Heparin and fibroblast growth factors affect surfactant protein gene expression in type II cells

Heparan Sulfate Proteoglycans in Viral Infection and Treatment: A Special Focus on SARS-CoV-2

Heparan sulfate proteoglycans (HSPGs) encompass a group of glycoproteins composed of unbranched negatively charged heparan sulfate (HS) chains covalently attached to a core protein. The complex HSPG biosynthetic machinery generates an extraordinary structural variety of HS chains that enable them to bind a plethora of ligands, including growth factors, morphogens, cytokines, chemokines, enzymes, matrix proteins, and bacterial and viral pathogens. These interactions translate into key regulatory activity of HSPGs on a wide range of cellular processes such as receptor activation and signaling, cytoskeleton assembly, extracellular matrix remodeling, endocytosis, cell-cell crosstalk, and others. Due to their ubiquitous expression within tissues and their large functional repertoire, HSPGs are involved in many physiopathological processes; thus, they have emerged as valuable targets for the therapy of many human diseases. Among their functions, HSPGs assist many viruses in invading host cells at various steps of their life cycle. Viruses utilize HSPGs for the attachment to the host cell, internalization, intracellular trafficking, egress, and spread. Recently, HSPG involvement in the pathogenesis of SARS-CoV-2 infection has been established. Here, we summarize the current knowledge on the molecular mechanisms underlying HSPG/SARS-CoV-2 interaction and downstream effects, and we provide an overview of the HSPG-based therapeutic strategies that could be used to combat such a fearsome virus.

Low molecular weight heparin promotes transcription and release of placental growth factor from endothelial cells

Circulating levels of placental growth factor (PlGF) are significantly reduced in women who develop preeclampsia. Low molecular weight heparin (LMWH) has been shown to acutely elevate circulating PlGF levels in pregnant women at increased risk of preeclampsia. The objective of the current investigation was to determine the mechanisms by which LMWH mediates the extracellular release of PlGF from endothelial cells. Cultured human aortic endothelial cells (HAECs) and human umbilical vein endothelial cells (HUVECs) were exposed to LMWH; PlGF transcription, translation, mobilization, and secretion were then assessed. LMWH significantly increased the release of PlGF from both HAECs and HUVECs. LMWH treatment promoted a significant increase of PlGF-1 mRNA expression in HAECs, accompanied by the intracellular transport and release of PlGF into the conditioned media. LMWH-mediated release of PlGF from HAECs was not directly mediated by extracellular mobilization, synthesis, or stability of PlGF mRNA/protein. LMWH exposure promotes the release of PlGF from endothelial cells through the upregulation of PlGF-1 mRNA expression. Stimulation of circulating PlGF levels by LMWH may be an important mechanism by which LMWH could reduce the risk of preeclampsia or minimize disease severity.NEW & NOTEWORTHY There are few therapeutic options available for the prevention of preeclampsia, a serious hypertensive disorder of pregnancy. Women who subsequently develop preeclampsia exhibit significantly reduced circulating levels of the proangiogenic placental growth factor protein. Low molecular weight heparin (LMWH) has previously been investigated as a preventative therapy against the development of preeclampsia; however, its mechanism of action is not known. The current study determined that LMWH promotes the transcription and release of placental growth factor protein from endothelial cells, providing a mechanistic basis by which LMWH could reduce the risk of preeclampsia or minimize disease severity.

Impact of bone marrow-derived mesenchymal stem cells on remodeling the lung injury induced by lipopolysaccharides in mice

AIM

This study evaluated the potential of bone marrow derived mesenchymal stem cells (MSCs) to regulate cytokines and remodel the lung induced by lipopolysaccharide (LPS; O-antigen).

MATERIALS & METHODS

A group of mice (n = 21) was inoculated intraperitoneally with one dose 0.1 ml containing 0.025 mg LPS/mouse, and another treated intravenously with one dose of labeling bone marrow derived MSCs at 7.5 × 10⁵ cell/mouse 4 h after LPS injection. All animals were sacrificed on the 1st, 7th and 14th days post-injection.

RESULTS

MSCs increased the level of IL-10 with suppression of TNF-α, decrease of collagen fibers and renewal of alveolar type I cells, together with lung tissue remodeling.

CONCLUSION

MSCs were shown to modulate inflammatory cytokines (TNF-α and IL-10) and to differentiate into alveolar type I cells, which prevented fibrosis in lung tissue from LPS-treated mice.

Heparan Sulfate in the Developing, Healthy, and Injured Lung

Remarkable progress has been achieved in understanding the regulation of gene expression and protein translation, and how aberrancies in these template-driven processes contribute to disease pathogenesis. However, much of cellular physiology is controlled by non-DNA, nonprotein mediators, such as glycans. The focus of this Translational Review is to highlight the importance of a specific glycan polymer-the glycosaminoglycan heparan sulfate (HS)-on lung health and disease. We demonstrate how HS contributes to lung physiology and pathophysiology via its actions as both a structural constituent of the lung parenchyma as well as a regulator of cellular signaling. By highlighting current uncertainties in HS biology, we identify opportunities for future high-impact pulmonary and critical care translational investigations.

