Role of latent TGF-beta 1 binding protein in vascular remodeling

Characteristic adaptations of the extracellular matrix in dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a relatively common heart muscle disease characterized by the dilation and thinning of the left ventricle accompanied with left ventricular systolic dysfunction. Myocardial fibrosis is a major feature in DCM and therefore it is inevitable that corresponding extracellular matrix (ECM) changes are involved in DCM onset and progression. Increasing our understanding of how ECM adaptations are involved in DCM could be important for the development of future interventions. This review article discusses the molecular adaptations in ECM composition and structure that have been reported in both animal and human studies of DCM. Furthermore, we provide a transcriptome-based catalogue of ECM genes that are associated with DCM, generated by using NCBI Gene Expression Omnibus database sets for DCM. Based on this in silico analysis, many novel ECM components involved in DCM are identified and discussed in this review. With the information gathered, we propose putative pathways of ECM adaptations in onset and progression of DCM.

Grafting and early expression of growth factors from adipose-derived stem cells transplanted into the cochlea, in a Guinea pig model of acoustic trauma

Noise exposure causes damage of multiple cochlear cell types producing permanent hearing loss with important social consequences. In mammals, no regeneration of either damaged hair cells or auditory neurons has been observed and no successful treatment is available to achieve a functional recovery. Loads of evidence indicate adipose-derived stem cells (ASCs) as promising tools in diversified regenerative medicine applications, due to the high degree of plasticity and trophic features. This study was aimed at identifying the path of in vivo cell migration and expression of trophic growth factors, upon ASCs transplantation into the cochlea, following noise-induced injury. ASCs were isolated in primary culture from the adipose tissue of a guinea pig, transduced using a viral vector to express the green fluorescent protein, and implanted into the scala tympani of deafened animals. Auditory function was assessed 3 and 7 days after surgery. The expression of trophic growth factors was comparatively analyzed using real-time PCR in control and noise-injured cochlear tissues. Immunofluorescence was used to assess the in vivo localization and expression of trophic growth factors in ASCs and cochleae, 3 and 7 days following homologous implantation. ASC implantation did not modify auditory function. ASCs migrated from the perilymphatic to the endolymphatic compartment, during the analyzed time course. Upon noise exposure, the expression of chemokine ligands and receptors related to the PDGF, VEGF, and TGFbeta pathways, increased in the cochlear tissues, possibly guiding in vivo cell migration. Immunofluorescence confirmed the increased expression, which appeared to be further strengthened by ASCs’ implantation. These results indicated that ASCs are able to migrate at the site of tissue damage and express trophic factors, upon intracochlear implantation, providing an original proof of principle, which could pave the way for further developments of ASC-based treatments of deafness.

Spontaneous massive necrosis of hepatocellular carcinoma with narrowing and occlusion of the arteries and portal veins

We herein present the case of a 77-year-old man who had fever and right hypochondriac pain. He visited his doctor and underwent contrast computed tomography (CT), and he was suspected to have a liver abscess. He received an antibiotic treatment and his symptoms soon disappeared, but the tumor did not get smaller and its density on contrast CT image got stronger. He underwent biopsy and moderately differentiated hepatocellular carcinoma (HCC) was found. Extended left hepatic and caudate lobectomy was performed. Histological examination showed moderately differentiated HCC with narrowing and occlusion both in the arteries and portal veins associated with mild chronic inflammation. The mechanisms of spontaneous regression of HCC, such as immunological reactions and tumor hypoxia, have been proposed. In our case, histological examination showed the same findings. However, the mechanism is complex, and therefore further investigations are essential to elucidate it.

