Biomedical subjects

T M Coffman

Publications and source records attributed to T M Coffman.

At least 73 records · Page 4Linked to original sources

PubMed1997

A genetic approach for studying the physiology of the type 1A (AT1A) angiotensin receptor.

The ability to create targeted mutations in the mouse genome using homologous recombination in embryonic stem cells (gene targeting) has proved to be an extremely useful experimental approach. Recently, mouse lines have been produced with targeted disruptions of various genes in the renin-angiotensin system, and studies of these animals have provided new insights into a well-studied physiological system. This article will review the phenotype of one of these lines: the Agtr1A (-/-) mouse, which lacks type 1A (AT1A) angiotensin receptors. The AT1A receptor is the major AT1 receptor in mice, and most of the known physiological functions of the renin angiotensin system are mediated by AT1 receptors. Agtr1A (-/-) mice grow and develop normally. In kidneys of Agtr1A (-/-) mice, AT1-specific binding is virtually undetectable and renal AT1-specific binding is reduced by approximately 50% in Agtr1A (+/-) heterozygotes. Agtr1A (-/-) mice have severely blunted vascular responses to angiotensin II and their blood pressures are reduced by more than 20 mm Hg, confirming the important role for this gene locus in mediating vascular responses to angiotensin II and in normal maintenance of blood pressure. Agtr1A (-/-) mice have also been useful in defining angiotensin responses that are mediated by receptors other than AT1A. Studies of mice with RAS gene knockouts represent examples of the productive use of gene targeting as a tool for physiological investigation.

Angiotensin II↗

PubMed1997

The C-terminus of the thromboxane receptor contributes to coupling and desensitization in a mouse mesangial cell line.

To investigate regulatory domains of the thromboxane A2 (TxA2) receptor, we constructed a truncated form of the mouse TxA2 receptor and expressed it in a mesangial cell line. The mutant receptor lacked 22 amino acids in the C-terminus including four potential phosphorylation sites. Ligand binding of mutant receptors was identical with the wild type. Stimulation with TxA2 agonist induced increases in inositol trisphosphate (IP3) generation and [Ca++]i by both wild-type and mutant receptors. However, the initial increase in IP3 generation by the mutant receptor was only approximately 50% of that seen in the wild type. Exposure of wild-type receptors to TxA2 agonist caused desensitization of IP3 and calcium responses. Pretreatment with TxA2 agonist caused some desensitization of mutant receptors, but the extent of desensitization was reduced compared with the wild type. The protein kinase C inhibitor staurosporine attenuated TxA2-induced desensitization of wild-type receptors, but had little effect on TxA2-induced desensitization of mutant receptors. Pretreatment with low concentrations of the phorbol ester, phorbol 12,13-dibutyrate (100 nM), reduced subsequent responsiveness of wild-type but not mutant TxA2 receptors. In contrast, high-dose phorbol 12,13-dibutyrate (1 microM) produced a similar degree of desensitization of both receptor types. These data suggest that: 1) the C-terminus participates in coupling of the TxA2 receptor to its effector systems; 2) the C-terminus contributes to agonist-specific desensitization of the TxA2 receptor; and 3) protein kinase C-induced desensitization of the TxA2 receptor is complex and depends, in part, on C-terminal domains of the TxA2 receptor.

Amino Acid Sequence↗

PubMed1996

The intragraft CD8+ T cell response in renal allograft rejection in the mouse.

