Biomedical subjects

R A Gomez

Publications and source records attributed to R A Gomez.

At least 19 recordsLinked to original sources

PubMed1999

Homeostasis in mice with genetically decreased angiotensinogen is primarily by an increased number of renin-producing cells.

Here we investigate the biochemical, molecular, and cellular changes directed toward blood pressure homeostasis that occur in the endocrine branch of the renin-angiotensin system of mice having one angiotensinogen gene inactivated. No compensatory up-regulation of the remaining normal allele occurs in the liver, the main tissue of angiotensinogen synthesis. No significant changes occur in expression of the genes coding for the angiotensin converting enzyme or the major pressor-mediating receptor for angiotensin, but plasma renin concentration in the mice having only one copy of the angiotensinogen gene is greater than twice wild-type. This increase is mediated primarily by a modest increase in the proportion of renal glomeruli producing renin in their juxtaglomerular apparatus and by four times wild-type numbers of renin-producing cells along afferent arterioles of the glomeruli rather than by up-regulating renin production in cells already committed to its synthesis.

Alleles↗

PubMed1999

Recent advances in renal development.

Anatomical development of the kidney is achieved by the reciprocal induction of the ureteric bud and the metanephric mesenchyma. This interaction triggers the process of nephrogenesis and culminates in the formation of the mature kidney. In vivo, nephrogenesis is coordinated with renal vascularization. In fact, vascular precursors, epithelial progenitors, and mesenchymal cells communicate with one another in a highly organized fashion. As a result of this complex interaction, a mature kidney, architecturally and functionally ready for extrauterine life, is produced. This review deals with the relevant molecules and mechanisms governing nephrovascular development.

Humans↗

PubMed1999

Vascular endothelial growth factor induces nephrogenesis and vasculogenesis.

The expression of vascular endothelial growth factor (VEGF) and its receptors Flt-1 and Flk-1 in the rat kidney was examined during ontogeny using Northern blot analysis and immunocytochemistry. In prevascular embryonic kidneys (embryonic day 14 [E14]), immunoreactive Flt-1 and Flk-1 were observed in isolated angioblasts, whereas VEGF was not detected. Angioblasts aligned forming cords before morphologically differentiating into endothelial cells. In late fetal kidneys (E19), immunoreactive VEGF was detected in glomerular epithelial and tubular cells, whereas Flt-1 and Flk-1 were expressed in contiguous endothelial cells. To determine whether VEGF induces endothelial cell differentiation and vascular development in the kidney, the effect of recombinant human VEGF (5 ng/ml) was examined on rat metanephric organ culture, a model known to recapitulate nephrogenesis in the absence of vessels. After 6 d in culture in serum-free, defined media, metanephric kidney growth and morphology were assessed. DNA content was higher in VEGF-treated explants (1.9 +/- 0.17 microg/kidney, n = 9) than in paired control explants (1.4 +/- 0.10 microg/kidney, n = 9) (P < 0.05). VEGF induced proliferation of tubular epithelial cells, as indicated by an increased number of tubules and tubular proliferating cell nuclear antigen-containing cells. VEGF induced upregulation of Flk-1 and Flt-1 expression, as assessed by Western blot analysis. Developing endothelial cells were identified and localized using immunocytochemistry and electron microscopy. Flt-1, Flk-1, and angiotensin-converting enzyme-containing cells were detected in VEGF-treated explants, whereas control explants were negative. These studies confirmed previous reports indicating that the expression of VEGF and its receptors is temporally and spatially associated with kidney vascularization and identified angioblasts expressing Flt-1 and Flk-1 in prevascular embryonic kidneys. The data indicate that VEGF expression is downregulated in standard culture conditions and that VEGF stimulates growth of embryonic kidney explants by expanding both endothelium and epithelium, resulting in vasculogenesis and enhanced tubulogenesis. These data suggest that VEGF plays a critical role in renal development by promoting endothelial cell differentiation, capillary formation, and proliferation of tubular epithelia.

