Genetic analysis of albuminuria in collaborative cross and multiple mouse intercross populations.

Albuminuria is an important marker of nephropathy that increases the risk of progressive renal and chronic cardiovascular diseases. The genetic basis of kidney disease is well-established in humans and rodent models, but the causal genes remain to be identified. We applied several genetic strategies to map and refine genetic loci affecting albuminuria in mice and translated the findings to human kidney disease. First, we measured albuminuria in mice from 33 inbred strains, used the data for haplotype association mapping (HAM), and detected 10 genomic regions associated with albuminuria. Second, we performed eight F(2) intercrosses between genetically diverse strains to identify six loci underlying albuminuria, each of which was concordant to kidney disease loci in humans. Third, we used the Oak Ridge National Laboratory incipient Collaborative Cross subpopulation to detect an additional novel quantitative trait loci (QTL) underlying albuminuria. We also performed a ninth intercross, between genetically similar strains, that substantially narrowed an albuminuria QTL on Chromosome 17 to a region containing four known genes. Finally, we measured renal gene expression in inbred mice to detect pathways highly correlated with albuminuria. Expression analysis also identified Glcci1, a gene known to affect podocyte structure and function in zebrafish, as a strong candidate gene for the albuminuria QTL on Chromosome 6. Overall, these findings greatly enhance our understanding of the genetic basis of albuminuria in mice and may guide future studies into the genetic basis of kidney disease in humans.

Cardiac-specific overexpression of AT1 receptor mutant lacking G alpha q/G alpha i coupling causes hypertrophy and bradycardia in transgenic mice.

Ang II type 1 (AT1) receptors activate both conventional heterotrimeric G protein-dependent and unconventional G protein-independent mechanisms. We investigated how these different mechanisms activated by AT1 receptors affect growth and death of cardiac myocytes in vivo. Transgenic mice with cardiac-specific overexpression of WT AT1 receptor (AT1-WT; Tg-WT mice) or an AT1 receptor second intracellular loop mutant (AT1-i2m; Tg-i2m mice) selectively activating G(alpha)q/G(alpha)i-independent mechanisms were studied. Tg-i2m mice developed more severe cardiac hypertrophy and bradycardia coupled with lower cardiac function than Tg-WT mice. In contrast, Tg-WT mice exhibited more severe fibrosis and apoptosis than Tg-i2m mice. Chronic Ang II infusion induced greater cardiac hypertrophy in Tg-i2m compared with Tg-WT mice whereas acute Ang II administration caused an increase in heart rate in Tg-WT but not in Tg-i2m mice. Membrane translocation of PKCepsilon, cytoplasmic translocation of G(alpha)q, and nuclear localization of phospho-ERKs were observed only in Tg-WT mice while activation of Src and cytoplasmic accumulation of phospho-ERKs were greater in Tg-i2m mice, consistent with the notion that G(alpha)q/G(alpha)i-independent mechanisms are activated in Tg-i2m mice. Cultured myocytes expressing AT1-i2m exhibited a left and upward shift of the Ang II dose-response curve of hypertrophy compared with those expressing AT1-WT. Thus, the AT1 receptor mediates downstream signaling mechanisms through G(alpha)q/G(alpha)i-dependent and -independent mechanisms, which induce hypertrophy with a distinct phenotype.

Amikacin Liposome Inhalation Suspension (ALIS) Penetrates Non-tuberculous Mycobacterial Biofilms and Enhances Amikacin Uptake Into Macrophages.

