A mouse bone marrow stromal cell line, TBR-B, shows inducible expression of smooth muscle-specific genes

Vitamin C in Stem Cell Biology: Impact on Extracellular Matrix Homeostasis and Epigenetics

Transcription factors and signaling molecules are well-known regulators of stem cell identity and behavior; however, increasing evidence indicates that environmental cues contribute to this complex network of stimuli, acting as crucial determinants of stem cell fate. l-Ascorbic acid (vitamin C (VitC)) has gained growing interest for its multiple functions and mechanisms of action, contributing to the homeostasis of normal tissues and organs as well as to tissue regeneration. Here, we review the main functions of VitC and its effects on stem cells, focusing on its activity as cofactor of Fe⁺²/αKG dioxygenases, which regulate the epigenetic signatures, the redox status, and the extracellular matrix (ECM) composition, depending on the enzymes' subcellular localization. Acting as cofactor of collagen prolyl hydroxylases in the endoplasmic reticulum, VitC regulates ECM/collagen homeostasis and plays a key role in the differentiation of mesenchymal stem cells towards osteoblasts, chondrocytes, and tendons. In the nucleus, VitC enhances the activity of DNA and histone demethylases, improving somatic cell reprogramming and pushing embryonic stem cell towards the naive pluripotent state. The broad spectrum of actions of VitC highlights its relevance for stem cell biology in both physiology and disease.

Effects of vitamin C treatment on collar-induced intimal thickening

Vitamin C has efficient antioxidant properties and is involved in important physiological processes such as collagen synthesis. As such, vitamin C deficiency leads to serious complications, including vascular diseases. The aim of this study was to investigate the effects of vitamin C treatment on collar-induced intimal thickening. Rabbits were fed a normocholesterolemic diet and a non-occlusive silicon collar was placed around the left carotid artery for 3, 7, and 14 days. The rabbits were treated with or without vitamin C (150 mg/kg/day). Collar-induced intimal thickening became apparent at day 7. The effect of the collar on intimal thickening was more prominent at day 14. Vitamin C treatment significantly inhibited collar-induced intimal thickening at day 14. The placement of the collar around the carotid artery decreased maximum contractile responses against contractile agents (KCl, phenylephrine, 5-hydroxytryptamine). The effect of the collar on contractile responses was enhanced as days elapsed. Decreased contractile responses of collared carotid arteries normalized at day 14 in the vitamin C treatment group. Vitamin C treatment also restored sensitivity to phenylephrine. The collar also significantly decreased acetylcholine-induced relaxations at day 3 and day 7. Acetylcholine-induced relaxations normalized in collared-arteries in the placebo group at day 14. Vitamin C treatment significantly increased acetylcholine-induced relaxations of both normal and collared carotid arteries at day 14. MMP-9 expression increased in collared arteries at day 3 and day 7 but did not change at day 14. MMP-2 expression increased in collared arteries at day 14. However, vitamin C treatment reduced collar-stimulated expression of MMP-2 at day 14. These findings indicate that vitamin C may have potentially beneficial effects on the early stages of atherosclerosis. Furthermore these results, for the first time, may indicate that vitamin C can also normalize decreased contractile response through perivascular collar placement.

A mouse bone marrow stromal cell line with skeletal stem cell characteristics to study osteogenesis in vitro and in vivo

Bone marrow stromal cells (BMSCs) are composed of progenitor and multipotent skeletal stem cells, which are able to differentiate in vitro into osteocytes, adipocytes, and chondrocytes. Mouse BMSCs (mBMSCs) are a versatile model system to investigate factors involved in BMSC differentiation in vitro and in vivo as a variety of transgenic mouse models are available. In this study, mBMSCs were isolated and osteogenic differentiation was investigated in tissue culture and in vivo. Three out of seven independent cell isolates showed the ability to differentiate into osteocytes, adipocytes, and chondrocytes in vitro. In vitro multipotency of an established mBMSC line was maintained over 45 passages. The osteogenic differentiation of this cell line was confirmed by quantitative polymerase chain reaction (qPCR) analysis of specific markers such as osteocalcin and shown to be Runx2 dependent. Notably, the cell line, when transplanted subcutaneously into mice, possesses full skeletal stem cell characteristics in vivo in early and late passages, evident from bone tissue formation, induction of vascularization, and hematopoiesis. This cell line provides, thus, a versatile tool to unravel the molecular mechanisms governing osteogenesis in vivo thereby aiding to improve current strategies in bone regenerative therapy.