Animals↗

PubMed1998

Genomic instability and catalase gene amplification induced by chronic exposure to oxidative stress.

Chronic exposure (>200 days) of HA1 fibroblasts to increasing concentrations of H2O2 or O2 results in the development of a stable oxidative stress-resistant phenotype characterized by increased cellular antioxidant levels, particularly catalase (D. R. Spitz et al, Arch. Biochem. Biophys., 279: 249-260, 1990; D. R. Spitz et al., Arch. Biochem. Biophys., 292: 221-227, 1992; S. J. Sullivan et al., Am. J. Physiol. (Lung Cell. Mol. Physiol.), 262: L748-L756, 1992). Acutely stressed cells failed to develop a stably resistant phenotype or increased catalase activity, suggesting that chronic exposure is required for the development of this phenotype. This study investigates the mechanism underlying increased catalase activity in the H2O2- and O2-resistant cell lines. In H2O2- and O2-resistant cells, catalase activity was found to be 20-30-fold higher than that in the parental HA1 cells and correlated with increased immunoreactive catalase protein and steady-state catalase mRNA levels. Resistant cell lines also demonstrated a 4-6-fold increase in catalase gene copy number by Southern blot analysis, which is indicative of gene amplification. Chromosome banding and in situ hybridization studies identified a single amplified catalase gene site located on a rearranged chromosome with banding similarities to Z-4 in the hamster fibroblast karyotype. Simultaneous in situ hybridization with a Z-4-specific adenine phosphoribosyltransferase (APRT) gene revealed that the amplified catalase genes were located proximate to APRT on the same chromosome in all resistant cells. In contrast, HA1 cells contained only single copies of the catalase gene that were not located on APRT-containing chromosomes, indicating that amplification is associated with a chromosomal rearrangement possibly involving Z-4. The fact that chronic exposure of HA1 cells to either HO2 or 95% O2 resulted in gene amplification suggests that gene amplification represents a generalized response to oxidative stress, contributing to the development of resistant phenotypes. These results support the hypothesis that chronic exposure to endogenous metabolic or exogenous environmental oxidative stress represents an important factor contributing to gene amplification and genomic instability.

Adenine Phosphoribosyltransferase↗

PubMed1998

Molecular cloning of KS, a novel rat gene expressed exclusively in the kidney.

BACKGROUND: We aimed to identify genes with kidney specific, developmentally regulated expression. Here we report the cDNA sequence and expression pattern of KS, a novel kidney-specific rat gene. METHODS: A partial cDNA was identified by differential display polymerase chain reaction (PCR) of a renal cell fraction enriched for proximal tubular and renin-expressing cells. Using the partial cDNA as a probe, a rat kidney cDNA library was screened. The full-length KS sequence was obtained by PCR amplification of cDNA ends. The expression pattern of KS was investigated by Northern blot. RNA was extracted from several organs of newborn and adult rats, as well as from the kidneys of rats with altered tubular function, that is, rats that had undergone unilateral nephrectomy, unilateral ureteral obstruction, neonatal losartan treatment, and the appropriate control animals. The expression of KS was also investigated in the kidneys of rats with spontaneous or renovascular hypertension. RESULTS: The KS cDNA (2426 bp) contained one open reading frame encoding a predicted 572 amino acid protein. The derived peptide sequence displayed approximately 70% similarity to the hypertension-related SA gene product and approximately 50% similarity to prokaryotic and eukaryotic acetyl-CoA synthases (EC 6. 2.1.1). KS was expressed in the kidney and not in any other organ assayed. KS RNA was not detected in fetal and newborn rat kidney but became apparent after one week of postnatal life. Gene expression was downregulated in rat models of altered tubular function. KS expression was decreased in spontaneously hypertensive rats but not in renovascular hypertension. CONCLUSION: KS, a novel rat gene, exhibits a unique tissue-specific expression exclusively in mature kidneys. The data suggest KS may encode an adenosine monophosphate binding enzyme.

Amino Acid Sequence↗

PubMed1998

Role of angiotensin in renal vascular development.

