The ErbB4 receptor in fetal rat lung fibroblasts and epithelial type II cells

Uncovering the prominent role of satellite cells in paravertebral muscle development and aging by single-nucleus RNA sequencing

To uncover the role of satellite cells (SCs) in paravertebral muscle development and aging, we constructed a single-nucleus transcriptomic atlas of mouse paravertebral muscle across seven timepoints spanning the embryo (day 16.5) to old (month 24) stages. Eight cell types, including SCs, fast muscle cells, and slow muscle cells, were identified. An energy metabolism-related gene set, TCA CYCLE IN SENESCENCE, was enriched in SCs. Forty-two skeletal muscle disease-related genes were highly expressed in SCs and exhibited similar expression patterns. Among them, Pdha1 was the core gene in the TCA CYCLE IN SENESCENCE; Pgam2, Sod1, and Suclg1 are transcription factors closely associated with skeletal muscle energy metabolism. Transcription factor enrichment analysis of the 42 genes revealed that Myod1 and Mef2a were also highly expressed in SCs, which regulated Pdha1 expression and were associated with skeletal muscle development. These findings hint that energy metabolism may be pivotal in SCs development and aging. Three ligand-receptor pairs of extracellular matrix (ECM)-receptor interactions, Lamc1-Dag1, Lama2-Dag1, and Hspg2-Dag1, may play a vital role in SCs interactions with slow/fast muscle cells and SCs self-renewal. Finally, we built the first database of a skeletal muscle single-cell transcriptome, the Musculoskeletal Cell Atlas (http://www.mskca.tech), which lists 630,040 skeletal muscle cells and provides interactive visualization, a useful resource for revealing skeletal muscle cellular heterogeneity during development and aging. Our study could provide new targets and ideas for developing drugs to inhibit skeletal muscle aging and treat skeletal muscle diseases.

Plasma Level’s of Neuregulin-1 in Healthy People

Aim. To determine the median levels of neuregulin-1 (NRG-1; endothelium-derived growth factor and the natural agonist of the ERBB3 and ERBB4 receptors) NRG-1 in healthy volunteers and to study the associations of NRG-1 levels with gender and age.

Material and Methods. Ninety seven healthy participants were enrolled (median age of 44 [32-54], men 45 men [46.4%]). The following age groups were identified: 20-29 y.о. (n=20, men – 50.0%),  30-39  y.о.  (n=21,  men  –  52.4%),  40-49  y.о.  (n=22,  men  –  45.5%),  50-59  y.о. (n=22, men – 36.4%); 60-69 y.о. (n=12, men – 50.0%). Peripheral blood samples were collected at the time of enrolment, standard laboratory tests were performed, and NRG-1 levels were determined in the plasma samples by ELISA.

Results. In the cohort of 97 healthy participants the median value of NRG-1 was 0.3 [0.121-2.24] ng/ml. NRG-1 levels did not differ significantly between men and women (p=0.145), indicating that NRG-1 levels are not influenced by gender. The levels of NRG-1 were similar in the different age groups: age 20-29 years=0.26 [0.17-0.37] ng/ml; age 30-39=0.24 [0.1-0.39] ng/ml; age 40-49=0.31 [0.19-1.15] ng/ml; age 50-59=0.37  [0.19-1.0] ng/ml; age 60-69=0.4 [0.13-0.81] ng/ml. Correlation analysis between NRG-1 levels and route blood measurements (haemoglobin, lipids, glucose, creatinine, and uretic acid) did not show significant associations.

Conclusions. In this study, the median value of NRG-1 plasma levels were determined. The results of the study show that age and gender had no influence on NRG-1 values.

