Development. Endothelium--chicken soup for the endoderm

A Bloody Conspiracy. Blood Vessels and Immune Cells in the Tumor Microenvironment

Simple Summary

The tumor microenvironment has risen over the last years as a significant contributor to the failure of antitumoral strategies due to its numerous pro-tumorigenic activities. In this review, we focused on two features of this microenvironment, namely angiogenesis and immunity, which have been the targets of therapies to tackle tumors via its microenvironmental part over the last decade. Increasing our knowledge of the complex interactions within this ecosystem is mandatory to optimize these therapeutic approaches. The development of innovative experimental models is of great help in reaching this goal.

Abstract

Cancer progression occurs in concomitance with a profound remodeling of the cellular microenvironment. Far from being a mere passive event, the re-orchestration of interactions between the various cell types surrounding tumors highly contributes to the progression of the latter. Tumors notably recruit and stimulate the sprouting of new blood vessels through a process called neo-angiogenesis. Beyond helping the tumor cope with an increased metabolic demand associated with rapid growth, this also controls the metastatic dissemination of cancer cells and the infiltration of immune cells in the tumor microenvironment. To decipher this critical interplay for the clinical progression of tumors, the research community has developed several valuable models in the last decades. This review offers an overview of the various instrumental solutions currently available, including microfluidic chips, co-culture models, and the recent rise of organoids. We highlight the advantages of each technique and the specific questions they can address to better understand the tumor immuno-angiogenic ecosystem. Finally, we discuss this development field’s fundamental and applied perspectives.

Ets-1 drives breast cancer cell angiogenic potential and interactions between breast cancer and endothelial cells

Ets-1 transcription factor overexpression in breast cancers is associated with invasive features and is associated with a poor prognosis. Beyond its role in driving carcinoma cell invasion, in this study, we wished to determine whether Ets-1 overexpression in cancer cells promotes angiogenesis by creating a paracrine pro-invasive environment for endothelial cells as well. To address this question, we set up different co-culture models of cancer cells with endothelial cells. Conditioned media from cancer cells induced endothelial cell proliferation, migration and morphogenesis in matrix models. Of note, co-culture assays in three-dimensional matrix models also revealed the reciprocal induction of cancer cell morphogenesis by endothelial cells, in support of an angiocrine action on tumor cells. Ets-1 emerged as a key regulator of the angiogenic potential of breast cancer cells, favoring their ability to induce, in a paracrine manner, the morphogenesis of endothelial cells and also to physically interact with the latter. Nevertheless, Ets-1 overexpression in cancer cells also restrained their chemoattractive potential for endothelial cells both in Boyden chambers and in ex vivo 3D co-cultures. Finally, Ets-1 modulation in breast cancer cells qualitatively altered the angiogenic pattern of experimental in vivo tumors, with a balance between vessel recruitment and intratumoral small capillaries sprouting. Taken together, our data highlight a critical and intriguing role for Ets-1 in the angiogenic potential of breast cancer cells, and reveal another facet of Ets-1 oncogenic activities.

Body Management: Mesenchymal Stem Cells Control the Internal Regenerator

SummaryIt has been assumed that adult tissues cannot regenerate themselves. With the current understanding that every adult tissue has its own intrinsic progenitor or stem cell, it is now clear that almost all tissues have regenerative potential partially related to their innate turnover dynamics. Moreover, it appears that a separate class of local cells originating as perivascular cells appears to provide regulatory oversight for localized tissue regeneration. The management of this regeneration oversight has a profound influence on the use of specific cells for cell therapies as a health care delivery tool set. The multipotent mesenchymal stem cell (MSC), now renamed the medicinal signaling cell, predominantly arises from pericytes released from broken and inflamed blood vessels and appears to function as both an immunomodulatory and a regeneration mediator. MSCs are being tested for their management capabilities to produce therapeutic outcomes in more than 480 clinical trials for a wide range of clinical conditions. Local MSCs function by managing the body's primary repair and regeneration activities. Supplemental MSCs can be provided from either endogenous or exogenous sources of either allogeneic or autologous origin. This MSC-based therapy has the potential to change how health care is delivered. These medicinal cells are capable of sensing their surroundings. Also, by using its complex signaling circuitry, these cells organize site-specific regenerative responses as if these therapeutic cells were well-programmed modern computers. Given these facts, it appears that we are entering a new age of cellular medicine.

