Biomedical subjects

Francesco Ramirez

Publications and source records attributed to Francesco Ramirez.

29 records · Page 2Linked to original sources

PubMed2004

Esophageal muscle physiology and morphogenesis require assembly of a collagen XIX-rich basement membrane zone.

Collagen XIX is an extremely rare extracellular matrix component that localizes to basement membrane zones and is transiently expressed by differentiating muscle cells. Characterization of mice harboring null and structural mutations of the collagen XIX (Col19a1) gene has revealed the critical contribution of this matrix protein to muscle physiology and differentiation. The phenotype includes smooth muscle motor dysfunction and hypertensive sphincter resulting from impaired swallowing-induced, nitric oxide-dependent relaxation of the sphincteric muscle. Muscle dysfunction was correlated with a disorganized matrix and a normal complement of enteric neurons and interstitial cells of Cajal. Mice without collagen XIX exhibit an additional defect, namely impaired smooth-to-skeletal muscle cell conversion in the abdominal segment of the esophagus. This developmental abnormality was accounted for by failed activation of myogenic regulatory factors that normally drive esophageal muscle transdifferentiation. Therefore, these findings identify collagen XIX as the first structural determinant of sphincteric muscle function, and as the first extrinsic factor of skeletal myogenesis in the murine esophagus.

Animals↗

PubMed2004

Therapy insight: aortic aneurysm and dissection in Marfan's syndrome.

Aortic dissection and aneurysm are common clinical problems with life-threatening consequences; they are also the hallmark of several genetic diseases, including Marfan's syndrome (MFS). In spite of clinical and surgical advances that have increased life expectancy for affected patients, cardiovascular manifestations remain significant contributors to morbidity and mortality in MFS. Dissecting aortic aneurysm in this disorder is accounted for by mutations in fibrillin-1, the major component of the microfibrils associated with elastin in the elastic fibers of the aortic media. Genetic studies of human patients and murine models have yielded invaluable insights into the pathophysiology of aneurysm formation and progression in MFS. They have also revealed a previously unappreciated role of microfibrils in regulating transforming growth factor and bone morphogenetic protein signaling. As a result, exciting new hypotheses have emerged regarding the pathogenesis of MFS, as well as opportunities to explore translational applications of this information that may be relevant to various manifestations of the disease.

Adrenergic beta-Antagonists↗

PubMed2004

Development of a functional skin matrix requires deposition of collagen V heterotrimers.

Collagen V is a minor component of the heterotypic I/III/V collagen fibrils and the defective product in most cases of classical Ehlers Danlos syndrome (EDS). The present study was undertaken to elucidate the impact of collagen V mutations on skin development, the most severely affected EDS tissues, using mice harboring a targeted deletion of the alpha2(V) collagen gene (Col5a2). Contrary to the original report, our studies indicate that the Col5a2 deletion (a.k.a. the pN allele) represents a functionally null mutation that affects matrix assembly through a complex sequence of events. First the mutation impairs assembly and/or secretion of the alpha1(V)(2)alpha2(V) heterotrimer with the result that the alpha1(V) homotrimer is the predominant species deposited into the matrix. Second, the alpha1(V) homotrimer is excluded from incorporation into the heterotypic collagen fibrils and this in turn severely impairs matrix organization. Third, the mutant matrix stimulates a compensatory loop by the alpha1(V) collagen gene that leads to additional deposition of alpha1(V) homotrimers. These data therefore underscore the importance of the collagen V heterotrimer in dermal fibrillogenesis. Furthermore, reduced thickness of the basement membranes underlying the epidermis and increased apoptosis of the stromal fibroblasts in pN/pN skin strongly indicate additional roles of collagen V in the development of a functional skin matrix.

Animals↗

PubMed2004

Identification of MoKA, a novel F-box protein that modulates Krüppel-like transcription factor 7 activity.

