Fluorapatite and fluorohydroxyapatite apatite surfaces drive adipose-derived stem cells to an osteogenic lineage.

PURPOSE: Hydroxyapatite (HA) scaffolds are common replacement materials used in the clinical management of critical-sized bone defects. This study was undertaken to examine the potential benefits of fluoridated derivatives of hydroxyapatite, fluorapatite (FA), and fluorohydroxyapatite (FHA) as bone scaffolds in conjunction with adipose-derived stem cells (ADSCs). If FHA and FA surfaces could drive the differentiation of stem cells to an osteogenic phenotype, the combination of these ceramic scaffolds with ADSCs could produce materials with mechanical strength and remodeling potential comparable to autologous bone. This study was designed to investigate the ability of the apatite surfaces HA, FA, and FHA produced at different sintering temperatures to drive ADSCs toward osteogenic lineages. METHODS: HA, FHA, and FA surfaces sintered at 1150 °C and 1250 °C were seeded with ADSCs and evaluated for cell growth and gene and protein expression of osteogenic markers at 2 and 10 days post-seeding. RESULTS: In vitro, ADSC cells were viable on all surfaces; however, differentiation of these cells into osteoblastic lineage only observed in apatite surfaces. ADSCs seeded on FA and FHA expressed genes and proteins related to osteogenic differentiation markers to a greater extent by Day 2 when compared to HA and cell culture controls. By day 10, HA, FA, and FHA all expressed more bone differentiation markers compared to cell culture controls. CONCLUSION: FA and FHA apatite scaffolds may promote the differentiation of ADSCs at an earlier time point than HA surfaces. Combining apatite scaffolds with ADSCs has the potential to improve bone regeneration following bone injury.

Histologic evaluation of therapeutic responses in ischemic myocardium elicited by dual growth factor delivery from composite glycosaminoglycan hydrogels.

In this project, the ability of dual growth factor-preloaded, silk-reinforced, composite hyaluronic acid-based hydrogels to elicit advantageous histologic responses when secured to ischemic myocardium was evaluated in vivo. Reinforced hydrogels containing both Vascular Endothelial Growth Factor (VEGF) and Platelet-derived Growth Factor (PDGF) were prepared by crosslinking chemically modified hyaluronic acid and heparin with poly(ethylene glycol)-diacrylate around a reinforcing silk mesh. Composite patches were sutured to the ventricular surface of ischemic myocardium in Sprague-Dawley rats, and the resulting angiogenic response was followed for 28 days. The gross appearance of treated hearts showed significantly reduced ischemic area and fibrous deposition compared to untreated control hearts. Histologic evaluation showed growth factor delivery to restore myofiber orientation to pre-surgical levels and to significantly increase elicited microvessel density and maturity by day 28 in infarcted myocardial tissue (p < 0.05). In addition, growth factor delivery reduced cell apoptosis and decreased the density of elicited mast cells and both CD68+ and anti-inflammatory CD163+ macrophages. These findings suggest that HA-based, dual growth factor-loaded hydrogels can successfully induce a series of beneficial responses in ischemic myocardium, and offer the potential for therapeutic improvement of ischemic myocardial remodeling.

The mitochondrial metal transporters mitoferrin1 and mitoferrin2 are required for liver regeneration and cell proliferation in mice.

Mitochondrial iron import is essential for iron-sulfur cluster formation and heme biosynthesis. Two nuclear-encoded vertebrate mitochondrial high-affinity iron importers, mitoferrin1 (Mfrn1) and Mfrn2, have been identified in mammals. In mice, the gene encoding Mfrn1, solute carrier family 25 member 37 (Slc25a37), is highly expressed in sites of erythropoiesis, and whole-body Slc25a37 deletion leads to lethality. Here, we report that mice with a deletion of Slc25a28 (encoding Mfrn2) are born at expected Mendelian ratios, but show decreased male fertility due to reduced sperm numbers and sperm motility. Mfrn2-/- mice placed on a low-iron diet exhibited reduced mitochondrial manganese, cobalt, and zinc levels, but not reduced iron. Hepatocyte-specific loss of Slc25a37 (encoding Mfrn1) in Mfrn2-/- mice did not affect animal viability, but resulted in a 40% reduction in mitochondrial iron and reduced levels of oxidative phosphorylation proteins. Placing animals on a low-iron diet exaggerated the reduction in mitochondrial iron observed in liver-specific Mfrn1/2-knockout animals. Mfrn1-/-/Mfrn2-/- bone marrow-derived macrophages or skin fibroblasts in vitro were unable to proliferate, and overexpression of Mfrn1-GFP or Mfrn2-GFP prevented this proliferation defect. Loss of both mitoferrins in hepatocytes dramatically reduced regeneration in the adult mouse liver, further supporting the notion that both mitoferrins transport iron and that their absence limits proliferative capacity of mammalian cells. We conclude that Mfrn1 and Mfrn2 contribute to mitochondrial iron homeostasis and are required for high-affinity iron import during active proliferation of mammalian cells.