SIGNIFICANCE

This report is a perspective from an active scientist and an active entrepreneur and commercial leader. It is neither a comprehensive review nor a narrowly focused treatise. The broad themes and the analogy to the working component of a computer and that of a cell are meant to draw several important scientific principles and health care themes together into the thesis that regenerative medicine is a constant throughout life and its management is the next frontier of health care. Mesenchymal stem cells are used as the central connection in the broad theme, not as multipotent progenitors but rather as an important control element in the natural local regeneration process.

Endothelium-derived essential signals involved in pancreas organogenesis

Endothelial cells (ECs) are essential for pancreas differentiation, endocrine specification, and endocrine function. They are also involved in the physiopathology of type 1 and type 2 diabetes. During embryogenesis, aortic ECs provide specific factors that maintain the expression of key genes for pancreas development such as pancreatic and duodenal homeobox-1. Other unknown factors are also important for pancreatic endocrine specification and formation of insulin-producing beta cells. Endocrine precursors proliferate interspersed with ductal cells and exocrine precursors and, at some point of development, these endocrine precursors migrate to pancreatic mesenchyme and start forming the islets of Langerhans. By the end of the gestation and close to birth, these islets contain immature beta cells with the capacity to express vascular endothelial growth factor and therefore to recruit ECs from the surrounding microenvironment. ECs in turn produce factors that are essential to maintain insulin secretion in pancreatic beta cells. Once assembled, a cross talk between endocrine cells and ECs maintain the integrity of islets toward an adequate function during the whole life of the adult individual. This review will focus in the EC role in the differentiation and maturation of pancreatic beta cells during embryogenesis as well as the current knowledge about the involvement of endothelium to derive pancreatic beta cells in vitro from mouse or human pluripotent stem cells.

Prognostic value and clinical pathology of MACC-1 and c-MET expression in gastric carcinoma

This study was to assess the expression of MACC-1 and c-MET in gastric cancer, and to correlate this expression with clinicohistological parameters and patient prognosis. Total RNA was extracted from cancer tissue and adjacent normal mucosa from frozen biopsy specimens of 30 patients with gastric cancer, and MACC-1 expression was assessed by RT-PCR. MACC-1 and c-MET protein expression were also assessed in paraffin-embedded tissues obtained from 436 tumor mucosa and 92 normal mucosa specimens by immunohistochemistry. The correlation between MACC-1 and c-MET expression and clinicopathological factors (age, sex, histology, tumor depth, lymph node status and vessel invasion) were also evaluated. RT-PCR analysis revealed that MACC-1 expression was significantly higher in cancerous mucosa compared with normal tissue. Immunohistochemical analysis indicated that MACC-1 and c-MET were moderately or strongly expressed in gastric cancer tissue, whereas expression was weak or absent in non-cancer tissue. Expression of MACC-1 or c-MET was significantly associated with larger tumor size, deeper tumor invasion, presence of lymph node metastasis, lymphatic involvement, venous invasion, distant metastasis and advanced clinical stage. However, only MACC-1 exhibited significantly greater expression in carcinomas from the higher age group. The intensity of MACC-1 and c-MET expression was also positively correlated. Survival analysis of the 436 gastric cancer patients revealed that patients in clinical stages I, II and III exhibiting lower MACC-1 and c-MET expression had a higher 5-year survival rate compared with patients expressing high levels of these proteins. Multivariate analysis revealed that MACC-1 and c-MET may be independent prognostic indexes of gastric carcinoma (P < 0.01). Our findings confirm that MACC-1 and c-MET expression is strongly related to gastric cancer stage and degree of malignancy, and is inversely correlated to patient prognosis. Thus, MACC-1 and c-MET may interact to promote tumorigenesis and their expression may be used as independent prognostic markers in gastric cancer.

Paracrine effects of bone marrow soup restore organ function, regeneration, and repair in salivary glands damaged by irradiation

BACKGROUND

There are reports that bone marrow cell (BM) transplants repaired irradiated salivary glands (SGs) and re-established saliva secretion. However, the mechanisms of action behind these reports have not been elucidated.