Generation of mesenchymal stem cell lines from murine bone marrow

Mesenchymal stem cells (MSC), because of their multipotency and ease of purification and amplification, are an ideal stem cell source for cell therapies. Bone-marrow-derived stem cells (BMSC) can be used to develop MSC-like immortalized cell lines with large proliferation and differentiation potentialities. Their immortalized status prevents the maintenance of MSC function and characters; this can be negated by modifying the isolation and maintenance protocol. Adult murine BMSC were isolated and maintained in media without additional growth factors together with passage-dependent reseeding following trypsinization. Cells maintained over 25 passages were considered as putative cell lines and characterized. The phenotypic and genotypic characteristics and multilineage differentiation potential of the cells were assessed by morphological, phenotypic, and molecular assays at various passages. The putative BMSC cell lines showed the characteristics of MSC and were able to maintain these characteristics, even after immortalization. The phenotypic data demonstrated difference among two cell lines; this was further validated by the difference in their multilineage differentiation potential following specific induction. More importantly, no changes were observed in the genotypic level in comparison with control cells, even after more than 50 passages. Our protocol thus advances the isolation and maintenance of BMSC and the development of putative BMSC cell lines that maintain characteristics of MSC, including multilineage differentiation potential, after more than 40 passages.

Microvascular mural cell functionality of human embryonic stem cell-derived mesenchymal cells

Microvascular mural or perivascular cells are required for the stabilization and maturation of the remodeling vasculature. However, much less is known about their biology and function compared to large vessel smooth muscle cells. We have developed lines of multipotent mesenchymal cells from human embryonic stem cells (hES-MC); we hypothesize that these can function as perivascular mural cells. Here we show that the derived cells do not form teratomas in SCID mice and independently derived lines show similar patterns of gene expression by microarray analysis. When exposed to platelet-derived growth factor-BB, the platelet-derived growth factor receptor β is activated and hES-MC migrate in response to a gradient. We also show that in a serum-free medium, transforming growth factor β1 (TGFβ1) induces robust expression of multiple contractile proteins (α smooth muscle actin, smooth muscle myosin heavy chain, smooth muscle 22α, and calponin). TGFβ1 signaling is mediated through the TGFβR1/Alk5 pathway as demonstrated by inhibition of α smooth muscle actin expression by treatment of the Alk5-specific inhibitor SB525334 and stable retroviral expression of the Alk5 dominant negative (K232R). Coculture of human umbilical vein endothelial cell (HUVEC) with hES-MC maintains network integrity compared to HUVEC alone in three-dimensional collagen I-fibronectin by paracrine signaling. Using high-resolution laser confocal microscopy, we show that hES-MC also make direct contact with HUVEC. This demonstrates that hESC-derived mesenchymal cells possess the molecular machinery expected in a perivascular progenitor cells and can play a functional role in stabilizing EC networks in in vitro three-dimensional culture.

Adipose stem cell differentiation into smooth muscle cells

The differentiation of adipose-derived stem cells (ASCs) into functional smooth muscle cells has received limited investigation. Various methodologies for both in vitro and in vivo differentiation is described. In vitro differentiation is obtained by either chemical or mechanical stimulation, and is determined by expression of smooth muscle cell markers. In vivo differentiation studies include animal models of cardiovascular disease and one study with urinary bladder reconstruction. The ease of obtaining an abundant number of ASCs render this cell population useful for potential vascular therapies that require autologous smooth muscle cells.

A Specific Subset of Mouse Bone Marrow Cells Has Smooth Muscle Cell Differentiation Capacity–Brief Report

Objective— To determine whether CX 3 CR1 + bone marrow cells have the capacity for smooth muscle cell (SMC) differentiation.

Methods and Results— CX 3 CR1 + and CX 3 CR1 − cells were isolated from marrow of CX 3 CR1 transgenic mice and cultured in SMC differentiation media. Phenotypic and functional analyses showed only CX 3 CR1 + bone marrow cells exhibit colony cell outgrowth with SMC-specific protein expression, calcium signaling, and contraction responses similar to mature SMC.

Conclusion— CX 3 CR1 marks a bone marrow cells population that enriches for progenitors with capacity to differentiate in vitro into SMC-like cells.

