Fibronectin Extra Domain A Promotes Liver Sinusoid Repair following Hepatectomy

Semi-autonomous wound invasion via matrix-deposited, haptotactic cues

Proper wound healing relies on invasion of fibroblasts via directed migration. While the related experimental and mathematical modeling literature has mainly focused on cell migration directed by soluble cues (chemotaxis), there is ample evidence that fibroblast migration is also directed by insoluble, matrix-bound cues (haptotaxis). Furthermore, numerous studies indicate that fibronectin (FN), a haptotactic ligand for fibroblasts, is present and dynamic in the provisional matrix throughout the proliferative phase of wound healing. In the present work, we show the plausibility of a hypothesis that fibroblasts themselves form and maintain haptotactic gradients in a semi-autonomous fashion. As a precursor to this, we examine the positive control scenario where FN is pre-deposited in the wound matrix, and fibroblasts maintain haptotaxis by removing FN at an appropriate rate. After developing conceptual and quantitative understanding of this scenario, we consider two cases in which fibroblasts activate the latent form of a matrix-loaded cytokine, TGFβ, which upregulates the fibroblasts' own secretion of FN. In the first of these, the latent cytokine is pre-patterned and released by the fibroblasts. In the second, fibroblasts in the wound produce the latent TGFβ, with the presence of the wound providing the only instruction. In all cases, wound invasion is more effective than a negative control model with haptotaxis disabled; however, there is a trade-off between the degree of fibroblast autonomy and the rate of invasion.

Characterization and role of collagen gene expressing hepatic cells following partial hepatectomy in mice

BACKGROUND AND AIMS

The mechanism underlying liver regeneration following partial hepatectomy (PH) is not fully elucidated. We aimed to characterize collagen gene expressing hepatic cells following PH and examine their contribution to liver regeneration.

APPROACH AND RESULTS

Col-GFP mice, which express GFP under the control of the collagen gene promoter, were used to detect collagen gene expressing cells following PH. The GFP-expressing cells were analyzed via single-cell RNA sequencing (scRNA-seq). Additionally, Col-ER Cre/RFP and Col-ER Cre/DTA mice were utilized to examine the cell fates and functional roles of collagen gene expressing cells in liver regeneration, respectively. The number of collagen gene expressing cells was found to be increased on day 3 and subsequently decreased on day 7 following PH. ScRNA-seq analysis of sorted collagen gene expressing cells showed that the regenerating liver was characterized by three distinct hepatic stellate cell (HSC) clusters, including one representing classic myofibroblasts. The other HSC clusters included an intermediately activated HSC cluster and a proliferating HSC cluster. Of these, the latter cluster was absent in the CCl 4 -induced liver fibrosis model. Cell fate tracing analysis using Col-ER Cre/RFP mice demonstrated that the collagen gene expressing cells escaped death during regeneration and remained in an inactivated state in the liver. Further, depletion of these cells using Col-ER Cre/DTA mice resulted in impaired liver regeneration.

CONCLUSIONS

Heterogeneous HSC clusters, one of which was a unique proliferating cluster, were found to appear in the liver following PH. Collagen gene expressing cells, including HSCs, were found to promote liver regeneration.

Insights into the use of genetically modified decellularized biomaterials for tissue engineering and regenerative medicine

Various modifications have been performed on biomaterials to improve their applications in tissue engineering and regenerative medicine. However, the challenges of immunogenicity and biocompatibility existed since the application of biomaterials. As a method to solve this problem, the decellularization process removes most living cells from biomaterials to minimize their immunogenicity; and preserves the native structures and compositions that favour cell growth and the subsequent construction of functional tissue. On the other hand, genetic modification of biomaterials aims to achieve specific functions (low immunogenicity, osteogenesis, etc.) or analyse the genetic mechanisms underlying some diseases (cardiac dysfunction, liver fibrosis, etc.). The combination of decellularization and gene modification is highly superior to biomaterials; thus, we must obtain a deeper understanding of these novel biomaterials. In this review, we summarize the fabrication approaches and current applications of genetically modified decellularized biomaterials and then discuss their disadvantages and corresponding future perspectives.

Zwitterionic Hydrogel Activates Autophagy to Promote Extracellular Matrix Remodeling for Improved Pressure Ulcer Healing

Pressure ulcer (PU) is a worldwide problem that is hard to heal because of its prolonged inflammatory response and impaired ECM deposition caused by local hypoxia and repeated ischemia/reperfusion. Our previous study discovered that the non-fouling zwitterionic sulfated poly (sulfobetaine methacrylate) (SBMA) hydrogel can improve PU healing with rapid ECM rebuilding. However, the mechanism of the SBMA hydrogel in promoting ECM rebuilding is unclear. Therefore, in this work, the impact of the SBMA hydrogel on ECM reconstruction is comprehensively studied, and the underlying mechanism is intensively investigated in a rat PU model. The in vivo data demonstrate that compared to the PEG hydrogel, the SBMA hydrogel enhances the ECM remolding by the upregulation of fibronectin and laminin expression as well as the inhibition of MMP-2. Further investigation reveals that the decreased MMP-2 expression of zwitterionic SBMA hydrogel treatment is due to the activation of autophagy through the inhibited PI3K/Akt/mTOR signaling pathway and reduced inflammation. The association of autophagy with ECM remodeling may provide a way in guiding the design of biomaterial-based wound dressing for chronic wound repair.