To identify the role of donor class I alloantigens in regulating the CD8+ T cell response to a kidney allograft, we analyzed and compared the CD8+ infiltrate in kidney transplants from MHC class I-deficient (class I-) mouse donors and class I+ controls. One week after transplantation, there was a prominent CD8+ infiltrate in control allografts, whereas CD8+ T cells were virtually absent in grafts from class I- donors. In class I+ allografts, infiltrating CD8+ cells utilized a wide range of T cell receptor (TCR) Vbeta families and their Vbeta usage was similar to that of the systemic CD8+ population. However, there was a modest but significant overrepresentation of cells bearing Vbeta8 in the graft compared with the spleen due to an expansion of CD8+ Vbeta8.3+ cells. This could be detected as early as 1 week and became more pronounced by 3 weeks after transplantation. In 3-week allografts, only 52% of CD8+ cells expressed alphabetaTCR. Among T cells isolated from class I+ grafts, the CD8+ Vbeta8+ cells demonstrated allospecific responses that were numerically larger than responses of the CD8+ Vbeta8- population. In contrast to the early (1 week) time point, significant numbers of CD8+ cells could be isolated from class I- grafts by 3 weeks after transplantation and their Vbeta repertoire resembled that seen in controls. While increasing numbers of CD8+ Vbeta8+ were present in the class I- grafts at 3 weeks, this increase was not statistically significant. Thus, expression of class I alloantigens on a kidney graft plays an important role in regulating the rate of accumulation of CD8+ T cells in rejecting kidney grafts. However, the TCR Vbeta repertoire of the CD8+ T cell infiltrate is largely determined by factors that are independent of normal class I expression on the graft.

Animals↗

PubMed1996

Transplant approach establishes that kidneys are responsible for serum CSF-1 but require a stimulus in MRL-lpr mice.

Colony stimulating factor-1 (CSF-1) is a chemoattractant and growth factor for macrophages. In autoimmune MRL-lpr mice, CSF-1 is detected in the circulation and there is an increase in CSF-1 transcripts and macrophages in the kidney. The purpose of this study was to establish whether the MRL-lpr kidney is responsible for increasing serum CSF-1, and to determine if the expression of CSF-1 requires a circulating component in MRL-lpr mice. We transplanted a MRL-lpr kidney with nephritis [serum CSF-1 = 32.6 +/- 5.1 colony forming units (CFU)] into a bilaterally nephrectomized normal MRL-++ recipient. Circulating CSF-1 increased from 1.2 +/- CFU to 14.1 +/_ 5.6 CFU in recipients by one week. Continuous production of CSF-1 required a stimulating component since: (1) CSF-1 in the kidney and circulation disappeared several weeks after engraftment into MRL-++ mice and (2) isolated glomeruli from MRL-lpr required stimulation to express CSF-1. In the transplanted MRL-lpr kidney, hypercellularity in the glomerulus and interstitium (predominantly macrophages) returned to normal as rapidly as two weeks after engraftment into MRL-++. Thus, this study establishes that the kidney is responsible for circulating CSF-1 in MRL-lpr mice. Without the autoimmune environment CSF-1, macrophages, but not T cells, disappear and nephritis resolves.

Animals↗

PubMed1996

Distribution of binding sites for thromboxane A2 in the mouse kidney.

Thromboxane A2 (TxA2) is a potent vasoconstrictor eicosanoid that has been implicated in the pathogenesis of both human and experimental renal diseases. The biological actions of TxA2 in the kidney are mediated through specific cell-surface receptors. In this report, we characterize the distribution of thromboxane receptors (TxR) within the normal mouse kidney by receptor autoradiography. With the iodinated TxR agonist [125I]BOP, TxA2 binding sites were detected throughout the kidney. Competitive inhibition curves of whole kidney binding demonstrated a half-maximal inhibitory concentration of 6.5 nM. When Scatchard analysis was performed on anatomically discrete regions, the [125I]BOP binding in the medulla was best fit by a one-site model, with a dissociation constant (Kd) of 8.2 +/- 2.2 nM. In contrast, [125I]BOP binding in the cortex was better described by a two-site model, with estimated Kd of 262 +/- 16 pM for a higher affinity site and 16.9 +/- 1.3 nM for a lower affinity site. These sites do not appear to represent receptor isoforms that arise from alternative splicing of mRNA. The lower affinity binding sites may represent a novel TxR or an alternative affinity state for the previously characterized high-affinity binding site.

Alternative Splicing↗

PubMed1995

Requirement of MIP-1 alpha for an inflammatory response to viral infection.

Macrophage inflammatory protein-1 alpha (MIP-1 alpha) is a chemokine that has pro-inflammatory and stem cell inhibitory activities in vitro. Its biologic role in vivo was examined in mice in which the gene encoding MIP-1 alpha had been disrupted. Homozygous MIP-1 alpha mutant (-/-) mice were resistant to Coxsackievirus-induced myocarditis seen in infected wild-type (+/+) mice. Influenza virus-infected -/- mice had reduced pneumonitis and delayed clearance of the virus compared with infected +/+ mice. The -/- mice had no overt hematopoietic abnormalities. These results demonstrate that MIP-1 alpha is an important mediator of virus-induced inflammation in vivo.

