Nutrient regulation of tumor and vascular endothelial cell proliferation

Specific bioactive dietary components, such as the steroid receptor superfamily ligands vitamins A and D, have been studied extensively as potential cancer preventive and therapeutic agents due to their ability to regulate key processes in a variety of cell types which are dysregulated in neoplastic transformation namely, proliferation and differentiation. Alteration of one or more factors that regulate cell cycle control has been described as a predisposing event for early tumor development. In addition to tumor cell proliferation, the viability, growth and metastasis of solid tumors are also dependent on the vascularization of the tumor and establishment of blood flow. Both vitamins A and D exhibit anti-angiogenic properties which further strengthen their role as potential targets for the prevention and treatment of cancer. This review focuses on the role of vitamins A and D in preventing early tumor initiation and progression via control of the cell cycle in both tumor and vascular endothelial cells.

Hematopoietic, vascular and cardiac fates of bone marrow-derived stem cells

Bone marrow contains many cell types, including stroma, vascular cells, adipocytes, osteoblasts and osteoclasts, as well as mesenchymal stem cells and hematopoietic stem cells. It was previously thought that cells within bone marrow solely functioned to regenerate cells within the marrow, as well as all circulating hematopoietic cells in peripheral blood. Recent reports, however, suggest that marrow-derived cells can also regenerate other cell types, including cardiac muscle, liver cell types, neuronal and non-neuronal cell types of the brain, as well as endothelial cells and osteoblasts. These multiple cell types could have originated from either of the stem cell populations within bone marrow or potentially other precursors. Therefore, it is not entirely clear whether each of these distinct cell lineages has a true progenitor within marrow or whether the marrow contains a multipotent population of cells that has been set aside during embryogenesis for postnatal repair and remodeling of a variety of tissues. It is clear, however, that directing the fate of bone marrow-derived progenitors (ie toward hematopoietic, vascular or cardiac cell fates) can only be accomplished if the phenotype of the stem cells is defined, and their homing and differentiation programs are elucidated. Much work is focused on these issues, wherein lie the key to harnessing the potential of adult stem cells for autologous cell and gene therapy.

Regeneration of ischemic cardiac muscle and vascular endothelium by adult stem cells

Myocyte loss in the ischemically injured mammalian heart often leads to irreversible deficits in cardiac function. To identify a source of stem cells capable of restoring damaged cardiac tissue, we transplanted highly enriched hematopoietic stem cells, the so-called side population (SP) cells, into lethally irradiated mice subsequently rendered ischemic by coronary artery occlusion for 60 minutes followed by reperfusion. The engrafted SP cells (CD34(-)/low, c-Kit(+), Sca-1(+)) or their progeny migrated into ischemic cardiac muscle and blood vessels, differentiated to cardiomyocytes and endothelial cells, and contributed to the formation of functional tissue. SP cells were purified from Rosa26 transgenic mice, which express lacZ widely. Donor-derived cardiomyocytes were found primarily in the peri-infarct region at a prevalence of around 0.02% and were identified by expression of lacZ and alpha-actinin, and lack of expression of CD45. Donor-derived endothelial cells were identified by expression of lacZ and Flt-1, an endothelial marker shown to be absent on SP cells. Endothelial engraftment was found at a prevalence of around 3.3%, primarily in small vessels adjacent to the infarct. Our results demonstrate the cardiomyogenic potential of hematopoietic stem cells and suggest a therapeutic strategy that eventually could benefit patients with myocardial infarction.

Stem cell plasticity in muscle and bone marrow

Recent discoveries have demonstrated the extraordinary plasticity of tissue-derived stem cells, raising fundamental questions about cell lineage relationships and suggesting the potential for novel cell-based therapies. We have examined this phenomenon in a potential reciprocal relationship between stem cells derived from the skeletal muscle and from the bone marrow. We have discovered that cells derived from the skeletal muscle of adult mice contain a remarkable capacity for hematopoietic differentiation. Cells prepared from muscle by enzymatic digestion and 5 day in vitro culture were harvested and introduced into each of six lethally irradiated recipients together with distinguishable whole bone marrow cells. Six and twelve weeks later, all recipients showed high-level engraftment of muscle-derived cells representing all major adult blood lineages. The mean total contribution of muscle cell progeny to peripheral blood was 56%, indicating that the cultured muscle cells generated approximately 10- to 14-fold more hematopoietic activity than whole bone marrow. Although the identity of the muscle-derived hematopoietic stem cells is still unknown, they may be identical to muscle satellite cells, some of which lack myogenic regulators and could respond to hematopoietic signals. We have also found that stem cells in the bone marrow can contribute to cardiac muscle repair and neovascularization after ischemic injury. We transplanted highly purified bone marrow stem cells into lethally irradiated mice that subsequently were rendered ischemic by coronary artery occlusion and reperfusion. The engrafted stem cells or their progeny differentiated into cardiomyocytes and endothelial cells and contributed to the formation of functional tissue.

