Biomedical subjects

Thomas Doetschman

Publications and source records attributed to Thomas Doetschman.

23 records · Page 2Linked to original sources

PubMed2002

Impaired renal NaCl absorption in mice lacking the ROMK potassium channel, a model for type II Bartter's syndrome.

ROMK is an apical K(+) channel expressed in the thick ascending limb of Henle (TALH) and throughout the distal nephron of the kidney. Null mutations in the ROMK gene cause type II Bartter's syndrome, in which abnormalities of electrolyte, acid-base, and fluid-volume homeostasis occur because of defective NaCl reabsorption in the TALH. To understand better the pathogenesis of type II Bartter's syndrome, we developed a mouse lacking ROMK and examined its phenotype. Young null mutants had hydronephrosis, were severely dehydrated, and approximately 95% died before 3 weeks of age. ROMK-deficient mice that survived beyond weaning grew to adulthood; however, they had metabolic acidosis, elevated blood concentrations of Na(+) and Cl(-), reduced blood pressure, polydipsia, polyuria, and poor urinary concentrating ability. Whole kidney glomerular filtration rate was sharply reduced, apparently as a result of hydronephrosis, and fractional excretion of electrolytes was elevated. Micropuncture analysis revealed that the single nephron glomerular filtration rate was relatively normal, absorption of NaCl in the TALH was reduced but not eliminated, and tubuloglomerular feedback was severely impaired. These data show that the loss of ROMK in the mouse causes perturbations of electrolyte, acid-base, and fluid-volume homeostasis, reduced absorption of NaCl in the TALH, and impaired tubuloglomerular feedback.

Animals↗

PubMed2002

Loss of heterozygosity and point mutation at Aprt locus in T cells and fibroblasts of Pms2-/- mice.

Mice null for the Pms2 mismatch repair (MMR) gene exhibit a predisposition to lymphoma, microsatellite repeat instability, and failure of spermatogenesis. To study the role of Pms2 in the maintenance of in vivo genomic integrity in somatic cells, we characterized Aprt mutations in T cells and fibroblasts of 129 x C3H Pms2-/-Aprt+/- mice. The spontaneous frequency of DAP-resistant T lymphocytes, as a consequence of APRT-deficiency, was increased threefold. Point mutation, which accounted for less than 20% of the DAP(r) mutant clones in Pms2+/+ mice, was predominant in the mutant T cell clones from Pms2-/- mice. These point mutations were predominantly TA to CG transitions. Fibroblasts of Pms2-/- mice exhibited only a modest increase in the frequency of clones with point mutations, such that mitotic recombination was still the primary cause of APRT deficiency. Thus, the mutator phenotype as a consequence of PMS2 deficiency is tissue-dependent, which may be related to the tissue-specific tumor proneness of Pms2-/- mice.

Adenine Phosphoribosyltransferase↗

PubMed2002

Altered apoptosis pattern during pharyngeal arch artery remodelling is associated with aortic arch malformations in Tgfbeta2 knock-out mice.

OBJECTIVE: The morphogenetic process underlying the remodelling of the embryonic mammalian pharyngeal arch artery system is unknown. Within this process, the right sixth, carotid ducts and the distal part of the dorsal aorta (right alpha-segment) regress. In order to unravel the underlying mechanism we studied the role of apoptosis in the normal regression of pharyngeal arch artery segments and in a mouse model that develops aortic arch malformations. METHODS: Normal remodelling was studied in wild-type Swiss (CPBS) and altered remodelling in the Tgfbeta2-/- compared to the Tgfbeta2+/+ (Swiss/Bl6) strain using immunohistochemistry and morphometric analysis. RESULTS: During normal remodelling, apoptosis occurs in the mesenchyme surrounding pharyngeal arch arteries before regression starts. With the onset of regression, apoptosis spreads from the mesenchyme to the media. Morphometric evaluation confirms the increase in apoptosis in the actin-positive media of the disappearing segments. In Tgfbeta2-/-, aberrant apoptosis was found in both fourth arch arteries, whereas the right dorsal aorta lacks apoptosis associated with normal regression. Fourth arch hypoplasia is the main arch abnormality. In the most severe case, the fourth arch is interrupted and the right dorsal aorta alpha-segment persists, giving rise to aortic arch interruption type-B and an aberrant right subclavian artery. CONCLUSIONS: We have shown for the first time that specific vascular apoptosis patterns accompany normal regression and that the incidence of apoptosis is selectively altered in the case of arch artery abnormalities in Tgfbeta2 knock-out mice.