METHODS

To test if a paracrine mechanism was the main effect behind this reported improvement in salivary organ function, whole BM cells were lysed and its soluble intracellular contents (termed as "BM Soup") injected into mice with irradiation-injured SGs. The hypothesis was that BM Soup would protect salivary cells, increase tissue neovascularization, function, and regeneration. Two minor aims were also tested a) comparing two routes of delivering BM Soup, intravenous (I.V.) versus intra-glandular injections, and b) comparing the age of the BM Soup's donors. The treatment-comparison group consisted of irradiated mice receiving injections of living whole BM cells. Control mice received irradiation and injections of saline or sham-irradiation. All mice were followed for 8 weeks post-irradiation.

RESULTS

BM Soup restored salivary flow rates to normal levels, protected salivary acinar, ductal, myoepithelial, and progenitor cells, increased cell proliferation and blood vessels, and up-regulated expression of tissue remodeling/repair/regenerative genes (MMP2, CyclinD1, BMP7, EGF, NGF). BM Soup was as an efficient therapeutic agent as injections of live BM cells. Both intra-glandular or I.V. injections of BM Soup, and from both young and older mouse donors were as effective in repairing irradiated SGs. The intra-glandular route reduced injection frequency/dosage by four-fold.

CONCLUSION

BM Soup, which contains only the cell by-products, can be advantageously used to repair irradiation-damaged SGs rather than transplanting whole live BM cells which carry the risk of differentiating into unwanted/tumorigenic cell types in SGs.

Expression of interleukin-15 and its receptor on the surface of stimulated human umbilical vein endothelial cells

Human interleukin-15 (hIL-15) is an important cytokine to activate endothelial cells and can be regulated by many other cytokines. The aim of this study is to examine the ability of interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha) to induce the production of human interleukin-15 (hIL-15) and IL-15 receptor (IL-15Ralpha) by human umbilical vein endothelial cells (HUVECs). The data are summarized as follows: 1. Northern blot revealed that IL-15 mRNA was up-regulated by IFN-gamma and TNF-alpha. 2. Intracellular IL-15 protein was visualized by fluorescence microscopy, whereas the expression of IL-15 on the surface of HUVECs was detected by fluorescence activated cell sorting (FACS), and no detectable IL-15 in the medium was verified by ELISA. 3. IL-15Ralpha was detected on the surface of HUVECs by FACS after IFN-gamma and TNF-alpha stimulation, whereas Western blotting revealed that the elevated expression on surface IL-15Ralpha was not due to the increased protein expression. The conclusion demonstrated from our results is that IFN-gamma and TNF-alpha play an important role in regulating the expression of IL-15 and IL-15Ralpha on the surface of HUVECs.

Stem cells to pancreatic beta-cells: new sources for diabetes cell therapy

The number of patients worldwide suffering from the chronic disease diabetes mellitus is growing at an alarming rate. Insulin-secreting beta-cells in the islet of Langerhans are damaged to different extents in diabetic patients, either through an autoimmune reaction present in type 1 diabetic patients or through inherent changes within beta-cells that affect their function in patients suffering from type 2 diabetes. Cell replacement strategies via islet transplantation offer potential therapeutic options for diabetic patients. However, the discrepancy between the limited number of donor islets and the high number of patients who could benefit from such a treatment reflects the dire need for renewable sources of high-quality beta-cells. Human embryonic stem cells (hESCs) are capable of self-renewal and can differentiate into components of all three germ layers, including all pancreatic lineages. The ability to differentiate hESCs into beta-cells highlights a promising strategy to meet the shortage of beta-cells. Here, we review the different approaches that have been used to direct differentiation of hESCs into pancreatic and beta-cells. We will focus on recent progress in the understanding of signaling pathways and transcription factors during embryonic pancreas development and how this knowledge has helped to improve the methodology for high-efficiency beta-cell differentiation in vitro.