Non-tuberculous mycobacteria (NTM) cause pulmonary infections in patients with structural lung damage, impaired immunity, or other risk factors. Delivering antibiotics to the sites of these infections is a major hurdle of therapy because pulmonary NTM infections can persist in biofilms or as intracellular infections within macrophages. Inhaled treatments can improve antibiotic delivery into the lungs, but efficient nebulization delivery, distribution throughout the lungs, and penetration into biofilms and macrophages are considerable challenges for this approach. Therefore, we developed amikacin liposome inhalation suspension (ALIS) to overcome these challenges. Nebulization of ALIS has been shown to provide particles within the respirable size range that distribute to both central and peripheral lung compartments in humans. The in vitro and in vivo efficacy of ALIS against NTM has been demonstrated previously. The key mechanistic questions are whether ALIS penetrates NTM biofilms and enhances amikacin uptake into macrophages. We found that ALIS effectively penetrated throughout NTM biofilms and concentration-dependently reduced the number of viable mycobacteria. Additionally, we found that ALIS improved amikacin uptake by ∼4-fold into cultured macrophages compared with free amikacin. In rats, inhaled ALIS increased amikacin concentrations in pulmonary macrophages by 5- to 8-fold at 2, 6, and 24 h post-dose and retained more amikacin at 24 h in airways and lung tissue relative to inhaled free amikacin. Compared to intravenous free amikacin, a standard-of-care therapy for refractory and severe NTM lung disease, ALIS increased the mean area under the concentration-time curve in lung tissue, airways, and macrophages by 42-, 69-, and 274-fold. These data demonstrate that ALIS effectively penetrates NTM biofilms, enhances amikacin uptake into macrophages, both in vitro and in vivo, and retains amikacin within airways and lung tissue. An ongoing Phase III trial, adding ALIS to guideline based therapy, met its primary endpoint of culture conversion by month 6. ALIS represents a promising new treatment approach for patients with refractory NTM lung disease.

Activation of Mst1 causes dilated cardiomyopathy by stimulating apoptosis without compensatory ventricular myocyte hypertrophy.

Activation of mammalian sterile 20-like kinase 1 (Mst1) by genotoxic compounds is known to stimulate apoptosis in some cell types. The importance of Mst1 in cell death caused by clinically relevant pathologic stimuli is unknown, however. In this study, we show that Mst1 is a prominent myelin basic protein kinase activated by proapoptotic stimuli in cardiac myocytes and that Mst1 causes cardiac myocyte apoptosis in vitro in a kinase activity-dependent manner. In vivo, cardiac-specific overexpression of Mst1 in transgenic mice results in activation of caspases, increased apoptosis, and dilated cardiomyopathy. Surprisingly, however, Mst1 prevents compensatory cardiac myocyte elongation or hypertrophy despite increased wall stress, thereby obscuring the use of the Frank-Starling mechanism, a fundamental mechanism by which the heart maintains cardiac output in response to increased mechanical load at the single myocyte level. Furthermore, Mst1 is activated by ischemia/reperfusion in the mouse heart in vivo. Suppression of endogenous Mst1 by cardiac-specific overexpression of dominant-negative Mst1 in transgenic mice prevents myocyte death by pathologic insults. These results show that Mst1 works as both an essential initiator of apoptosis and an inhibitor of hypertrophy in cardiac myocytes, resulting in a previously unrecognized form of cardiomyopathy.

Genome-wide association mapping of quantitative traits in outbred mice.

Recent developments in high-density genotyping and statistical analysis methods that have enabled genome-wide association studies in humans can also be applied to outbred mouse populations. Increased recombination in outbred populations is expected to provide greater mapping resolution than traditional inbred line crosses, improving prospects for identifying the causal genes. We carried out genome-wide association mapping by using 288 mice from a commercially available outbred stock; NMRI mice were genotyped with a high-density single-nucleotide polymorphism array to map loci influencing high-density lipoprotein cholesterol, systolic blood pressure, triglyceride levels, glucose, and urinary albumin-to-creatinine ratios. We found significant associations (P < 10(-5)) with high-density lipoprotein cholesterol and identified Apoa2 and Scarb1, both of which have been previously reported, as candidate genes for these associations. Additional suggestive associations (P < 10(-3)) identified in this study were also concordant with published quantitative trait loci, suggesting that we are sampling from a limited pool of genetic diversity that has already been well characterized. These findings dampen our enthusiasm for currently available commercial outbred stocks as genetic mapping resources and highlight the need for new outbred populations with greater genetic diversity. Despite the lack of novel associations in the NMRI population, our analysis strategy illustrates the utility of methods that could be applied to genome-wide association studies in humans.

Genetic analysis of blood pressure in 8 mouse intercross populations.

