Characterization of blood pressure and morphological traits in cardiovascular-related organs in 13 different inbred mouse strains

Mousepost 2.0, a major expansion of the resource

The Mousepost 1.0 online search tool, launched in 2017, allowed to search for variations in all protein-coding gene sequences of 36 sequenced mouse inbred strains, compared to the reference strain C57BL/6J, which could be linked to strain-specific phenotypes and modifier effects. Because recently these genome sequences have been significantly updated and sequences of 16 extra strains added by the Mouse Genomes Project, a profound update, correction and expansion of the Mousepost 1.0 database has been performed and is reported here. Moreover, we have added a new class of protein disturbing sequence polymorphisms (besides stop codon losses, stop codon gains, small insertions and deletions, and missense mutations), namely start codon mutations. The current version, Mousepost 2.0 (https://mousepost.be), therefore is a significantly updated and invaluable tool available to the community and is described here and foreseen by multiple examples.

Involvement of GPR37L1 in murine blood pressure regulation and human cardiac disease pathophysiology

Multiple mouse lines lacking the orphan G protein-coupled receptor, GPR37L1, have elicited disparate cardiovascular phenotypes. The first Gpr37l1 knockout mice study to be published reported a marked elevation in systolic blood pressure (SBP; ∼60 mmHg), revealing a potential therapeutic opportunity. The phenotype differed from our own independently generated knockout line, where male mice exhibited equivalent baseline blood pressure to wild type. Here, we attempted to reproduce the first study by characterizing the cardiovascular phenotype of both the original knockout and transgenic lines alongside a C57BL/6J control line, using the same method of blood pressure measurement. The present study supports the findings from our independently developed Gpr37l1 knockout line, finding that SBP and diastolic blood pressure (DBP) are not different in the original Gpr37l1 knockout male mice (SBP: 130.9 ± 5.3 mmHg; DBP: 90.7 ± 3.0 mmHg) compared with C57BL/6J mice (SBP: 123.1 ± 4.1 mmHg; DBP: 87.0 ± 2.7 mmHg). Instead, we attribute the apparent hypertension of the knockout line originally described to comparison with a seemingly hypotensive transgenic line (SBP 103.7 ± 5.0 mmHg; DBP 71.9 ± 3.7 mmHg). Additionally, we quantified myocardial GPR37L1 transcript in humans, which was suggested to be downregulated in cardiovascular disease. We found that GPR37L1 has very low native transcript levels in human myocardium and that expression is not different in tissue samples from patients with heart failure compared with sex-matched healthy control tissue. These findings indicate that cardiac GPR37L1 expression is unlikely to contribute to the pathophysiology of human heart failure.NEW & NOTEWORTHY This study characterizes systolic blood pressure (SBP) in a Gpr37l1 knockout mouse line, which was previously reported to have ∼60 mmHg higher SBP compared with a transgenic line. We observed only a ∼27 mmHg SBP difference between the lines. However, when compared with C57BL/6J mice, knockout mice showed no difference in SBP. We also investigated GPR37L1 mRNA abundance in human hearts and observed no difference between healthy and failing heart samples.

Activation of the Thiazide-Sensitive Sodium-Chloride Cotransporter by Beta3-Adrenoreceptor in the Distal Convoluted Tubule

We previously showed that the beta-3 adrenergic receptor (BAR3) is expressed in most segments of the nephron where its agonism promotes a potent antidiuretic effect. We localized BAR3 in distal convoluted tubule (DCT) cells expressing the thiazide-sensitive sodium-chloride cotransporter (NCC). Aim of this study is to investigate the possible functional role of BAR3 on NCC modulation in DCT cells. Here, we found that, in mice, the knockout of BAR3 was paralleled by a significant attenuation of NCC phosphorylation, paralleled by reduced expression and activation of STE-20/SPS1-related proline-alanine-rich kinase (SPAK) and WNKs the main kinases involved in NCC activation. Conversely, in BAR1/2 knockout mice, we found reduced NCC abundance with no changes in the phosphorylation state of NCC. Moreover, selective BAR3 agonism promotes both SPAK and NCC activation in wild-type mouse kidney slices. In conclusion, our findings suggest a novel role for BAR3 in the regulation of NCC in DCT.

