Hepatocyte growth factor inhibits the formation of the basement membrane of alveolar epithelial cells in vitro

The influence of PM2.5 on lung injury and cytokines in mice

Exposure to particulate matter ≤2.5 µm in diameter (PM_2.5) profoundly affects human health. However, the role of PM_2.5 on lung injury and cytokine levels in mice is currently unknown. The aim was to examine the effect of PM_2.5 pollution on lung injury in mice fed at an underground parking lot. A total of 20 female Kunming mice were randomly divided into control and polluted groups, with 10 rats in each group. The control group was kept in the laboratory, while the pollution group was fed in an underground parking lot. The concentrations of pollutants were measured using ambient air quality monitoring instruments. After 3 months of treatment, the lungs were collected and examined using electron microscopy, and the morphological structures were assessed using hematoxylin and eosin staining. The polarization of macrophages was evaluated by immunofluorescence. The concentration of interleukin (IL)-4, tumor necrosis factor (TNF)-α and transforming growth factor (TGF)-β1 in peripheral sera were assessed by ELISA. The mRNA and protein levels of IL-4, TNF-α, and TGF-β1 in lung tissues were assessed by reverse transcription-quantitative polymerase chain reaction and western blot analyses, respectively. In the polluted group, the levels of CO, NO_x and PM_2.5 were significantly higher compared with the control group. Compared with the controls, intracellular edema, an increased number of microvilli and lamellar bodies, smaller lamellar bodies in type II alveolar epithelial cells, and abundant particles induced by PM_2.5 in macrophages were observed in the polluted group. The lung ultrastructure changed in the polluted group, revealing exhaust-induced lung injury: The tissues were damaged, and the number of inflammatory cells, neutrophils, polylymphocytes and eosinophils increased in the polluted group compared with the control group. The authors also observed that the number of M1 and M2 macrophages markedly increased after the exhaust treatment. The levels of IL-4, TNF-α and TGF-β1 in the sera and tissues were significantly increased in the polluted group. PM_2.5 pollutants in underground garages can lead to lung injury and have a significant impact on the level of inflammatory cytokines in mice. Therefore, the authors suggest that PM_2.5 can activate the inflammatory reaction and induce immune dysfunction, leading to ultrastructural damage.

Lung fibroblasts accelerate wound closure in human alveolar epithelial cells through hepatocyte growth factor/c-Met signaling

There are 190,600 cases of acute lung injury/acute respiratory distress syndrome (ALI/ARDS) each year in the United States, and the incidence and mortality of ALI/ARDS increase dramatically with age. Patients with ALI/ARDS have alveolar epithelial injury, which may be worsened by high-pressure mechanical ventilation. Alveolar type II (ATII) cells are the progenitor cells for the alveolar epithelium and are required to reestablish the alveolar epithelium during the recovery process from ALI/ARDS. Lung fibroblasts (FBs) migrate and proliferate early after lung injury and likely are an important source of growth factors for epithelial repair. However, how lung FBs affect epithelial wound healing in the human adult lung has not been investigated in detail. Hepatocyte growth factor (HGF) is known to be released mainly from FBs and to stimulate both migration and proliferation of primary rat ATII cells. HGF is also increased in lung tissue, bronchoalveolar lavage fluid, and serum in patients with ALI/ARDS. Therefore, we hypothesized that HGF secreted by FBs would enhance wound closure in alveolar epithelial cells (AECs). Wound closure was measured using a scratch wound-healing assay in primary human AEC monolayers and in a coculture system with FBs. We found that wound closure was accelerated by FBs mainly through HGF/c-Met signaling. HGF also restored impaired wound healing in AECs from the elderly subjects and after exposure to cyclic stretch. We conclude that HGF is the critical factor released from FBs to close wounds in human AEC monolayers and suggest that HGF is a potential strategy for hastening alveolar repair in patients with ALI/ARDS.

Therapeutic potential of growth factors in pulmonary emphysematous condition

Pulmonary emphysema is a major manifestation of chronic obstructive pulmonary disease (COPD), which is characterized by progressive destruction of alveolar parenchyma with persistent inflammation of the small airways. Such destruction in the distal respiratory tract is irreversible and irreparable. All-trans-retinoic acid was suggested as a novel therapy for regeneration of lost alveoli in emphysema. However, profound discrepancies were evident between studies. At present, no effective therapeutic options are available that allow for the regeneration of lost alveoli in emphysematous human lungs. Recently, some reports on rodent's models have suggested the beneficial effects of various growth factors toward alveolar maintenance and repair processes.

