Regulation Of Collagen Gene Expression Research Articles

MicroRNA-29a: a novel target for non-operative management of symptomatic lumbar spinal stenosis.

Lumbar spinal stenosis (LSS) is the most common reason for spinal surgery in patients over the age of 65, and there are few effective non-surgical treatments. Therefore, the development of novel treatment or preventative modalities to decrease overall cost and morbidity associated with LSS is an urgent matter. The cause of LSS is multifactorial; however, a significant contributor is ligamentum flavum hypertrophy (LFH) which causes mechanical compression of the cauda equina or nerve roots. We assessed the role of a novel target, microRNA-29a (miR-29a), in LFH and investigated the potential for using miR-29a as a therapeutic means to combat LSS. Ligamentum flavum (LF) tissue was collected from patients undergoing decompressive surgery for LSS and assessed for levels of miR-29a and pro-fibrotic protein expression. LF cell cultures were then transfected with either miR-29a over-expressor (agonist) or inhibitor (antagonist). The effects of over-expression and under-expression of miR-29a on expression of pro-fibrotic proteins was assessed. We demonstrated that LF at stenotic levels had a loss of miR-29a expression. This was associated with greater LF tissue thickness and higher mRNA levels of collagen I and III. We also demonstrated that miR29-a plays a direct role in the regulation of collagen gene expression in ligamentum flavum. Specifically, agents that increase miR-29a may attenuate LFH, while those that decrease miR-29a promote fibrosis and LFH. This study demonstrates that miR-29a may potentially be used to treat LFH and provides groundwork to initiate the development of a therapeutic product for LSS.

α-Lipoic Acid Increases Collagen Synthesis and Deposition in Nondiabetic and Diabetic Rat Kidneys.

α-Lipoic acid (ALA) is widely used as a nutritional supplement and therapeutic agent in diabetes management. Well-established antioxidant and hypoglycemic effects of ALA were considered to be particularly important in combating diabetic complications including renal injury. The present study evaluated the potential of ALA to affect profibrotic events in kidney that could alter its structure and functioning. ALA was administered intraperitoneally (10 mg/kg) to nondiabetic and streptozotocin-induced diabetic male Wistar rats for 4 and 8 weeks. The effects of ALA were assessed starting from structural/morphological alterations through changes that characterize profibrotic processes, to regulation of collagen gene expression in kidney. Here, we demonstrated that ALA improved systemic glucose and urea level, reduced formation of renal advanced glycation end products (AGEs), and maintained renal structural integrity in diabetic rats. However, profibrotic events provoked in diabetes were not alleviated by ALA since collagen synthesis/deposition and expression of transforming growth factor-β1 (TGF-β1) and α-smooth muscle actin (α-SMA) remained elevated in ALA-treated diabetic rats, especially after 8 weeks of diabetes onset. Moreover, 8 weeks treatment of nondiabetic rats with ALA led to the development of profibrotic features reflected in increased collagen synthesis/deposition. Besides the TGF-β1 downstream signaling, the additional mechanism underlying the upregulation of collagen IV in nondiabetic rats treated with ALA involves decreased DNA methylation of its promoter that could arise from increased Tet1 expression. These findings emphasize the therapeutic caution in the use of ALA, especially in patients with renal diabetic complication.

PITX2 deficiency and associated human disease: insights from the zebrafish model.

The PITX2 (paired-like homeodomain 2) gene encodes a bicoid-like homeodomain transcription factor linked with several human disorders. The main associated congenital phenotype is Axenfeld-Rieger syndrome, type 1, an autosomal dominant condition characterized by variable defects in the anterior segment of the eye, an increased risk of glaucoma, craniofacial dysmorphism and dental and umbilical anomalies; in addition to this, one report implicated PITX2 in ring dermoid of the cornea and a few others described cardiac phenotypes. We report three novel PITX2 mutations—c.271C > T, p.(Arg91Trp); c.259T > C, p.(Phe87Leu); and c.356delA, p.(Gln119Argfs*36)—identified in independent families with typical Axenfeld-Rieger syndrome characteristics and some unusual features such as corneal guttata, Wolf-Parkinson-White syndrome, and hyperextensibility. To gain further insight into the diverse roles of PITX2/pitx2 in vertebrate development, we generated various genetic lesions in the pitx2 gene via TALEN-mediated genome editing. Affected homozygous zebrafish demonstrated congenital defects consistent with the range of PITX2-associated human phenotypes: abnormal development of the cornea, iris and iridocorneal angle; corneal dermoids; and craniofacial dysmorphism. In addition, via comparison of pitx2M64* and wild-type embryonic ocular transcriptomes we defined molecular changes associated with pitx2 deficiency, thereby implicating processes potentially underlying disease pathology. This analysis identified numerous affected factors including several members of the Wnt pathway and collagen types I and V gene families. These data further support the link between PITX2 and the WNT pathway and suggest a new role in regulation of collagen gene expression during development.