[Circulating Neuregulin-1 and Chronic Heart Failure with Preserved Ejection]

Chronic heart failure (CHF) with preserved ejection fraction (CHFpEF) is an unsolved, socially relevant challenge since it is associated with a high level of morbidity and mortality. Early markers for this pathology are unavailable, and therapeutic approaches are undeveloped. This necessitates extensive studying the mechanisms of CHFpEF to identify therapeutic targets. According to current notions, systemic inflammation and endothelial dysfunction play an important role in the pathogenesis of CHFpEF. These processes induce the development of myocardial fibrosis and impairment of cardiomyocyte relaxation, thereby resulting in diastolic dysfunction and increased left ventricular (LV) filling pressure. Neuregulin-1 (NRG-1) is a paracrine growth factor and a natural agonist of ErbB receptor family synthesized in the endothelium of coronary microvessels. The NRG-1 / ErbB4 system of the heart is activated at early stages of CHFpEF to enhance the cardiomyocyte resistance to oxidative stress. Preclinical and clinical (phases II and III) studies have shown that the recombinant NRG-1 therapy results in improvement of myocardial contractility and in LV reverse remodeling. Results of recent studies suggest possible anti-inflammatory and antifibrotic effects of NRG-1, which warrants studying the activity of this system in patients with CHFpEF.

Bone marrow stem cells accelerate lung maturation and prevent the LPS-induced delay of morphological and functional fetal lung development in the presence of ErbB4

ErbB4 is a regulator in lung development and disease. Prenatal infection is an important risk factor for the delay of morphologic lung development, while promoting the maturation of the surfactant system. Bone marrow-derived mesenchymal stem cells (BMSCs) have the potential to prevent lung injury. We hypothesized that BMSCs in comparison with hematopoietic control stem cells (HPSCs) minimize the lipopolysaccharide (LPS)-induced lung injury only when functional ErbB4 receptor is present. We injected LPS and/or murine green fluorescent protein-labeled BMSCs or HPSCs into the amniotic cavity of transgenic ErbB4^heart mothers at gestational day 17. Fetal lungs were analyzed 24 h later. BMSCs minimized significantly LPS-induced delay in morphological lung maturation consisting of a stereologically measured increase in mesenchyme and septal thickness and a decrease of future airspace and septal surface. This effect was more prominent and significant in the ErbB4^heart+/- lungs, suggesting that the presence of functioning ErbB4 signaling is required. BMSC also diminished the LPS induced increase in surfactant protein (Sftp)a mRNA and decrease in Sftpc mRNA is only seen if ErbB4 is present. The reduction of morphological delay of lung development and of levels of immune-modulating Sftp was more pronounced in the presence of the ErbB4 receptor. Thus, ErbB4 may be required for the protective signaling of BMSCs.

What is the identity of fibroblast-pneumocyte factor?

Glucocorticoid induction of pulmonary surfactant involves a mesenchyme-derived protein first characterized in 1978 by Smith and termed fibroblast-pneumocyte factor (FPF). Despite a number of agents having been postulated as being FPF, its identity has remained obscure. In the past decade, three strong candidates for FPF have arisen. This review examines the evidence that keratinocyte growth factor (KGF), leptin or neuregulin-1β (NRG-1β) act as FPF or components of it. As with FPF production, glucocorticoids enhance the concentration of each of these agents in fibroblast-conditioned media. Moreover, each stimulates the synthesis of surfactant-associated phospholipids and proteins in type II pneumocytes. Further, some have unique activities, for example, KGF also minimizes lung injury through enhanced epithelial cell proliferation and NRG-1β enhances surfactant phospholipid secretion and β-adrenergic receptor activity in type II cells. However, even though these agents have attributes in common with FPF, it is inappropriate to specify any one of these agents as FPF. Rather, it appears that each contributes to separate mesenchymal-epithelial signaling mechanisms involved in different aspects of lung development. Given that the production of pulmonary surfactant is essential for postnatal survival, it is reasonable to suggest that several mechanisms independently regulate surfactant synthesis.

Interdependent TTF1 - ErbB4 interactions are critical for surfactant protein-B homeostasis in primary mouse lung alveolar type II cells