Oxidized low density lipoprotein-induced transdifferentiation of bone marrow-derived smooth muscle-like cells into foam-like cells in vitro

Oxidized-low density lipoprotein (ox-LDL) is believed to contribute to atherogenesis in part by being taken up into smooth muscle cells (SMC) via specific scavenger receptors; however, it is not clear whether ox-LDL receptor(s) are expressed in bone marrow-derived smooth muscle-like cells (SMLCs) and whether they play a role in the process of SMLC development. Therefore, we examined the ox-LDL-induced transdifferentiation of SMLCs that is mediated by lectin-like ox-LDL receptor-1 (LOX-1). Smooth muscle progenitor cells (SMPCs) from bone marrow mesenchymal stem cells (BMSCs) were isolated using a tissue-specific promoter sorting method with a mouse SM22_ promoter (_480 bp)/green fluorescent protein recombinant plasmid. The SMPCs were myocardin+CD105+KDR+CD45(-)CD34(-), but did not express SMC-specific markers alpha-smooth muscle actin (alpha-SMA), SM22, smooth muscle myosin heavy chain (SM-MHC) and smoothelin. After long-term culture with platelet-derived growth factor-BB (PDGF-BB), SMPCs expressed alpha-SMA, SM22 and SM-MHC and differentiated into SMLCs. When SMLCs were incubated with different concentrations of ox-LDL, LOX-1 expression on the surface of SMLCs gradually increased with the increase of the ox-LDL concentration, but myocardin and SMC-specific marker genes decreased, accordingly. Furthermore, receptor-mediated endocytosis was enhanced and lipid droplets accumulated in the cytoplasm of SMLCs. A subpopulation of myocardin+CD105+KDR+CD45(-)CD34(-) SMPCs exist in BMSCs that can differentiate into SMLCs under induction with PDGF-BB. Moreover, LOX-1 contributes to the ox-LDL-induced transdifferentiation of bone marrow-derived SMLCs into foam-like cells.

Effects of transforming growth factor-beta 1 and ascorbic acid on differentiation of human bone-marrow-derived mesenchymal stem cells into smooth muscle cell lineage

Bone-marrow-derived mesenchymal stem cells (MSCs) can differentiate into a variety of cell types including smooth muscle cells (SMCs). We have attempted to demonstrate that, following treatment with transforming growth factor-beta 1 (TGF-beta1) and ascorbic acid (AA), human bone-marrow-derived MSCs differentiate into the SMC lineage for use in tissue engineering. Quantitative polymerase chain reaction for SMC-specific gene (alpha smooth muscle actin, h1-calponin, and SM22alpha) expression was performed on MSCs, which were cultured with various concentrations of TGF-beta1 or AA. TGF-beta1 had a tendency to up-regulate the expression of SMC-specific genes in a dose-dependent manner. The expression of SM22alpha was significantly up-regulated by 30 microM AA. We also investigated the additive effect of TGF-beta1 and AA for differentiation into SMCs and compared this effect with that of other factors including platelet-derived growth factor BB (PDGF-BB). In addition to SMC-specific gene expression, SMC-specific proteins increased by two to four times when TGF-beta1 and AA were used together compared with their administration alone. PDGF did not increase the expression of SMC-specific markers. MSCs cultured with TGF-beta1 and AA did not differentiate into osteoblasts and adipocytes. These results suggest that a combination of TGF-beta1 and AA is useful for the differentiation of MSCs into SMCs for use in tissue engineering.

Ascorbic acid uptake and regulation of type I collagen synthesis in cultured vascular smooth muscle cells

BACKGROUND/AIMS

Vascular smooth muscle cells contribute both to the structure and function of arteries, but are also involved in pathologic changes that accompany inflammatory diseases such as atherosclerosis. Since inflammation is associated with oxidant stress, we examined the uptake and cellular effects of the antioxidant vitamin ascorbic acid in cultured A10 vascular smooth muscle cells.