Patterning mechanisms of branched organs

Branching morphogenesis is one of the earliest events essential for the success of metazoans. By branching out and forming cellular or tissue extensions, cells can maximize their surface area and overcome space constraints posed by organ size. Over the past decade, tremendous progress has been made toward understanding the branching mechanisms of various invertebrate and vertebrate organ systems. Despite their distinct origins, morphologies and functions, different cell and tissue types use a remarkably conserved set of tools to undergo branching morphogenesis. Recent studies have shed important light on the basis of molecular conservation in the formation of branched structures in diverse organs.

An illustrated review of early pancreas development in the mouse

Pancreas morphogenesis and cell differentiation are highly conserved among vertebrates during fetal development. The pancreas develops through simple budlike structures on the primitive gut tube to a highly branched organ containing many specialized cell types. This review presents an overview of key molecular components and important signaling sources illustrated by an extensive three-dimensional (3D) imaging of the developing mouse pancreas at single cell resolution. The 3D documentation covers the time window between embryonic days 8.5 and 14.5 in which all the pancreatic cell types become specified and therefore includes gene expression patterns of pancreatic endocrine hormones, exocrine gene products, and essential transcription factors. The 3D perspective provides valuable insight into how a complex organ like the pancreas is formed and a perception of ventral and dorsal pancreatic growth that is otherwise difficult to uncover. We further discuss how this global analysis of the developing pancreas confirms and extends previous studies, and we envisage that this type of analysis can be instrumental for evaluating mutant phenotypes in the future.

Endothelium-Mediated Hepatocyte Recruitment in the Establishment of Liver-like TissueIn Vitro

A major goal of liver tissue engineering is to understand how the constituent cell types interact to achieve liver-specific structure and function. Here we show that hepatocytes migrate toward and adhere to endothelial vascular structures formed on Matrigel in vitro, and that hepatocyte recruitment is dependent on endothelium-derived hepatocyte growth factor. The hepatocyte-decorated endothelial vascular structures resemble In vivo sinusoids containing plate-like structures, bile canaliculi, and a lumen. The sinusoid-like structures retained cytochrome P450 expression and activity, in addition to stable albumin expression and secretion rate for over 2 months in vitro. The stability of the sinusoid-like structures was dependent on the presence of vimentin-positive fibroblasts in culture. The sinusoid-like structures formed by hepatocytes and pure populations of endothelial cells collapsed after 10 days in culture. In contrast, culture of hepatocytes with fibroblast-contaminated human dermal microvascular endothelial cells or a combination of human umbilical vein endothelial cells and normal human dermal fibroblasts resulted in stable sinusoid-like structures surrounded by a fibroblastic capsule that maintained liver specific functions for several months in vitro. These results demonstrate that specification of endothelial cell position ultimately determines hepatocyte position in vitro, suggesting that similar interactions might occur In vivo. The novelty of the culture's sinusoid-like organization and long-term function suggest a new model for the study of liver toxicity, ischemia/reperfusion injury, and fibrosis.

Phenotype characterisation using integrated gene transcript, protein and metabolite profiling

Multifactorial diseases present a significant challenge for functional genomics. Owing to their multiple compartmental effects and complex biomolecular activities, such diseases cannot be adequately characterised by changes in single components, nor can pathophysiological changes be understood by observing gene transcripts alone. Instead, a pattern of subtle changes is observed in multifactorial diseases across multiple tissues and organs with complex associations between corresponding gene, protein and metabolite levels. This article presents methods for exploratory and integrative analysis of pathophysiological changes at the biomolecular level. In particular, novel approaches are introduced for the following challenges: (i) data processing and analysis methods for proteomic and metabolomic data obtained by electrospray ionisation (ESI) liquid chromatography-tandem mass spectrometry (LC/MS); (ii) association analysis of integrated gene, protein and metabolite patterns that are most descriptive of pathophysiological changes; and (iii) interpretation of results obtained from association analyses in the context of known biological processes. These novel approaches are illustrated with the apolipoprotein E3-Leiden transgenic mouse model, a commonly used model of atherosclerosis. We seek to gain insight into the early responses of disease onset and progression by determining and identifying--well in advance of pathogenic manifestations of disease--the sets of gene transcripts, proteins and metabolites, along with their putative relationships in the transgenic model and associated wild-type cohort. Our results corroborate previous findings and extend predictions for three processes in atherosclerosis: aberrant lipid metabolism, inflammation, and tissue development and maintenance.