Injury-activated transforming growth factor β controls mobilization of mesenchymal stem cells for tissue remodeling

Upon secretion, transforming growth factor β (TGFβ) is maintained in a sequestered state in extracellular matrix as a latent form. The latent TGFβ is considered as a molecular sensor that releases active TGFβ in response to the perturbations of the extracellular matrix at the situations of mechanical stress, wound repair, tissue injury, and inflammation. The biological implication of the temporal discontinuity of TGFβ storage in the matrix and its activation is obscure. Here, using several animal models in which latent TGFβ is activated in vascular matrix in response to injury of arteries, we show that active TGFβ controls the mobilization and recruitment of mesenchymal stem cells (MSCs) to participate in tissue repair and remodeling. MSCs were mobilized into the peripheral blood in response to vascular injury and recruited to the injured sites where they gave rise to both endothelial cells for re-endothelialization and myofibroblastic cells to form thick neointima. TGFβs were activated in the vascular matrix in both rat and mouse models of mechanical injury of arteries. Importantly, the active TGFβ released from the injured vessels is essential to induce the migration of MSCs, and cascade expression of monocyte chemotactic protein-1 stimulated by TGFβ amplifies the signal for migration. Moreover, sustained high levels of active TGFβ were observed in peripheral blood, and at the same time points following injury, Sca1+ CD29+ CD11b- CD45- MSCs, in which 91% are nestin+ cells, were mobilized to peripheral blood and recruited to the remodeling arteries. Intravenously injection of recombinant active TGFβ1 in uninjured mice rapidly mobilized MSCs into circulation. Furthermore, inhibitor of TGFβ type I receptor blocked the mobilization and recruitment of MSCs to the injured arteries. Thus, TGFβ is an injury-activated messenger essential for the mobilization and recruitment of MSCs to participate in tissue repair/remodeling.

Latent transforming growth factor-beta binding protein-1, a component of latent transforming growth factor-beta complex, accelerates the migration of aortic smooth muscle cells in diabetic rats through integrin-beta3

Aortic smooth muscle cells (SMCs) of diabetic animals have unique properties, including the overexpression of transforming growth factor-beta (TGF-beta) type II receptor, fibronectin, and platelet-derived growth factor beta-receptor. TGF-beta1 is produced and secreted as latent high-molecular weight complex consisting of mature TGF-beta1, latency-associated peptide (LAP), and a latent TGF-beta1 binding protein (LTBP-1). LAP has an important function in the latency of TGF-beta complex, but the role of LTBP-1 is not known in diabetic angiopathy. SMC migration from the medial layer to the intimal layer of an artery is an initial major process of the formation of intimal thickening of an artery. Migration activities of SMCs from diabetic rat with 1-500 pg/ml of LTBP-1 increased significantly compared with that without LTBP-1. LTBP-1 at 10-500 pg/ml stimulated the migration of diabetic SMCs more than SMCs from control rat. An anti-integrin-beta(3) antibody reduced LTBP-1-stimulated migration of diabetic SMCs to 51% compared with no antibody, but it did not reduce that of control SMCs. Furthermore, cross-linking experiments show that LTBP-1 binds integrin-beta(3) in diabetic SMCs much more than in control SMCs in coincidence with the increase of integrin-beta(3) in diabetic aorta by immunohistochemistry. Taken together, these observations suggest that LTBP-1 plays a critical role in intimal thickening of diabetic artery through the acceleration of SMC migration via integrin-beta(3).

Hypoxia induces different genes in the lungs of rats compared with mice

Different animal species have a varying response to hypoxia. Mice develop less pulmonary artery thickening after chronic hypoxia exposure than rats. We hypothesized that the lung tissue gene expression pattern displayed in hypoxic rats would differ from that of hypoxic mice. We exposed Sprague-Dawley rats and C57BL/6 mice to both 1 and 3 wk of hypobaric hypoxia. Although both species developed pulmonary hypertension, mice showed less pulmonary vascular remodeling than rats. Microarray gene analysis demonstrated a distinct pattern of gene expression between mice and rats when exposed to hypoxic conditions. In addition, some genes appeared to be more responsive at an earlier time point of 1 wk of hypoxia. Hypoxic conditions in the rat induce genes involved in endothelial cell proliferation, repression of apoptosis, and vasodilation. Mice exposed to hypoxic conditions decrease the expression of genes involved in vasodilation and in endothelial cell proliferation. Although we cannot determine whether the differential expression of genes during chronic hypoxia is cause or consequence of the differential pulmonary vascular remodeling, we propose that a balance between over- and under-expression of a selective group of genes may be responsible for lung vascular remodeling and vascular tone control.