Role of Free Radical Formation in Murine Cytomegalovirus-Induced Hearing Loss.

OBJECTIVES: The goal of the study was to determine whether reactive oxygen species (ROS) mediates cytomegalovirus (CMV)-induced labyrinthitis. STUDY DESIGN: Murine model of CMV infection. SETTING: University of Utah laboratory. SUBJECTS AND METHODS: Nrf2 knockout mice were inoculated with murine CMV. Auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAEs) were then performed on these and uninfected controls. BALB/c mice were inoculated with murine CMV to determine whether a marker for ROS production, dihydroethidium (DHE), is expressed 7 days after inoculation. Finally, 2 antioxidants-D-methionine and ACE-Mg (vitamins A, C, and E with magnesium)-were administered 1 hour before and after infection in inoculated mice for 14 days. Temporal bones were harvested at postnatal day 10 for DHE detection. ABR and DPOAE testing was done at postnatal day 30. Scanning electron microscopy was also performed at postnatal day 30 to evaluate outer hair cell integrity. RESULTS: Nrf2-infected mice had worse hearing than uninfected mice (P < .001). A statistically significant increase in DHE fluorescence was detected in BALB/c-infected mice as compared with uninfected mice 7 days after inoculation. D-methionine- and ACE-Mg-treated mice demonstrated an attenuation of the DHE fluorescence and a significant improvement in ABR and DPOAE thresholds when compared with untreated infected controls (P < .0001). Scanning electron microscopy demonstrated less outer hair cell loss in the treated versus untreated infected controls. CONCLUSION: These results demonstrate for the first time that excessive ROS mediates CMV-induced hearing loss in a mouse model.

Effects of ganciclovir treatment in a murine model of cytomegalovirus-induced hearing loss.

OBJECTIVE: To determine whether ganciclovir (GCV) treatment reduces sensorineural hearing loss in cytomegalovirus (CMV)-infected mice. The effects of GCV on viral load, absolute neutrophil count (ANC), and outer hair cell (OHC) integrity were also investigated. METHODS: Infected BALB/c mice were inoculated with murine CMV on postnatal day 3. Those treated with GCV received an intraperitoneal injection twice a day for 14 days. Auditory thresholds were assessed using distortion product otoacoustic emission (DPOAE) and auditory brainstem response (ABR) testing 4 weeks after inoculation. Temporal bones were used for determination of viral load by quantitative polymerase chain reaction and hair cell quantification by scanning electron microscopy. ANCs were completed by an automated hematology analyzer, with manual review for confirmation. RESULTS: GCV-treated CMV-infected mice had lower ABR (P < 0.0001, Kruskal-Wallis test) and DPOAE (P < 0.0001) thresholds compared to CMV-infected untreated mice, indicating that GCV protected mice from CMV-induced hearing loss. Viral load in infected populations undergoing GCV treatment was significantly decreased (P = 0.03) relative to untreated mice. GCV treatment alone had no effect on ABR and DPOAE compared to untreated, uninfected controls (P = 0.1, P = 0.24, respectively). GCV-treated mice received increased protection from OHC loss when compared to untreated groups, with total OHC losses of approximately 7% and 14%, respectively (P < 0.05). Neutropenia was absent after 7 days of GCV treatment. CONCLUSION: Ganciclovir effectively ameliorated SNHL and partially protected from OHC loss in a preclinical model of congenital CMV infection, seemingly by reducing viral load. LEVEL OF EVIDENCE: NA Laryngoscope, 130:1064-1069, 2020.

Natural killer cells attenuate cytomegalovirus-induced hearing loss in mice.

