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Deletion of Trpm7 disrupts embryonic development and thymopoiesis without altering Mg2+ homeostasis.

ABSTRACT: The gene transient receptor potential-melastatin-like 7 (Trpm7) encodes a protein that functions as an ion channel and a kinase. TRPM7 has been proposed to be required for cellular Mg2+ homeostasis in vertebrates. Deletion of mouse Trpm7 revealed that it is essential for embryonic development. Tissue-specific deletion of Trpm7 in the T cell lineage disrupted thymopoiesis, which led to a developmental block of thymocytes at the double-negative stage and a progressive depletion of thymic medullary cells. However, deletion of Trpm7 in T cells did not affect acute uptake of Mg2+ or the maintenance of total cellular Mg2+. Trpm7-deficient thymocytes exhibited dysregulated synthesis of many growth factors that are necessary for the differentiation and maintenance of thymic epithelial cells. The thymic medullary cells lost signal transducer and activator of transcription 3 activity, which accounts for their depletion when Trpm7 is disrupted in thymocytes.

SUBMITTER: Jin J

PROVIDER: S-EPMC2605283 | biostudies-literature | 2008 Oct

REPOSITORIES: biostudies-literature

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Deletion of Trpm7 disrupts embryonic development and thymopoiesis without altering Mg2+ homeostasis.

Jin Jie J Desai Bimal N BN Navarro Betsy B Donovan Adriana A Andrews Nancy C NC Clapham David E DE

Science (New York, N.Y.) 20081001 5902

The gene transient receptor potential-melastatin-like 7 (Trpm7) encodes a protein that functions as an ion channel and a kinase. TRPM7 has been proposed to be required for cellular Mg2+ homeostasis in vertebrates. Deletion of mouse Trpm7 revealed that it is essential for embryonic development. Tissue-specific deletion of Trpm7 in the T cell lineage disrupted thymopoiesis, which led to a developmental block of thymocytes at the double-negative stage and a progressive depletion of thymic medullary ...[more]

PMID: 18974357

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Project description:Transient receptor potential (TRP) channels are a superfamily of broadly expressed ion channels with diverse physiological roles. TRPC1, TRPC3, and TRPC6 are believed to contribute to cardiac hypertrophy in mouse models. Human mutations in TRPM4 have been linked to progressive familial heart block. TRPM7 is a divalent-permeant channel and kinase of unknown function, recently implicated in the pathogenesis of atrial fibrillation; however, its function in ventricular myocardium remains unexplored.We generated multiple cardiac-targeted knockout mice to test the hypothesis that TRPM7 is required for normal ventricular function. Early cardiac Trpm7 deletion (before embryonic day 9; TnT/Isl1-Cre) results in congestive heart failure and death by embryonic day 11.5 as a result of hypoproliferation of the compact myocardium. Remarkably, Trpm7 deletion late in cardiogenesis (about embryonic day 13; ?MHC-Cre) produces viable mice with normal adult ventricular size, function, and myocardial transcriptional profile. Trpm7 deletion at an intermediate time point results in 50% of mice developing cardiomyopathy associated with heart block, impaired repolarization, and ventricular arrhythmias. Microarray analysis reveals elevations in transcripts of hypertrophy/remodeling genes and reductions in genes important for suppressing hypertrophy (Hdac9) and for ventricular repolarization (Kcnd2) and conduction (Hcn4). These transcriptional changes are accompanied by action potential prolongation and reductions in transient outward current (Ito; Kcnd2). Similarly, the pacemaker current (If; Hcn4) is suppressed in atrioventricular nodal cells, accounting for the observed heart block.Trpm7 is dispensable in adult ventricular myocardium under basal conditions but is critical for myocardial proliferation during early cardiogenesis. Loss of Trpm7 at an intermediate developmental time point alters the myocardial transcriptional profile in adulthood, impairing ventricular function, conduction, and repolarization.

Project description:We have previously shown that experimental infection caused by Trypanosoma cruzi is associated with changes in the hypothalamus-pituitary-adrenal axis. Increased glucocorticoid (GC) levels are believed to be protective against the effects of acute stress during infection but result in depletion of CD4(+)CD8(+) thymocytes by apoptosis, driving to thymic atrophy. However, very few data are available concerning prolactin (PRL), another stress-related hormone, which seems to be decreased during T. cruzi infection. Considering the immunomodulatory role of PRL upon the effects caused by GC, we investigated if intrathymic cross-talk between GC and PRL receptors (GR and PRLR, respectively) might influence T. cruzi-induced thymic atrophy. Using an acute experimental model, we observed changes in GR/PRLR cross-activation related with the survival of CD4(+)CD8(+) thymocytes during infection. These alterations were closely related with systemic changes, characterized by a stress hormone imbalance, with progressive GC augmentation simultaneously to PRL reduction. The intrathymic hormone circuitry exhibited an inverse modulation that seemed to counteract the GC-related systemic deleterious effects. During infection, adrenalectomy protected the thymus from the increase in apoptosis ratio without changing PRL levels, whereas an additional inhibition of circulating PRL accelerated the thymic atrophy and led to an increase in corticosterone systemic levels. These results demonstrate that the PRL impairment during infection is not caused by the increase of corticosterone levels, but the opposite seems to occur. Accordingly, metoclopramide (MET)-induced enhancement of PRL secretion protected thymic atrophy in acutely infected animals as well as the abnormal export of immature and potentially autoreactive CD4(+)CD8(+) thymocytes to the periphery. In conclusion, our findings clearly show that Trypanosoma cruzi subverts mouse thymus homeostasis by altering intrathymic and systemic stress-related endocrine circuitries with major consequences upon the normal process of intrathymic T cell development.

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Deletion of Trpm7 disrupts embryonic development and thymopoiesis without altering Mg2+ homeostasis.

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Deletion of Trpm7 disrupts embryonic development and thymopoiesis without altering Mg2+ homeostasis.

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