All components of the renin-angiotensin system (RAS) are expressed in the developing kidney in a temporospatial pattern that suggests a role for this system in kidney morphogenesis. Pharmacological blockade of angiotensin actions in fetal and newborn animals results in striking alterations in kidney architecture, including immature glomeruli and papillae, dilated tubuli, and arrested vascular development. Inactivation of angiotensinogen or angiotensin converting enzyme genes in mice results in similar anomalies that begin as subtle alterations in early life and become more pronounced as extrauterine life progresses. However, inactivation of each angiotensin receptor subtype does not result in obvious morphological abnormalities, suggesting functional redundancy at the receptor level. Crossing of mice lacking the various receptor subtypes should be revealing. Overall, the available information suggests that the RAS is necessary for the normal morphological and functional development of the kidney and the preservation of kidney architecture in adult life.

Angiotensin II↗

PubMed1998

Angiotensin-dependent gene expression in the developing rat kidney.

We aimed to identify genes involved in the growth effects of angiotensin II (Ang II) during kidney development. In rats treated from birth with the Ang II type-1 receptor blocker losartan, expression of transforming growth factor beta1 (TGF-beta1), platelet-derived growth factor B (PDGF-B), vascular endothelial growth factor (VEGF), and epidermal growth factor (EGF), as measured by Northern blot, did not change significantly (N = 4 to 6 per group each). Differential display methods, used to identify genes with Ang II-dependent expression, produced mostly false positives. We identified one novel rat partial cDNA, termed AD.5, that is related to a human orphan receptor. AD.5 was expressed in a developmentally regulated pattern and may be involved in kidney development and/or the trophic actions of Ang II.

Amino Acid Sequence↗

PubMed1998

Renin-expressing cells are associated with branching of the developing kidney vasculature.

To define the relationship between renal vascular development and renin distribution during kidney ontogeny, the complete renal arterial tree of Sprague Dawley rats during fetal (20 d) and postnatal (1 to 90 d) life was microdissected and immunostained for renin. A shift in renin distribution from interlobar and arcuate arteries in the fetus to the afferent arterioles in the adult was observed. In addition, seven types of renin distribution along the afferent arterioles were identified. In type I, renin was distributed continuously along the whole length of the afferent vessel. This pattern was most frequently observed in the fetus. In type II, renin extended upstream from the glomerulus but did not occupy the whole length of the arteriole. This type was relatively constant throughout postnatal life. In type III, renin was present as bands along the afferent vessel; it was most frequently observed in the fetal and early perinatal periods. In type IV, renin was restricted to the "classical" juxtaglomerular localization. It was the most frequent type observed in the adult rat. In type V, no renin was found in the arteriole. It was the second most frequent type observed in the adult rat. In addition, two "mixed" patterns, type III/IV and type III/II, were occasionally observed. The distribution of renin-expressing cells was spatially and temporally associated with the development of blood vessels. Development of a new arterial branch was preceded by the appearance of renin-expressing cells at the point of branching. This was followed by an outpouching of the arterial wall that progressively elongated to form a new arteriole. During this process, renin-expressing cells were distributed along the whole of the newly formed vessel. As the vessel matured, renin-expressing cells became restricted to the juxtaglomerular portion of the afferent arteriole. It is concluded that throughout life and within each individual arterial tree, expression of renin is heterogeneous, following patterns that are unique for each developmental stage. Furthermore, the association of renin-expressing cells with branching of renal arterioles suggests a role for these cells in the development of the kidney vasculature.

Aging↗

PubMed1998

Embryonic development of the ureter and bladder: acquisition of smooth muscle.