Molecular approaches to studying nutrient metabolism and function: an array of possibilities

Genomics promises to revolutionize the study of nutrient function and requirements and, thereby, solidify the connection of this field to basic sciences, such as molecular genetics. In this short review, we address the general concepts and techniques used in high throughput measurements of gene expression. We also speculate on how these technologies can be used to further our understanding of basic metabolism and nutrient regulation of gene expression in developmental and pathological conditions.

Morphologic and mechanical characteristics of engineered bovine arteries

OBJECTIVE

The ideal small-caliber arterial graft remains elusive despite several decades of intense research. A novel approach to the development of small-caliber arterial prostheses with a biomimetic system for in vitro vessel culture has recently been described. In this study we examined the effects of culture time and tissue culture scaffolding on engineered vessel morphology and function and found that these parameters greatly influence the function of engineered vessels.

METHODS

This report describes the effects of culture time and scaffold type on vessel morphology, cellular differentiation, and vessel mechanical characteristics. Engineered vessels were cultured from bovine aortic smooth muscle cells (SMCs) and endothelial cells that were seeded onto biodegradable polymer scaffolds and cultured under physiologically pulsatile conditions. Engineered vessels were subjected to histologic, ultrastructural, immunocytochemical, and mechanical analyses.

RESULTS

Vessel morphology and mechanical characteristics improved as time in culture increased to 8 weeks. SMCs in the engineered vessel wall were organized into a highly lamellar structure, with cells separated by alternating layers of collagen fibrils. Polymer scaffold remnants were present in vessels cultured for 8 weeks, and SMCs that were in proximity to polymer remnants exhibited a dedifferentiated phenotype.

CONCLUSIONS

These findings aid in the systematic understanding of the effects of in vitro parameters on engineered vessels and will be useful for the translation of vessel culture techniques to human cells for the development of autologous human vascular grafts.

Functional arteries grown in vitro

A tissue engineering approach was developed to produce arbitrary lengths of vascular graft material from smooth muscle and endothelial cells that were derived from a biopsy of vascular tissue. Bovine vessels cultured under pulsatile conditions had rupture strengths greater than 2000 millimeters of mercury, suture retention strengths of up to 90 grams, and collagen contents of up to 50 percent. Cultured vessels also showed contractile responses to pharmacological agents and contained smooth muscle cells that displayed markers of differentiation such as calponin and myosin heavy chains. Tissue-engineered arteries were implanted in miniature swine, with patency documented up to 24 days by digital angiography.

Endothelial cells modulate the proliferation of mural cell precursors via platelet-derived growth factor-BB and heterotypic cell contact

Embryological data suggest that endothelial cells (ECs) direct the recruitment and differentiation of mural cell precursors. We have developed in vitro coculture systems to model some of these events and have shown that ECs direct the migration of undifferentiated mesenchymal cells (10T1/2 cells) and induce their differentiation toward a smooth muscle cell/pericyte lineage. The present study was undertaken to investigate cell proliferation in these cocultures. ECs and 10T1/2 cells were cocultured in an underagarose assay in the absence of contact. There was a 2-fold increase in bromodeoxyuridine labeling of 10T1/2 cells in response to ECs, which was completely inhibited by the inclusion of neutralizing antiserum against platelet-derived growth factor (PDGF)-B. Antisera against PDGF-A, basic fibroblast growth factor, or transforming growth factor (TGF)-beta had no effect on EC-stimulated 10T1/2 cell proliferation. EC proliferation was not influenced by coculture with 10T1/2 cells in the absence of contact. The cells were then cocultured so that contact was permitted. Double labeling and fluorescence-activated cell sorter analysis revealed that ECs and 10T1/2 cells were growth-inhibited by 43% and 47%, respectively. Conditioned media from contacting EC-10T1/2 cell cocultures inhibited the growth of both cell types by 61% and 48%, respectively. Although we have previously shown a role for TGF-beta in coculture-induced mural cell differentiation, growth inhibition resulting from contacting cocultures or conditioned media was not suppressed by the presence of neutralizing antiserum against TGF-beta. Furthermore, the decreased proliferation of 10T1/2 cells in the direct cocultures could not be attributed to downregulation of the PDGF-B in ECs or the PDGF receptor-beta in the 10T1/2 cells. Our data suggest that modulation of proliferation occurs during EC recruitment of mesenchymal cells and that heterotypic cell-cell contact and soluble factors play a role in growth control during vessel assembly.