No evidence for prolactin's involvement in the post-ejaculatory refractory period

In many species, ejaculation is followed by a state of decreased sexual activity, the post-ejaculatory refractory period. Several lines of evidence have suggested prolactin, a pituitary hormone released around the time of ejaculation in humans and other animals, to be a decisive player in the establishment of the refractory period. However, data supporting this hypothesis is controversial. We took advantage of two different strains of house mouse, a wild derived and a classical laboratory strain that differ substantially in their sexual performance, to investigate prolactin's involvement in sexual activity and the refractory period. First, we show that there is prolactin release during sexual behavior in male mice. Second, using a pharmacological approach, we show that acute manipulations of prolactin levels, either mimicking the natural release during sexual behavior or inhibiting its occurrence, do not affect sexual activity or shorten the refractory period, respectively. Therefore, we show compelling evidence refuting the idea that prolactin released during copulation is involved in the establishment of the refractory period, a long-standing hypothesis in the field of behavioral endocrinology.

Enhancing face validity of mouse models of Alzheimer's disease with natural genetic variation

Classical laboratory strains show limited genetic diversity and do not harness natural genetic variation. Mouse models relevant to Alzheimer's disease (AD) have largely been developed using these classical laboratory strains, such as C57BL/6J (B6), and this has likely contributed to the failure of translation of findings from mice to the clinic. Therefore, here we test the potential for natural genetic variation to enhance the translatability of AD mouse models. Two widely used AD-relevant transgenes, APPswe and PS1de9 (APP/PS1), were backcrossed from B6 to three wild-derived strains CAST/EiJ, WSB/EiJ, PWK/PhJ, representative of three Mus musculus subspecies. These new AD strains were characterized using metabolic, functional, neuropathological and transcriptional assays. Strain-, sex- and genotype-specific differences were observed in cognitive ability, neurodegeneration, plaque load, cerebrovascular health and cerebral amyloid angiopathy. Analyses of brain transcriptional data showed strain was the greatest driver of variation. We identified significant variation in myeloid cell numbers in wild type mice of different strains as well as significant differences in plaque-associated myeloid responses in APP/PS1 mice between the strains. Collectively, these data support the use of wild-derived strains to better model the complexity of human AD.

Technique of Minimally Invasive Transverse Aortic Constriction in Mice for Induction of Left Ventricular Hypertrophy

Transverse aortic constriction (TAC) in mice is one of the most commonly used surgical techniques for experimental investigation of pressure overload-induced left ventricular hypertrophy (LVH) and its progression to heart failure. In the majority of the reported investigations, this procedure is performed with intubation and ventilation of the animal which renders it demanding and time-consuming and adds to the surgical burden to the animal. The aim of this protocol is to describe a simplified technique of minimally invasive TAC without intubation and ventilation of mice. Critical steps of the technique are emphasized in order to achieve low mortality and high efficiency in inducing LVH. Male C57BL/6 mice (10-week-old, 25-30 g, n=60) were anesthetized with a single intraperitoneal injection of a mixture of ketamine and xylazine. In a spontaneously breathing animal following a 3-4 mm upper partial sternotomy, a segment of 6/0 silk suture threaded through the eye of a ligation aid was passed under the aortic arch and tied over a blunted 27-gauge needle. Sham-operated animals underwent the same surgical preparation but without aortic constriction. The efficacy of the procedure in inducing LVH is attested by a significant increase in the heart/body weight ratio. This ratio is obtained at days 3, 7, 14 and 28 after surgery (n = 6 - 10 in each group and each time point). Using our technique, LVH is observed in TAC compared to sham animals from day 7 through day 28. Operative and late (over 28 days) mortalities are both very low at 1.7%. In conclusion, our cost-effective technique of minimally invasive TAC in mice carries very low operative and post-operative mortalities and is highly efficient in inducing LVH. It simplifies the operative procedure and reduces the strain put on the animal. It can be easily performed by following the critical steps described in this protocol.