Arachidonic acid predominates in the membrane phosphoglycerides of the early and term human placenta

The aim of this study was to determine whether the high concentration of arachidonic acid (AA) in term placentae accumulates during pregnancy or is an inherent characteristic of placental lipids. We investigated the lipid content and fatty acid composition of the human placental phospholipids at 2 gestational periods, early in pregnancy (8-14 wk, n = 48) and at term (38-41 wk of gestation, n = 19). The subjects were healthy, normotensive, and free of medical and obstetric complications. The lipid concentration of placentae increased from 0.8% in early gestation to 1.4% at term (P < 0.0001). The mean proportions of AA were lower in the choline (P < 0.05), inositol (P < 0.0001), and ethanolamine (P < 0.0001) phosphoglycerides of the term compared with the early placenta. In contrast, the proportions of the immediate precursor of AA, dihomo-gamma-linolenic acid (DGLA), were higher in the term placenta, particularly in the inositol and serine phosphoglycerides (P < 0.0001). In sphingomyelin, the percentage of lignoceric acid was increased and that of nervonic acid was reduced at term (P < 0.01). The dominance of AA, particularly in the early placenta, suggests that it has an important role for placental development, i.e., organogenesis and vascularization. There was no evidence of an accumulation of AA in the placenta toward term, which might be a trigger for parturition. In contrast, the increased proportion of DGLA (precursor of the vasorelaxant and anticoagulant prostaglandin E(1)) at term is more consistent with a profile favoring optimal blood flow to nourish the fetal growth spurt.

Autocrine and paracrine functions of vascular endothelial growth factor (VEGF) in renal tubular epithelial cells

BACKGROUND

VEGF secreted by organ parenchymal cells controls vascularization by recruiting endothelial cells and supporting their proliferation. In the developing kidney VEGF-expressing epithelial cells also express VEGF receptors. We showed that VEGF stimulates tubulogenesis in addition to promoting vascularization in metanephric explants. Since explants are grown in serum-free media and are not perfused, we hypothesized that VEGF secreted by renal epithelia may induce their proliferation in an autocrine manner and chemoattract endothelial cells.

METHODS

To test these hypotheses, we analyzed VEGF-mediated responses in vitro using several renal epithelial cell lines [immortalized rat proximal tubular cells (IRPT), transformed mouse proximal tubular cells (tsMPT), and normal rat kidney cells (NRK-52E)] expressing VEGF receptors (VEGFR).

RESULTS

We demonstrated that VEGFR-2 phosphorylates upon human recombinant VEGF (rhVEGF) exposure, indicating that VEGFR-2 is the signaling receptor. All three cell lines secreted VEGF into the media as indicated by enzyme-linked immunosorbent assay (ELISA) and Western blotting. We showed that these tubular epithelial cells chemoattract endothelial cells when cocultured in vitro and that the chemoattraction is abolished by anti-VEGF neutralizing antibody. rhVEGF (10 ng/mL) induced a mitogenic effect similar to 10% fetal bovine serum (FBS) as assessed by H(3)-thymidine incorporation and elicited 30% decrease in apoptosis as determined by annexin V-fluorescein isothiocyanate (FITC) staining.

CONCLUSION

These in vitro studies indicate that (1) tubular epithelial cells chemoattract endothelial cells in a paracrine fashion by secreting VEGF, and (2) VEGF stimulates proliferation and promotes survival of renal epithelial cells in an autocrine manner via VEGFR-2. Taken together, our results suggest that VEGF supports the growth of renal epithelia in addition to mediating kidney vascularization.

