Jonathan C. Neumann

Functional Roles of the α Isoforms of the Na,K-ATPase

Abstract: The Na,K‐ATPase is composed of two subunits, α and β, and each subunit consists of multiple isoforms. In the case of α, four isoforms, α1, α2, α3, and α4 are present in mammalian cells. The distribution of these isoforms is tissue‐ and developmental‐specific, suggesting that they may play specific roles, either during development or coupled to specific physiological processes. In order to understand the functional properties of each of these isoforms, we are using gene targeting, where animals are produced lacking either one copy or both copies of the corresponding gene or have a modified gene. To date, we have produced animals lacking the α1 and α2 isoform genes. Animals lacking both copies of the α1 isoform gene are not viable, while animals lacking both copies of the α2 isoform gene make it to birth, but are either born dead or die very soon after. In the case of animals lacking one copy of the α1 or α2 isoform gene, the animals survive and appear healthy. Heart and EDL muscle from animals lacking one copy of the α2 isoform exhibit an increase in force of contraction, while there is reduced force of contraction in both muscles from animals lacking one copy of the α1 isoform gene. These studies indicate that the α1 and α2 isoforms carry out different physiological roles. The α2 isoform appears to be involved in regulating Ca2+ transients involved in muscle contraction, while the α1 isoform probably plays a more generalized role. While we have not yet knocked out the α3 or α4 isoform genes, studies to date indicate that the α4 isoform is necessary to maintain sperm motility. It is thus possible that the α2, α3, and α4 isoforms are involved in specialized functions of various tissues, helping to explain their tissue‐ and developmental‐specific regulation.

Reduced Levels of microRNAs miR-124a and miR-150 Are Associated with Increased Proinflammatory Mediator Expression in Krüppel-like Factor 2 (KLF2)-deficient Macrophages

Background: Inactivation of Krüppel-like factor 2 (KLF2) in myeloid cells induces activation of proinflammatory mediators. Results: Macrophage KLF2 deficiency increases chemokine expression and modulates microRNA levels. Conclusion: KLF2 suppresses expression of proinflammatory chemokines Ccl2 and Cxcl1 via modulation of miR-124a and miR-150 levels in myeloid cells. Significance: The anti-inflammatory properties of KLF2 include modification of microRNA expression in macrophages. Previous studies have shown that the myeloid-specific deficiency of the transcription factor Krüppel-like factor 2 (KLF2) accelerates atherosclerosis in hypercholesterolemic Ldlr−/− mice due to the enhanced adhesion of myeloid cells to activated endothelial cells in the vessel wall. This study revealed elevated basal inflammation with elevated plasma levels of Ccl2, Ccl4, Ccl5, and Ccl11 in the myeloid-specific KLF2 knock-out (myeKlf2−/−) mice. Peritoneal macrophages isolated from myeKlf2−/− mice showed increased mRNA levels of several inflammatory mediators, including Ccl2, Ccl5, Ccl7, Cox-2, Cxcl1, and IL-6. In contrast, the levels of two microRNAs, miR-124a and miR-150, were lower in Klf2−/− macrophages compared with Klf2+/+ macrophages. Additional studies showed a direct inverse relationship between miR-124a levels with Ccl2 expression, with anti-miR-124a increasing Ccl2 mRNA levels in Klf2+/+ macrophages, whereas the restoration of miR-124a levels in Klf2−/− macrophages significantly reduced Ccl2 mRNA expression. Likewise, the inverse relationship was observed between miR-150 levels and Cxcl1 expression in Klf2+/+ and Klf2−/− mice. Moreover, miR150 likely regulates the miR124a expression and thus augments expression of inflammatory mediators in myeKlf2−/− macrophages. This study documented that the transcription factor KLF2 modulates inflammatory chemokine production via regulation of microRNA expression levels in immune cells.

Knockout of the Na,K-ATPase α2-isoform in the cardiovascular system does not alter basal blood pressure but prevents ACTH-induced hypertension

The α(2)-isoform of Na,K-ATPase (α(2)) is thought to play a role in blood pressure regulation, but the specific cell type(s) involved have not been identified. Therefore, it is important to study the role of the α(2) in individual cell types in the cardiovascular system. The present study demonstrates the role of vascular smooth muscle α(2) in the regulation of cardiovascular hemodynamics. To accomplish this, we developed a mouse model utilizing the Cre/LoxP system to generate a cell type-specific knockout of the α(2) in vascular smooth muscle cells using the SM22α Cre. We achieved a 90% reduction in the α(2)-expression in heart and vascular smooth muscle in the knockout mice. Interestingly, tail-cuff blood pressure analysis reveals that basal systolic blood pressure is unaffected by the knockout of α(2) in the knockout mice. However, knockout mice do fail to develop ACTH-induced hypertension, as seen in wild-type mice, following 5 days of treatment with ACTH (Cortrosyn; wild type = 119.0 ± 6.8 mmHg; knockout = 103.0 ± 2.0 mmHg). These results demonstrate that α(2)-expression in heart and vascular smooth muscle is not essential for regulation of basal systolic blood pressure, but α(2) is critical for blood pressure regulation under chronic stress such as ACTH-induced hypertension.

Identification of maternally regulated fetal gene networks in the placenta with a novel embryo transfer system in mice

The mechanisms for provisioning maternal resources to offspring in placental mammals involve complex interactions between maternally regulated and fetally regulated gene networks in the placenta, a tissue that is derived from the zygote and therefore of fetal origin. Here we describe a novel use of an embryo transfer system in mice to identify gene networks in the placenta that are regulated by the mother. Mouse embryos from the same strain of inbred mice were transferred into a surrogate mother either of the same strain or from a different strain, allowing maternal and fetal effects on the placenta to be separated. After correction for sex and litter size, maternal strain overrode fetal strain as the key determinant of fetal weight (P < 0.0001). Computational filtering of the placental transcriptome revealed a group of 81 genes whose expression was solely dependent on the maternal strain [P < 0.05, false discovery rate (FDR) < 0.10]. Network analysis of this group of genes yielded highest statistical significance for pathways involved in the regulation of cell growth (such as insulin-like growth factors) as well as those involved in regulating lipid metabolism [such as the low-density lipoprotein receptor-related protein 1 (LRP1), LDL, and HDL], both of which are known to play a role in fetal development. This novel technique may be generally applied to identify regulatory networks involved in maternal-fetal interaction and eventually help identify molecular targets in disorders of fetal growth.