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K T Weber

Publications and source records attributed to K T Weber.

At least 37 records · Page 2Linked to original sources
PubMed1999

Angiotensin II receptor blockade during gestation attenuates collagen formation in the developing rat heart.

OBJECTIVE: Fetal cardiac development includes rapid formation of a three-dimensional collagen network, composed mainly of type I and III fibrillar collagens. Collagen fibrils have been found in cardiac jelly at very early stages of cardiac development and are thought to have structural and functional properties. In adult rat cardiac tissue, angiotensin II (AngII) via AT1 receptor binding and AngII-regulated expression of transforming growth factor beta-1 (TGF-beta 1) each upregulate collagen transcription. AT1 and AT2 receptor subtypes are developmentally regulated; both have been localized in fetal tissue where the AT2 receptor is considered a determinant of morphogenesis. We sought to determine whether blockade of either receptor would result in attenuation of collagen mRNA expression and fibrillar collagen accumulation and alter TGF-beta 1 mRNA expression in the developing fetal heart examined at birth. METHODS: Pregnant rats were treated either with an AT1 receptor antagonist losartan or an AT2 receptor antagonist PD123319 and compared with untreated age-matched controls. Offspring were studied within 24 h of birth. Type I and type III collagen mRNA expression, as well as TGF-beta 1 mRNA expression, were examined by in situ hybridization. Collagen concentration was determined spectrophotometrically by picrosirius red staining and type I and III collagens were detected by immunoblotting. RESULTS: We found: (1) comparable birth weights in control and PD123319-treated animals, but reduced body weight in newborn losartan-treated animals; (2) compared to untreated animals, type I collagen and TGF-beta 1 mRNA expression in cardiac tissue were each equally reduced in both losartan and PD123319-treated animals; (3) increased type III collagen mRNA expression in both PD123319- and losartan-treated groups; and (4) a significant decrease in total soluble cardiac collagen concentration in both losartan and PD123319-treated groups, confirmed by attenuated immunoreactivity of type I and III collagens in whole heart extracts by Western blotting. CONCLUSIONS: The results of these pharmacologic interventions suggest AngII receptors are expressed in cardiac tissue during gestation, where both AT1 and AT2 receptors are involved in the regulation of type I and III collagen expression and structural protein accumulation. These effects appear to be mediated, in part, by attenuated cardiac TGF-beta 1 levels. The marked decrease in newborn cardiac collagen content has yet undefined functional consequences.

Angiotensin II↗
PubMed1998

chk-YB-1b, a Y-box binding protein activates transcription from rat alpha1(I) procollagen gene promoter.

Type-I collagen, the predominant component of extracellular matrix, is a triple-helical protein consisting of two alpha1 polypeptides and one alpha2 polypeptide. Expression of alpha1 and alpha2 procollagen genes is co-ordinately regulated under both normal and various pathological conditions. However, the basis of this co-ordinate regulation is not well known. YB-1b, a Y-box protein, has been shown to bind to the polypyrimidine tract present in the alpha2 procollagen gene. Here, we show that chk-YB-1b, a YB-1 homologue, binds in a single-strand-sequence-specific manner to the highly conserved pyrimidine-rich sequences in both alpha1(I) and alpha2(I) procollagen promoters from different species, as demonstrated by electrophoretic-mobility-shift assays and by DNaseI footprinting experiments. Transiently transfected and retrovirally expressed antisense oligonucleotides directed against chk-YB-1b specifically inhibited the alpha1(I) procollagen promoter-driven transcription in cultured fibroblasts. Considering these data and the fact that the chk-YB-1b binding site is one of the few sites between alpha1(I) and alpha2(I) procollagen promoters that is conserved from chicken to human, it is proposed that chk-YB-1b may be involved in co-ordinate expression of these two collagen genes.

Animals↗
PubMed1998

Triple helix formation with the promoter of human alpha1(I) procollagen gene by an antiparallel triplex-forming oligodeoxyribonucleotide.

The promoters of alpha1(I) procollagen genes of vertebrates contain two contiguous stretches of polypyrimidine/polypurine sequences, referred to as C1 (-140 to -170) and C2 (-171 to -200). Antiparallel triplex-forming upstream oligonucleotides form efficient triplexes with C1. The C1 tract of human differs from rodent alpha1(I) promoters by 7 nt which are mainly A-->G transitions. Human triplex-forming oligodeoxyribonucleotide (TFO) formed stable triplexes efficiently with a K d of approximately 10-20 nM compared with a K d of approximately 100 nM for rodent TFO. Mutational analysis indicated that 3 or 4 nt (-153 to -155) are sufficient for this higher affinity. TFOs specific for human C1 inhibited transcription from human promoter both in vitro in HeLa cell nuclear extracts and in vivo in cultured chick embryo fibroblasts.