Animals↗

PubMed1995

In vivo transfer of GPI-linked complement restriction factors from erythrocytes to the endothelium.

Many proteins are associated with the outer layer of the cell membrane through a posttranslationally added glycosyl phosphatidylinositol (GPI) anchor. The functional significance of this type of protein linkage is unclear, although it results in increased lateral mobility, sorting to the apical surface of the cell, reinsertion into cell membranes, and possibly cell signaling. Here evidence is presented that GPI-linked proteins can undergo intermembrane transfer in vivo. GPI-linked proteins expressed on the surface of transgenic mouse red blood cells were transferred in a functional form to endothelial cells in vivo. This feature of GPI linkage may be potentially useful for the delivery of therapeutic proteins to vascular endothelium.

Animals↗

PubMed1995

Regulation of blood pressure by the type 1A angiotensin II receptor gene.

The renin-angiotensin system plays a critical role in sodium and fluid homeostasis. Genetic or acquired alterations in the expression of components of this system are strongly implicated in the pathogenesis of hypertension. To specifically examine the physiological and genetic functions of the type 1A receptor for angiotensin II, we have disrupted the mouse gene encoding this receptor in embryonic stem cells by gene targeting. Agtr1A(-/-) mice were born in expected numbers, and the histomorphology of their kidneys, heart, and vasculature was normal. AT1 receptor-specific angiotensin II binding was not detected in the kidneys of homozygous Agtr1A(-/-) mutant animals, and Agtr1A(+/-) heterozygotes exhibited a reduction in renal AT1 receptor-specific binding to approximately 50% of wild-type [Agtr1A(+/+)] levels. Pressor responses to infused angiotensin II were virtually absent in Agtr1A(-/-) mice and were qualitatively altered in Agtr1A(+/-) heterozygotes. Compared with wild-type controls, systolic blood pressure measured by tail cuff sphygmomanometer was reduced by 12 mmHg (1 mmHg = 133 Pa) in Agtr1A(+/-) mice and by 24 mmHg in Agtr1A(-/-) mice. Similar differences in blood pressure between the groups were seen when intraarterial pressures were measured by carotid cannulation. These studies demonstrate that type 1A angiotensin II receptor function is required for vascular and hemodynamic responses to angiotensin II and that altered expression of the Agtr1A gene has marked effects on blood pressures.

Angiotensin II↗

PubMed1995

Genetic control of blood pressure and the angiotensinogen locus.

Variants of the human angiotensinogen gene have been linked in some studies to increased circulating angiotensinogen levels and essential hypertension. To test for direct causality between genotypes at the angiotensinogen locus and blood pressures, we have studied mice carrying zero, one, two, three, or four functional copies of the murine wild-type angiotensinogen gene (Agt) at its normal chromosomal location. Plasma angiotensinogen levels increase progressively, although not linearly, from zero in the zero-copy animals to 145% of normal in the four-copy animals. Mice of all genotypes are normal at birth, but most zero-copy animals die before weaning. The kidneys of the zero-copy animals show pathological changes as adults, but the kidneys are normal in the other genotypes. One adult zero-copy male tested was fertile. The blood pressures of the one-copy through four-copy animals show significant and almost linear increases of approximately 8 mmHg per gene copy despite their normal compensatory mechanisms being intact. These results establish a direct causal relationship between Agt genotypes and blood pressures.

Aging↗

PubMed1995

Rejection of kidney allografts by MHC class I-deficient mice.