Congenital cytomegalovirus (CMV) infection is the most common non-hereditary cause of sensorineural hearing loss (SNHL) yet the mechanisms of hearing loss remain obscure. Natural Killer (NK) cells play a critical role in regulating murine CMV infection via NK cell recognition of the Ly49H cell surface receptor of the viral-encoded m157 ligand expressed at the infected cell surface. This Ly49H NK receptor/m157 ligand interaction has been found to mediate host resistance to CMV in the spleen, and lung, but is much less effective in the liver, so it is not known if this interaction is important in the context of SNHL. Using a murine model for CMV-induced labyrinthitis, we have demonstrated that the Ly49H/m157 interaction mediates host resistance in the temporal bone. BALB/c mice, which lack functional Ly49H, inoculated with mCMV at post-natal day 3 developed profound hearing loss and significant outer hair cell loss by 28 days of life. In contrast, C57BL/6 mice, competent for the Ly49H/m157 interaction, had minimal hearing loss and attenuated outer hair cell loss with the same mCMV dose. Administration of Ly49H blocking antibody or inoculation with a mCMV viral strain deleted for the m157 gene rendered the previously resistant C57BL/6 mouse strain susceptible to hearing loss to a similar extent as the BALB/c mouse strain indicating a direct role of the Ly49H/m157 interaction in mCMV-dependent hearing loss. Additionally, NK cell recruitment to sites of infection was evident in the temporal bone of inoculated susceptible mouse strains. These results demonstrate participation of NK cells in protection from CMV-induced labyrinthitis and SNHL in mice.

Cytomegalovirus (CMV) Infection Causes Degeneration of Cochlear Vasculature and Hearing Loss in a Mouse Model.

Cytomegalovirus (CMV) infection is one of the most common causes of congenital hearing loss in children. We have used a murine model of CMV infection to reveal functional and structural cochlear pathogenesis. The cerebral cortex of Balb/c mice (Mus musculus) was inoculated with 2000 pfu (plaque forming units) of murine CMV on postnatal day 3. At 6 weeks of age, cochlear function was monitored using auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) measures. Histological assessment of cochlear vasculature using a corrosion cast technique was made at 8 weeks. Vascular casts of mCMV-damaged cochleas, and those of untreated control animals, were examined using scanning electron microscopy. We find very large variations in the degree of vascular damage in animals given identical viral injections (2000 pfu). The primary lesion caused by CMV infection is to the stria vascularis and to the adjacent spiral limbus capillary network. Capillary beds of the spiral ligament are generally less affected. The initial vascular damage is found in the mid-apical turn and appears to progress to more basal cochlear regions. After viral migration to the inner ear, the stria vascularis is the primary affected structure. We suggest that initial auditory threshold losses may relate to the poor development or maintenance of the endocochlear potential caused by strial dysfunction. Our increased understanding of the pathogenesis of CMV-related hearing loss is important for defining methods for early detection and treatment.

Amelioration of hepatic inflammation in a mouse model of NASH using a dithiocarbamate derivative.

PURPOSE: The process whereby liver inflammation develops in non-alcoholic steatohepatitis (NASH) is not fully understood. While modification of the inflammatory milieu is an attractive target to prevent the development of hepatocellular injury, most antiinflammatory agents have proven ineffective in this setting. Tetraethylthiuram disulfide (TDSF) is able to induce S-glutathionylation of NF-κB along with critical signaling proteins involved with inflammation, especially when complexed with a heavy metal. For this reason, we hypothesized that administration of TDSF would function to ameliorate necroinflammatory activity in a mouse model of NASH. METHODS: Mice were divided into five groups and received control chow versus a methionine-choline-deficient diet. After 6 weeks of TDSF versus sham gavage, animals were necropsied. Using conventional H&E staining, livers were examined using the Brunt scoring system by a hepatopathologist blinded to treatment groups. Validated mouse primer sets were used for quantitative real-time PCR to evaluate changes in mRNA expression. RESULTS: Livers treated with TDSF demonstrated a qualitative reduction in lobular inflammation, lipogranuloma formation, and Kupffer cell accumulation, but not steatosis. Significant reductions in inflammatory transcripts for α-1-collagen, TGF-ß, Mmp2, MCP-1, and TNF-1α were also observed. CONCLUSIONS: Animals treated with TDSF exhibit a reduction in lobular inflammation that is independent of lipid accumulation when administered MCD diet. Similar reductions are seen in several inflammatory transcripts associated with NASH. Additional work in this area may reveal a therapeutic role for TDSF or similar agents in curtailing inflammatory signaling within the liver.

Overexpression of mouse angiotensinogen in renal proximal tubule causes salt-sensitive hypertension in mice.