Cardiovascular effects of exogenous adrenomedullin and CGRP in Ramp and Calcrl deficient mice

Adrenomedullin (AM) and calcitonin gene-related peptide (CGRP) are potent vasodilator peptides and serve as ligands for the G-protein coupled receptor (GPCR) calcitonin receptor-like receptor (CLR/Calcrl). Three GPCR accessory proteins called receptor activity-modifying proteins (RAMPs) modify the ligand binding affinity of the receptor such that the CLR/RAMP1 heterodimer preferably binds CGRP, while CLR/RAMP2 and CLR/RAMP3 have a stronger affinity for AM. Here we determine the contribution of each of the three RAMPs to blood pressure control in response to exogenous AM and CGRP by measuring the blood pressure of mice with genetic reduction or deletion of the receptor components. Thus, the cardiovascular response of Ramp1^-/-, Ramp2^+/-, Ramp3^-/-, Ramp1^-/-/Ramp3^-/- double-knockout (dKO), and Calcrl^+/- mice to AM and CGRP were compared to wildtype mice. While under anesthesia, Ramp1^-/- male mice had significantly higher basal blood pressure than wildtype males; a difference which was not present in female mice. Additionally, anesthetized Ramp1^-/-, Ramp3^-/-, and Calcrl^+/- male mice exhibited significantly higher basal blood pressure than females of the same genotype. The hypotensive response to intravenously injected AM was greatly attenuated in Ramp1^-/- mice, and to a lesser extent in Ramp3^-/- and Calcrl^+/- mice. However, Ramp1^-/-/Ramp3^-/- dKO mice retained some hypotensive response to AM. These results suggest that the hypotensive effect of AM is primarily mediated through the CLR/RAMP1 heterodimer, but that AM signaling via CLR/RAMP2 and CLR/RAMP3 also contributes to some hypotensive action. On the other hand, CGRP's hypotensive activity seems to be predominantly through the CLR/RAMP1 heterodimer. With this knowledge, therapeutic AM or CGRP peptides could be designed to cause less hypotension while maintaining canonical receptor-RAMP mediated signaling.

Low-dose dasatinib rescues cardiac function in Noonan syndrome

Noonan syndrome (NS) is a common autosomal dominant disorder that presents with short stature, craniofacial dysmorphism, and cardiac abnormalities. Activating mutations in the PTPN11 gene encoding for the Src homology 2 (SH2) domain-containing protein tyrosine phosphatase-2 (SHP2) causes approximately 50% of NS cases. In contrast, NS with multiple lentigines (NSML) is caused by mutations that inactivate SHP2, but it exhibits some overlapping abnormalities with NS. Protein zero-related (PZR) is a SHP2-binding protein that is hyper-tyrosyl phosphorylated in the hearts of mice from NS and NSML, suggesting that PZR and the tyrosine kinase that catalyzes its phosphorylation represent common targets for these diseases. We show that the tyrosine kinase inhibitor, dasatinib, at doses orders of magnitude lower than that used for its anticancer activities inhibited PZR tyrosyl phosphorylation in the hearts of NS mice. Low-dose dasatinib treatment of NS mice markedly improved cardiomyocyte contractility and functionality. Remarkably, a low dose of dasatinib reversed the expression levels of molecular markers of cardiomyopathy and reduced cardiac fibrosis in NS and NSML mice. These results suggest that PZR/SHP2 signaling is a common target of both NS and NSML and that low-dose dasatinib may represent a unifying therapy for the treatment of PTPN11-related cardiomyopathies.