A Novel Small Compound That Promotes Nuclear Translocation of YB-1 Ameliorates Experimental Hepatic Fibrosis in Mice

Transforming growth factor-β (TGF-β) is considered to be a major factor contributing to liver fibrosis. We have previously shown that nuclear translocation of YB-1 antagonizes the TGF-β/Smad3 signaling in regulating collagen gene expression. More recently, we have demonstrated that the novel small compound HSc025 promotes nuclear translocation of YB-1, resulting in the improvement of skin and pulmonary fibrosis. Here, we presented evidence as to the mechanism by which HSc025 stimulates nuclear translocation of YB-1 and the pharmacological effects of HSc025 on a murine model of hepatic fibrosis. A proteomics approach and binding assays using HSc025-immobilized resin showed that HSc025 binds to the amino acid sequence within the C-tail region of YB-1. In addition, immunoprecipitation experiments and glutathione S-transferase pulldown assays identified poly(A)-binding protein (PABP) as one of the cytoplasmic anchor proteins of YB-1. HSc025 directly binds to YB-1 and interrupts its interaction with PABP, resulting in accelerated nuclear translocation of YB-1. Transfection of cells with PABP siRNA promoted nuclear translocation of YB-1 and subsequently inhibited basal and TGF-β-stimulated collagen gene expression. Moreover, HSc025 significantly suppressed collagen gene expression in cultured activated hepatic stellate cells. Oral administration of HSc025 to mice with carbon tetrachloride-induced hepatic fibrosis improved liver injury as well as the degree of hepatic fibrosis. Altogether, the results provide a novel insight into therapy for organ fibrosis using YB-1 modulators.

The basic helix–loop–helix transcription factor scleraxis regulates fibroblast collagen synthesis

The transcription factor scleraxis has been implicated in regulating the development of collagen-rich tissues such as tendons and cardiac valves, but its role in general collagen synthesis in the heart is unknown. Scleraxis expression in cardiac fibroblasts was examined, and its ability to regulate gene expression of collagen Iα2, the predominant cardiac collagen isoform, was assayed. Using real-time PCR, we demonstrate here that scleraxis mRNA is up-regulated by the profibrotic agonist TGF-β 1 in rat cardiac myofibroblasts, and that phenoconversion of fibroblasts to myofibroblasts similarly increases scleraxis expression. Over-expression of scleraxis in NIH-3T3 or primary rat cardiac fibroblasts by adenoviral gene delivery is sufficient to significantly increase collagen Iα2 gene expression. Using luciferase reporter assays, we demonstrate that scleraxis transactivates the human collagen Iα2 promoter in a DNA- and protein-binding dependent manner. Intriguingly, examination of infarcted rat hearts reveals a nearly four-fold increase in scleraxis expression in the infarct scar, but not in non-infarcted tissue. These data support a novel and previously unknown role for scleraxis in the regulation of collagen gene expression in the heart, including in post-infarct scar formation.

Regulation of collagen gene expression by the DBL-1/TGF-β signaling pathway

Regulation of collagen gene expression by the DBL-1/TGF-β signaling pathway

Connective tissue growth factor/CCN2-null mouse embryonic fibroblasts retain intact transforming growth factor-β responsiveness