Temporal changes in expression of FoxA1 and Wnt7A in isolated adult human alveolar epithelial cells enhanced by heparin

Pre- and postnatal developmental studies of the lung have provided compelling evidence demonstrating multiple factors that orchestrate alveolar epithelial cell differentiation. The extent to which reactivation of certain developmental pathways in the adult might influence the course of differentiation of alveolar type 2 cells (AT2) into AT1 cells is not known. In this study, we examined selected members of the forkhead (Fox) family of transcription factors and the Wnt (wingless) family of signaling proteins for expression during human alveolar cell differentiation in vitro and determined their potential responses to sulfated components of extracellular matrix (ECM), like those shed from cell surfaces or found in basement membrane and modeled by heparin. Isolated adult human AT2 cells cultured over a 9-day period were used to define the temporal profile of expression of targeted factors during spontaneous differentiation to AT1-like cells. FoxA1 protein was upregulated at early to intermediate time points, where it was strongly elevated by heparin. Gene expression of wnt7A increased dramatically beginning on day 3 and was enhanced even further on days 7 and 9 by heparin, whereas protein expression appeared at days 7 and 9. These temporal changes of expression suggest that sulfated ECMs may act to enhance the increase in FoxA1 at the critical juncture when AT2 cells commence the differentiation process to AT1 cells, in addition to enhancing the increase in wnt7A when the AT1 cell phenotype stabilizes. Collectively, these factors may act to modulate differentiation in the adult human pulmonary alveolus.

Bidirectional extracellular matrix signaling during tissue morphogenesis

Normal tissue development and function are regulated by the interplay between cells and their surrounding extracellular matrix (ECM). The ECM provides biochemical and mechanical contextual information that is conveyed from the cell membrane through the cytoskeleton to the nucleus to direct cell phenotype. Cells, in turn, remodel the ECM and thereby sculpt their local microenvironment. Here we review the mechanisms by which cells interact with, respond to, and influence the ECM, with particular emphasis placed on the role of this bidirectional communication during tissue morphogenesis. We also discuss the implications for successful engineering of functional tissues ex vivo.

Primary human coculture model of alveolo-capillary unit to study mechanisms of injury to peripheral lung

In order to delineate individual pathomechanisms in acute lung injury and pulmonary toxicology, we developed a primary coculture system to simulate the human alveolo-capillary barrier. Human pulmonary microvascular endothelial cells (HPMEC) were cocultivated with primary isolated human type II alveolar epithelial cells (HATII) on opposite sides of a permeable filter support, thereby constituting a bilayer. Within 7-11 days of coculture, the HATII cells partly transdifferentiated to type-I-like (HATI-like) cells, as demonstrated by morphological changes from a cuboidal to a flattened morphology, the loss of HATII-cell-specific organelles and the increase of HATI-cell-related markers (caveolin-1, aquaporin-5, receptor for advanced glycation end-products). Immunofluorescent analysis detected type-II-like and type-I-like alveolar epithelial cells mimicking the heterocellular composition of alveolar epithelium in vivo. The heterocellular epithelial monolayer showed a circumferential staining of tight-junctional (ZO-1, occludin) and adherens-junctional (E-cadherin, beta-catenin) proteins. HPMEC on the opposite side also developed tight and adherens junctions (VE-cadherin, beta-catenin). Under integral barrier properties, exposure to the proinflammatory cytokine tumour necrosis factor-alpha from either the endothelial (basolateral) or the epithelial (apical) side caused a largely compartmentalized release of the chemokines interleukin-8 and monocyte chemoattractant protein-1. Thus, the established coculture provides a suitable in vitro model to examine barrier function at the distal lung, including the interaction of microvascular endothelial cells with ATII-like and ATI-like epithelial cells. The compartmentalization of the barrier-forming bilayer also allows mechanisms of lung injury to be studied in both the epithelial (intra-alveolar) and the endothelial (intravascular) compartments.

Fibroblast growth factor-binding protein and N-deacetylase/N-sulfotransferase-1 expression in type II cells is modulated by heparin and extracellular matrix

Fibroblast growth factors (FGFs) play critical roles in development, maintenance, and repair following injury or disease in the lung. Their activity is modulated by a variety of factors, including FGF-binding protein (FGF-BP; HBp-17) and N-deacetylase/N-sulfotransferase-1 (NDST-1). Functionally, FGF-BP shuttles FGFs from binding sites in ECMs to cell surfaces and enhances FGF binding and signaling, whereas NDST-1 adds sulfate groups to FGF coreceptor proteoglycans and modulates alveolar type II (ATII) cell maturation and differentiation. Since the sulfated nature of ECMs is a critical determinant of their relationship with FGFs, we predicted that ECMs and their sulfation would modulate the expression of FGF-BP and NDST-1. To examine this question, selected culture conditions of rat ATII cells were manipulated [with and without coculture with rat lung fibroblasts (RLFs)] by treatment with heparin or sodium chlorate (inhibitor of sulfation) for 24-96 h. In addition, ECMs biosynthesized by RLFs for up to 10 days before coculture were used as model intervening barriers to communication between alveolar cells and fibroblasts. FGF-BP expression was enhanced in ATII cells by coculture with RLF cells and least suppressed by desulfated heparin. NDST-1 expression in ATII cells was most sensitive to the amount of sulfation in medium and ECM and enhanced by fully sulfated heparin. Preformed ECM appears to supply factors that modify subsequent treatment effects. These results demonstrate a potentially important modulatory influence of sulfated ECMs and fibroblasts on FGF-BP and NDST-1 at the gene expression level.