Novel non-TGF-β-binding splice variant of LTBP-4 in human cells and tissues provides means to decrease TGF-β deposition

Small latent TGF-β consists of latency associated peptide (LAP) bound to the 25 kDa TGF-β by noncovalent interactions. Small latent TGF-β is secreted from cells and deposited into the extracellular matrix as covalent complexes with its binding proteins, LTBPs. Four LTBPs have been molecularly cloned and their structures contain repetitive sequences. The 3rd 8-Cys repeats of LTBP-1, -3 and -4 are able to associate with small latent TGF-β. We analyzed by RT-PCR the expression of LTBPs 1-4 in a panel of cultured human cell lines including fibroblasts of different origin, endothelial cells and immortalized keratinocytes. LTBPs were expressed in an overlapping manner, but differences in their expression levels were detected. SV-40 transformed human embryonic lung fibroblasts contained less of the mRNAs for the LTBPs, suggesting that malignant transformation leads to decrease in LTBP expression. A novel alternatively spliced form of LTBP-4 lacking the 3rd 8-Cys repeat (LTBP-4Δ8-Cys3rd) was identified. LTBP-4Δ8-Cys3rd does not bind TGF-β and it was found to be expressed in the same tissues as the full length LTBP-4. The exon-intron structure of LTBP-4 around the 3rd 8-Cys repeat was similar to those of LTBP-2 and -3. LTBP-4Δ8-Cys3rd was produced by alternative splicing over two exons. In addition, HL-60 promyelocytic leukemia cells expressed a splice variant lacking only one exon of this region. The expression of the non-TGF-β-binding variant of LTBP-4 may be important for the regulation of TGF-β deposition in tissues. Since LTBPs are a part of the extracellular matrix microfibrils, the LTBP-4Δ8-Cys3rd protein may also be involved in various structural functions not related to TGF-β signaling.

Latency, activation, and binding proteins of TGF-beta

The TGF-beta superfamily of growth factors consists of an increasing number of different polypeptide modulators of cell growth, differentiation, and morphogenesis. Three mammalian isoforms have been molecularly cloned. Numerous ways to regulate the expression of the TGF-beta genes have been identified. TGF-betas are, for example, subject to regulation by retinoids, steroid hormones, and vitamin D. A characteristic feature in the biology of TGF-betas is that they are usually secreted from cells in latent forms. The large latent complex consists of the small latent complex (TGF-beta and its propeptide) and a high molecular weight protease resistant binding protein, latent TGF-beta binding protein (LTBP). LTBPs are required for the proper folding and secretion of TGF-beta. TGF-beta is not just secreted from cultured cells but is deposited via LTBPs to the pericellular space, namely to the extracellular matrix. Release of these complexes and activation by proteases is under tight regulation and provides a means to rapidly increase local concentrations of TGF-beta. Biological events, where enhanced or focal proteolysis and activation of latent TGF-beta takes place, include cell invasion, tissue remodeling, and wound healing.

The latent transforming growth factor-beta-binding protein-1 promotes in vitro differentiation of embryonic stem cells into endothelium