ErbB4 receptor and thyroid transcription factor (TTF)-1 are important modulators of fetal alveolar type II (ATII) cell development and injury. ErbB4 is an upstream regulator of TTF-1, promoting its expression in MLE-12 cells, an ATII cell line. Both proteins are known to promote surfactant protein-B gene (SftpB) and protein (SP-B) expression, but their feedback interactions on each other are not known. We hypothesized that TTF-1 expression has a feedback effect on ErbB4 expression in an in-vitro model of isolated mouse ATII cells. We tested this hypothesis by analyzing the effects of overexpressing HER4 and Nkx2.1, the genes of ErbB4 and TTF-1 on TTF-1 and ErbB4 protein expression, respectively, as well as SP-B protein expression in primary fetal mouse lung ATII cells. Transient ErbB4 protein overexpression upregulated TTF-1 protein expression in primary fetal ATII cells, similarly to results previously shown in MLE-12 cells. Transient TTF-1 protein overexpression down regulated ErbB4 protein expression in both cell types. TTF-1 protein was upregulated in primary transgenic ErbB4-depleted adult ATII cells, however SP-B protein expression in these adult transgenic ATII cells was not affected by the absence of ErbB4. The observation that TTF-1 is upregulated in fetal ATII cells by ErbB4 overexpression and also in ErbB4-deleted adult ATII cells suggests additional factors interact with ErbB4 to regulate TTF-1 levels. We conclude that the interdependency of TTF-1 and ErbB4 is important for surfactant protein levels. The interactive regulation of ErbB4 and TTF-1 needs further elucidation.

Immunohistochemical localization of epidermal growth factor system in the lung of the Japanese quail (Coturnix coturnix japonica) during the post-hatching period

The purpose of this study is to determine the possible changes in the localization of the four Epidermal Growth Factor Receptors and three ligands in quail lungs from the first day of hatching until the 125th after hatching using immunohistochemical methods. Immunohistochemical results demonstrated that four EGFRs and their ligands are chiefly located in the cytoplasm of cells. Additionally, ErbB4, AREG, and NRG1 are localized to the nucleus and nucleolus, but EGF is present in the nucleolus. ErbB2 was also found in the cell membrane. In the epithelium of secondary bronchi, the goblet cells only exhibited ErbB1 and ErbB2, whereas the basal and ciliated cells exhibited EGFRs and ligands immunoreactivity. The atrial granular cells displayed moderate levels of ErbB1-ErbB3 and EGF and strong levels of ErbB4, AREG, and NRG1 immunoreactivity. While the squamous atrial cells and squamous respiratory cells of air capillaries and endothelial cells of blood capillaries exhibited moderate to strong ErbB2, ErbB4, AREG, and NRG1 immunoreactivity, they had negative or weak ErbB1, ErbB3, and EGF immunoreactivity. The expression levels of ErbB2-ErbB4, EGF, AREG, and NRG1 were also detected in fibroblasts. Although ErbB2 was highly expressed in the bronchial and vascular smooth muscle cells, weak expression of ErbB1, ErbB3, AREG and EGF and moderate expression of ErbB4 and NRG1 were observed. Macrophages were only negative for ErbB1. In conclusion, these data indicate that the EGFR-system is functionally active at hatching, which supports the hypothesis that the members of EGFR-system play several cell-specific roles in quail lung growth after hatching.

Neuregulin-ErbB4 signaling in the developing lung alveolus: a brief review

Lung immaturity is the major cause of morbidity and mortality in premature infants, especially those born <28 weeks gestation. Proper lung development from 23-28 weeks requires coordinated cell proliferation and differentiation. Infants born at this age are at high risk for respiratory distress syndrome (RDS), a lung disease characterized by insufficient surfactant production due to immaturity of the alveoli and its constituent cells in the lung. The ErbB4 receptor and its stimulation by neuregulin (NRG) plays a critical role in surfactant synthesis by alveolar type II epithelial cells. In this review, we first provide an introduction to normal human alveolar development, followed by a discussion of the neuregulin and ErbB4-mediated mechanisms regulating alveolar development and surfactant production.

Role of neuregulin-1β in dexamethasone-enhanced surfactant synthesis in fetal type II cells

It is well established that glucocorticoids elevate the production of fibroblast-pneumocyte factor (FPF), which induces type II cells to synthesize surfactant phospholipids. FPF, however, has not been identified and it is not clear whether it is a single factor or a complex mixture of factors. In this study it has been shown that, when lung fibroblasts are exposed to dexamethasone, the concentration of neuregulin-1β (NRG1β) in conditioned medium is elevated 2-fold (P<0.05), even though NRG1β gene expression is unaffected. This, together with the finding that exposure of type II cells to NRG1β directly stimulates by 3-fold the rate of phospholipid synthesis (P<0.05), suggests that NRG1β is a component of FPF that promotes lung development.