To delineate the temporal and spatial acquisition of the smooth muscle of the ureter, Sprague-Dawley rat embryos and newborn pups were immunostained with alpha-smooth muscle actin (alpha-SM actin) antibody. Alpha-SM actin expression was first detected in the urinary tract at 16 days of gestation (E16) in a thin subserosal zone about the urogenital sinus. At this time, the E16 ureter is composed of a simple cuboidal epithelium which is surrounded by 1 to 2 layers of condensed alpha-SM actin negative spindle shaped cells. No immunostaining was detected along the ureter or its intrarenal branches until the 20th day of gestation (E20). Alpha-SM actin expression in the E20 ureter exhibited regional differences. The number of alpha-SM actin positive smooth muscle cells was greatest in the distal ureter, intermediate in the mid ureter, and least in the proximal ureter near the kidney. While smooth muscle formation in the bladder was subserosal, in the ureter it was subepithelial. During postnatal life, alpha-SM actin expression increased in both organs as all periepithelial spindle cells stained positive and intensified their staining. Smooth muscle differentiation of the ureter and bladder occurs later in embryonic life than other visceral and vascular organs and occurs in an ascending fashion from the bladder to the intrarenal collecting system. It is likely that the activation of visceral smooth muscle myogenesis within the urinary tract is governed by positional information specific to the embryonic development of each organ.

Actins↗

PubMed1998

Embryonic development of the ureter.

During human embryonic development, the ureteric bud, a simple epithelial tube that arises from the Wolffian duct, initiates a cascade of events which results in the formation of the metanephros and its collecting system. In this review, the anatomic and molecular basis of ureteric development are discussed. Although it is difficult to separate metanephrogenesis from ureterogenesis of the proximal segment, the data presented are biased toward the latter. Some of the factors involved in the budding and branching of the embryonic ureter and the maturation of the fetal ureter into a peristaltic conduit are discussed as presently understood. Finally, a brief description of congenital abnormalities in ureteral development is presented with some putative mechanisms.

Animals↗

PubMed1997

Renin-angiotensin system genes in kidney development.

The renin-angiotensin system (RAS) plays a key role in cardiovascular homeostasis through the interactions of angiotensin II with its receptors. All components of the RAS are developmentally regulated in the kidney. The functions of the system in the maturing kidney overlap those of the adult, but higher levels of expression and novel locations of expression in the fetus suggest that the RAS has alternate functions as well. Increasing evidence suggests that the RAS may regulate renal growth and development by initiating a complex cascade of events, involving growth factors and proto-oncogenes and other unidentified factors. These same cascades may also be important in renal disease states. Recent advances in the field of molecular and cell biology are providing new tools and strategies to elucidate the intimate mechanism whereby the RAS regulates growth processes and disease states.

Angiotensinogen↗

PubMed1997

Development of the kidney vasculature.

Renal vascularization and nephrogenesis occur simultaneously following a tightly regulated developmental program influenced by growth factors, extracellular matrix components and cell membrane receptors. Both processes of angiogenesis and vasculogenesis probably participate in the formation of renal vessels. The origin and fate of the various renal vascular cells and the molecular mechanisms that initiate and guide intrarenal vascularization are fundamental questions that remain to be answered.

Animals↗

PubMed1997

Biomechanical coupling in renin-releasing cells.

The renin-angiotensin system is a major regulatory system controlling extracellular fluid volume and blood pressure. The rate-limiting enzyme in this hormonal cascade is renin, which is synthesized and secreted into the circulation by renal juxtaglomerular (JG) cells. The renal baroreceptor is a key physiologic regulator of renin secretion, whereby a change in renal perfusion pressure is sensed by these cells and results in a change in renin release. However, the mechanism, direct or indirect, underlying pressure transduction is unknown. We studied the direct application of mechanical stretch to rat JG cells and human renin-expressing (CaLu-6) cells on the release of renin. JG cells released a low level of baseline renin, comprising < 5% of their total renin content. By contrast, renin secretion from CaLu-6 cells comprised approximately 30% of cellular stores, yet was also stimulated twofold by 10 microM forskolin (P </= 0.001). In JG cells, mechanical stretch inhibited basal renin release by 42% (P < 0.01) and forskolin-stimulated renin release by 25% (P < 0.05). In CaLu-6 cells, stretch inhibited basal- and forskolin-stimulated renin release by 30 and 26%, respectively (both P < 0.01). Northern blot analysis demonstrated a stretch-induced reduction in baseline renin mRNA accumulation of 26% (P < 0.05) in JG and 46% (P < 0.05) in CaLu-6 cells. The data demonstrate that mechanical stretch in renin-releasing cells inhibits basal and stimulated renin release accompanied by a decrease in renin mRNA accumulation. Further studies will be necessary to characterize the intracellular events mediating biomechanical coupling in renin-expressing cells and the relationship of this signaling pathway to the in vivo baroreceptor control of renin secretion.