Angiopoietin-1 causes reversible degradation of the portal microcirculation in mice: implications for treatment of liver disease

In many different liver diseases, such as cirrhosis, degradation of the microcirculation, including obliteration of small portal or hepatic veins contributes to disease-associated portal hypertension. The present study demonstrates the importance of angiogenesis in the establishment of arteriovenous shunts and the accompanying changes to the venous bed. One aspect of angiogenesis involves the branching of new vessels from pre-existing ones, and the molecular mechanisms controlling it are complex and involve a coordinated effort between specific endothelial growth factors and their receptors, including the angiopoietins. We modulated the hepatic vasculature in mice by conditionally expressing angiopoietin-1 in hepatocytes. In mice exposed to angiopoietin-1 during development, arterial sprouting, enlarged arteries, marked loss of portal vein radicles, hepatic vein dilation, and suggestion of arteriovenous shunting were observed. Most importantly, these phenotypic changes were completely reversed within 14 days of turning off transgene expression. Expression of excess angiopoietin-1 beginning in adulthood did not fully recapitulate the phenotype, but did result in enlarged vessels. Our findings suggest that controlling excessive angiogenesis during liver disease may promote the restoration of the portal vein circuit and aid in the resolution of disease-associated portal hypertension.

Ductuloinsular tumors of the pancreas: endocrine tumors with entrapped nonneoplastic ductules

Rare pancreatic neoplasms have been reported that show both endocrine and exocrine differentiation in the neoplastic components. In addition, pancreatic endocrine tumors may contain small, cytologically bland ductules intimately admixed with the endocrine component. It was recently suggested that these ductules represent an intrinsic part of the tumor, ie, that the ductules are neoplastic, and the term "ductulo-insular tumors of the pancreas" was proposed. In the present study, the nature of the ductular component of 16 cases of ductule-containing pancreatic endocrine tumors was investigated at the molecular level. Molecular genetic changes often present in ductal pancreatic neoplasms were not found by immunohistochemistry for DPC4, p53, and ERBB2 and by sequence analysis of KRAS codon 12. An X-chromosome inactivation clonality assay of one such tumor from a female patient indicated that the neuroendocrine component was monoclonal, contrasting with the ductular component that was polyclonal. The lymph node and liver metastases from three patients only contained the neuroendocrine component, and no ductules were observed. Although certain morphologic features of ductule-containing endocrine tumors are reminiscent of the embryonic development of the human pancreas, none of the tumors expressed PDX-1, a transcription factor essential in pancreatic organ development. Based on our results, it is suggested that the ductular component occasionally found in pancreatic endocrine tumors is the result of entrapment of preexisting nonneoplastic ductules and that the tumors are otherwise not distinctive from conventional pancreatic endocrine tumors. Although the phenomenon is rare, it is important to recognize and to distinguish these tumors from true mixed ductal-endocrine neoplasms, which are generally more clinically aggressive. "Pancreatic endocrine tumors with entrapped ductules" would be the preferred nomenclature since it better reflects the nonneoplastic nature of the ductules.

Mécanotransduction des forces hémodynamiques et organogenèse

Endothelial cells (EC) of the vertebrate cardiovascular system (CVS) are bona fide, yet enigmatic mechanoreceptors. When cultured in vitro and exposed to fluid forces, EC modify their physiological behaviour at the structural, metabolical and gene expression levels in response to the mechanical stimulus. However, as a direct consequence of the hypoxic bias (and often the lethality) that results from blocking blood flow in most animal systems, the in vivo role of EC mechanosensation (ECMS) remains poorly understood. The zebrafish has recently emerged as an alternative genetic model for the study of vertebrate development. Its striking ability to survive until larval stages in the absence of blood circulation circumveys the usual caveats that are inherent to CVS research, and offers the exciting opportunity to dissect the function of ECMS in vivo. Two groups have already uncovered an essential role for ECMS in zebrafish organogenesis, particularly in heart morphogenesis. In embryos in which intracardiac blood flow is genetically or physically compromised, several features of the normally developing heart, including valve formation, are specifically disrupted. In addition, impressive imaging studies of zebrafish hemodynamics demonstrate that the shear stress exerted upon the cardiac endothelium is largely in the range of the stimulus that in vitro activates cytoskelettal remodeling and gene expression changes in EC. Hence the cardiac phenotypes observed in vivo may indeed directly result from a lack of ECMS-dependent EC activity. These data shed first light on the role of ECMS in vivo. Notably, they also suggest that a number of human congenital cardiomyopathies may arise through abnormal fetal hemodynamics and/or EC sensory activity. Finally, these discoveries reinforce the too often neglected role of epigenetic factors (in this case, fluid forces) in the regulation of animal development.