Background The matricellular protein connective tissue growth factor (CCN2) has been implicated in pathological fibrosis, but its physiologic role remains elusive. In vitro, transforming growth factor-β (TGF-β) induces CCN2 expression in mesenchymal cells. Because CCN2 can enhance profibrotic responses elicited by TGF-β, it has been proposed that CCN2 functions as an essential downstream signaling mediator for TGF-β. To explore this notion, we characterized TGF-β-induced activation of fibroblasts from CCN2-null (CCN2 −/−) mouse embryos. Methods The regulation of CCN2 expression was examined in vivo in a model of fibrosis induced by bleomycin. Cellular TGF-β signal transduction and regulation of collagen gene expression were examined in CCN2 −/− MEFs by immunohistochemistry, Northern, Western and RT-PCR analysis, immunocytochemistry and transient transfection assays. Results Bleomycin-induced skin fibrosis in the mouse was associated with substantial CCN2 up-regulation in lesional fibroblasts. Whereas in vitro proliferation rate of CCN2 −/− MEFs was markedly reduced compared to wild type MEFs, TGF-β-induced activation of the Smad pathways, including Smad2 phosphorylation, Smad2/3 and Smad4 nuclear accumulation and Smad-dependent transcriptional responses, were unaffected by loss of CCN2. The stimulation of COL1A2 and fibronectin mRNA expression and promoter activity, and of corresponding protein levels, showed comparable time and dose-response in wild type and CCN2 −/− MEFs, whereas stimulation of alpha smooth muscle actin and myofibroblast transdifferentiation showed subtle impairment in MEFs lacking CCN2. Conclusion Whereas endogenous CCN2 plays a role in regulation of proliferation and TGF-β-induced myofibroblast transdifferentiation, it appears to be dispensable for Smad-dependent stimulation of collagen and extracellular matrix synthesis in murine embryonic fibroblasts.

Regulation of collagen gene expression in the Tsk2 mouse

The tight skin 2 (Tsk2) mutation is an ENU induced dominant mutation localized on mouse chromosome 1. While the molecular defect is unknown, Tsk2/+ mice display cutaneous thickening associated with excessive matrix production and are used as a model of scleroderma. The purpose of this study was to examine the cellular mechanisms associated with the excessive synthesis of matrix macromolecules using a collagen promoter GFP reporter transgene (pOBCol3.6GFP) as a marker of Col1a1 expression. This analysis of pOBCol3.6GFP expression in Tsk2/+ skin showed an increase in transgene activity compared to wild-type (+/+) samples. In addition, an increased area of "high" GFP fluorescence in Tsk2/+ dermis in both 1- and 4-month-old mice was observed that was also associated with an increased number of dermal fibroblasts per unit area of dermis. These data collectively suggest an important mechanism of Tsk2/+ skin fibrosis; an increased number of collagen expressing cells as well as elevated collagen expression on a per cell basis. During this study it was noted that Tsk2/+ mice appeared consistently smaller than wild-type (+/+) siblings and measurements of body length revealed a decrease (5-10%) in 1- and 2-month-old Tsk2/+ mice as well as a decrease in body weight in both age groups as compared to wild-type (+/+) control mice. Femur length was also decreased (2-9%) in Tsk2/+ mice. Finally, in contrast to Tsk/+ mice that display an emphysema-like lung pathology, histological sections of lungs from Tsk2/+ mice were normal and indistinguishable from wild-type (+/+) controls.

IL-6 Signaling Pathway in Keloids: A Target for Pharmacologic Intervention?

Keloids are cosmetically devastating lesions with considerable morbidity. Ghazizadeh et al. document enhanced expression of IL-6 and its receptors in keloid fibroblasts, with a concomitant increase in collagen biosynthesis. Anti-IL-6 antibodies or blocking the IL-6 receptors elicits reduced collagen synthesis, suggesting a role for IL-6 in the regulation of collagen gene expression. These observations imply the feasibility of a pharmacologic platform, based on the targeting of the IL-6 signaling pathway, in keloids.

Hernia disease and collagen gene regulation: are there clues for intervention?

Collagens belong to the most abundant proteins in the body. After tissue injury, a coordinated regulation of collagen gene expression guides the formation of a provisional matrix that subsequently evolves into a mature scar with tensile strength. In the following, knowledge regarding collagen gene regulation that may provide insight into how to specifically address the biological problem of soft tissue weakness and recurrent hernia disease is summarized.

CREB-AP1 Protein Complexes Regulate Transcription of the Collagen XXIV Gene (Col24a1) in Osteoblasts