The genetic basis of hypertension is well established, yet very few genes that cause common forms of hypertension are known. Quantitative trait locus (QTL) analyses in rodent models can guide the search for human hypertension genes, but the excellent genetic resources for mice have been underused in this regard. To address this issue, we surveyed blood pressure variation in mice from 37 inbred strains and generated 2577 mice in 8 intercross populations to perform QTL analyses of blood pressure. We identified 14 blood pressure QTL in these populations, including > or =7 regions of the mouse genome not linked previously to blood pressure. Many QTL were detected in multiple crosses, either within our study or in studies published previously, which facilitates the use of bioinformatics methods to narrow the QTL and focus the search for candidate genes. The regions of the human genome that correspond to all but 1 of the 14 blood pressure QTL in mice are linked to blood pressure in humans, suggesting that these regions contain causal genes with a conserved role in blood pressure control. These results greatly expand our knowledge of the genomic regions underlying blood pressure regulation in mice and support future studies to identify the causal genes within these QTL intervals.

Propranolol prevents enhanced stress signaling in Gs alpha cardiomyopathy: potential mechanism for beta-blockade in heart failure.

Beta-adrenergic receptor (beta-AR) blockade is now widely utilized therapeutically for heart failure, but its cellular mechanism of action is not clear. Mice with cardiac-specific overexpressed Gs alpha develop cardiomyopathy with age, which can be prevented by beta-AR blockade, making this model potentially useful for addressing this question. Our hypothesis was that distal mechanisms in beta-AR signaling, i.e. mitogen-activated protein kinases, were a potential mechanism. At 6-9 months, when cardiomyopathy began to develop in Gs alpha mice, there were significant increases in phospho-kinase levels of p38 MAP kinase (p38 MAPK), and p70(S6K) compared to wild type. In contrast, phospho-kinase levels of ERK and Akt were increased at 9-10 months, but phospho-kinase levels of c-Jun N-terminal kinase (JNK) increased only at 15-20 months (when cardiomyopathy was fully manifest). Treatment of 9-10 months old Gs alpha mice with propranolol for 5 weeks reverted the phospho-kinase levels of these kinases known to be involved in the growth and death of cardiac myocytes. Another novel observation of this study was that there were also decreases in total protein levels of p38 MAPK, p70(S6K), JNK, and Akt following beta-AR blockade. Thus, chronically enhanced beta-AR signaling elicits a differential pattern of altered mitogen-activated protein kinases, which was reversed with beta-AR blockade, raising the possibility that the beneficial effects of beta-AR blockade therapy in heart failure may be due in part to the inhibition of these pathways.

Mechanism of enhanced cardiac function in mice with hypertrophy induced by overexpressed Akt.

Transgenic mice with cardiac-specific overexpression of active Akt (TG) not only exhibit hypertrophy but also show enhanced left ventricular (LV) function. In 3-4-month-old TG, heart/body weight was increased by 60% and LV ejection fraction was elevated (84 +/- 2%, p < 0.01) compared with nontransgenic littermates (wild type (WT)) (73 +/- 1%). An increase in isolated ventricular myocyte contractile function (% contraction) in TG compared with WT (6.1 +/- 0.2 versus 3.5 +/- 0.2%, p < 0.01) was associated with increased Fura-2 Ca2+ transients (396 +/- 50 versus 250 +/- 24 nmol/liter, p < 0.05). The rate of relaxation (+dL/dt) was also enhanced in TG (214 +/- 15 versus 98 +/- 18 microm/s, p < 0.01). L-type Ca2+ current (ICa) density was increased in TG compared with WT (-9.0 +/- 0.3 versus 7.2 +/- 0.3 pA/pF, p < 0.01). Sarcoplasmic reticulum Ca2+ ATPase 2a (SERCA2a) protein levels were increased (p < 0.05) by 6.6-fold in TG, which could be recapitulated in vitro by adenovirus-mediated overexpression of Akt in cultured adult ventricular myocytes. Conversely, inhibiting SERCA with either ryanodine or thapsigargin affected myocyte contraction and relaxation and Ca2+ channel kinetics more in TG than in WT. Thus, myocytes from mice with overexpressed Akt demonstrated enhanced contractility and relaxation, Fura-2 Ca2+ transients, and Ca2+ channel currents. Furthermore, increased protein expression of SERCA2a plays an important role in mediating enhanced LV function by Akt. Up-regulation of SERCA2a expression and enhanced LV myocyte contraction and relaxation in Akt-induced hypertrophy is opposite to the down-regulation of SERCA2a and reduced contractile function observed in many other forms of LV hypertrophy.