The latent transforming growth factor-beta-binding protein-1 (LTBP-1) belongs to a family of extracellular glycoproteins that includes three additional isoforms (LTBP-2, -3, and -4) and the matrix proteins fibrillin-1 and -2. Originally described as a TGF-beta-masking protein, LTBP-1 is involved both in the sequestration of latent TGF-beta in the extracellular matrix and the regulation of its activation in the extracellular environment. Whereas the expression of LTBP-1 has been analyzed in normal and malignant cells and rodent and human tissues, little is known about LTBP-1 in embryonic development. To address this question, we used murine embryonic stem (ES) cells to analyze the appearance and role of LTBP-1 during ES cell differentiation. In vitro, ES cells aggregate to form embryoid bodies (EBs), which differentiate into multiple cell lineages. We analyzed LTBP-1 gene expression and LTBP-1 fiber appearance with respect to the emergence and distribution of cell types in differentiating EBs. LTBP-1 expression increased during the first 12 d in culture, appeared to remain constant between d 12 and 24, and declined thereafter. By immunostaining, fibrillar LTBP-1 was observed in those regions of the culture containing endothelial, smooth muscle, and epithelial cells. We found that inclusion of a polyclonal antibody to LTBP-1 during EB differentiation suppressed the expression of the endothelial specific genes ICAM-2 and von Willebrand factor and delayed the organization of differentiated endothelial cells into cord-like structures within the growing EBs. The same effect was observed when cultures were treated with either antibodies to TGF-beta or the latency associated peptide, which neutralize TGF-beta. Conversely, the organization of endothelial cells was enhanced by incubation with TGF-beta 1. These results suggest that during differentiation of ES cells LTBP-1 facilitates endothelial cell organization via a TGF-beta-dependent mechanism.

Latent transforming growth factor-beta binding proteins (LTBPs)--structural extracellular matrix proteins for targeting TGF-beta action

Growth factors of the transforming growth factor-beta family are potent regulators of the extracellular matrix formation, in addition to their immunomodulatory and regulatory roles for cell growth. TGF-beta s are secreted from cells as latent complexes containing TGF-beta and its propeptide, LAP (latency-associated peptide). In most cells LAP is covalently linked to an additional protein, latent TGF-beta binding protein (LTBP), forming the large latent complex. LTBPs are required for efficient secretion and correct folding of TGF-beta s. The secreted large latent complexes associate covalently with the extracellular matrix via the N-termini of the LTBPs. LTBPs belong to the fibrillin-LTBP family of extracellular matrix proteins, which have a typical repeated domain structure consisting mostly of epidermal growth factor (EGF)-like repeats and characteristic eight cysteine (8-Cys) repeats. Currently four different LTBPs and two fibrillins have been identified. LTBPs contain multiple proteinase sensitive sites, providing means to solubilize the large latent complex from the extracellular matrix structures. LTBPs are now known to exist both as soluble molecules and in association with the extracellular matrix. An important consequence of this is LTBP-mediated deposition and targeting of latent, activatable TGF-beta into extracellular matrices and connective tissues. LTBPs have a dual function, they are required both for the secretion of the small latent TGF-beta complex as well as directing bound latent TGF-beta to extracellular matrix microfibrils. However, it is not known at present whether LTBPs are capable of forming microfibrils independently, or whether they are a part of the fibrillin-containing fibrils. Most LTBPs possess RGD-sequences, which may have a role in their interactions with the cell surface. At least LTBP-1 is chemotactic to smooth muscle cells, and is involved in vascular remodelling. Analyses of the expressed LTBPs have revealed considerable variations throughout the molecules, generated both by alternative splicing and utilization of multiple promoter regions. The significance of this structural diversity is mostly unclear at present.

Cellular and extracellular biology of the latent transforming growth factor-beta binding proteins

The latent transforming growth factor-beta binding proteins (LTBP) are a recently identified family of widely expressed multidomain glycoproteins that range in size from 125 kDa to 240 kDa. Four LTBP genes have been described, and the homology of latent transforming growth factor-beta binding proteins molecules to the fibrillins has resulted in their inclusion in the so-called 'fibrillin superfamily'. They form intracellular covalent complexes with latent transforming growth factor-beta and target these growth factors to the extracellular matrix. This review describes their structure, summarizes current understanding of their dual roles as growth factor binding proteins and components of the extracellular matrix, and highlights their significance in tissue development and disease.