Sex Differences in the Cerebral Collateral Circulation

Premenopausal women and intact female rodents sustain smaller cerebral infarctions than males. Several sex-dependent differences have been identified as potential contributors, but many questions remain unanswered. Mice exhibit wide variation in native collateral number and diameter (collateral extent) that is dependent on differences in genetic background, aging, and other comorbidities and that contributes to their also-wide differences in infarct volume. Likewise, variation in infarct volume correlates with differences in collateral-dependent blood flow in patients with acute ischemic stroke. We examined whether extent of pial collateral arterioles and posterior communicating collateral arteries (PComAs) differ depending on sex in young, aged, obese, hypertensive, and genetically different mice. We combined new data with meta-analysis of our previously published data. Females of C57BL/6J (B6) and BALB/cByJ (BC) strains sustained smaller infarctions than males after permanent MCA occlusion. This protection was unchanged in BC mice after introgression of the B6 allele of Dce1, the major genetic determinant of variation in pial collaterals among mouse strains. Consistent with this, collateral extent in these and other strains did not differ with sex. Extent of PComAs and primary cerebral arteries also did not vary with sex. No dimorphism was evident for loss of pial collateral number and/or diameter (collateral rarefaction) caused by aging, obesity, and hypertension, nor for collateral remodeling after pMCAO. However, rarefaction was greater in females with long-standing hypertension. We conclude that smaller infarct volume in female mice is not due to greater collateral extent, greater remodeling, or less rarefaction caused by aging, obesity, or hypertension.

Sex- and age-related differences in arterial pressure and albuminuria in mice

Background

Animal models have become valuable experimental tools for understanding the pathophysiology and therapeutic interventions in cardiovascular disease. Yet to date, few studies document the age- and sex-related differences in arterial pressure, circadian rhythm, and renal function in normotensive mice under basal conditions, across the life span. We hypothesized that mice display similar sex- and age-related differences in arterial pressure and renal function to humans.

Methods

Mean arterial pressure (MAP) and circadian rhythm of arterial pressure were measured over 3 days via radiotelemetry, in 3- and 5-month-old (adult) and 14- and 18-month-old (aged) FVB/N and in 5-month-old (adult) C57BL/6 male and female normotensive mice. In FVB/N mice, albuminuria from 24-h urine samples as well as body, heart, and kidney weights were measured at each age.

Results

Twenty-four-hour MAP was greater in males than females at 3, 5, and 14 months of age. A similar sex difference in arterial pressure was observed in C57BL/6 mice at 5 months of age. In FVB/N mice, 24-h MAP increased with age, with females displaying a greater increase between 3 and 18 months of age than males, such that MAP was no longer different between the sexes at 18 months of age. A circadian pattern was observed in arterial pressure, heart rate, and locomotor activity, with values for each greater during the active (night/dark) than the inactive (day/light) period. The night-day dip in MAP was greater in males and increased with age in both sexes. Albuminuria was greater in males than females, increased with age in both sexes, and rose to a greater level in males than females at 18 months of age.

Conclusions

Arterial pressure and albuminuria increase in an age- and sex-specific manner in mice, similar to patterns observed in humans. Thus, mice represent a useful model for studying age and sex differences in the regulation of arterial pressure and renal disease. Understanding the mechanisms that underlie the pathophysiology of cardiovascular disease may lead to new and better-tailored therapies for men and women.