To evaluate the requirement for CD8+ T cells in kidney transplant rejection, we studied class I-deficient (class I-) mice that had received vascularized renal allografts. Because of the absence of MHC class I expression, these mice are grossly deficient in CD4-CD8+ alpha beta TCR+ cells. Despite the deficiency of CD8+ T cells in naive class I- mice, kidney allografts transplanted into class I- recipients developed significant reductions in renal blood flow and glomerular filtration rate to levels comparable to allograft controls. This functional deterioration was associated with histologic changes consistent with cellular rejection. There were no significant differences in the pattern, severity, or phenotypic character of the cellular infiltrate in allografts transplanted into class I- recipients compared to controls. In fact, substantial numbers of CD8+ T cells were present in these allografts, and the intensity and pattern of anti-CD8 staining was not different from controls. Virtually all of the CD8+ cells in the kidney grafts were class I- and CD4- and co-expressed CD8 alpha and beta chains; the majority were alpha beta TCR+. The CD8+ infiltrating cells were cytotoxic to donor targets but also exhibited activity against class I+ cells bearing self-MHC. Despite the marked CD8+ T cell infiltration of grafts, CD8+ T cells could not be detected by flow cytometry in freshly isolated splenocytes from the class I- recipients of allografts. High levels of circulating anti-class I antibodies were present in the serum of class I- recipients of kidney allografts, and these antibodies had unusual specificity in that they appeared to recognize framework epitopes of MHC class I. Thus, class I- mice readily reject kidney allografts. Although the number of CD8+ alloreactive precursors is substantially reduced in class mice, and their specificities are atypical, the pattern and character of the intra-graft CD8+ cellular response is not significantly altered. Thus, factors unrelated to precursor frequency determine the dimension of the intra-graft CD8+ response. Such factors might include cellular and/or biochemical properties of microenvironment within the graft.

Animals↗

PubMed1995

Late withdrawal of cyclosporine in stable renal transplant recipients.

The use of cyclosporine (CsA) in renal transplantation has been associated with an improvement in 1-year graft survival, but has not changed the rate of late graft loss. We sought to determine whether the intent to withdraw CsA late after renal transplantation affects renal transplant survival and whether there is a racial difference in the effect of CsA withdrawal. This retrospective study included 384 consecutive patients receiving a renal transplant during the 1984 to 1991 period who were treated with CsA/azathioprine/prednisone and who had a functioning allograft 6 months following transplantation. Of these, 97 were electively withdrawn from CsA at a median of 22 months following transplantation. Factors significantly associated with the decision to withdraw CsA included white race, older age, and lower serum creatinine. Acute rejection within 6 months of stopping CsA occurred in 12 patients (12.4%), including nine of 78 (11.5%) white patients and three of 19 (15.8%) black patients. For the group of 287 patients who were not withdrawn from CsA, the 6-year graft survival rate was 59% (95% confidence interval, 52%, 66%). For the group of patients taken off of CsA, the 6-year graft survival rate was 84% (95% confidence interval, 76%, 92%). Cox proportional hazard survival analysis indicated that the intent to discontinue CsA was associated with better graft survival, with a hazard ratio of 0.37 (95% confidence interval, 0.20, 0.70), independent of other variables that may affect graft survival. A separate analysis controlling for waiting time bias also favored the CsA withdrawal group. There was no detectable racial difference in the effect of CsA withdrawal on graft survival.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1995

Transport of phosphorothioate oligonucleotides in kidney: implications for molecular therapy.

The systemic administration of phosphorothioated antisense oligonucleotides has been demonstrated to be an effective strategy for the control of gene expression. Because previous studies have suggested both hepatic and renal accumulation of systemically administered oligonucleotides, we explored whether the kidney might be a site of free DNA transport. [32P]-phosphorothioate oligonucleotides (20 mers) were excreted in urine but cleared at only 30% of glomerular filtration rate. Plasma clearance of the label was very rapid (t1/2 approximately 5 min) but the half life of labeled S-deoxynucleotide excreted in urine was much slower (28 min). Infused oligonucleotide appeared in urine with little degradation. By autoradiography of renal tissue, labeled antisense oligonucleotides appeared within Bowman's capsule and the proximal tubule lumen. DNA was detected in association with brush border membrane and within tubular epithelial cells. Brush border membrane preparations from rat kidney contained oligonucleotide binding proteins as determined by gel mobility shift and UV cross linking assays. Because renal epithelial cells efficiently take up phosphorothioate oligonucleotides without apparent degradation, the kidney appears to be an excellent target for site-directed antisense therapy, but may be a site of antisense toxicity as well.

Animals↗

PubMed1995

Role of platelet activating factor in kidney transplant rejection in the rat.