PDGF, TGF-beta, and heterotypic cell-cell interactions mediate endothelial cell-induced recruitment of 10T1/2 cells and their differentiation to a smooth muscle fate

We aimed to determine if and how endothelial cells (EC) recruit precursors of smooth muscle cells and pericytes and induce their differentiation during vessel formation. Multipotent embryonic 10T1/2 cells were used as presumptive mural cell precursors. In an under-agarose coculture, EC induced migration of 10T1/2 cells via platelet-derived growth factor BB. 10T1/2 cells in coculture with EC changed from polygonal to spindle-shaped, reminiscent of smooth muscle cells in culture. Immunohistochemical and Western blot analyses were used to examine the expression of smooth muscle (SM)-specific markers in 10T1/2 cells cultured in the absence and presence of EC. SM-myosin, SM22alpha, and calponin proteins were undetectable in 10T1/2 cells cultured alone; however, expression of all three SM-specific proteins was significantly induced in 10T1/2 cells cocultured with EC. Treatment of 10T1/2 cells with TGF-beta induced phenotypic changes and changes in SM markers similar to those seen in the cocultures. Neutralization of TGF-beta in the cocultures blocked expression of the SM markers and the shape change. To assess the ability of 10T1/2 cells to contribute to the developing vessel wall in vivo, prelabeled 10T1/2 cells were grown in a collagen matrix and implanted subcutaneously into mice. The fluorescently marked cells became incorporated into the medial layer of developing vessels where they expressed SM markers. These in vitro and in vivo observations shed light on the cell-cell interactions that occur during vessel development, as well as in pathologies in which developmental processes are recapitulated.

Control of angiogenesis by the pericyte: molecular mechanisms and significance

The microvasculature consists of endothelial cells (EC) with albuminally located pericytes. A number of clinical and experimental observations suggest that pericytes contribute to the regulation of microvascular growth and function. EC and pericytes appear to have a variety of means whereby they may influence one another, including soluble growth factors, gap junctions and adhesion molecules, to name a few. Co-culture systems have provided a good deal of evidence to support the concept that these two cells interact and that these communications are central to vessel assembly, growth control and normal function.

Pericytes in the microvasculature

Pericytes, also known as Rouget cells or mural cells, are associated abluminally with all vascular capillaries and post-capillary venules. Differences in pericyte morphology and distribution among vascular beds suggest tissue-specific functions. Based on their location and their complement of muscle cytoskeletal proteins, pericytes have been proposed to play a role in the regulation of blood flow. In vitro studies demonstrating the contractile ability of pericytes support this concept. Pericytes have also been suggested to be oligopotential and have been reported to differentiate into adipocytes, osteoblasts and phagocytes. The mechanisms involved in vessel formation have yet to be elucidated but observations indicate that the primordial endothelium can recruit undifferentiated mesenchymal cells and direct their differentiation into pericytes in microvessels, and smooth muscle cells in large vessels. Communication between endothelial cells and pericytes, or their precursors, may take many forms. Soluble factors such as platelet-derived growth factor and transforming growth factors-beta are likely to be involved. In addition, physical contact mediated by cell adhesion molecules, integrins and gap junctions appear to contribute to the control of vascular growth and function. Development of culture methods has allowed some functions of pericytes to be directly examined. Co-culture of pericytes with endothelial cells leads to the activation of transforming growth factor-beta, which in turn influences the growth and differentiation of the vascular cells. Finally, the pericyte has been implicated in the development of a variety of pathologies including hypertension, multiple sclerosis, diabetic microangiopathy and tumor vascularization.