Exploring Female Mice Interstrain Differences Relevant for Models of Depression

Depression is an extremely heterogeneous disorder. Diverse molecular mechanisms have been suggested to underlie its etiology. To understand the molecular mechanisms responsible for this complex disorder, researchers have been using animal models extensively, namely mice from various genetic backgrounds and harboring distinct genetic modifications. The use of numerous mouse models has contributed to enrich our knowledge on depression. However, accumulating data also revealed that the intrinsic characteristics of each mouse strain might influence the experimental outcomes, which may justify some conflicting evidence reported in the literature. To further understand the impact of the genetic background, we performed a multimodal comparative study encompassing the most relevant parameters commonly addressed in depression, in three of the most widely used mouse strains: Balb/c, C57BL/6, and CD-1. Moreover, female mice were selected for this study taken into account the higher prevalence of depression in women and the fewer animal studies using this gender. Our results show that Balb/c mice have a more pronounced anxious-like behavior than CD-1 and C57BL/6 mice, whereas C57BL/6 animals present the strongest depressive-like trait. Furthermore, C57BL/6 mice display the highest rate of proliferating cells and brain-derived neurotrophic factor (Bdnf) expression levels in the hippocampus, while hippocampal dentate granular neurons of Balb/c mice show smaller dendritic lengths and fewer ramifications. Of notice, the expression levels of inducible nitric oxide synthase (iNos) predict 39.5% of the depressive-like behavior index, which suggests a key role of hippocampal iNOS in depression. Overall, this study reveals important interstrain differences in several behavioral dimensions and molecular and cellular parameters that should be considered when preparing and analyzing experiments addressing depression using mouse models. It further contributes to the literature by revealing the predictive value of hippocampal iNos expression levels in depressive-like behavior, irrespectively of the mouse strain.

The Pathology of Aging 129S6/SvEvTac Mice

The 129 mouse strain is commonly used for the generation of genetically engineered mice. Genetic drift or accidental contamination during outcrossing has resulted in several 129 substrains. Comprehensive data on spontaneous age-related pathology exist for the 129S4/SvJae substrain, whereas only limited information is available for other 129 substrains. This longitudinal aging study describes the life span and spontaneous lesions of 44 male and 18 female mice of the 129S6/SvEvTac substrain. Median survival time was 778 and 770 days for males and females, respectively. Tumors of lung and Harderian gland were the most common neoplasms in both sexes. Hepatocellular tumors occurred mainly in males. Hematopoietic tumors were observed at low frequency. Suppurative and ulcerative blepharoconjunctivitis was the most common nonneoplastic condition in both sexes. Corynebacteria (primarily Corynebacterium urealyticum and C. pseudodiphtheriticum) were isolated from animals with blepharoconjunctivitis and in some cases from unaffected mice, although a clear causal association between corynebacterial infections and blepharoconjunctivitis could not be inferred. Polyarteritis occurred only in males and was identified as the most common nonneoplastic contributory cause of death. Eosinophilic crystalline pneumonia occurred in both sexes and was a relevant cause of death or comorbidity. Epithelial hyalinosis at extrapulmonary sites was noted at higher frequency in females. This study contributes important data on the spontaneous age-related pathology of the 129S6/SvEvTac mouse substrain and is a valuable reference for evaluation of the phenotype in genetically engineered mice obtained with this 129 substrain.

Calcitonin gene-related peptide (CGRP) receptors are important to maintain cerebrovascular reactivity in chronic hypertension

Cerebral blood flow autoregulation (CA) shifts to higher blood pressures in chronic hypertensive patients, which increases their risk for brain damage. Although cerebral vascular smooth muscle cells express the potent vasodilatatory peptides calcitonin gene-related peptide (CGRP) and adrenomedullin (AM) and their receptors (calcitonin receptor-like receptor (Calclr), receptor-modifying proteins (RAMP) 1 and 2), their contribution to CA during chronic hypertension is poorly understood. Here we report that chronic (10 weeks) hypertensive (one-kidney-one-clip-method) mice overexpressing the Calclr in smooth muscle cells (CLR-tg), which increases the natural sensitivity of the brain vasculature to CGRP and AM show significantly better blood pressure drop-induced cerebrovascular reactivity than wt controls. Compared to sham mice, this was paralleled by increased cerebral CGRP-binding sites (receptor autoradiography), significantly in CLR-tg but not wt mice. AM-binding sites remained unchanged. Whereas hypertension did not alter RAMP-1 expression (droplet digital (dd) PCR) in either mouse line, RAMP-2 expression dropped significantly in both mouse lines by about 65%. Moreover, in wt only Calclr expression was reduced by about 70% parallel to an increase of smooth muscle actin (Acta2) expression. Thus, chronic hypertension induces a stoichiometric shift between CGRP and AM receptors in favor of the CGRP receptor. However, the parallel reduction of Calclr expression observed in wt mice but not CLR-tg mice appears to be a key mechanism in chronic hypertension impairing cerebrovascular reactivity.