KLF7, a member of the Krüppel-like transcription factor family, is believed to regulate neurogenesis and cell cycle progression. Here, a yeast two-hybrid screen for KLF7 cofactors in the developing nervous system identified a novel 140-kDa protein named MoKA, for modulator of KLF7 activity. Interaction between MoKA and KLF7 was confirmed by the in vitro glutathione S-transferase pull-down assay and by coimmunoprecipitation of the proteins overexpressed in mammalian cells. Functional assays documented that MoKA is a KLF7 coactivator, and in situ hybridizations identified the developing nervous system and the adult testes as two sites of MoKA and Klf7 coexpression. Chromatin immunoprecipitation experiments demonstrated KLF7 binding to the p21(WAF1/Cip1) gene while transient transfection assays documented KLF7 stimulation of the p21(WAF1/Cip1) proximal promoter. Additional tests revealed that distinct structural motifs of MoKA direct interaction with KLF7 and shuttling between the nucleus and cytoplasm of asynchronously cycling cells. Altogether, our results strongly suggest that MoKA and KLF7 interact functionally to regulate gene expression during cell differentiation and identify the cell cycle regulator p21(WAF1/Cip1) as one of the targeted genes.

Amino Acid Sequence↗

PubMed2003

Identification of the Drosophila progenitor of mammalian Krüppel-like factors 6 and 7 and a determinant of fly development.

The Krüppel-like transcription factors (KLFs) represent a family of 15 different zinc finger proteins of the C(2)H(2) type that are involved in vertebrate development and which control cell proliferation, growth and differentiation. Structural-functional considerations have segregated KLF6 and KLF7 into a phylogenetically distinct group. Here we report the identification of Luna, the Drosophila progenitor of the mammalian KLF6/KLF7 group. This conclusion is based on the near sequence identity, as well as the comparable location of the DNA-binding domains and nuclear localization signals of the insect and mammalian proteins. The homology extends to the composition and function of the amino-terminal segment of Luna which, similarly to the mammalian counterparts, stimulates transcription in a reporter gene assay. We also present preliminary in vivo evidence of Luna involvement in embryonic development and cell differentiation. First, luna RNA interference and luna overexpression during early Drosophila embryogenesis leads to developmental arrest at different embryonic stages. Second, targeted perturbation of luna expression in the forming compound eye interferes with terminal cell differentiation, but not cell specification. We therefore propose that Luna is a novel transcriptional determinant of Drosophila development.

Amino Acid Sequence↗

PubMed2003

Downregulation and growth inhibitory effect of epithelial-type Krüppel-like transcription factor KLF4, but not KLF5, in bladder cancer.

Krüppel-like factors (KLFs) are key transcriptional regulators of cell differentiation and proliferation. Among the KLF family, the expression of KLF4 (GKLF) and KLF5 (IKLF) is highly restricted in the epithelial cells of several organs such as the gut and skin, and it has been reported that these epithelial-type KLF genes may be involved in colon carcinogenesis. Recently we found that Klf4 and Klf5 genes were significantly expressed in the developmental bladder epithelium of mice as well. Therefore, in this report we studied the involvement of the KLF4 and KLF5 genes in bladder carcinogenesis. First, we analyzed the expression of KLF4 and KLF5 in a variety of human bladder cancer cell lines and surgical specimens by RNA blot and in situ hybridization analyses. Both genes were highly expressed in the normal bladder epithelium, whereas KLF4, but not KLF5, was frequently downregulated in bladder cancer cell lines and cancer tissues. We then transduced the KLF4 and KLF5 genes into the bladder cancer cell lines using adenoviral vectors to examine the biological activities of the genes on those cells. The transduction of KLF4, but not KLF5, suppressed cell growth and induced apoptosis. Our study suggests that inactivation of KLF4 is one of the frequent steps towards bladder carcinogenesis.

Adenoviridae↗

PubMed2003

Collagen XXIV, a vertebrate fibrillar collagen with structural features of invertebrate collagens: selective expression in developing cornea and bone.

Tissue-specific assembly of fibers composed of the major collagen types I and II depends in part on the formation of heterotypic fibrils, using the quantitatively minor collagens V and XI. Here we report the identification of a new fibrillar-like collagen chain that is related to the fibrillar alpha1(V), alpha1(XI), and alpha2(XI) collagen polypeptides and which is coexpressed with type I collagen in the developing bone and eye. The new collagen was designated the alpha1(XXIV) chain and consists of a long triple helical domain flanked by typical propeptide-like sequences. The carboxyl propeptide is classic, with 8 conserved cysteine residues. The amino-terminal peptide contains a thrombospodin-N-terminal-like (TSP) motif and a highly charged segment interspersed with several tyrosine residues, like the fibril diameter-regulating collagen chains alpha1(V) and alpha1(XI). However, a short imperfection in the triple helix makes alpha1(XXIV) unique from other chains of the vertebrate fibrillar collagen family. The triple helical interruption and additional select features in both terminal peptides are common to the fibrillar chains of invertebrate organisms. Based on these data, we propose that collagen XXIV is an ancient molecule that may contribute to the regulation of type I collagen fibrillogenesis at specific anatomical locations during fetal development.