Pericytes in the microvasculature

Pericytes, also known as Rouget cells or mural cells, are associated abluminally with all vascular capillaries and post-capillary venules. Differences in pericyte morphology and distribution among vascular beds suggest tissue-specific functions. Based on their location and their complement of muscle cytoskeletal proteins, pericytes have been proposed to play a role in the regulation of blood flow. In vitro studies demonstrating the contractile ability of pericytes support this concept. Pericytes have also been suggested to be oligopotential and have been reported to differentiate into adipocytes, osteoblasts and phagocytes. The mechanisms involved in vessel formation have yet to be elucidated but observations indicate that the primordial endothelium can recruit undifferentiated mesenchymal cells and direct their differentiation into pericytes in microvessels, and smooth muscle cells in large vessels. Communication between endothelial cells and pericytes, or their precursors, may take many forms. Soluble factors such as platelet-derived growth factor and transforming growth factors-beta are likely to be involved. In addition, physical contact mediated by cell adhesion molecules, integrins and gap junctions appear to contribute to the control of vascular growth and function. Development of culture methods has allowed some functions of pericytes to be directly examined. Co-culture of pericytes with endothelial cells leads to the activation of transforming growth factor-beta, which in turn influences the growth and differentiation of the vascular cells. Finally, the pericyte has been implicated in the development of a variety of pathologies including hypertension, multiple sclerosis, diabetic microangiopathy and tumor vascularization.

Gap junction genes Cx26 and Cx43 individually suppress the cancer phenotype of human mammary carcinoma cells and restore differentiation potential

Normal human mammary epithelial cells express hcx43 and hCx26 proteins, which form functional gap junction channels. Both Cx genes are transcriptionally down-regulated in mammary carcinoma cell lines; consequently, no protein is made and gap junctions are absent. This result suggests that the loss of gap junctional communication may play an important role in carcinogenesis. To address this question, two sets of stable transfectants were produced in a recloned line of human mammary carcinoma cells (MDA-MB-435). One set expressed hCx26, and the other expressed hCx43. Studies of transfectants that contain functional gap junctions showed that they grew more slowly in culture than controls, and that their tumor-forming ability was strongly suppressed. In studies designed to examine their differentiation capacity, these transfectants were found to have regained the capacity to form three-dimensional structures in a matrigel matrix. This property is characteristic of normal mammary epithelial cells, but it is lost in the parental tumor cells and neo-transfectant controls. Thus, junctional communication is shown here to play a decisive role in the morphogenesis of mammary gland structures. The hCx26 and hCx43 genes behave as classical tumor suppressor genes both in culture and in animal tests in restoring growth regulatory properties to metastatic mammary carcinoma cells. Expression of these genes further induces the ability to differentiate as shown by the formation of three-dimensional structures when transfected cells are embedded in a matrigel matrix. These findings suggest that the reexpression of gap junctions may play a vital role in normalizing tumor cell behavior.

Effects of secretin and caerulein on pancreatic digestive enzymes in cultured rat acinar cells

Caerulein is proposed to regulate the synthesis of pancreatic proteases and amylase. Similarly, secretin is implicated in the regulation of pancreatic lipase synthesis. Evidence of these regulations is predominantly from in vivo studies. We therefore examined the effects of caerulein and secretin directly on acinar cells to eliminate possible interactions with other regulatory factors. Cellular and media enzyme activities and relative synthesis were measured after 24 h of hormonal treatment. Cells were incubated with [14C]-amino acids and then subjected to two-dimensional gel electrophoresis to separate individual acinar proteins for subsequent determination of incorporated radioactivity and relative synthesis. In general, all enzyme activities decreased (33%; p < 0.02) over time in culture and medium enzyme activities increased (370%; p < 0.00001) in all treatment groups. Caerulein further decreased cellular content of all enzymes (p < 0.002) and increased media amylase and lipase activities (p < 0.02). Caerulein, however, significantly increased the relative synthesis of trypsin (28%) and tended to increase that of chymotrypsin (25%; p < 0.06), which supports its proposed role in protease regulation. Secretin, on the other hand, did not significantly affect the cellular or medium activities or the relative synthesis of any pancreatic enzyme evaluated. Therefore, this study does not support the proposed role of secretin in lipase regulation.