Steroidogenesis-adrenal cell signal transduction

The purpose of this article is to review fundamentals in adrenal gland histophysiology. Key findings regarding the important signaling pathways involved in the regulation of steroidogenesis and adrenal growth are summarized. We illustrate how adrenal gland morphology and function are deeply interconnected in which novel signaling pathways (Wnt, Sonic hedgehog, Notch, β-catenin) or ionic channels are required for their integrity. Emphasis is given to exploring the mechanisms and challenges underlying the regulation of proliferation, growth, and functionality. Also addressed is the fact that while it is now well-accepted that steroidogenesis results from an enzymatic shuttle between mitochondria and endoplasmic reticulum, key questions still remain on the various aspects related to cellular uptake and delivery of free cholesterol. The significant progress achieved over the past decade regarding the precise molecular mechanisms by which the two main regulators of adrenal cortex, adrenocorticotropin hormone (ACTH) and angiotensin II act on their receptors is reviewed, including structure-activity relationships and their potential applications. Particular attention has been given to crucial second messengers and how various kinases, phosphatases, and cytoskeleton-associated proteins interact to ensure homeostasis and/or meet physiological demands. References to animal studies are also made in an attempt to unravel associated clinical conditions. Many of the aspects addressed in this article still represent a challenge for future studies, their outcome aimed at providing evidence that the adrenal gland, through its steroid hormones, occupies a central position in many situations where homeostasis is disrupted, thus highlighting the relevance of exploring and understanding how this key organ is regulated. © 2014 American Physiological Society. Compr Physiol 4:889-964, 2014.

Expression and localization of pChAT as a novel method to study cholinergic innervation of rat adrenal gland

Cholinergic innervation of the rat adrenal gland has been analyzed previously using cholinergic markers including acetylcholinesterase (AChE), choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT). In the present study, we demonstrate putative cholinergic neurons in the rat adrenal gland using an antibody to pChAT, which is the product of a splice variant of ChAT mRNA that is preferentially localized in peripheral cholinergic nerves. Most of the ganglionic neurons as well as small single sporadic neurons in the adrenal gland were stained intensely for pChAT. The density of pChAT-immunoreactive (IR) fibers was distinct in the adrenal cortex and medulla. AChE-, cChAT- and VAChT-immunoreactivities were also observed in some cells and fibers of the adrenal medulla, while the cortex had few positive nerve fibers. These results indicate that ganglionic neurons of the adrenal medulla and nerve fibers heterogeneously express cholinergic markers, especially pChAT. Furthermore, the innervation of the adrenal gland, cortex and medulla, by some cholinergic fibers provides additional morphological evidence for a significant role of cholinergic mechanisms in adrenal gland functions.

Gender differences in normal left ventricle of adult FVB/N mice due to variation in interleukins and natriuretic peptides expression levels

This study examined the sex differences for physical, morphological, histological, mRNA, and protein expression levels changes for interleukins and natriuretic peptides in left ventricle (LV) of two groups of adult FVB/N mice; males (WM) and females (WF). LV morphological, histological, reverse transcription and quantitative real-time PCR (RT-PCR), and immunohistochemical (IHC) alterations were determined in FVB/N mice at 34-35 weeks on gender basis. Confirming the gender dimorphism, FVB/N males (WM) illustrated a significant reduction in ANP and IL1-A levels as well as significantly increased body weight (BW (gm)), tibia length (TL (mm)), heart weight (HW (mg)), heart weight-to-body weight (HW/BW (mg/gm)) ratio, heart weight-to-tibia length (HW/TL (mg/mm)) ratio, left ventricle weight (LV (mg)), left ventricle-to-body weight (LV/BW (mg/gm)) ratio, and left ventricle-to-tibia length (LV/TL (mg/mm)) ratio, left ventricular (LV) cardiomyocyte diameter, high BNP, NPRA, IL-1B, and IL1R1 expression in comparison with FVB/N females (WF). Gender differences in relation to left ventricle (LV) may be due to differences in the interleukins and natriuretic peptides levels as an outcome of sex related hormones.