BACKGROUND: The role of proximal tubule (PT) angiotensinogen (AGT) in modulating blood pressure has previously been examined using mice expressing PT human AGT and human renin, or rat AGT. These animals are hypertensive; however, the question remains whether alterations in mouse PT AGT alone affects arterial pressure. METHODS: Mouse AGT cDNA was knocked-in to the endogenous kidney androgen protein (KAP) gene using an internal ribosomal entry site (IRES)-based strategy. RESULTS: The KAP-mAGT animals showed kidney-specific KAP-AGT mRNA expression; renal in situ hybridization detected KAP-AGT mRNA only in PT. Urinary AGT was markedly increased in KAP-mAGT mice. On a high Na diet, radiotelemetric arterial pressure showed a systolic pressure elevation; no significant difference in arterial pressure was observed on a normal diet. Plasma renin concentration (PRC) was reduced in KAP-mAGT animals given a high Na diet, but was not different between mouse lines during normal Na intake. Plasma AGT concentration was not altered by overexpression of PT mouse AGT. CONCLUSIONS: In summary, PT overexpression of mouse AGT leads to salt-sensitive hypertension without recruitment of the systemic renin-angiotensin system.

A real-time, telemetric method for continuous measurement of portal pressures.

The ability to longitudinally monitor portal and splanchnic pressures would greatly enhance the understanding of acute and chronic liver disease by helping to assess the immediate and long-term impact of therapeutic manipulations. However, a technique for measuring portal pressures in the ambulatory setting is not currently available. To overcome this difficulty, we utilized an approach that involved the implantation of a miniature telemetric device, equipped with a specially-designed pressure transmission catheter, into the spleen of an anesthetized mouse. Using this approach, portal pressures were measured continuously over 5 d in conscious, unrestrained animals, the availability of which will help facilitate studies of the portal circulation requiring long-term stability.

Contribution of insulin and Akt1 signaling to endothelial nitric oxide synthase in the regulation of endothelial function and blood pressure.

Impaired insulin signaling via phosphatidylinositol 3-kinase/Akt to endothelial nitric oxide synthase (eNOS) in the vasculature has been postulated to lead to arterial dysfunction and hypertension in obesity and other insulin resistant states. To investigate this, we compared insulin signaling in the vasculature, endothelial function, and systemic blood pressure in mice fed a high-fat (HF) diet to mice with genetic ablation of insulin receptors in all vascular tissues (TTr-IR(-/-)) or mice with genetic ablation of Akt1 (Akt1-/-). HF mice developed obesity, impaired glucose tolerance, and elevated free fatty acids that was associated with endothelial dysfunction and hypertension. Basal and insulin-mediated phosphorylation of extracellular signal-regulated kinase 1/2 and Akt in the vasculature was preserved, but basal and insulin-stimulated eNOS phosphorylation was abolished in vessels from HF versus lean mice. In contrast, basal vascular eNOS phosphorylation, endothelial function, and blood pressure were normal despite absent insulin-mediated eNOS phosphorylation in TTr-IR(-/-) mice and absent insulin-mediated eNOS phosphorylation via Akt1 in Akt1-/- mice. In cultured endothelial cells, 6 hours of incubation with palmitate attenuated basal and insulin-stimulated eNOS phosphorylation and NO production despite normal activation of extracellular signal-regulated kinase 1/2 and Akt. Moreover, incubation of isolated arteries with palmitate impaired endothelium-dependent but not vascular smooth muscle function. Collectively, these results indicate that lower arterial eNOS phosphorylation, hypertension, and vascular dysfunction following HF feeding do not result from defective upstream signaling via Akt, but from free fatty acid-mediated impairment of eNOS phosphorylation.

Response to genetic manipulations of liver angiotensinogen in the physiological range.

Genetic variation in the human angiotensinogen gene (AGT) influences plasma AGT concentration and susceptibility to essential hypertension by a mechanism that remains to be clarified. When one or two additional copies of the gene were inserted by gene titration (by homologous recombination with gap-repair at the AGT locus), both plasma AGT and arterial pressure were elevated in the physiological range in the mouse. The causal dependency between plasma AGT and blood pressure and the relative contribution of the various tissues that express AGT to these two phenotypic parameters remained to be determined. To address these issues, we generated a transgenic mouse with overexpression of the mouse AGT gene restricted to the liver. The transgene was examined in two contrasted genetic backgrounds, the sodium-sensitive C57BL/6J and the sodium-resistant A/J. Transgenic and control male animals underwent continuous cardiovascular monitoring by telemetry for 14 days while under a standard sodium diet (0.2%). Moderate but significant increases in plasma AGT (40%, p = 0.01) and systolic blood pressure (4-6 mmHg, p ranging from 0.01 to <0.001) were observed in the sodium-sensitive background, but not in the sodium-resistant animals. Statistical analysis of a large number of consecutive, repeated measurements of blood pressure afforded power to detect small effects in the physiological range by use of advanced mixed models of analysis of variances and covariances. Although plasma renin activity was increased in the sodium-sensitive background, it did not reach statistical significance. These observations underline a potential contribution of systemic AGT to the mechanism of AGT-mediated hypertension, but the significance of sodium sensitivity in the genetic background suggests participation of the kidney in expression of the elevated blood pressure phenotype, a matter that will warrant further studies. They also highlight the challenge of identifying the contribution of individual genes in complex inheritance, as their effects are modulated by other genetic and environmental determinants.