Oleic acid differentially affects gap junction-mediated communication in heart and vascular smooth muscle cells

The effects of oleic acid (OA) on gap junction-mediated intercellular communication between A7r5 cells and neonatal rat cardiac myocytes were determined. In A7r5 cells the extent of dye coupling was influenced in a biphasic manner by increasing concentrations of OA. Low concentrations of OA (0.1-1 microM) reduced the incidence of dye coupling from 90% (in control cells) to approximately 50%. Further increases in OA concentration, up to 100 microM, had no further effect on extent of dye coupling. In contrast, dye coupling between cardiac myocytes was reduced to near zero levels in a linear fashion by 1-25 microM OA. Whereas high OA concentrations reduce junctional conductance (gj) between heart cells to zero [J. M. Burt, K. D. Massey, and B. N. Minnich. Am. J. Physiol. 260 (Cell Physiol. 29): C439-C448, 1991], gj between A7r5 cells was decreased by a maximum of 45% by OA. These differences in OA sensitivity between the two cell types were not explained by differences in the rate or magnitude of OA uptake by the cells or by differences in the fraction of incorporated OA accessible to albumin washout, i.e., the plasma membrane fraction. Instead, the activity of the individual channel types exhibited different sensitivities to OA. In the presence of increasing concentrations of OA, the activities of first the 70-pS channel population [composed of connexin40 (Cx40)] and then the 108-pS channel population (composed of Cx43) were diminished, leaving predominantly the 140-pS channels (composed of Cx43) at high OA concentrations. The uncoupling effects of OA in both cell types could be reversed by washout with albumin-containing solution; however, higher concentrations of albumin and more vigorous wash conditions were required for full recovery in the A7r5 cells. In addition, albumin also reversed the effects of OA on channel activity. These data suggest that OA binds with greater affinity to the 70- vs. 108- or 140-pS channels and associated with binding is reduced channel activity.

Effects of secretin and caerulein on enzymes of cultured pancreatic acinar cells

We examined the effects of secretin (0 to 200 nM) and caerulein (0 to 100 nM) on rat pancreatic acinar cells cultured 0 to 48 h in serum-free medium. The effects of 100 nM secretin with 1 nM caerulein were also studied because secretin may potentiate the effects of caerulein. Cellular and media (secreted) lipase and amylase were analyzed as were cellular DNA and protein content. Cellular lipase and amylase activities significantly decreased (P less than 0.0001) over time in all treatment groups, whereas media amylase and lipase significantly increased (P less than 0.0001). Neither secretin nor caerulein affected cellular lipase or media amylase. However, secretin significantly increased (P less than 0.04) and caerulein tended to increase (P less than 0.08) media lipase in a dose-dependent manner. At 12 h, 10 nM secretin maximally increased media lipase (58%) suggesting that cultured acinar cells remain responsive to secretin in vitro. Caerulein, at all concentrations, significantly decreased (P less than 0.001) cellular amylase but exhibited a dose-dependent effect only at 24 h when 100 nM caerulein maximally decreased cellular amylase (34%). Secretin (100 nM) did not alter these effects of caerulein. These results support the proposed role of caerulein in the regulation of amylase but not a direct role of secretin in the regulation of lipase.

Effects of diet and ketones on rat pancreatic lipase in cultured acinar cells

The activity, synthesis rate and mRNA level of pancreatic lipase increase with dietary fat intake. Ketones, intermediates of lipid metabolism, have been proposed to mediate this change. Therefore, we investigated their direct effect on cultured pancreatic acinar cells and examined their possible interactive effects with glucose and dietary fat. beta-Hydroxybutyrate (0.01 to 2 mmol/L) did not affect lipase activity in cells isolated from rats fed a commercial nonpurified (NP) diet and cultured in high glucose (HG, 27.8 mmol/L) or low glucose (LG, 6.9 mmol/L) medium. The effects of ketones were also examined in acinar cells isolated from rats fed purified high fat (HF, 67% of energy from fat) or low fat (LF, 11% of energy from fat) diet. Cellular lipase was significantly higher in cells from HF-fed rats at both 24 and 48 h (264% and 145% of LF values, respectively; P less than 0.0001). beta-Hydroxybutyrate significantly increased (P less than 0.04) lipase activity in LF cells at 48 h but did not affect lipase activity in HF cells. These studies suggest that ketones may be involved in the regulation of pancreatic lipase in rats fed a LF diet, but their role is complex and interactive with dietary carbohydrate and fat.