The phenotype of gingival fibroblasts and their potential use in advanced therapies

Advanced therapies in medicine use stem cells, gene editing, and tissues to treat a wide range of conditions. One of their goals is to stimulate endogenous repair of tissues and organs by manipulating stem cells and their niche, as well as to optimize the intrinsic characteristics and plasticity of differentiated cells in adult tissues. In this context, fibroblasts emerge as an alternative source to stem cells because they share phenotypic and regenerative characteristics. Specifically, fibroblasts of the oral mucosae have been shown to have improved regenerative capacity compared to other fibroblast populations. Additionally, their easy access by means of minimally invasive procedures without generating aesthetic problems, with easy and rapid in vitro expansion and with great capacity to respond to extrinsic factors, make oral fibroblasts an attractive and interesting resource for regenerative medicine. This review summarizes current concepts regarding the phenotypic and functional aspects of human Gingival Fibroblasts and their niche, differentiating them from other fibroblast populations of oral-lining mucosa and skin fibroblasts. Furthermore, some applications are presented in regenerative medicine, emphasizing on the biological potential of human Gingival Fibroblasts.

The Endothelium as a Driver of Liver Fibrosis and Regeneration

Liver fibrosis is a common feature of sustained liver injury and represents a major public health problem worldwide. Fibrosis is an active research field and discoveries in the last years have contributed to the development of new antifibrotic drugs, although none of them have been approved yet. Liver sinusoidal endothelial cells (LSEC) are highly specialized endothelial cells localized at the interface between the blood and other liver cell types. They lack a basement membrane and display open channels (fenestrae), making them exceptionally permeable. LSEC are the first cells affected by any kind of liver injury orchestrating the liver response to damage. LSEC govern the regenerative process initiation, but aberrant LSEC activation in chronic liver injury induces fibrosis. LSEC are also main players in fibrosis resolution. They maintain liver homeostasis and keep hepatic stellate cell and Kupffer cell quiescence. After sustained hepatic injury, they lose their phenotype and protective properties, promoting angiogenesis and vasoconstriction and contributing to inflammation and fibrosis. Therefore, improving LSEC phenotype is a promising strategy to prevent liver injury progression and complications. This review focuses on changes occurring in LSEC after liver injury and their consequences on fibrosis progression, liver regeneration, and resolution. Finally, a synopsis of the available strategies for LSEC-specific targeting is provided.

Inflammatory networks cultivate cancer cell metastasis to the liver

The liver is the most frequent site of metastatic spread in malignancies that arise from the digestive system, including pancreatic ductal adenocarcinoma (PDAC). Metastasis to the liver is a major cause of morbidity and mortality in cancer patients, yet mechanisms that govern this process remain poorly understood. Until recently, liver tropism of metastasis was believed to be driven by mechanical factors that direct the passive flow of circulating cancer cells to the liver. However, emerging evidence now shows that liver metastasis is a dynamic process that is, at least in part, dependent on the formation of a "pro-metastatic niche". Key features of this niche are myeloid cells and fibrosis that support cancer cell colonization and growth. Inflammatory responses that are mounted early during primary tumor development are critical for the recruitment of myeloid cells and the deposition of extracellular matrix (ECM) proteins within the liver. Intriguingly, the inflammatory processes that direct the formation of a pro-metastatic niche share remarkable resemblance to mechanisms of liver injury and regeneration, suggesting that cancer co-opts physiological liver functions to support metastasis. Therefore, therapeutic strategies that target key elements of liver inflammation that form the basis of a pro-metastatic niche may lead to effective treatments for metastatic cancer.

The Impact of Different Augmentative Methods on the Expression of Inflammatory Factors