Glucocorticoid metabolism in the developing lung: adrenal-like synthesis pathway

Glucocorticoids (GCs) are essential to normal lung development. They participate in the regulation of important developmental events including morphological changes, and lung maturation leading to the surge of surfactant synthesis by type II epithelial cells. Antenatal GC is administered to mothers at risk of premature delivery to reduce the risk of respiratory distress syndrome (RDS). Sex differences were reported in RDS, in the efficiency of antenatal GC treatment independently of surfactant levels, and in surfactant lipid synthesis. Type II epithelial cell maturation is regulated by epithelial-fibroblast cell-cell communication and involves paracrine factors secreted by fibroblasts under the stimulatory effect of GC. This positive action of GC can be inhibited by androgens through the androgen receptor (AR) present in fibroblasts. In fact, lung development is regulated not only by GC and androgens but also by GC and androgen metabolisms within the developing lung. We recently reviewed the metabolism of androgens in the fetal lung [45]. Here, we review multiple aspects of GC metabolism in the developing lung including inactivation and re-activation by 11β-HSDs, synthesis from the adrenal-like synthesis pathway expressed within the lung and the putative role of CRH and ACTH originating from lung in the regulation of this pathway. This article is part of a Special Issue entitled 'Pregnancy and Steroids'.

Stretch-induced fetal type II cell differentiation is mediated via ErbB1-ErbB4 interactions

Stretch-induced differentiation of lung fetal type II epithelial cells is mediated through EGFR (ErbB1) via release of HB-EGF and TGF-α ligands. Employing an EGFR knock-out mice model, we further investigated the role of the ErbB family of receptors in mechanotranduction during lung development. Deletion of EGFR prevented endogenous and mechanical stretch-induced type II cell differentiation via the ERK pathway, which was rescued by overexpression of a constitutively active MEK. Interestingly, the expression of ErbB4, the only ErbB receptor that EGFR co-precipitates in wild-type cells, was decreased in EGFR-deficient type II cells. Similar to EGFR, ErbB4 was activated by stretch and participated in ERK phosphorylation and type II cell differentiation. However, neuregulin (NRG) or stretch-induced ErbB4 activation were blunted in EGFR-deficient cells and not rescued after ErbB4 overexpression, suggesting that induction of ErbB4 phosphorylation is EGFR-dependent. Finally, we addressed how shedding of ligands is regulated by EGFR. In knock-out cells, TGF-α, a ligand for EGFR, was not released by stretch, while HB-EGF, a ligand for EGFR and ErbB4, was shed by stretch although to a lower magnitude than in normal cells. Release of these ligands was inhibited by blocking EGFR and ERK pathway. In conclusion, our studies show that EGFR and ErbB4 regulate stretch-induced type II cell differentiation via ERK pathway. Interactions between these two receptors are important for mechanical signals in lung fetal type II cells. These studies provide novel insights into the cell signaling mechanisms regulating ErbB family receptors in lung cell differentiation.

Estrogen-induced upregulation of Sftpb requires transcriptional control of neuregulin receptor ErbB4 in mouse lung type II epithelial cells

Estrogen is known for its positive stimulatory effects on surfactant proteins. ErbB4 receptor and its ligand neuregulin (NRG) positively stimulate lung development. ErbB receptors interact with nuclear receptors and ErbB4 co-regulates estrogen receptor (ER)α expression in breast cells. ERβ is highly expressed in pneumocytes and its deletion leads to fewer alveoli and reduced elastic recoil. A similar picture was seen in ErbB4-deleted lungs. We hypothesized that estrogen signals its effect on surfactant protein B (Sftpb) expression through interactions of ERβ and ErbB4. Estrogen and NRG treatment decreased cell numbers and stimulated Sftpb expression in type II cells. Estrogen and NRG both stimulated phosphorylation of ERβ and co-localization of both receptors. Overexpression of ERβ increased the cell number and Sftpb expression, which was further augmented by estrogen and NRG. Finally, estrogen and NRG stimulated ERβ and ErbB4 binding to the Sftpb promoter. Overexpression of these receptors stimulated Sftpb promoter activation, which was further enhanced by estrogen and NRG. The stimulatory effect of estrogen and NRG was abolished in ErbB4 deletion and reconstituted by re-expression of full-length ErbB4 in fetal ErbB4-deleted type II cells. Estrogen-induced nuclear translocation of ErbB4 required the intact γ-secretase cleavage site but not the nuclear localization sequence of the ErbB4 receptor, suggesting that ERβ might function as a nuclear chaperone for ErbB4. These studies demonstrate that estrogen effects on Sftpb expression require an interaction of ERβ and ErbB4. We speculate that the stimulatory effects of estrogen on Sftpb are under transcriptional control of ErbB4.