Collagen XXIV is a newly discovered and poorly characterized member of the fibril-forming family of collagen molecules, which displays unique structural features of invertebrate fibrillar collagens and is expressed predominantly in bone tissue. Here we report the characterization of the proximal promoter of the mouse gene (Col24a1) and its regulation in osteoblastic cells. Using well characterized murine models of osteoblast differentiation, we found that the Col24a1 gene is activated sometime before onset of the late differentiation marker osteocalcin. Additional analyses revealed that Col24a1 produces equal amounts of two alternatively spliced products with different 5'-untranslated sequences that originate from distinct transcriptional start sites. Cell transfection experiments in combination with DNA binding assays demonstrated that Col24a1 promoter activity in ROS17/2.8 osteosarcoma cells is under the control of an upstream cis-acting element, which is shared by both transcripts and is recognized by specific combinations of c-Jun, CREB1, ATF1, and ATF2 dimers. Consistent with these results, overexpression of c-Jun, ATF1, ATF2, or CREB1 in transiently transfected osteoblastic cells stimulated transcription from reporter gene constructs driven by the Col24a1 promoter to different degrees. Moreover, chromatin immunoprecipitation experiments showed that these nuclear factors bind the same upstream sequence of the endogenous Col24a1 gene. Collectively these data provide new information about transcriptional control of collagen fibrillogenesis, in addition to implicating for the first time CREB-AP1 protein complexes in the regulation of collagen gene expression in osteoblasts.

Molecular Aspects of Regulation of Collagen Gene Expression in Fibrosis

Fibrosis, the hyper-accumulation of scar tissue, is characterized by the overproduction and deposition of type I and III collagen by fibroblasts and is the one of the main pathologic outcomes of the autoimmune disorder scleroderma. While the causes of fibrosis in scleroderma are unknown, cytokines such as TGF-beta, IL-4 and IL-13, play a crucial role in the stimulation of collagen production have been implicated in the disease process. In fibroblasts stimulation of collagen production by these cytokines is dependent on the Smad and STAT6 signaling pathways induced by TGF-beta and IL-4, IL-13 respectively. Furthermore, mounting evidence suggest cytokine crosstalk is relevant in the sclerotic process. Our laboratory demonstrated an increase in TGF-beta1 gene transcription from fibroblasts stimulated with IL-4. In addition, TSK/+ mice lacking the IL-4alpha receptor show impaired transcription of the TGF-beta1 gene and did not display fibrosis. Likewise, it appears that STAT6 plays a role in fibroblast TGF-beta1 transcription after IL-4 or IL-13 stimulation. These findings suggest that an epistatic interaction between IL-4 and TGF-beta may exist which is crucial for pathologic sclerotic activity.

The Tumor Suppressor p53 Abrogates Smad-dependent Collagen Gene Induction in Mesenchymal Cells

The pleiotropic cytokine transforming growth factor-beta (TGF-beta) is a potent inducer of collagen synthesis and is implicated in the pathogenesis of fibrosis. Acting in concert with transcriptional coactivators p300/CBP, the Smads mediate TGF-beta stimulation of collagen synthesis in human dermal fibroblasts. Little information exists regarding positive and negative modulation of physiological TGF-beta responses. Because the tumor suppressor p53 is implicated in connective tissue homeostasis, here we examined the regulation of collagen gene expression by p53. Forced expression of ectopic p53 in dermal fibroblasts repressed basal and TGF-beta-stimulated collagen gene expression, whereas the absence of cellular p53 was associated with significantly enhanced transcriptional activity of the Type I collagen gene (COL1A2) and collagen synthesis. Ectopic expression of p53 also repressed TGF-beta stimulation of promoter activity driven by minimal Smad-binding elements, suggesting that p53 modulated Smad-dependent intracellular signaling. Inhibition was not due to altered levels, phosphorylation, or nuclear translocation of cellular Smads. Treatment of fibroblasts with etoposide, a potent inducer of cellular p53, abrogated TGF-beta stimulation of COL1A2 promoter activity and collagen synthesis in a p53-dependent manner. Overexpression of the transcriptional coactivator p300 rescued TGF-beta stimulation of COL1A2 promoter activity in fibroblasts overexpressing p53. Furthermore, the ligand-induced interaction of cellular Smad3 with p300 or with its cognate Smad-binding DNA element and recruitment of p300 to the DNA-protein complex assembled on the Smad-binding element were markedly reduced in p53-overexpressing fibroblasts. Collectively, these results indicate, for the first time, that p53 is a potent and selective endogenous repressor of TGF-beta-regulated collagen gene expression in dermal fibroblasts. The ligand-dependent interaction of Smad3 with p300 may be one of the targets of p53-mediated inhibition of TGF-beta responses. These findings suggest that a novel and important physiologic function for the tumor suppressor p53 is the regulation of fibrotic cellular responses.