Platelet activating factor (PAF) is a potent lipid mediator with a broad range of biologic activities. Experimental evidence suggests that PAF plays a role in the pathogenesis of a variety of inflammatory processes including allograft rejection. In this study, we evaluated the effects of the PAF antagonist BN52021 on the course of renal allograft rejection in a rat model. Kidneys from ACI (RT1a) rats were transplanted into fully allogeneic PVG (RT1c) rat recipients. Animals received 60 mg/kg/day of the PAF antagonist or vehicle beginning immediately prior to the transplantation procedure. In rats treated with the PAF antagonist, allograft GFR and plasma flow were maintained at levels that were significantly greater than controls. Despite the improvement in renal allograft function, BN52021 had no effect on allograft histomorphology and both groups manifested intense inflammatory cell infiltration consistent with acute cellular rejection. PAF antagonism reduced urinary excretion of thromboxane metabolites and decreased thromboxane production by homogenates prepared from kidney allografts. The PAF antagonist had no effect on urinary excretion of peptidoleukotriene metabolites or on the production of LTB4 by allografts. These data support a role for PAF in the pathophysiology of acute renal allograft rejection, and they suggest that the hemodynamic effects of PAF during rejection may be mediated through stimulation of thromboxane A2. In view of the beneficial effects of PAF blockade in rejection as well as recent reports describing efficacy in models of cyclosporine nephrotoxicity, PAF antagonists may have clinical applications in human renal allograft recipients.

Animals↗

PubMed1995

Effects of low-dose aspirin therapy on plasma levels of polyunsaturated fatty acids: a preliminary investigation.

Polyunsaturated fatty acids play an important yet poorly understood role in pregnancy complications. We are interested in the effects of aspirin therapy on the metabolism of these compounds. To determine the effects of low-dose aspirin on plasma levels of polyunsaturated fatty acid precursors, we assayed linoleic, linolenic, arachidonic, eicosapentaenoic, and docosahexaenoic acids using high-performance liquid chromatography. Seventeen pregnant women being treated with aspirin therapy (81 mg/day) were evaluated between 9 and 37 weeks' gestation. Blood was drawn before initiation of aspirin therapy and after 3 or 4 days, and again after 3 or 4 weeks of therapy. We found no significant change in the plasma levels of fatty acids during aspirin therapy at either 3 or 4 days or 3 or 4 weeks compared with baseline. In this group of women with preexisting disease, low-dose aspirin does not appear to change the plasma levels of polyunsaturated fatty acid precursors of eicosanoids. Data on pregnant women without hypertensive disorders is needed to help in understanding the role and physiology of these important compounds.

Adult↗

PubMed1995

Prevention of experimental cyclosporin-induced interstitial fibrosis by losartan and enalapril.

The pathogenesis of renal scarring in chronic cyclosporin nephropathy is unknown. In this study, we evaluated the effects of renin-angiotensin system blockade by enalapril and losartan in a salt-dependent model of cyclosporin-associated chronic tubulointerstitial fibrosis (TIF). Rats kept on normal or low-salt diet were given cyclosporin, cyclosporin+enalapril, cyclosporin+losartan, cyclosporin+enalapril#losartan, or vehicle for 14 and 28 days. Cyclosporin reduced glomerular filtration rate (GFR) in rats fed either diet, but only salt-depleted animals developed significant TIF. Cyclosporin also impaired renal concentrating ability and caused tubular enzymuria. Renin-angiotensin system blockade decreased blood pressure (BP) and promoted afferent arteriolar vasodilatation. Losartan reduced plasma renin activity and prevented cyclosporin-induced increment of cortical alpha 1(I) procollagen mRNA. Renin-angiotensin blockade did not improve GFR and tubular function; however, it strikingly prevented TIF development, even in presence of very low BP. Rats treated with cyclosporin, hydralazine, and furosemide achieved BP values similar to losartan or enalapril groups, but there was no protection against interstitial fibrosis development. These results suggest that cyclosporin-related chronic interstitial injury is mediated by angiotensin II and that the mechanisms promoting the interstitial scarring can be dissociated from glomerular and tubular dysfunction in cyclosporin nephropathy.