Animals↗

PubMed1997

Oxygen regulates vascular endothelial growth factor-mediated vasculogenesis and tubulogenesis.

To determine whether low oxygen is a stimulus for endothelial cell differentiation and vascular development in the kidney, we examined the effect of low oxygen on rat metanephric organ culture, a model known to recapitulate nephrogenesis in the absence of vessels. After 6 days in culture in standard (20% O2) or low oxygen (1-3% O2) conditions, metanephric kidney growth and morphology were assessed by DNA measurement, and light and electron microscopy. DNA content was higher in 3% O2-treated explants (2.5 +/- 0.17 microgram/kidney, n = 9) than in 20% O2 explants (1.5 +/- 0.09 microgram/kidney, n = 9), P < 0.05. Low oxygen induced proliferation of tubular epithelial cells, resulting in enhanced number of tubules of similar size. Endothelial cells forming capillaries were localized in 3% O2 explants by light and electron microscopy and by immunocytochemistry using endothelial cell markers. Flt-1, Flk-1, and ACE-containing cells were detected in 3% O2-treated explants, whereas 20% O2 explants were virtually negative. VEGF mRNA levels were 10-fold higher in 3% O2-treated explants than in 20% O2-treated explants. Addition of anti-VEGF antibodies to 3% O2-treated explants prevented low oxygen-induced growth and endothelial cell differentiation and proliferation. Our data indicate that low oxygen stimulates growth by cell proliferation and induces tubulogenesis, endothelial cell differentiation, and vasculogenesis in metanephric kidneys in culture. Upregulation of VEGF expression by low oxygen and prevention of low oxygen-induced tubulogenesis and vasculogenesis by anti-VEGF antibodies indicate that these changes were mediated by VEGF. These data suggest that low oxygen is the stimulus to initiate renal vascularization.

Animals↗

PubMed1997

Differential expression of angiotensin II receptors during early renal morphogenesis.

Angiotensin II (ANG II) and its receptors, AT1 and AT2, may modulate kidney development. To define the temporal and spatial distribution of AT1 and AT2 receptors and their mRNAs during nephrogenesis, fetal, newborn, and adult rat kidneys were studied using reverse transcription-polymerase chain reaction and radioligand binding autoradiography. AT1 expression was minimal at embryonic day 14 (E14), highly expressed at E20, and persisted into adulthood. Conversely, AT2 expression was easily detected from E14 through postnatal day 7 but was undetectable by postnatal day 28. At E14, 76% of the receptors were AT2, 24% were AT1, and both were found in the undifferentiated mesenchyme. By E17, AT1 comprised 40% of the receptors and localized to mature nephron segments, whereas AT2 remained within both condensed mesenchyme and differentiating epithelia. The dissociation constants for AT1 and AT2 were 0.45 +/- 0.09 nM and 0.73 +/- 0.15 nM, respectively, at E17, similar to adult values. By E20, AT1 and AT2 colocalized to the outer medullary stripe, deep nephrons, medullary rays, and blood vessels, while AT2 continued to predominate in the actively differentiating cortex. The presence of both subtypes of receptors capable of binding ANG II during early nephrogenesis and the time-dependent and structure-specific regulation of receptor localization confirm a regulated developmental program for receptor expression and suggest important roles for AT1 and AT2 in renal morphogenesis.

Aging↗

PubMed1997

Zis: a developmentally regulated gene expressed in juxtaglomerular cells.