Substrain specific response to cardiac pressure overload in C57BL/6 mice

The C57BL/6 mouse strain is one of the most commonly used in experimental research. It is known to differ from other strains in baseline cardiovascular phenotypes as well as in response to pressure overload induced by aortic constriction. Since the generation of the C57BL/6 mouse line over a century ago, multiple substrains have been generated from the original. To identify potential substrain specific differences in response to pressure overload, we evaluated the effects of transverse aortic constriction (TAC) on survival, cardiac function, and expression of hypertrophic markers in three commonly used C57BL/6 substrains: C57BL/6J (JL), C57BL/6NCrl (CL), and C57BL/6NTac (TF). Survival and cardiac function were significantly lower in the CL and TF substrains compared with JL mice after TAC. Furthermore, the heart weight and lung weight as well as the expression of the hypertrophic marker Bnp were significantly greater in the CL mice compared with the JL. Histological assessment revealed marked left ventricular dilatation of CL and TF hearts while JL hearts showed increased wall thickness without dilatation. Our data demonstrate that cardiac response to pressure overload is distinct among the three commonly used C57BL/6 substrains of mice, which raises a cautionary note in study design and data interpretation.

Mice from lines selectively bred for high voluntary wheel running exhibit lower blood pressure during withdrawal from wheel access

Exercise is known to be rewarding and have positive effects on mental and physical health. Excessive exercise, however, can be the result of an underlying behavioral/physiological addiction. Both humans who exercise regularly and rodent models of exercise addiction sometimes display behavioral withdrawal symptoms, including depression and anxiety, when exercise is denied. However, few studies have examined the physiological state that occurs during this withdrawal period. Alterations in blood pressure (BP) are common physiological indicators of withdrawal in a variety of addictions. In this study, we examined exercise withdrawal in four replicate lines of mice selectively bred for high voluntary wheel running (HR lines). Mice from the HR lines run almost 3-fold greater distances on wheels than those from non-selected control lines, and have altered brain activity as well as increased behavioral despair when wheel access is removed. We tested the hypothesis that male HR mice have an altered cardiovascular response (heart rate, systolic, diastolic, and mean arterial pressure [MAP]) during exercise withdrawal. Measurements using an occlusion tail-cuff system were taken during 8 days of baseline, 6 days of wheel access, and 2 days of withdrawal (wheel access blocked). During withdrawal, HR mice had significantly lower systolic BP, diastolic BP, and MAP than controls, potentially indicating a differential dependence on voluntary wheel running in HR mice. This is the first characterization of a cardiovascular withdrawal response in an animal model of high voluntary exercise.

Chronic creatine kinase deficiency eventually leads to congestive heart failure, but severity is dependent on genetic background, gender and age

The creatine kinase (CK) energy transport and buffering system supports cardiac function at times of high demand and is impaired in the failing heart. Mice deficient in muscle- and mitochondrial-CK (M/Mt-CK^−/−) have previously been described, but exhibit an unexpectedly mild phenotype of compensated left ventricular (LV) hypertrophy. We hypothesised that heart failure would develop with age and performed echocardiography and LV haemodynamics at 1 year. Since all previous studies have utilised mice with a mixed genetic background, we backcrossed for >10 generations on to C57BL/6, and repeated the in vivo investigations. Male M/Mt-CK^−/− mice on the mixed genetic background developed congestive heart failure as evidenced by significantly elevated end-diastolic pressure, impaired contractility, LV dilatation, hypertrophy and pulmonary congestion. Female mice were less severely affected, only showing trends for these parameters. After backcrossing, M/Mt-CK^−/− mice had LV dysfunction consisting of impaired isovolumetric pressure changes and reduced contractile reserve, but did not develop congestive heart failure. Body weight was lower in knockout mice as a consequence of reduced total body fat. LV weight was not significantly elevated in relation to other internal organs and gene expression of LVH markers was normal, suggesting an absence of hypertrophy. In conclusion, the consequences of CK deficiency are highly dependent on genetic modifiers, gender and age. However, the observation that a primary defect in CK can, under the right conditions, result in heart failure suggests that impaired CK activity in the failing heart could contribute to disease progression.