Animals↗

PubMed1994

Altered inflammatory responses in leukotriene-deficient mice.

Leukotrienes have been implicated in the regulation of immune responses, including inflammation and immediate hypersensitivity reactions. Here, we describe the phenotypic analysis of leukotriene-deficient mice generated by inactivation of the 5-lipoxygenase (5LO) gene. These 5LO(-/-) mice were unable to synthesize detectable levels of leukotrienes and were more resistant to lethal anaphylaxis induced by platelet-activating factor. The intensity of an acute inflammatory response induced by arachidonic acid was similar in 5LO(-/-) mice and controls. However, the response in 5LO(-/-) mice, but not in controls, could be virtually eliminated by a cyclooxygenase inhibitor. These data suggest that inflammatory responses are modulated by arachidonic acid metabolites through a variety of interconnected mechanisms. This has important implications for understanding the early events of an inflammatory response and for designing drugs for use in therapeutic intervention.

Anaphylaxis↗

PubMed1994

Leukotrienes in renal transplant rejection in rats. Distinct roles for leukotriene B4 and peptidoleukotrienes in the pathogenesis of allograft injury.

To investigate the role of leukotrienes in renal allograft rejection, we studied the effects of specific leukotriene inhibitors in a rat kidney transplant model. The enhanced renal production of leukotrienes observed in allograft recipients was reduced in a dose-dependent manner by the specific 5-lipoxygenase inhibitor MK886. This suppression of leukotriene production caused a substantial improvement in renal function. Inhibition of 5-lipoxygenase also reduced the severity of vascular inflammation and endothelial injury in allografts, and profoundly inhibited expression of donor MHC class II Ag on kidney cells. Survival of renal allograft recipients was prolonged from 10 +/- 1 days in controls to 16 +/- 1 days in animals that received a 6-day course of MK886 (p < 0.05). To investigate the relative roles of LTB4 compared to peptidoleukotrienes in these processes, we treated a separate group of animals with the specific peptidoleukotriene receptor antagonist SKF106203. This agent inhibits the interaction of peptidoleukotrienes with their receptor(s) but does not affect the biologic actions of LTB4. In these studies, SKF106203 caused a modest improvement in renal allograft function that was of lesser magnitude than that seen with the 5-lipoxygenase inhibitor. SKF106203 also reduced vascular inflammation in allografts, but had no effect on expression of MHC class II Ag. We conclude that leukotrienes play a key role in the pathogenesis of renal allograft rejection. Furthermore, the detrimental effects of leukotrienes in rejection are mediated by distinct actions of LTB4 and peptidoleukotrienes.

Animals↗

PubMed1994

Fish oil feeding modulates leukotriene production in murine lupus nephritis.

Diets enriched with fish oil (FO) ameliorate kidney disease in the MRL-lpr/lpr murine model of lupus nephritis. Although the mechanisms of this effect are not known, FO is rich in the polyunsaturated fatty acid eicosapentaenoic acid (EPA) which may have profound effects on eicosanoid metabolism. In MRL-lpr/lpr mice, FO feeding reduces renal production of cyclooxygenase metabolites. However, EPA may also affect the metabolism of arachidonate by the 5-lipoxygenase (5-LO) pathway and enhanced production of 5-LO metabolites has been implicated in the pathogenesis of kidney disease in MRL-lpr/lpr mice. We therefore investigated the effects of FO feeding on production of 5-LO metabolites in 20 week old MRL-lpr/lpr mice. After 8 weeks of dietary supplementation with FO, both renal hemodynamic function and glomerular histology were improved compared to safflower oil (SO) controls. Amelioration of kidney disease was associated with alterations in the pattern of leukotriene production by macrophages and kidneys from FO fed mice. There was a significant decrease in the production of leukotriene B4 (LTB4) and tetraene peptidoleukotrienes by peritoneal macrophages isolated from mice given FO compared to control animals. Similarly, dietary supplementation with FO decreased renal production of LTB4. Reduced production of tetraene leukotrienes was accompanied by a modest increase in the production of pentaene leukotrienes by macrophages from FO fed mice. We speculate that this modulation of leukotriene production by FO feeding may have beneficial effects on renal disease in autoimmune nephritis.

Administration, Oral↗