Animals↗

PubMed2002

TGF-beta1 mediates the hypertrophic cardiomyocyte growth induced by angiotensin II.

Angiotensin II (Ang II), a potent hypertrophic stimulus, causes significant increases in TGFb1 gene expression. However, it is not known whether there is a causal relationship between increased levels of TGF-beta1 and cardiac hypertrophy. Echocardiographic analysis revealed that TGF-beta1-deficient mice subjected to chronic subpressor doses of Ang II had no significant change in left ventricular (LV) mass and percent fractional shortening during Ang II treatment. In contrast, Ang II-treated wild-type mice showed a >20% increase in LV mass and impaired cardiac function. Cardiomyocyte cross-sectional area was also markedly increased in Ang II-treated wild-type mice but unchanged in Ang II-treated TGF-beta1-deficient mice. No significant levels of fibrosis, mitotic growth, or cytokine infiltration were detected in Ang II-treated mice. Atrial natriuretic factor expression was approximately 6-fold elevated in Ang II-treated wild-type, but not TGF-beta1-deficient mice. However, the alpha- to beta-myosin heavy chain switch did not occur in Ang II-treated mice, indicating that isoform switching is not obligatorily coupled with hypertrophy or TGF-beta1. The Ang II effect on hypertrophy was shown not to result from stimulation of the endogenous renin-angiotensis system. These results indicate that TGF-beta1 is an important mediator of the hypertrophic growth response of the heart to Ang II.

Angiotensin II↗

PubMed2002

TGFbeta2 mediates the effects of hedgehog on hypertrophic differentiation and PTHrP expression.

The development of endochondral bones requires the coordination of signals from several cell types within the cartilage rudiment. A signaling cascade involving Indian hedgehog (Ihh) and parathyroid hormone related peptide (PTHrP) has been described in which hypertrophic differentiation is limited by a signal secreted from chondrocytes as they become committed to hypertrophy. In this negative-feedback loop, Ihh inhibits hypertrophic differentiation by regulating the expression of Pthrp, which in turn acts directly on chondrocytes in the growth plate that express the PTH/PTHrP receptor. Previously, we have shown that PTHrP also acts downstream of transforming growth factor beta (TGFbeta) in a common signaling cascade to regulate hypertrophic differentiation in embryonic mouse metatarsal organ cultures. As members of the TGFbeta superfamily have been shown to mediate the effects of Hedgehog in several developmental systems, we proposed a model where TGFbeta acts downstream of Ihh and upstream of PTHrP in a cascade of signals that regulate hypertrophic differentiation in the growth plate. This report tests the hypothesis that TGFbeta signaling is required for the effects of Hedgehog on hypertrophic differentiation and expression of PTHRP: We show that Sonic hedgehog (Shh), a functional substitute for Ihh, stimulates expression of Tgfb2 and Tgfb3 mRNA in the perichondrium of embryonic mouse metatarsal bones grown in organ cultures and that TGFbeta signaling in the perichondrium is required for inhibition of differentiation and regulation of Pthrp expression by Shh. The effects of Shh are specifically dependent on TGFbeta2, as cultures from Tgfb3-null embryos respond to Shh but cultures from Tgfb2-null embryos do not. Taken together, these data suggest that TGFbeta2 acts as a signal relay between Ihh and PTHrP in the regulation of cartilage hypertrophic differentiation.

Animals↗