080 Synergistic Effect of TGF Beta 1 and HIF‐1A on the Expression of a Hypoxia‐Responsive Element‐Containing Promoter

Accumulating data strongly suggests that under hypoxic conditions the adaptive physiological response of the cells involves co‐operation between oxygen sensing and growth factor signals that cause HIF‐1 mediated gene expression. The HIF‐1 has been identified as a central and critical molecule in oxygen sensing and possibly a master switch. Of the many cytokines that have been shown to modulate collagen production, TGFβ1 appears to be crucial as it can sustain stimulation of collagen production as well as autoinduction of its own synthesis. Several genes that are known to be hypoxia inducible are also up‐regulated by TGFβs, and the promoter of TGFβ3, a member of the family, has a hypoxia‐response element (HRE). Recent reports indicate that HIF‐1α physically interacts with Smad3 and that the TGFβ and hypoxia signaling pathways synergize at the transcriptional level to regulate gene expression. To determine if this interaction upregulates gene expression through the HRE element, we have co‐transfected cultured human dermal fibroblasts with the mammalian expression plasmid for HIF‐1α(pCEP1‐HIF‐1α) with a reporter construct 5HRE‐luc, containing a concatemer of five copies of HRE derived from human vascular endothelial growth factor (VEGF), a minimal cytomegalovirus (CMV) promoter and a reporter gene,luciferase.). When treated with 2 ng/ml of TGFβ1 protein, co‐ transfected hypoxic aged and young human dermal fibroblasts showed significant synergistic upregulation of the reporter gene expression. To further confirm the TGFβ‐HIF‐1α interaction we have created a TGFβ1 ‐RNAi construct by subcloning a 19‐nucleotide sequence derived from rabbit in a mammalian expression vector (p‐SUPER) that directs the synthesis of small interfering RNAs (siRNAs). Hypoxic rabbit cultured dermal fibroblasts co‐transfected with TGFβ1‐RNAi and 5HRE‐luc showed down‐regulation of reporter gene expression.As a prerequisite to understanding the biology of physiological and pathological ischemic tissue repair process it is important to delineate the molecular basis of regulation of collagen gene expression in fibroblasts. Each step in the TGFβ signaling cascade is a potential target for highly specific therapy and information about how hypoxic low‐oxygen microenvironments affect the TGFβ cascade could be useful to develop novel therapeutic strategies that will involve agonist and antagonist agents that directly interfere with these steps.

Role of protein kinase C-δ in the regulation of collagen gene expression in scleroderma fibroblasts

Role of protein kinase C-δ in the regulation of collagen gene expression in scleroderma fibroblasts

Role of protein kinase C-delta in the regulation of collagen gene expression in scleroderma fibroblasts.

Working with cultured dermal fibroblasts derived from control individuals and patients with systemic sclerosis (SSc), we have examined the effects of protein kinase C-delta (PKC-delta) on type I collagen biosynthesis and steady-state levels of COL1A1 and COL3A1 mRNAs. Rottlerin, a specific inhibitor of PKC-delta, exerted a powerful, dose-dependent inhibition of type I and type III collagen gene expression in normal and SSc cells. Optimal rottlerin concentrations caused a 70-90% inhibition of type I collagen production, a >80% reduction in COL1A1 mRNA, and a >70% reduction in COL3A1 mRNA in both cell types. In vitro nuclear transcription assays and transient transfections with COL1A1 promoter deletion constructs demonstrated that rottlerin profoundly reduced COL1A1 transcription and that this effect required a 129-bp promoter region encompassing nucleotides -804 to -675. This COL1A1 segment imparted rottlerin sensitivity to a heterologous promoter. Cotransfections of COL1A1 promoter constructs with a dominant-negative PKC-delta expression plasmid showed that suppression of this kinase silenced COL1A1 promoter activity. The results indicate that PKC-delta participates in the upregulation of collagen gene transcription in SSc and suggest that treatment with PKC-delta inhibitors could suppress fibrosis in this disease.

Cytokine modulation of extracellular matrix gene expression: relevance to fibrotic skin diseases

Fibrotic skin diseases demonstrate a spectrum of phenotypic manifestations with a unifying histopathologic hallmark, i.e. the accumulation of collagen in the lesional skin. Mechanistically, collagen deposition could result either from enhanced biosynthetic activity or reduced rate of degradation, thus leading to an imbalance in physiological turnover of collagen in the dermis. This overview summarizes the mechanisms of regulation of collagen gene expression in fibroblasts as exemplified by cytokine modulation. This summary also provides evidence in support of the notion that transcriptional activation of collagen gene expression is the underlying mechanism leading to development of fibrotic cutaneous lesions, as documented in keloids, a prototypic example of cutaneous fibrosis.