METHODS/RESULTS

A10 cells concentrated ascorbate against a gradient in a sodium-dependent manner, most likely on the sodium-dependent vitamin C transporter type 2 (SVCT2) ascorbate transporter, which was present in immunoblots of cell extracts. Although ascorbate did not affect A10 cell proliferation, it stimulated radiolabeled proline incorporation and type I collagen synthesis. The latter was evident in the cells as increases in proalpha1(I) collagen and conversion of proalpha1(I) and proalpha2(I) collagen to mature forms that were released from the cells and deposited as extracellular matrix. Intracellular type I procollagen maturation was optimal at intracellular ascorbate concentrations of 200 microM and below, which were readily achieved by culture of the cells at plasma physiologic ascorbate concentrations.

CONCLUSION

These results show that the SVCT2 facilitates ascorbate uptake by vascular smooth muscle cells, which in turn increases both the synthesis and maturation of type I collagen.

Inflammation in the vascular bed: importance of vitamin C

Despite decreases in atherosclerotic coronary vascular disease over the last several decades, atherosclerosis remains a major cause of mortality in developed nations. One possible contributor to this residual risk is oxidant stress, which is generated by the inflammatory response of atherosclerosis. Although there is a wealth of in vitro, cellular, and animal data supporting a protective role for antioxidant vitamins and nutrients in the atherosclerotic process, the best clinical trials have been negative. This may be due to the fact that antioxidant therapies are applied "too little and too late." This review considers the role of vitamin C, or ascorbic acid in preventing the earliest inflammatory changes in atherosclerosis. It focuses on the three major vascular cell types involved in atherosclerosis: endothelial cells, vascular smooth muscle cells, and macrophages. Ascorbate chemistry, recycling, and function are described for these cell types, with emphasis on whether and how the vitamin might affect the inflammatory process. For endothelial cells, ascorbate helps to prevent endothelial dysfunction, stimulates type IV collagen synthesis, and enhances cell proliferation. For vascular smooth muscle cells, ascorbate inhibits dedifferentiation, recruitment, and proliferation in areas of vascular damage. For macrophages, ascorbate decreases oxidant stress related to their activation, decreases uptake and degradation of oxidized LDL in some studies, and enhances several aspects of their function. Although further studies of ascorbate function in these cell types and in novel animal models are needed, available evidence generally supports a salutary role for this vitamin in ameliorating the earliest stages of atherosclerosis.

Centrifugal seeding increases seeding efficiency and cellular distribution of bone marrow stromal cells in porous biodegradable scaffolds

Bone marrow stromal cells (MSCs) are a promising cell source for a variety of tissue engineering applications, given their ready availability and ability to differentiate into multiple cell lineages. MSCs have been successfully used to create neotissue for cardiovascular, urological, and orthopedic reconstructive surgical procedures in preclinical studies. The ability to optimize seeding techniques of MSCs onto tissue engineering scaffolds and the ability to control neotissue formation in vitro will be important for the rational design of future tissue engineering applications using MSCs. In this study we investigated the effect of centrifugal force on seeding MSCs into a biodegradable polyester scaffold. MSCs were isolated and seeded onto porous scaffold sections composed of nonwoven polyglycolic acid mesh coated with poly(L-lactide-co-epsilon-caprolactone). Compared to standard static seeding techniques, centrifugal seeding increased the seeding efficiency by 38% (p < 0.007) and significantly improved cellular distribution throughout the scaffold. Overall, centrifugal seeding of MSCs enhances seeding efficiency and improves cellular penetration into scaffolds, making it a potentially useful technique for manipulating neotissue formation by MSCs for tissue engineering applications.

Smooth muscle alpha-actin expression and myofibroblast differentiation by TGFbeta are dependent upon MK2

Fibroblasts play a major role in processes such as wound repair, scarring, and fibrosis. Differentiation into myofibroblasts, characterized by upregulation of smooth muscle alpha-actin (smalpha) in response to profibrotic agents such as TGFbeta is believed to be an important step in fibrosis. Therefore, elucidating mechanisms of myofibroblast differentiation might reveal novel targets in treating diseases such as idiopathic pulmonary fibrosis (IPF). MK2 is a kinase substrate of p38 MAP kinase that mediates some effects of p38 activation on the actin cytoskeleton. Using mouse embryonic fibroblasts (MEF) from MK2 knockout (MK2(-/-)) mice, we demonstrate that disrupting expression of MK2 expression reduces filamentous actin and stress fibers. It also causes MK2(-/-) MEF to express less smalpha than their corresponding wild-type (WT) MEF at baseline and in response to TGFbeta. Furthermore, TGFbeta causes downregulation of smalpha in MK2(-/-) MEF, instead of upregulation observed in WT MEF. Expression of other fibroblast markers, such as collagen, is not altered in MK2(-/-) MEF. Our results further suggest that downregulation of smalpha in MK2(-/-) MEF is not due to lack of activation of serum responsive promoter elements, but probably due to reduced smalpha message stability in these cells. These results indicate that MK2 plays a key role in regulation of smalpha expression, and that targeting MK2 might present a therapeutic approach in managing conditions such as pulmonary fibrosis.