Amino Acid Motifs↗

PubMed2003

Dysregulation of TGF-beta activation contributes to pathogenesis in Marfan syndrome.

Marfan syndrome is an autosomal dominant disorder of connective tissue caused by mutations in fibrillin-1 (encoded by FBN1 in humans and Fbn1 in mice), a matrix component of extracellular microfibrils. A distinct subgroup of individuals with Marfan syndrome have distal airspace enlargement, historically described as emphysema, which frequently results in spontaneous lung rupture (pneumothorax; refs. 1-3). To investigate the pathogenesis of genetically imposed emphysema, we analyzed the lung phenotype of mice deficient in fibrillin-1, an accepted model of Marfan syndrome. Lung abnormalities are evident in the immediate postnatal period and manifest as a developmental impairment of distal alveolar septation. Aged mice deficient in fibrillin-1 develop destructive emphysema consistent with the view that early developmental perturbations can predispose to late-onset, seemingly acquired phenotypes. We show that mice deficient in fibrillin-1 have marked dysregulation of transforming growth factor-beta (TGF-beta) activation and signaling, resulting in apoptosis in the developing lung. Perinatal antagonism of TGF-beta attenuates apoptosis and rescues alveolar septation in vivo. These data indicate that matrix sequestration of cytokines is crucial to their regulated activation and signaling and that perturbation of this function can contribute to the pathogenesis of disease.

Animals↗

PubMed2003

Magnetic resonance microscopy quantifies the disease progression in Marfan syndrome mice.

PURPOSE: To use noninvasive magnetic resonance microscopy (MRM) to examine aneurysmal disease in the mouse model of Marfan syndrome (MFS). MATERIALS AND METHODS: A total of eight wild-type (WT) and MFS mice were imaged using MRM; four of them at three different time points over an 8-week period and the remaining animals were imaged at one time point. The maximal cross-sectional area of the aorta was measured by manual tracing and by automated means from combined cardiac and respiratory-gated bright-blood images. Relationships between aortic size and age and the differences between WT and mutant mice aortic size were established. RESULTS: Maximal cross-sectional aortic areas differed significantly (P < 0.05) between WT and mutant mice for all time points, with MFS mice having larger aortic size. There was a positive correlation between aortic size and age in MFS mice (r = 0.80) with a significant increase from the 14th to the 22nd week (P < 0.05). CONCLUSION: MRM detected the differences in aortic size between WT and mutant mice over time, demonstrating a potential for noninvasive technique for the assessment of potential therapies in MFS mice.

Analysis of Variance↗

PubMed2003

Cell signaling events: a view from the matrix.

Cellular activities are primarily initiated, modulated and sustained by multifunctional molecules (cytokines and growth factors) that are secreted into the extracellular space and that signal through membrane-bound, high-affinity receptors. In contrast to the fairly well understood mechanisms that mediate the specificity of signal transduction within the confined and compartmentalized environment of the cell, significantly less is known about the mechanisms that regulate the availability of signaling molecules in the extracellular milieu. Recent findings have implicated the participation of extracellular protein macroaggregates in signaling events controlling patterning and morphogenesis. The results suggest a functional coupling between the tissue-specific organization of collagenous and elastic macroaggregates and their ability to perform instructive as well as structural functions. These observations open the way to a novel understanding in these poorly understood and critically important areas of cell and developmental biology.

Animals↗

PubMed2002

A report on the 3rd Workshop on Heritable Disorders of Connective Tissue.

The 3rd Workshop on Heritable Disorders of Connective Tissue was held at the National Institutes of Health from 16th to 18th November, 2000. The Workshop was sponsored by the National Institute of Arthritis and Musculoskeletal and Skin Diseases, NIH Office of Rare Diseases, March of Dimes, Coalition for Heritable Disorders of Connective Tissue, and the Foundation for Basic Cutaneous Research. It was supported by specific grants R13 AR46912 (US Public Health Service) and 4-FY00-4511 (March of Dimes Birth Defects Foundation). The Workshop was divided into six sessions, featuring 29 invited presentations. In addition to the invited participants, more than eighty guests (scientists, NIH staff, and members of the Coalition for Heritable Disorders of Connective Tissue) attended.

Collagen↗