Lipopolysaccharide-induced injury is more pronounced in fetal transgenic ErbB4-deleted lungs

Pulmonary ErbB4 deletion leads to a delay in fetal lung development, alveolar simplification, and lung function disturbances in adult mice. We generated a model of intrauterine infection in ErbB4 transgenic mice to study the additive effects of antenatal LPS administration and ErbB4 deletion during fetal lung development. Pregnant mice were treated intra-amniotically with an LPS dose of 4 μg at E17 of gestation. Lungs were analyzed 24 h later. A significant influx of inflammatory cells was seen in all LPS-treated lungs. In heterozygote control lungs, LPS treatment resulted in a delay of lung morphogenesis characterized by a significant increase in the fraction of mesenchyme, a decrease in gas exchange area, and disorganization of elastic fibers. Surfactant protein (Sftp)b and Sftpc were upregulated, but mRNA of Sftpb and Sftpc was downregulated compared with non-LPS-treated controls. The mRNA of Sftpa1 and Sftpd was upregulated. In ErbB4-deleted lungs, the LPS effects were more pronounced, resulting in a further delay in morphological development, a more pronounced inflammation in the parenchyma, and a significant higher increase in all Sftp. The effect on Sftpb and Sftpc mRNA was somewhat different, resulting in a significant increase. These results imply a major role of ErbB4 in LPS-induced signaling in structural and functional lung development.

Neuregulin receptor ErbB4 functions as a transcriptional cofactor for the expression of surfactant protein B in the fetal lung

Sufficient pulmonary surfactant production is required for the fetal-neonatal transition, especially in preterm infants. Neuregulin (NRG) and its transmembrane receptor ErbB4 positively regulate the onset of fetal surfactant synthesis. Details of this signaling process remain to be elucidated. ErbB4 is known to regulate gene expression in the mammary gland, where the receptor associates with the signal transducer and activator of transcription Stat5a to transactivate the β-casein gene promoter. We hypothesized that in the fetal lung, ErbB4 functions as a transcriptional regulator for surfactant protein B (Sftpb), the most critical surfactant protein gene. Re-expressing full-length ErbB4 in primary fetal ErbB4-depleted Type II epithelial cells led to an increased expression of Sftpb mRNA. This stimulatory effect required the nuclear translocation of ErbB4 and association with Stat5a, with the resultant binding to and activation of the Sftpb promoter. We conclude that ErbB4 directly regulates important aspects of fetal lung maturation that help prepare for the fetal-neonatal transition.

Presenilin-1 processing of ErbB4 in fetal type II cells is necessary for control of fetal lung maturation

Maturation of pulmonary fetal type II cells to initiate adequate surfactant production is crucial for postnatal respiratory function. Little is known about specific mechanisms of signal transduction controlling type II cell maturation. The ErbB4 receptor and its ligand neuregulin (NRG) are critical for lung development. ErbB4 is cleaved at the cell membrane by the γ-secretase enzyme complex whose active component is either presenilin-1 (PSEN-1) or presenilin-2. ErbB4 cleavage releases the 80kDa intracellular domain (4ICD), which associates with chaperone proteins such as YAP (Yes-associated protein) and translocates to the nucleus to regulate gene expression. We hypothesized that PSEN-1 and YAP have a development-specific expression in fetal type II cells and are important for ErbB4 signaling in surfactant production. In primary fetal mouse E16, E17, and E18 type II cells, PSEN-1 and YAP expression increased at E17 and E18 over E16. Subcellular fractionation showed a strong cytosolic and a weaker membrane location of both PSEN-1 and YAP. This was enhanced by NRG stimulation. Co-immunoprecipitations showed ErbB4 associated separately with PSEN-1 and with YAP. Their association, phosphorylation, and co-localization were induced by NRG. Confocal immunofluorescence and nuclear fractionation confirmed these associations in a time-dependent manner after NRG stimulation. Primary ErbB4-deleted E17 type II cells were transfected with a mutant ErbB4 lacking the γ-secretase binding site. When compared to transfection with wild-type ErbB4, the stimulatory effect of NRG on surfactant protein mRNA expression was lost. We conclude that PSEN-1 and YAP have crucial roles in ErbB4 signal transduction during type II cell maturation.