Hypervolemia of pregnancy is not maintained in mice chronically overexpressing angiotensinogen.

OBJECTIVE: Women who develop pre-eclampsia show significantly less hypervolemia of pregnancy, compared with controls. We have shown that chronically elevated angiotensinogen expression increases a woman's risk of developing pre-eclampsia. Our objective was to determine whether increased angiotensinogen expression is sufficient to cause failed hypervolemia. STUDY DESIGN: To isolate the effects of elevated angiotensinogen expression, we studied transgenic mice with either 2 or 3 copies of the murine angiotensinogen gene. Plasma volume was measured by Evans blue dye dilution, and kidney sections were immunostained for angiotensinogen and renin. RESULTS: Three-copy mice failed to maintain hypervolemia after midgestation (P < .01) and failed to up-regulate renin expression in the distal nephron, compared with 2-copy controls. Intrarenal angiotensinogen was up-regulated during pregnancy in both genotypes. CONCLUSION: Chronically elevated angiotensinogen expression is sufficient to cause failed hypervolemia of pregnancy. Whether this observation is related to failed up-regulation of distal tubule renin expression requires further study.

Expression and function of COX isoforms in renal medulla: evidence for regulation of salt sensitivity and blood pressure.

Expression of cyclooxygenase (COX)-2, but not COX-1, in the renal medulla is stimulated by chronic salt loading; yet the functional implication of this phenomenon is incompletely understood. The present study examined the cellular localization and antihypertensive function of high-salt-induced COX-2 expression in the renal medulla, with a parallel assessment of the function of COX-1. COX-2 protein expression in response to high-salt loading, assessed by immunostaining, was found predominantly in inner medullary interstitial cells, whereas COX-1 protein was abundant in collecting duct (CD) and inner medullary interstitial cells and was not affected by high salt. We compared mRNA expressions of COX-1 and COX-2 in CD vs. non-CD cells isolated from aquaporin 2-green fluorescent protein transgenic mice. A low level of COX-2 mRNA, but a high level of COX-1 mRNA, as determined by real-time RT-PCR, was detected in CD compared with non-CD segments. During high-salt intake, chronic infusions of the COX-2 blocker NS-398 and the COX-1 blocker SC-560 into the renal medulla of Sprague-Dawley rats for 5 days induced approximately 30- and 15-mmHg increases in mean arterial pressure, respectively. During similar high-salt intake, COX-1 knockout mice exhibited a gradual, but significant, increase in systolic blood pressure that was associated with a marked suppression of urinary PGE2 excretion. Therefore, we conclude that the two COX isoforms in the renal medulla play a similar role in the stabilization of arterial blood pressure during salt loading.

Expression of angiotensinogen in proximal tubule as a function of glomerular filtration rate.

BACKGROUND: Proximal tubule (PT) angiotensinogen (AGT) is part of a tubular renin-angiotensin system (RAS) that participates in the regulation of sodium reabsorption along the entire nephron. Physiologic maneuvers affecting AGT expression in PT also affect systemic RAS. Here, we tested the hypothesis that PT AGT is regulated by increased glomerular filtration rate (GFR). METHODS: Complete unilateral nephrectomy (UNX) in mice was used to induce a sustained increase in GFR in the remaining kidney. AGT expression was monitored by quantitative reverse transcription-polymerase chain reaction (RT-PCR). AGT protein in PT was investigated by semiquantitative histology. We also measured AGT concentration in plasma and in 24-hour urine by a specific enzyme-linked immunosorbent assay (ELISA). RESULTS: Seven weeks after nephrectomy, UNX animals exhibited a 2-fold increase in tubular AGT mRNA (P <.001) compared with sham-operated control animals. The proportion of PT sections exhibiting AGT immunostaining was significantly increased at day 3 (P <.05), and remained elevated at seven weeks (UNX = 0.63 +/- 0.09, sham = 0.38 +/- 0.02, P <.01), revealing recruitment of AGT-producing cells along the PT. AGT excretion in final urine corrected for creatinine and kidney weight was also elevated by UNX at seven weeks (UNX = 209 +/- 42 pmol/mg/g, sham = 147 +/- 29 pmol/mg/g, P <.05), with no difference in plasma AGT between UNX and control animals. CONCLUSION: These observations suggest that AGT expression in PT adapts in the long-term to changes in GFR. In the UNX model, urinary AGT excretion is also elevated as a consequence of increase in net tubular flow.