Regulatory role of vitamins E and C on extracellular matrix components of the vascular system

The protective effect of vitamins E (alpha-tocopherol) and C (L-ascorbic acid) in the prevention of cardiovascular disease (CVD) has been shown in a number of situations but a secure correlation is not universally accepted. Under certain conditions, both, L-ascorbic acid and alpha-tocopherol can exhibit antioxidant properties and thus may reduce the formation of oxidized small molecules, proteins and lipids, which are a possible cause of cellular de-regulation. However, non-antioxidant effects have also been suggested to play a role in the prevention of atherosclerosis. Vitamin E and C can modulate signal transduction and gene expression and thus affect many cellular reactions such as the proliferation of smooth muscle cells, the expression of cell adhesion and extracellular matrix molecules, the production of O(2)(-) by NADPH-oxidase, the aggregation of platelets and the inflammatory response. Vitamins E and C may modulate the extracellular matrix environment by affecting VSMC differentiation and the expression of connective tissue proteins involved in vascular remodeling as well as the maintenance of vascular wall integrity. This review summarizes individually the molecular activities of vitamins E and C on the cells within the connective tissue of the vasculature, which are centrally involved in the maintenance of an intact vascular wall as well as in the repair of atherosclerotic lesions during disease development.

The immortalized cell lines with differentiation potentials: their establishment and possible application

Approximately 200 types of the cells are qualified as differentiated cells in the human body. If these different types of cells can be separated from each other (or cloned) and obtained in sufficient quantity, it will be beneficial for studying development, morphogenesis, tissue maintenance, cancer and aging, and for reconstructing functional tissues in vitro for regenerative medicine. We produced the transgenic mouse and rat harboring SV40 T-antigen gene to make the immortalized cell lines in the primary tissue culture and succeeded in establishing many functionally active cell lines from various tissues. Many immortalized cell lines from various tissues are shown to exhibit the unique characteristics of tissue functions and they should be useful as an in vitro model of various tissues for physiological and pharmacological investigations. Future application of these cells to drug screening is discussed.

Mechanical stimulation induces morphological and phenotypic changes in bone marrow-derived progenitor cells within a three-dimensional fibrin matrix

One of the major limitations in tissue engineering is cell sourcing. Multipotent progenitor cells appear to have many promising features for that purpose. Mechanical stimulation is known to play an important role in determining cell phenotype. The aim of this work was to investigate the effects of cyclic stretch on rat bone marrow derived progenitor cell (BMPC) morphology and smooth muscle-directed differentiation within a three-dimensional fibrin matrix. BMPCs were suspended in a fibrin gel, pipetted into the trough of Flexcell Tissue-Train plates, and stimulated with 10% longitudinal cyclic stretch at 1 Hz for 6 days. Unconstrained (stress- and strain-free) and static anchored (constrained but not stretched) samples were used as controls. Stress filament area per cell was increased in the stretched samples compared to static anchored and free-float controls. Cells in the free float controls were randomly aligned, while they aligned parallel to the direction of the stress or strain in the other groups. Immunofluorescence suggested an increased expression of smooth muscle markers (smooth muscle alpha actin and h1-calponin) in both stretched and constrained control samples, but not in unconstrained controls. Qualitative assessment suggested that collagen production was increased in both mechanically stimulated samples. Proliferation was inhibited in stretched samples compared to the constrained controls. This work suggests an ability of rat BMPCs to differentiate toward a smooth-muscle-cell-like lineage when exposed to biomechanical stimulation in a three-dimensional model. The observation that the constrained samples induced changes in BMPCs suggests that stress alone may be stimulatory, but addition of cyclic stretch appears to augment the responses.