Many animal studies show that an intact periosteum plays an important role in osseous regeneration. The potential effect of an in vivo periosteal barrier membrane on the expression of specific proteins has not been examined sufficiently. The aim of the present study is to investigate the influence of the flap preparation method and collagen membrane on the emission of inflammatory factors. This study examines 20 patients with dental implants who had previously undergone an augmentation. A soft tissue sample was taken during augmentation and 3 months later from the same location. Samples were always taken from the margins of a previously prepared mucoperiosteal flap. The flap was raised with a conventional periosteal elevator in the control group and with a piezoelectric device in the test group. In both groups, we covered half of the augmented bone with a native collagen membrane (NCM; Geistlich Bio-Gide). This allowed us to examine the same incision area with and without a membrane. An immunohistochemical analysis was performed for collagen IV, fibronectin, and inflammatory factors such as cluster of differentiation 31 (CD31), cyclooxygenase-2 (COX-2), and interleukin 6 (IL-6). There was a clear difference in the expression of specific proteins after the piezoelectric device and the periosteal elevator were used. The expression of fibronectin, IL-6, and COX-2 was higher after preparation with the periosteal elevator than after piezoelectric periosteum dissection. The expression of collagen IV was higher after the piezoelectric procedure. No difference was observed for CD31. The membrane had no effect on the expression of collagen IV, fibronectin, IL-6, and COX-2. The type of periosteal preparation influences the expression of specific proteins. With regard to the factors examined here, NCM did not appear to influence the wound healing cascade.

Mechanical Stretch Increases Expression of CXCL1 in Liver Sinusoidal Endothelial Cells to Recruit Neutrophils, Generate Sinusoidal Microthombi, and Promote Portal Hypertension

BACKGROUND & AIMS

Mechanical forces contribute to portal hypertension (PHTN) and fibrogenesis. We investigated the mechanisms by which forces are transduced by liver sinusoidal endothelial cells (LSECs) into pressure and matrix changes.

METHODS

We isolated primary LSECs from mice and induced mechanical stretch with a Flexcell device, to recapitulate the pulsatile forces induced by congestion, and performed microarray and RNA-sequencing analyses to identify gene expression patterns associated with stretch. We also performed studies with C57BL/6 mice (controls), mice with deletion of neutrophil elastase (NE^-/-) or peptidyl arginine deiminase type IV (Pad4^-/-) (enzymes that formation of neutrophil extracellular traps [NETs]), and mice with LSEC-specific deletion of Notch1 (Notch1^iΔEC). We performed partial ligation of the suprahepatic inferior vena cava (pIVCL) to simulate congestive hepatopathy-induced portal hypertension in mice; some mice were given subcutaneous injections of sivelestat or underwent bile-duct ligation. Portal pressure was measured using a digital blood pressure analyzer and we performed intravital imaging of livers of mice.

RESULTS

Expression of the neutrophil chemoattractant CXCL1 was up-regulated in primary LSECs exposed to mechanical stretch, compared with unexposed cells. Intravital imaging of livers in control mice revealed sinusoidal complexes of neutrophils and platelets and formation of NETs after pIVCL. NE^-/- and Pad4^-/- mice had lower portal pressure and livers had less fibrin compared with control mice after pIVCL and bile-duct ligation; neutrophil recruitment into sinusoidal lumen of liver might increase portal pressure by promoting sinusoid microthrombi. RNA-sequencing of LSECs identified proteins in mechanosensitive signaling pathways that are altered in response to mechanical stretch, including integrins, Notch1, and calcium signaling pathways. Mechanical stretch of LSECs increased expression of CXCL1 via integrin-dependent activation of transcription factors regulated by Notch and its interaction with the mechanosensitive piezo calcium channel.

CONCLUSIONS

In studies of LSECs and knockout mice, we identified mechanosensitive angiocrine signals released by LSECs which promote PHTN by recruiting sinusoidal neutrophils and promoting formation of NETs and microthrombi. Strategies to target these pathways might be developed for treatment of PHTN. RNA-sequencing accession number: GSE119547.

The fibronectin ED-A domain enhances recruitment of latent TGF-β-binding protein-1 to the fibroblast matrix

Dysregulated secretion and extracellular activation of TGF-β1 stimulates myofibroblasts to accumulate disordered and stiff extracellular matrix (ECM) leading to fibrosis. Fibronectin immobilizes latent TGF-β-binding protein-1 (LTBP-1) and thus stores TGF-β1 in the ECM. Because the ED-A fibronectin splice variant is prominently expressed during fibrosis and supports myofibroblast activation, we investigated whether ED-A promotes LTBP-1-fibronectin interactions. Using stiffness-tuneable substrates for human dermal fibroblast cultures, we showed that high ECM stiffness promotes expression and colocalization of LTBP-1 and ED-A-containing fibronectin. When rescuing fibronectin-depleted fibroblasts with specific fibronectin splice variants, LTBP-1 bound more efficiently to ED-A-containing fibronectin than to ED-B-containing fibronectin and fibronectin lacking splice domains. Function blocking of the ED-A domain using antibodies and competitive peptides resulted in reduced LTBP-1 binding to ED-A-containing fibronectin, reduced LTBP-1 incorporation into the fibroblast ECM and reduced TGF-β1 activation. Similar results were obtained by blocking the heparin-binding stretch FNIII12-13-14 (HepII), adjacent to the ED-A domain in fibronectin. Collectively, our results suggest that the ED-A domain enhances association of the latent TGF-β1 by promoting weak direct binding to LTBP-1 and by enhancing heparin-mediated protein interactions through HepII in fibronectin.