Renin and kallikrein in connecting tubule of mouse.

BACKGROUND: The observation of renin expression in connecting tubule, a segment that also expresses tissue kallikrein (KLK-1), raises two questions. Are the genes expressed in the same or in different cells of connecting tubule? Does this topography support the hypothesis that KLK-1 activates prorenin or is it more likely that it affords coordinated gene regulation? METHODS: Renin and KLK-1 were examined by immunostaining and in situ hybridization. Renin activation by KLK-1 was investigated in vitro. In vivo, excretion of prorenin and active renin was compared in mice homozygous for targeted inactivation of KLK-1 (TK(-/-)) and normal littermates (TK(+/+)). RESULTS: Using in situ immunostaining for renin and in situ hybridization for KLK-1 mRNA, we found that connecting tubule cells expressing renin also expressed KLK-1. We confirmed in vitro activation of prorenin by KLK-1, but found no difference in the ratio of active renin to prorenin in urine of TK(-/-) and TK(+/+) animals. Compared to TK(+/+) controls, TK(-/-) mice exhibited significantly lower 24-hour excretion of prorenin (5.05 +/- 1.16 mg Ang I/hour vs. 9.39 +/- 1.96 mg Ang I/hour, P < 0.05) and active renin (1.98 +/- 0.25 mg Ang I/hour vs. 3.58 +/- 0.39 mg Ang I/hour, P < 0.05), with no difference in either urine volumes or plasma renin concentrations. CONCLUSION: Direct interaction between renin and KLK-1, not ruled out in vitro, is not supported in vivo. By contrast, lower excretion of active renin and prorenin in TK(-/-) compared to TK(+/+) suggest coordinated regulation of the two proteins in their participation to collecting duct function.

Effects of dietary sodium and genetic background on angiotensinogen and Renin in mouse.

Elements of a renin-angiotensin system expressed along the entire nephron, including angiotensinogen secreted by proximal tubule and renin expressed in connecting tubule, may participate in the regulation of sodium reabsorption at multiple sites of the nephron. The response of this tubular renin-angiotensin system to stepwise changes in dietary sodium was investigated in 2 mouse strains, the sodium-sensitive inbred C57BL/6 and the sodium-resistant CD1 outbred. Plasma angiotensinogen was not affected by sodium regimen, whereas plasma renin increased 2-fold under low sodium. In both strains, the variation in urinary parameters did not parallel the changes observed in plasma. Angiotensinogen and renin excretion were significantly higher under high sodium than under low sodium. Water deprivation, by contrast, induced significant activation in the tubular expression of angiotensinogen and renin. C57BL/6 exhibited significantly higher urinary excretion of angiotensinogen than did CD1 animals under both conditions of sodium intake. The extent to which these urinary parameters reflect systemic or tubular responses to challenges of sodium homeostasis may depend on the relative contribution of sodium restriction and volume depletion.

Contribution of Sp1 to initiation of transcription of angiotensinogen.

Several genetic polymorphisms have been identified in the proximal promoter of angiotensinogen ( AGT). Gene titration experiments in transgenic animals have demonstrated that small increases in the basal expression of AGT can lead to elevated blood pressure. The direct proof that promoter variants of AGT can lead to elevated blood pressure will ultimately require the development of specific animal models. Before such work can be contemplated, however, a formal understanding of the mechanisms controlling transcriptional activation of AGT needs to be developed. Analysis of DNA-protein interactions in vitro and transactivation experiments in cultured cells reveal the critical role of an Sp1 binding site immediately upstream of the TATA box of AGT in both mouse and human. Both sites are required for transcription initiation in the mouse. By contrast, a minimal human AGT promoter can initiate transcription in the absence of either this Sp1 site or the TATA box, albeit at a lower level. Further analysis and consideration of these interspecific differences will be essential for the development of meaningful animal models to probe the mechanism by which AGT may predispose to human essential hypertension.