Regulation of alpha-smooth muscle actin protein expression in adipose-derived stem cells

The objective of this work was to study the response of adipose-derived stem cells (ASCs) to exogenous biochemical stimulation, and the potential of ASCs to differentiate toward the smooth muscle cell (SMC) lineage. Immunofluorescence staining and Western blot analysis detected protein expression of the early SMC marker alpha-smooth muscle actin (alpha-SMA) in both control and experiment groups. Expression of alpha-SMA in ASCs significantly increased when treated with transforming growth factor-beta1, while alpha-SMA expression only slightly increased in the presence of retinoic acid (RA), beta-mercaptoethanol and ascorbic acid. Treatment with platelet-derived growth factor-BB, RA and dibutyryl-cyclic adenosine monophosphate decreased the expression of alpha-SMA significantly. While beta-mercaptoethanol and ascorbic acid, as well as RA have resulted in increased alpha-SMA expression in marrow-derived mesenchymal stem cells and other progenitor cells, our results demonstrate that these treatments do not significantly increase alpha-SMA expression, indicating that the differentiation potential of ASCs and mesenchymal stem cells may be fundamentally different.

Temporal and spatial characterization of cellular constituents during neointimal hyperplasia after vascular injury: Potential contribution of bone-marrow-derived progenitors to arterial remodeling

BACKGROUND

Exuberant smooth muscle cells (SMCs) hyperplasia is the major cause of postangioplasty restenosis. We suggested that circulating smooth muscle progenitor cells might contribute to lesion formation after vascular injury.

METHODS

We extensively investigated the cellular constituents during neointimal formation after mechanical vascular injury.

RESULTS

A large wire was inserted into the mouse femoral artery, causing complete endothelial denudation and marked enlargement of the lumen with massive apoptosis of medial SMCs. At 2 h, the injured artery remained dilated with a thin media containing very few cells. A scanning electron microscopy showed fibrin and platelet deposition at the luminal side. One week after the injury, CD45-positive hematopoietic cells accumulated at the luminal side. Those CD45-positive cells gradually disappeared, whereas neointimal hyperplasia was formed with alpha-smooth muscle actin (SMA) positive cells. Bone marrow cells and peripheral mononuclear cells differentiated into alpha-SMA-positive cells in the presence of PDGF and basic FGF. Moreover, in bone marrow chimeric mice, bone-marrow-derived cells substantially contributed to neointimal hyperplasia after wire injury.

CONCLUSION

These results suggest that early accumulation of hematopoietic cells may play a role in the pathogenesis of SMC hyperplasia under certain circumstances.

Chondrogenesis mediated by PPi depletion promotes spontaneous aortic calcification in NPP1-/- mice

OBJECTIVE

We recently linked human arterial media calcification of infancy to heritable PC-1/nucleotide pyrophosphatase phosphodiesterase 1 (NPP1) deficiency. NPP1 hydrolyzes ATP to generate PP(i), a physicochemical inhibitor of hydroxyapatite crystal growth. But pathologic calcification in NPP1 deficiency states is tissue-restricted and in perispinal ligaments is endochondral differentiation-mediated rather than simply a dystrophic process. Because ectopic chondro-osseous differentiation promotes artery calcification in atherosclerosis and other disorders, we tested the hypothesis that NPP1 and PP(i) deficiencies regulate cell phenotype plasticity to promote artery calcification.

METHODS AND RESULTS

Using cultured multipotential NPP1-/- mouse bone marrow stromal cells, we demonstrated spontaneous chondrogenesis inhibitable by treatment with exogenous PP(i). We also demonstrated cartilage-specific gene expression, upregulated alkaline phosphatase, decreased expression of the physiological calcification inhibitor osteopontin, and increased calcification in NPP1-/- aortic smooth muscle cells (SMCs). Similar changes were demonstrated in aortic SMCs from ank/ank mice, which are extracellular PP(i)-depleted because of defective ANK transmembrane PP(i) transport activity. Moreover, NPP1-/- and ank/ank mice demonstrated aortic media calcification by von Kossa staining, and intra-aortic cartilage-specific collagen gene expression was demonstrated in situ in NPP1-/- mice.

CONCLUSIONS

NPP1 and PP(i) deficiencies modulate phenotype plasticity in artery SMCs and chondrogenesis in mesenchymal precursors, thereby stimulating artery calcification by modulating cell differentiation.