Animals↗
PubMed1998

Myocardial fibrosis associated with aldosterone or angiotensin II administration: attenuation by calcium channel blockade.

Chronic administration of either angiotensin II (Ang II) or aldosterone (ALDO) leads to myocardial fibrosis. Myofibroblasts (myoFb) play a major role in collagen accumulation at sites of tissue repair. Pathophysiologic bases of cardiac fibrosis in such chronic primary or secondary hyperaldosteronism are under investigation. In vitro studies have shown that Ang II and ALDO each increase intracellular calcium and this second messenger is involved in altered fibroblast collagen turnover and growth. In the present study, we tested our hypothesis that calcium channel blockade would attenuate myocardial fibrosis that accompanies administration of either circulating Ang II or ALDO. Five animal groups were studied: (1) untreated age- and sex-matched control rats; (2) intact rats receiving Ang II (75 ng/min) for 2 weeks; (3) rats receiving Ang II plus mibefradil (30 mg/kg/day p.o.), a calcium channel blocker, for 2 weeks; (4) uninephrectomized rats receiving ALDO (0.75 microgram/h) together with a high salt diet for 6 weeks; and (5) uninephrectomized rats receiving ALDO and high salt diet plus mibefradil. Myocardial fibrosis was assessed by hydroxyproline concentration and interstitial and perivascular collagen volume fraction examined by videodensitometry on heart sections stained with collagen-specific picrosirius red. MyoFb were identified by immunohistochemical alpha-smooth muscle actin (SMA) labeling. ACE binding was determined by in vitro quantitative autoradiography. Compared to controls, in rats receiving either Ang II or ALDO we found: (1) myocardial fibrosis, expressed as microscopic scars, and perivascular fibrosis in both right and left ventricles with increased (P<0.05) hydroxyproline concentration and collagen volume fraction; (2) myoFb at sites of fibrosis, where high ACE binding density was also present; and (3) hydroxyproline concentration and collagen volume fraction were significantly (P<0.05) attenuated and the extent of alpha-SMA labeling and ACE binding density were each markedly (P<0.01) reduced in rats receiving either hormone plus mibefradil. This study therefore suggests calcium may modulate fibrous tissue formation in rat models of hyperaldosteronism by altering MyoFb collagen turnover and cell growth. It further is our contention that these findings implicate calcium as a signal used by effector hormones of the RAAS to promote tissue repair and that calcium channel blockade may offer advantage as a cardioprotective strategy in this setting.

Aldosterone↗
PubMed1998

Pouch tissue and angiotensin peptide generation.

Myofibroblasts and their potential to generate angiotensin (Ang) II and transforming growth factor beta 1 (TGF-beta 1) at sites of infarction in the rat heart have been implicated in tissue repair. These cells likewise contribute to repair in a subcutaneous pouch model of fibrous tissue formation. Their appearance in pouch tissue coincides with high density ACE and Ang II receptor binding, suggesting a role for Ang II in tissue repair. Using pouch tissue studied at different time points of repair, the present study examined the expression of requisite mRNA for Ang peptide generation: angiotensinogen, Ao; an aspartyl protease, either cathepsin-D, Cat-D, or renin: and angiotensin converting enzyme, ACE, TGF-beta 1 and type I collagen mRNA expression was also addressed. Unlike pouch studied on day 2 and 4, at 7, 14 and 21 days, we found: (a) expression of Ao, Cat-D but not renin, ACE and TGF-beta 1 mRNA; (b) Ang I and Ang II peptides in pouch tissue and exudate; (c) the presence of Cat-D activity but no renin activity; (d) an increase in type I collagen mRNA with time; (e) upregulation of pouch tissue ACE mRNA expression by lisinopril treatment, whereas AT1 and AT2 receptor antagonists (losartan and PD 123177, respectively) downregulated the expression of mRNA for ACE, when compared to untreated controls; (f) downregulation of TGF-beta 1 mRNA expression by lisinopril and losartan compared to untreated controls; and (g) PD 123177 had no effect, whereas lisinopril and losartan treatment significantly (P < 0.05) reduced type I collagen mRNA expression. Thus, in this model of fibrous tissue formation, we found expression of component genes involved in Ang peptide (I and II) and TGF-beta 1 generation and Ang II upregulation of TGF-beta 1 expression, suggesting Ang II and/or TGF-beta 1 may upregulate type I collagen expression during tissue repair. Pharmacologic intervention studies with lisinopril or losartan indicate Ang II plays a role in the reciprocal regulation of ACE mRNA expression, which modulates Ang II levels at sites of repair.

Angiotensin I↗