Cell-specific expression of human HGF by alveolar type II cells induces remodeling of septal wall tissue in the lung: a morphometric study

Hepatocyte growth factor (HGF) is involved in development and regeneration of the lungs. Human HGF, which was expressed specifically by alveolar epithelial type II cells after gene transfer, attenuated the bleomycin-induced pulmonary fibrosis in an animal model. As there are also regions that appear morphologically unaffected in fibrosis, the effects of this gene transfer to normal lungs is of interest. In vitro studies showed that HGF inhibits the formation of the basal lamina by cultured alveolar epithelial cells. Thus we hypothesized that, in the healthy lung, cell-specific expression of HGF induces a remodeling within septal walls. Electroporation of a plasmid of human HGF gene controlled by the surfactant protein C promoter was applied for targeted gene transfer. Using design-based stereology at light and electron microscopic level, structural alterations were analyzed and compared with a control group. HGF gene transfer increased the volume of distal air spaces, as well as the surface area of the alveolar epithelium. The volume of septal walls, as well as the number of alveoli, was unchanged. Volumes per lung of collagen and elastic fibers were unaltered, but a marked reduction of the volume of residual extracellular matrix (all components other than collagen and elastic fibers) and interstitial cells was found. A correlation between the volumes of residual extracellular matrix and distal air spaces, as well as total surface area of alveolar epithelium, could be established. Cell-specific expression of HGF leads to a remodeling of the connective tissue within the septal walls in the healthy lung, which is associated with more pronounced stretching of distal air spaces at a given hydrostatic pressure during instillation fixation.

The impact of compositional topography of amniotic membrane scaffold on tissue morphogenesis of salivary gland

Amniotic membrane (AM) has been widely used in the reconstruction of oral epithelial defects. However, whether it is also effective in facilitating tissue formation of salivary gland, an appendix of oral epithelia, has never been explored. To investigate the effects and the underlying mechanism of AM on salivary gland morphogenesis, murine fetal submandibular gland (SMG) explants were cultured on different preparations of AM scaffolds. It was found that, on AM stromal scaffold, SMG demonstrated well-developed branching morphogenesis. Nonetheless, on AM epithelial scaffold, SMG epithelial cell converted to a spindle-shape, lost intercellular connection, changed cytoskeletal organization, and exhibited scattering behaviors. Meanwhile, the integrity of SMG basement membrane was dismantled as well. However, when acellular AM epithelial scaffold was used, cultured SMG demonstrated organized morphology, indicating that AM epithelial component provided specific surface features for SMG morphogenesis. To further investigate AM scaffold morphogenetic effect, it was found hepatocyte growth factor (HGF), an epithelial scattering factor, was expressed abundantly in cultivated AM epithelia. After blocking HGF function of AM, cultured SMG regained branching activity, reorganized cell adhesion and subcellular organization, and reproduced basement membranes. Therefore, AM-derived bioactive factor profoundly influences cell behaviors and structure formation of SMG. Together, this study showed that compositional topography of AM scaffold is important in affecting SMG morphogenesis. By understanding the effects of AM scaffold on SMG morphogenesis, it provides important information for rationally designing and fabricating AM scaffold for salivary gland regeneration.

Epithelial repair mechanisms in the lung

The recovery of an intact epithelium following lung injury is critical for restoration of lung homeostasis. The initial processes following injury include an acute inflammatory response, recruitment of immune cells, and epithelial cell spreading and migration upon an autologously secreted provisional matrix. Injury causes the release of factors that contribute to repair mechanisms including members of the epidermal growth factor and fibroblast growth factor families (TGF-alpha, KGF, HGF), chemokines (MCP-1), interleukins (IL-1beta, IL-2, IL-4, IL-13), and prostaglandins (PGE(2)), for example. These factors coordinate processes involving integrins, matrix materials (fibronectin, collagen, laminin), matrix metalloproteinases (MMP-1, MMP-7, MMP-9), focal adhesions, and cytoskeletal structures to promote cell spreading and migration. Several key signaling pathways are important in regulating these processes, including sonic hedgehog, Rho GTPases, MAP kinase pathways, STAT3, and Wnt. Changes in mechanical forces may also affect these pathways. Both localized and distal progenitor stem cells are recruited into the injured area, and proliferation and phenotypic differentiation of these cells leads to recovery of epithelial function. Persistent injury may contribute to the pathology of diseases such as asthma, chronic obstructive pulmonary disease, and pulmonary fibrosis. For example, dysregulated repair processes involving TGF-beta and epithelial-mesenchymal transition may lead to fibrosis. This review focuses on the processes of epithelial restitution, the localization and role of epithelial progenitor stem cells, the initiating factors involved in repair, and the signaling pathways involved in these processes.

Hepatocytes maintain their function on basement membrane formed by epithelial cells

To establish liver tissue engineering, the effective substratum for hepatocytes culture should be developed. Up to now, it is believed that Matrigel, which contains several basement membrane proteins produced by sarcoma cells, is the most effective substratum. Matrigel does not contain extracellular matrix molecules derived from epithelial cells although the space of Disse contains the molecules such as laminin-511/521 (laminin-10/11). Therefore, the basement membrane formed by epithelial cells can be more effective substratum than Matrigel. In this study, we evaluated hepatocytes behavior on basement membrane (rBM) formed by alveolar epithelial cells. The viability of hepatocytes on rBM is higher than that of Matrigel within 5 days. Also, the expression of Cyp1a2 induced by beta-naphthoflavone can be observed in hepatocytes on rBM but not in Matrigel. These results indicate that rBM is a more effective substratum for hepatocyte culture than Matrigel.