Midkine is regulated by hypoxia and causes pulmonary vascular remodeling

Midkine (MK) is expressed in a precise temporal-spatial pattern during lung morphogenesis; however, its role in pulmonary homeostasis is unknown. Increased MK staining and mRNA expression were observed in the lungs of hypoxia-susceptible CAST/eiJ mice during hypoxia. MK expression was induced by hypoxia in cell lines in vitro. Because the transcription factor hypoxiainducible factor-1alpha (HIF-1alpha) modulates cellular responses to hypoxia, we tested whether increased expression of MK in the lung was mediated by HIF-1alpha. HIF-1alpha enhanced the transcription of MK, acting on HIF-1alpha regulatory elements located in the MK gene promoter. Site-directed mutagenesis of the 3' HIF response element in the MK promoter blocked the stimulatory effects of HIF-1alpha. To directly assess the role of MK on lung morphogenesis, transgenic mice were generated in which MK was expressed in the respiratory epithelial cells of the developing lung. MK increased muscularization of small pulmonary arteries, increasing alpha-smooth muscle actin and caldesmon staining and the expression of myocardin. MK directly enhanced the expression of myocardin and the smooth muscle-specific genes alpha-smooth muscle actin, calponin, and SM-22 in vascular smooth muscle precursor cells. Expression of MK in the respiratory epithelium is regulated by hypoxia and HIF-1alpha. These data provide a model wherein the respiratory epithelium responds to hypoxia via HIF-1alpha-dependent regulation of MK, enhancing myocardin expression to influence pulmonary vascular gene expression.

Isolation and characterisation of mesenchymal stem cells from adult mouse bone marrow

The future use of adult mesenchymal stem cells (MSCs) for human therapies depends on the establishment of preclinical studies with other mammals such as mouse. Surprisingly, purification and characterisation of murine MSCs were only poorly documented. The aim of this study was to purify mouse MSCs from adult bone marrow and to functionally characterise their abilities to differentiate along diverse lineages. Adherent cells from adult C57Bl/6J mouse bone marrow were depleted of granulo-monocytic cells and subsequently allowed to grow on fibronectin-coated dishes in presence of fetal bovine serum and growth factors. The growing fibroblastoid cell population primarily consisted of spindle- and star-shaped cells with significant renewal capacity as they were cultured until 30 passages (about 60 doubling population). We fully demonstrated the MSC phenotype of these cells by inducing them to differentiate along osteoblastic, adipocytic, and chondrocytic pathways. Mouse MSCs (mMSCs) sharing the same morphological and functional characteristics as human MSCs can be successfully isolated from adult bone marrow without previous mouse or bone marrow treatment. Therefore, mMSCs will be an important tool to study the in vivo behaviour and fate of this cell type after grafting in mouse pathology models.

Characterization of the Response of Bone Marrow-Derived Progenitor Cells to Cyclic Strain: Implications for Vascular Tissue-Engineering Applications

One of the major failings in vascular tissue engineering is the limited capacity of autologous differentiated cells to reconstitute tissues. A logical solution is to use multipotent progenitor cells, which in vascular treatments have been underutilized. Although biochemical stimulation has been explored to differentiate bone marrow-derived progenitor cells (BMPCs) to smooth muscle cells (SMCs), the use of biomechanical forces in differentiation remains unexplored. The purpose of this work was to explore the effects of cyclic strain alone on BMPC morphology, proliferation, and differentiation. BMPCs were isolated from rat bone marrow and, after 7 days in culture, the cells grew in distinct multilayered colonies. BMPCs were stimulated with 10% strain at 1 Hz for 7 days. Observations showed that cyclic strain inhibited proliferation (p < 0.05) and caused alignment of the cells (p < 0.05) and of the F-actin cytoskeleton perpendicular to the direction of strain. In addition, cyclic strain resulted in expression by the cells of vascular smooth muscle alpha-actin and h1-calponin. This work demonstrates the potential of physiologic biomechanical stimulation in the differentiation of BMPCs to SMCs, and this could have important implications for vascular tissue engineering and other therapies in which cell sourcing is a major concern.