ErbB4 regulates the timely progression of late fetal lung development

The ErbB4 receptor has an important function in fetal lung maturation. Deletion of ErbB4 leads to alveolar hypoplasia and hyperreactive airways similar to the changes in bronchopulmonary dysplasia (BPD). BPD is a chronic pulmonary disorder affecting premature infants as a consequence of lung immaturity, lung damage, and abnormal repair. We hypothesized that proper ErbB4 function is needed for the timely progression of fetal lung development. An ErbB4 transgenic cardiac rescue mouse model was used to study the effect of ErbB4 deletion on fetal lung structure, surfactant protein (SP) expression, and synthesis, and inflammation. Morphometric analyses revealed a delayed structural development with a significant decrease in saccular size at E18 and more pronounced changes at E17, keeping these lungs in the canalicular stage. SP-B mRNA expression was significantly down regulated at E17 with a subsequent decrease in SP-B protein expression at E18. SP-D protein expression was significantly decreased at E18. Surfactant phospholipid synthesis was significantly decreased on both days, and secretion was down regulated at E18. We conclude that pulmonary ErbB4 deletion results in a structural and functional delay in fetal lung development, indicating a crucial regulatory role of ErbB4 in the timely progression of fetal lung development.

ErbB4 regulates surfactant synthesis and proliferation in adult rat pulmonary epithelial cells

ErbB4 is a predominant heterodimer for other ErbB receptors in late fetal lung development where it participates in regulating type II cell surfactant synthesis. To further elucidate the role of ErbB4 in pulmonary alveolar epithelial cell function, the authors hypothesized that ErbB4 participates in maintaining adult lung type II cell homeostasis. The authors used small interfering RNA (siRNA) to down-regulate endogenous, ErbB4 receptors in the adult rat lung epithelial L2 cell line and measured neuregulin 1beta (NRG1beta)-, and fibroblast conditioned medium (FCM)-induced effects on L2 cell surfactant phospholipid synthesis and proliferation. Under control conditions, total and phosphorylated ErbB4 were significantly increased after both NRG1beta and FCM treatment, as were surfactant phospholipids synthesis and cell proliferation. Down-regulation of ErbB4 with siRNA reduced stimulation of NRG1beta- and FCM-induced ErbB4 phosphorylation, decreased endogenous surfactant phospholipid synthesis, and blocked NRG1beta- and FCM-stimulated surfactant phospholipid synthesis. NRG1beta- and FCM-induced cell proliferation was not affected. The authors conclude that ErbB4 participates in maintaining adult lung alveolar epithelial cell surfactant synthesis and proliferation with development-specific functions.

The ERBB3 receptor in cancer and cancer gene therapy

ERBB3, a member of the epidermal growth factor receptor (EGFR) family, is unique in that its tyrosine kinase domain is functionally defective. It is activated by neuregulins, by other ERBB and nonERBB receptors as well as by other kinases, and by novel mechanisms. Downstream it interacts prominently with the phosphoinositol 3-kinase/AKT survival/mitogenic pathway, but also with GRB, SHC, SRC, ABL, rasGAP, SYK and the transcription regulator EBP1. There are likely important but poorly understood roles for nuclear localization and for secreted isoforms. Studies of ERBB3 expression in primary cancers and of its mechanistic contributions in cultured cells have implicated it, with varying degrees of certainty, with causation or sustenance of cancers of the breast, ovary, prostate, certain brain cells, retina, melanocytes, colon, pancreas, stomach, oral cavity and lung. Recent results link high ERBB3 activity with escape from therapy targeting other ERBBs in lung and breast cancers. Thus a wide and centrally important role for ERBB3 in cancer is becoming increasingly apparent. Several approaches for targeting ERBB3 in cancers have been tested or proposed. Small inhibitory RNA (siRNA) to ERBB3 or AKT is showing promise as a therapeutic approach to treatment of lung adenocarcinoma.