Lung microvascular adaptation in infants with chronic lung disease

Microvascular development is critical for normal lung maturation. The aims of this study were (1) to quantitatively and qualitatively assess lung microvascular growth in the human fetus, from 22 to 40 weeks' gestation, and (2) to compare development in these infants to those with mild, moderate and severe chronic lung disease (CLD). Using 1- and 4-microm thick sections and electron microscopy, lungs were morphometrically assessed for surface density of distal air spaces; volume density of parenchymal vessels having an air-blood barrier (ABB); percent of distal air space wall having an ABB, and capillary loading, defined as ABB/mm2 of epithelial surface area. The percent of vessels with ABB increased in controls during development in parallel with increasing lung parenchyma. Infants with severe CLD had fewer ABBs and less capillary loading than controls up to 34 weeks' post-conceptional age (PCA), but by 36-40 weeks, showed catch-up growth. Microvasculature vessel diameter, septal thickness, and air sac diameter at 36-40 weeks' PCA were increased with severe CLD, and vessels were more distant from the air surface. We conclude that infants with severe CLD have both stunted secondary septation and microvascular development, but over time, the primary septal wall adapts by thinning and increasing the number of ABBs, thereby taking on the function of secondary septa.

Blood vessels and nerves: common signals, pathways and diseases

Both blood vessels and nerves are vital channels to and from tissues. Recent genetic insights show that they have much more in common than was originally anticipated. They use similar signals and principles to differentiate, grow and navigate towards their targets. Moreover, the vascular and nervous systems cross-talk and, when dysregulated, this contributes to medically important diseases. The realization that both systems use common genetic pathways should not only form links between vascular biology and neuroscience, but also promises to accelerate the discovery of new mechanistic insights and therapeutic opportunities.

Toward a theory of intracrine hormone action

A growing body of evidence indicates that in some cases, peptide hormones can function in the intracellular space. These findings are reviewed. In addition, this laboratory has made proposals regarding the origin, nature and function of intracrines--that is, intracellularly acting peptide hormones that also function in an autocrine, paracrine or endocrine manner. Here, these hypotheses are developed, and potential implications/applications of this point of view are discussed. Possible implications for cellular differentiation, cellular memory and hormonal responsiveness, as well as for the assumption of novel functions by intracellular regulatory proteins are discussed.

Visualization of lymphotoxin-beta and lymphotoxin-beta receptor expression in mouse embryos

The heteromeric lymphotoxin alphabeta ligand (LT) binds to the LTbeta receptor (LTbetaR) and provides an essential trigger for lymph node (LN) development. LTbetaR signaling is also critical for the emergence of pathological ectopic lymph node-like structures and the maintenance of an organized splenic white pulp. To better understand the role of LT in development, the expression patterns of LTbeta and LTbetaR mRNA were examined by in situ hybridization in the developing mouse embryo. Images of LTbeta ligand expression in developing peripheral LN in the E18.5 embryo revealed a relatively early phase structure and allowed for comparative staging with LN development in rat and humans. The LTbetaR is expressed from E16.5 onward in respiratory, salivary, bronchial, and gastric epithelium, which may be consistent with early communication events between lymphoid elements and epithelial specialization over emerging mucosal LN. Direct comparison of mouse fetal and adult tissues by FACS analysis confirmed the elevated expression of LTBR in some embryonic epithelial layers. Therefore, surface LTBR expression may be elevated during fetal development in some epithelial layers.

Stromal effects on mammary gland development and breast cancer

Breast cancer manifests itself in the mammary epithelium, yet there is a growing recognition that mammary stromal cells also play an important role in tumorigenesis. During its developmental cycle, the mammary gland displays many of the properties associated with breast cancer, and many of the stromal factors necessary for mammary development also promote or protect against breast cancer. Here we review our present knowledge of the specific factors and cell types that contribute to epithelial-stromal crosstalk during mammary development. To find cures for diseases like breast cancer that rely on epithelial-stromal crosstalk, we must understand how these different cell types communicate with each other.