L-ascorbic acid stimulates expression of smooth muscle-specific markers in smooth muscle cells both in vitro and in vivo

The dedifferentiation of vascular smooth muscle cells (VSMCs) plays a critical role in the progression of atherosclerosis and restenosis after angioplasty. Thus, factors that stimulate smooth muscle cell differentiation should be useful for therapy for these diseases. Previously, we found that l-ascorbic acid (L-Asc) induces the expression of smooth muscle-specific genes in a pluripotent bone marrow stromal cell line, TBR-B. This finding suggests that l-Asc stimulates the differentiation of smooth muscle cells. In the present study, we investigated the effects of l-Asc and its derivatives on the differentiation state of VSMCs in vitro and in vivo. l-Asc and its long-lasting derivatives stimulated the production of smooth muscle-specific myosin heavy chain-1 (SM1) and calponin 1 in a dose-dependent manner in rat cultured VSMCs, and the elevated production of SM1 and calponin 1 was maintained for at least 2 weeks. Moreover, oral administration of 3 g/kg of l-Asc to the balloon-injured rats induced a higher expression of SM1 and calponin 1 in the injured arteries compared with that from administration of the delivery vehicle alone. These data demonstrated new biologic activity, such as the stimulation of VSMC differentiation, of l-Asc and its long-lasting derivatives. In addition, these compounds may serve as useful tools for analysis of the differentiation of VSMCs and for therapy for vascular diseases.

Isolation of bone marrow stromal cell-derived smooth muscle cells by a human SM22alpha promoter: in vitro differentiation of putative smooth muscle progenitor cells of bone marrow

BACKGROUND

Bone marrow stromal cells (BMSCs) have many characteristics of mesenchymal stem cells that can differentiate into smooth muscle cells (SMCs). However, there have been few studies closely following the cell development of smooth muscle lineage among BMSCs.

METHODS AND RESULTS

To investigate the possible existence of a cell population committed to the SMC lineage among bone marrow adhesion cells, we tried to detect and follow the in vitro differentiation of such a cell type by using a promoter-sorting method with a human SM22alpha promoter (-480 bp)/green fluorescent protein (GFP) construct. The construct was transfected to adhesion cells that appeared 5 days after the seeding of mononuclear cells from bone marrow. GFP was first detectable 5 days after the transfection in a cell population [Ad(G) cells], which expressed PDGF-beta but neither mature (calponin) nor immature (SMemb) SMC-specific proteins at that time. However, the cells were eventually grown into individual clones that expressed SMC-specific proteins (alpha-smooth muscle actin, calponin, and SM-1), suggesting that Ad(G) cells have partly at least progenitor properties. Because early studies have reported that PDGF-beta signaling plays pivotal roles in the differentiation of mesenchymal smooth muscle progenitor cells, Ad(G) cells might be putative mesenchymal smooth muscle progenitors expressing PDGF-beta.

CONCLUSIONS

We demonstrated the presence of a cell population fated to become SMCs and followed their differentiation into SMCs among BMSCs.

Distinct progenitor populations in skeletal muscle are bone marrow derived and exhibit different cell fates during vascular regeneration

Vascular progenitors were previously isolated from blood and bone marrow; herein, we define the presence, phenotype, potential, and origin of vascular progenitors resident within adult skeletal muscle. Two distinct populations of cells were simultaneously isolated from hindlimb muscle: the side population (SP) of highly purified hematopoietic stem cells and non-SP cells, which do not reconstitute blood. Muscle SP cells were found to be derived from, and replenished by, bone marrow SP cells; however, within the muscle environment, they were phenotypically distinct from marrow SP cells. Non-SP cells were also derived from marrow stem cells and contained progenitors with a mesenchymal phenotype. Muscle SP and non-SP cells were isolated from Rosa26 mice and directly injected into injured muscle of genetically matched recipients. SP cells engrafted into endothelium during vascular regeneration, and non-SP cells engrafted into smooth muscle. Thus, distinct populations of vascular progenitors are resident within skeletal muscle, are derived from bone marrow, and exhibit different cell fates during injury-induced vascular regeneration.

Possible applications of conditionally immortalized tissue cell lines with differentiation functions

If all individual cell types of the body could be clonally isolated and stocked, similar to cDNA or genomic DNA libraries, they would be invaluable for studying the tissue and cellular functions. We developed a new method of establishing conditionally immortalized cell lines that retain differentiated cell functions similar to the original tissues, using temperature-sensitive (ts) simian virus 40 large tumor antigen gene transgenic animals. In this review the properties of such conditionally immortalized cell lines and their possible applications are discussed.