Alterations in the regulation of expression of the alpha 1(I) collagen gene (COL1A1) in systemic sclerosis (scleroderma).

At present, the mechanisms that regulate the expression of collagen genes in normal and pathologic fibroblasts are not known. Thus, the detailed study of transcriptional regulation of COL1A1 in SSc cells will increase our current understanding of the pathophysiology of fibrotic diseases. These studies will yield valuable information regarding the important biological process of regulation of collagen gene expression under normal and pathologic conditions, a process that has remained elusive despite intense recent investigations. It is now evident that persistent overproduction of collagen is responsible for the progressive nature of tissue fibrosis in SSc. Up-regulation of collagen gene expression in SSc fibroblasts appears to be a critical event in this process. The coordinate transcriptional activation of numerous collagen genes suggests a fundamental alteration in the regulatory control of gene expression in SSc fibroblasts. Trans-acting nuclear factors which bind to cis-acting elements in enhancer (intronic) and promoter regions of the genes modulate the basal and inducible transcriptional activity of the collagen genes. The identification of the nuclear transcription factors that regulate normal collagen gene expression may provide promising approaches to the therapy of this incurable disease.

Pulmonary and systemic vascular tissue collagen, growth factor, and cytokine gene expression in the rabbit

During development, the vascular wall composition of the pulmonary and systemic capacitance vessels and their intravascular pressure changes. Little is known, however, about the factors controlling vascular collagen gene expression in both circulations during growth and development. The purpose of this study was to compare the developmental changes in collagen, major growth factors, and cytokines gene expression, in order to ascertain whether a circulation specific pattern is present in the rabbit. Fetal, neonatal, and adult rabbit extrapulmonary and aortic tissues were obtained and the mRNA levels for collagen I and III, as well as major growth factors and cytokines, were measured by a semi-quantitative RT-PCR technique. Collagen I, but not collagen III, expression was developmentally regulated in pulmonary vascular and aorta tissues. Collagen I expression was greatest during the fetal and neonatal period (P < 0.01) and higher in the aorta as compared with the pulmonary artery at these ages (P < 0.05). Significant developmental changes in growth factor mRNA levels were observed for TGF-beta, IGF-2, and bFGF (P < 0.01). IGF-2 mRNA levels significantly declined in both arteries from neonatal to adult, but bFGF increased only in the pulmonary artery during this transition. With regards to inducible enzymes, COX-2 mRNA levels changed developmentally, whereas iNOS mRNA levels were similar for both vessels at all ages. When comparing the two vessels, COX-2 transcripts were relatively more abundant in the adult pulmonary artery tissue and fetal aorta, with similar levels in the newborn. We conclude that circulation specific developmental regulation of collagen gene expression is present in the rabbit in a pattern that is unrelated to the intravascular pressure.

Pulmonary and systemic vascular tissue collagen, growth factor, and cytokine gene expression in the rabbit

During development, the vascular wall composition of the pulmonary and systemic capacitance vessels and their intravascular pressure changes. Little is known, however, about the factors controlling vascular collagen gene expression in both circulations during growth and development. The purpose of this study was to compare the developmental changes in collagen, major growth factors, and cytokines gene expression, in order to ascertain whether a circulation specific pattern is present in the rabbit. Fetal, neonatal, and adult rabbit extrapulmonary and aortic tissues were obtained and the mRNA levels for collagen I and III, as well as major growth factors and cytokines, were measured by a semi-quantitative RT-PCR technique. Collagen I, but not collagen III, expression was developmentally regulated in pulmonary vascular and aorta tissues. Collagen I expression was greatest during the fetal and neonatal period (P < 0.01) and higher in the aorta as compared with the pulmonary artery at these ages (P < 0.05). Significant developmental changes in growth factor mRNA levels were observed for TGF-beta, IGF-2, and bFGF (P < 0.01). IGF-2 mRNA levels significantly declined in both arteries from neonatal to adult, but bFGF increased only in the pulmonary artery during this transition. With regards to inducible enzymes, COX-2 mRNA levels changed developmentally, whereas iNOS mRNA levels were similar for both vessels at all ages. When comparing the two vessels, COX-2 transcripts were relatively more abundant in the adult pulmonary artery tissue and fetal aorta, with similar levels in the newborn. We conclude that circulation specific developmental regulation of collagen gene expression is present in the rabbit in a pattern that is unrelated to the intravascular pressure.