Differentiation of tracheal basal cells to ciliated cells and tissue reconstruction on the synthesized basement membrane substratum in vitro

Although lung epithelial cells directly attach to the basement membrane underneath in vivo, harvested epithelial cells are typically cultured on type I collagen gel (Col I-gel) in vitro. Recently we developed new culture substratum, designated as "synthesized Basement Membrane" (sBM), that has bared lamina densa on fibrillar collagen. To validate the usefulness of sBM substratum in airway tissue reconstitution in vitro, we cultured rat tracheal epithelial cells on sBM substratum and Col I-gel. When starting the air-liquid interface culture, most of the epithelial cells were squamous and positive for the basal cell marker cytokeratin 14 (CK14). After 14 days on sBM substratum, CK14-positive cells differentiated not only to Clara and mucous cells, but also to ciliated cells. Those differentiated cells formed pseudostratified-like epithelium and the remaining CK14-positive cells were polarized to the basal side. However, on Col I-gel, the CK14-positive cells were still squamous and not polarized, and ciliated cells did not appear. In conclusion, we established a new culture model on sBM substratum in which basal cells could differentiate to ciliated cells. The application of sBM substratum is useful in the study of the airway epithelial cell differentiation in vitro.

Regulation of epithelial cell growth factor receptor protein and gene expression using a rat periodontitis model

BACKGROUND AND OBJECTIVE

Regulation of epithelial cell behavior associated with periodontitis is not well elucidated but many responses will ultimately be regulated by growth factor receptors. Using a rat experimental periodontitis model, protein and gene expression of select growth factor receptors in junctional and pocket epithelium were examined.

MATERIAL AND METHODS

Periodontal disease was induced by daily topical application of lipopolysaccharide using an established protocol. Animals were killed at time 0 (control), and at 2 and 8 wk. Frozen tissue samples were collected from the right palatal gingival soft tissue, and the left periodontal tissues were decalcified and embedded in paraffin. Laser microdissection and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was used to quantify keratinocyte growth factor receptor (KGFR), hepatocyte growth factor receptor (HGFR), epidermal growth factor receptor (EGFR) and fibroblast growth factor receptor 1 (FGFR1) gene expression, and in situ RT-PCR localized these increases to specific epithelial cells. Receptor protein expression was examined immunohistochemically. In cell culture, induction of HGFR and KGFR protein expression by serum, lipopolysaccharide and pro-inflammatory cytokines were examined using flow cytometry.

RESULTS

Eight-week tissue samples exhibited histological changes consistent with periodontitis. KGFR and HGFR gene and protein expression were significantly induced at the 8 wk time point. KGFR expression was significantly up-regulated in basal and parabasal pocket epithelial cells, but HGFR was up-regulated throughout the pocket epithelium. In cell culture serum, lipopolysaccharide and pro-inflammatory cytokines, interleukin-1beta and tumour necrosis factor-alpha significantly induced KGFR protein receptor expression, but HGFR expression was only induced by serum.

CONCLUSION

KGFR and HGFR are highly up-regulated in this model of periodontal disease and may play a significant role in regulating the proliferation and migration of pocket epithelium.

Defect of hepatocyte growth factor production by fibroblasts in human pulmonary emphysema

Pulmonary emphysema results from an excessive degradation of lung parenchyma associated with a failure of alveolar repair. Secretion by pulmonary fibroblasts of hepatocyte growth factor (HGF) and keratinocyte growth factor (KGF) is crucial to an effective epithelial repair after lung injury. We hypothesized that abnormal HGF or KGF secretion by pulmonary fibroblasts could play a role in the development of emphysema. We measured in vitro production of HGF and KGF by human fibroblasts cultured from emphysematous and normal lung samples. HGF and KGF production was quantified at basal state and after stimulation. Intracellular content of HGF was lower in emphysema (1.52 pg/μg, range of 0.15–7.40 pg/μg) than in control fibroblasts (14.16 pg/μg, range of 2.50–47.62 pg/μg; P = 0.047). HGF production by emphysema fibroblasts (19.3 pg/μg protein, range of 10.4–39.2 pg/μg) was lower than that of controls at baseline (57.5 pg/μg, range of 20.4–116 pg/μg; P = 0.019) and after stimulation with interleukin-1β or prostaglandin E2. Neither retinoic acids (all- trans and 9- cis) nor N-acetylcysteine could reverse this abnormality. KGF production by emphysema fibroblasts (5.3 pg/μg, range of 2.2–9.3 pg/μg) was similar to that of controls at baseline (2.6 pg/μg, range of 1–6.1 pg/μg; P = 0.14) but could not be stimulated with interleukin-1β. A decreased secretion of HGF by pulmonary fibroblasts could contribute to the insufficient alveolar repair in pulmonary emphysema.