Renal juxtaglomerular (JG) cells are specialized myoepithelioid cells located in the afferent arteriole at the entrance to the glomerulus. Their main function and distinctive feature is the synthesis and release of renin, the key hormone-enzyme of the renin-angiotensin system that regulates arterial blood pressure. Despite their relevance to health and disease, not much is known about factors that confer and/or maintain JG cell identity. To identify genes uniquely expressed in JG cells, we used a cell culture model and RNA differential display. JG cells cultured for 2 days express renin and renin mRNA, but after 10 days in culture they no longer contain or release renin and renin mRNA is reduced 700-fold. We report one cDNA differentially expressed in the 2-day JG cell culture that detects a 2.6-kb mRNA expressed at higher levels in newborn than adult kidney. Screening a 2-day culture JG cell cDNA library yielded clones representing differentially spliced transcripts. These cDNAs encode one unique protein (Zis) containing zinc fingers and domains characteristic of splicing factors and RNA binding proteins. Northern blot analysis confirmed Zis mRNA expression in differentiated JG cells, and identified an additional unique 1.5-kb transcript. The Zis transcripts are developmentally regulated in kidney and a number of other organs. The features of the Zis protein and its organ distribution suggest a possible role in regulation of transcription and/or splicing, both important steps for controlling developmentally expressed genes.

Aging↗

PubMed1997

Aberrant renal vascular morphology and renin expression in mutant mice lacking angiotensin-converting enzyme.

To determine whether angiotensin-converting enzyme plays a role in the development and maintenance of normal renal architecture, the renal morphology of 10- to 12-month-old female mice homozygous for a disruption of the converting enzyme gene was compared with that of age-matched wild-type mice. Tubular obstruction, dilatation, and atrophy were present in all kidneys from the homozygous mutant mice but absent in wild types; two kidneys from 4 mutant mice but none from the wild types were hydronephrotic. The entire arterial vascular tree, microdissected from mice with no converting enzyme, was grossly distorted in comparison to the vasculature of wild-type mice; all intrarenal arterial vessels were widened and thickened, including the terminal (afferent) arterioles. In wild-type mice kidneys, renin-positive cells were detected exclusively in a juxtaglomerular localization. In contrast, abnormal distribution of renin immunostaining was observed in mice without converting enzyme; scattered renin-positive cells were seen along the arterial vessels, often in a perivascular localization, and interstitial renin-positive cells surrounded glomeruli. Kidney renin mRNA was increased more than 32-fold in the mutant mice compared with wild types. Northern blot analysis revealed that this increase included the accumulation of large amounts of smaller renin RNA transcripts. In summary, mice lacking the converting enzyme exhibit abnormal renal vessels and tubules. Renin synthesis is increased, accompanied by the presence of small renin mRNA species, and renin is present mainly in interstitial and perivascular cells. We conclude that angiotensin-converting enzyme is necessary to preserve normal kidney architecture and the normal pattern of renin expression.

Animals↗

PubMed1997

Angiotensin's role in renal development.

All the components of the renin-angiotensin system (RAS) are highly expressed in the developing kidney in a unique spatial and temporal pattern that is associated with nephrogenesis, vascularization, and the proper architectural and functional development of this organ. Pharmacological inhibition of the RAS results in structural and functional developmental abnormalities of the kidneys in several animal species, including humans. Similarly, altered renal morphology and functional abnormalities have been described in mice with targeted inactivation of the angiotensinogen (Agt) and the angiotensin-converting enzyme (ACE) genes. In contrast, inactivation of angiotensin receptors have not resulted in renal morphological abnormalities, suggesting a redundancy at this level of the RAS cascade that prevents the development of renal pathology. More importantly, inactivation of the ACE or Ao genes results in a renal phenotype remarkably similar to that obtained with pharmacological inhibition of the RAS. Taken together, the available information suggests that angiotensin is necessary for normal kidney development and for the maintenance of the functional and structural integrity of the adult kidney.

Adult↗