in different cell types of the amygdala after TBI and provide direct evidence that Dcn relieves fear conditioning by regulating PNNs.

Oncosuppressive roles of decorin through regulation of multiple receptors and diverse signaling pathways

Decorin is a stromal-derived prototype member of the small leucine-rich proteoglycan gene family. In addition to its functions as a regulator of collagen fibrillogenesis and TGF-β activity soluble decorin acts as a pan-receptor tyrosine kinase (RTK) inhibitor. Decorin binds to various RTKs including EGFR HER2 HGFR/Met VEGFR2 TLR and IGFR. Although the molecular mechanism for the action of decorin on these receptors is not entirely elucidated overall decorin evokes transient activation of these receptors with suppression of downstream signaling cascades culminating in growth inhibition followed by their physical downregulation via caveosomal internalization and degradation. In the case of Met decorin leads to decreased β-catenin signaling pathway and growth suppression. As most of these RTKs are responsible for providing a growth advantage to cancer cells the result of decorin treatment is oncosuppression. Another decorin-driven mechanism to restrict cancer growth and dissemination is by impeding angiogenesis via vascular endothelial growth factor receptor 2 (VEGFR2) and the concurrent activation of protracted endothelial cell autophagy. In this review we will dissect the multiple roles of decorin in cancer biology and its potential use as a next-generation protein-based adjuvant therapy to combat cancer.

Novel regulatory roles of small leucine-rich proteoglycans in remodeling of the uterine cervix in pregnancy

The cervix undergoes rapid and dramatic shifts in collagen and elastic fiber structure to achieve its disparate physiological roles of competence during pregnancy and compliance during birth. An understanding of the structure-function relationships of collagen and elastic fibers to maintain extracellular matrix (ECM) homeostasis requires an understanding of the mechanisms executed by non-structural ECM molecules. Small-leucine rich proteoglycans (SLRPs) play key functions in biology by affecting collagen fibrillogenesis and regulating enzyme and growth factor bioactivities. In the current study, we evaluated collagen and elastic fiber structure-function relationships in mouse cervices using mice with genetic ablation of decorin and/or biglycan genes as representative of Class I SLRPs, and lumican gene representative of Class II SLRP. We identified structural defects in collagen fibril and elastic fiber organization in nonpregnant mice lacking decorin, or biglycan or lumican with variable resolution of defects noted during pregnancy. The severity of collagen and elastic fiber defects was greater in nonpregnant mice lacking both decorin and biglycan and defects were maintained throughout pregnancy. Loss of biglycan alone reduced tissue extensibility in nonpregnant mice while loss of both decorin and biglycan manifested in decreased rupture stretch in late pregnancy. Collagen cross-link density was similar in the Class I SLRP null mice as compared to wild-type nonpregnant and pregnant controls. A broader range in collagen fibril diameter along with an increase in mean fibril spacing was observed in the mutant mice compared to wild-type controls. Collectively, these findings uncover functional redundancy and hierarchical roles of Class I and Class II SLRPs as key regulators of cervical ECM remodeling in pregnancy. These results expand our understating of the critical role SLRPs play to maintain ECM homeostasis in the cervix.

The role of cell-matrix interactions in connective tissue mechanics

Living tissue is able to withstand large stresses in everyday life, yet it also actively adapts to dynamic loads. This remarkable mechanical behaviour emerges from the interplay between living cells and their non-living extracellular environment. Here we review recent insights into the biophysical mechanisms involved in the reciprocal interplay between cells and the extracellular matrix and how this interplay determines tissue mechanics, with a focus on connective tissues. We first describe the roles of the main macromolecular components of the extracellular matrix in regards to tissue mechanics. We then proceed to highlight the main routes via which cells sense and respond to their biochemical and mechanical extracellular environment. Next we introduce the three main routes via which cells can modify their extracellular environment: exertion of contractile forces, secretion and deposition of matrix components, and matrix degradation. Finally we discuss how recent insights in the mechanobiology of cell-matrix interactions are furthering our understanding of the pathophysiology of connective tissue diseases and cancer, and facilitating the design of novel strategies for tissue engineering.

Partial Ablation of Non-Myogenic Progenitor Cells as a Therapeutic Approach to Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD), caused by the loss of dystrophin, remains incurable. Reduction in muscle regeneration with DMD is associated with the accumulation of fibroadipogenic progenitors (FAPs) differentiating into myofibroblasts and leading to a buildup of the collagenous tissue aggravating DMD pathogenesis. Mesenchymal stromal cells (MSCs) expressing platelet-derived growth factor receptors (PDGFRs) are activated in muscle during DMD progression and give rise to FAPs promoting DMD progression. Here, we hypothesized that muscle dysfunction in DMD could be delayed via genetic or pharmacologic depletion of MSC-derived FAPs. In this paper, we test this hypothesis in dystrophin-deficient mdx mice. To reduce fibro/adipose infiltration and potentiate muscle progenitor cells (MPCs), we used a model for inducible genetic ablation of proliferating MSCs via a suicide transgene, viral thymidine kinase (TK), expressed under the Pdgfrb promoter. We also tested if MSCs from fat tissue, the adipose stromal cells (ASCs), contribute to FAPs and could be targeted in DMD. Pharmacological ablation was performed with a hunter-killer peptide D-CAN targeting ASCs. MSC depletion with these approaches resulted in increased endurance, measured based on treadmill running, as well as grip strength, without significantly affecting fibrosis. Although more research is needed, our results suggest that depletion of pathogenic MSCs mitigates muscle damage and delays the loss of muscle function in mouse models of DMD.