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Activation of type 1 angiotensin (AT(1)) receptors causes hypertension, leading to progressive kidney injury. AT(1) receptors are expressed on immune cells, and previous studies have identified a role for immune cells in angiotensin II-dependent hypertension. We, therefore, examined the role of AT(1) receptors on immune cells in the pathogenesis of hypertension by generating bone marrow chimeras with wild-type donors or donors lacking AT(1A) receptors (BMKO). The 2 groups had virtually identical blood pressures at baseline, suggesting that AT(1) receptors on immune cells do not make a unique contribution to the determination of baseline blood pressure. By contrast, in response to chronic angiotensin II infusion, the BMKOs had an augmented hypertensive response, suggesting a protective effect of AT(1) receptors on immune cells with respect to blood pressure elevation. The BMKOs had 50% more albuminuria after 4 weeks of angiotensin II-dependent hypertension. Angiotensin II-induced pathological injury to the kidney was similar in the experimental groups. However, there was exaggerated renal expression of the macrophage chemokine monocyte chemoattractant protein 1 in the BMKO group, leading to persistent accumulation of macrophages in the kidney. This enhanced mononuclear cell infiltration into the BMKO kidneys was associated with exaggerated renal expression of the vasoactive mediators interleukin-1beta and interleukin-6. Thus, in angiotensin II-induced hypertension, bone marrow-derived AT(1) receptors limited mononuclear cell accumulation in the kidney and mitigated the chronic hypertensive response, possibly through the regulation of vasoactive cytokines. [ABSTRACT FROM AUTHOR]

Glutathione S-transferase-micro1, GSTM1, belongs to a superfamily of glutathione S-transferases that metabolizes a broad range of reactive oxygen species and xenobiotics. Across species, genetic variants that result in decreased expression of the Gstm1 gene are associated with increased susceptibility for vascular diseases, including atherosclerosis in humans. We previously identified Gstm1 as a positional candidate in our gene mapping study for susceptibility to renal vascular injury characterized by medial hypertrophy and hyperplasia of the renal vessels. To determine the role of Gstm1 in vascular smooth muscle cells (VSMCs), we isolated VSMCs from mouse aortas. We demonstrate that VSMCs from the susceptible C57BL/6 mice have reduced expression of Gstm1 mRNA and its protein product compared with that of the resistant 129 mice. After serum stimulation, C57BL/6 VSMCs proliferate and migrate at a much faster rate than 129 VSMCs. Furthermore, C57BL/6 VSMCs have higher levels of reactive oxygen species and exhibit exaggerated p38 mitogen-activated protein kinase phosphorylation after exposure to H(2)O(2). To establish causality, we show that knockdown of Gstm1 by small interfering RNA results in increased proliferation of VSMCs in a dose-dependent manner, as well as in increased reactive oxygen species levels and VSMC migration. Moreover, Gstm1 small interfering RNA causes increased p38 mitogen-activated protein kinase phosphorylation and attenuates the antiproliferative effect of Tempol. Our data suggest that Gstm1 is a novel regulator of VSMC proliferation and migration through its role in handling reactive oxygen species. Genetic variants that cause a decremental change in expression of Gstm1 may permit an environment of exaggerated oxidative stress, leading to susceptibility to vascular remodeling and atherosclerosis. [ABSTRACT FROM AUTHOR]

Background: The molecular processes regulating the development of renin producing juxtaglomerular (JG) cells are not fully understood. We have previously shown that LXRα and cAMP treatment can induce mesenchymal stromal cells (MSCs) from different sources to differentiate into renin expressing JG-like cells. Here, we investigated the LXRα/cAMP induced transcriptional networks involved in the commitment of progenitor cells to the JG lineage.METHODS: Adult renal CD44+ MSCs were isolated from C57BL/6 Ren1c YFP mice. MSCs were differentiated into YFP+ renin expressing cells by treatment with LXRα ligand (T0901317) or cAMP. The Affymetrix Mouse 430 2.0 array was used for profiling. Data analysis was focused on transcriptional and epigenetic regulators and performed by using Dchip, David or Toppgene.Results: Differentiated YFP+ cells from either cAMP or LXRα treatment expressed high levels of renin and renin regulators such as Hoxd8 and Cebp. Untreated MSCs showed expression of metanephric markers such as Foxd1, Sox11 and Eya. Treatment with cAMP resulted in differential expression of 108 transcripts in YFP+ cells as compared to control MSC. The majority of these genes (82) were down-regulated and involved in chromatin acetylation (23 out of 82, P<2E-5) or embryonic and hematopoietic development (36 out of 82 respectively, P<2E-5). Mesenchymal markers (i.e. Sox11, FC= -3) and repressors of differentiation (i.e. Id2, FC= -2) were also decreased significantly. Similarly, MSC activation by LXRα resulted in differential expression of 98 transcripts, 67 of which were decreased compared to baseline. As with cAMP, the majority of genes were involved in differentiation and chromatin remodeling (i.e Tbx3, Klfs and Mll); still, the overlap of genes between the two treatments was minimal (24 genes) suggesting that cAMP and LXRα might act complementary to each other.Conclusion: Our data indicate that cAMP and LXRα, rather than directly define JG cell fate, modulate the epigenetic status of MSCs and prevent differentiation to other lineages. Systems biology approaches are under way to evaluate the importance of the transcriptional networks identified. We anticipate that these results will provide novel insights into the mechanisms regulating JG cell fate. [ABSTRACT FROM AUTHOR]

Background: We have previously shown that CD44+ MSCs exist in the adult kidney and that under chronic sodium deprivation these cells migrate to the juxtaglomerular (JG) area and differentiate to new renin expressing cells. The mechanisms mediating these biological processes remain elusive. Renin expression and release by JG cells is initiated at the Macula densa (MD) primarily by the release of PGE2. Interestingly, renal MSC expresses the PGE2 receptor EP4. Here, we hypothesized that MD-derived PGE2 acting via the EP4 is responsible for the migration of renal MSCs and their differentiation to renin expressing cells.Methods: MSCs were isolated by FACS from the kidney of C57BL/6 adult mice and co-cultured in a transwell system with the MD cell line MMDD1 at normal or low NaCl medium. For the in vivo study, wild type and EP4 knockout mice were fed a low salt diet and given furosemide to induce JG hyperplasia. Renin, CD44 and B-catenin stabilization were detected by immunochemistry staining and Western blot analysis.Results: Low salt stimulation of MMDD1 cells significantly increased MSC migration in transwell assays (P<0.05). These effects were abrogated by addition of a COX2 inhibitor (NS398) to MMDD1 cells or an EP4 receptor antagonist (AH23848) to the MSCs. Treatment of MSCs with a PGI2 receptor antagonist (CAY 10441) had no effect on this migratory response. Furthermore, direct addition of PGE2, but not PGI2 to MSCs increased cell migration as compared to controls (P<0.05). PGE2 did not affect proliferation of MSCs but did induce renin expression, suggesting that PGE2 plays an important role in promoting the migration and differentiation of renal MSCs. PGE2 treatment also resulted in increased beta catenin stabilization and activation of canonical Wnt signaling; a pathway that plays an important role in progenitor cell migration and differentiation. Finally, the absence of the EP4 receptor in mice attenuated expansion, migration of renal CD44+ cells and JG hyperplasia induced by sodium deprivation.Conclusion: The MD/ PGE2/ EP4 axis plays a key role in the activation of MSCs and their differentiation to renin producing cells. This process could potentially be an important physiologic mechanism of maintaining blood pressure under conditions of sodium deprivation. [ABSTRACT FROM AUTHOR]