Lysophosphatidic acid signaling protects pulmonary vasculature from hypoxia-induced remodeling

OBJECTIVE

Lysophosphatidic acid (LPA) is a bioactive lipid molecule produced by the plasma lysophospholipase D enzyme autotaxin that is present at ≥100 nmol/L in plasma. Local administration of LPA promotes systemic arterial remodeling in rodents. To determine whether LPA contributes to remodeling of the pulmonary vasculature, we examined responses in mice with alterations in LPA signaling and metabolism.

METHODS AND RESULTS

Enpp2(+/-) mice, which are heterozygous for the autotaxin-encoding gene and which have reduced expression of autotaxin/lysophospholipase D and approximately half normal plasma LPA, were hyperresponsive to hypoxia-induced vasoconstriction and remodeling, as evidenced by the development of higher right ventricular (RV) systolic pressure, greater decline in peak flow velocity across the pulmonary valve, and a higher percentage of muscularized arterioles. Mice lacking LPA(1) and LPA(2), 2 LPA receptors abundantly expressed in the vasculature, also had enhanced hypoxia-induced pulmonary remodeling. With age, Lpar1(-/-)2(-/-) mice spontaneously developed elevated RV systolic pressure and RV hypertrophy that was not observed in Lpar1(-/-) mice or Lpar2(-/-) mice. Expression of endothelin-1, a potent vasoconstrictor, was elevated in lungs of Lpar1(-/-)2(-/-) mice, and expression of endothelin(B) receptor, which promotes vasodilation and clears endothelin, was reduced in Enpp2(+/-) and Lpar1(-/-)2(-/-) mice.

CONCLUSIONS

Our findings indicate that LPA may negatively regulate pulmonary vascular pressure through LPA(1) and LPA(2) receptors and that in the absence of LPA signaling, upregulation in the endothelin system favors remodeling.

The relationship between nephron number, kidney size and body weight in two inbred mouse strains

While some reports in humans have shown that nephron number is positively correlated with height, body weight or kidney weight, other studies have not reproduced these findings. To understand the impact of genetic and environmental variation on these relationships, we examined whether nephron number correlates with body weight, kidney planar surface area, or kidney weight in two inbred mouse strains with contrasting kidney sizes but no overt renal pathology: C3H/HeJ and C57BL/6J. C3H/HeJ mice had smaller kidneys at birth and larger kidneys by adulthood, however there was no significant difference in nephron number between the two strains. We did observe a correlation between kidney size and body weight at birth and at adulthood for both strains. However, there was no relationship between nephron number and body weight or between nephron number and kidney size. From other studies, it appears that a greater than two-fold variation is required in each of these parameters in order to demonstrate these relationships, suggesting they are highly dependent on scale. Our results are therefore not surprising since there was a less than two-fold variation in each of the parameters examined. In summary, the relationship between nephron number and body or kidney size is most likely to be demonstrated when there is greater phenotypic variation either from genetic and/or environmental factors.

An alternative method for intrathymic injections in mice

The thymus is a bi-lobed lymphatic organ located in the anterior portion of the ventral thoracic cavity, just behind the sternum. Because the thymus is the site of development of T lymphocytes (T cells), it is frequently targeted in research studies that involve the immune system. Furthermore, the rapid expansion of transgenic and gene-targeted mouse models of immune disorders has enabled a concomitant increase in the number of studies of T-cell development. Such studies may require the administration of intrathymic injections, which have traditionally been done using a surgical approach. Surgical manipulation can result in pain or distress to the animal, which may affect the immune system, potentially confounding experimental results. Here, the authors describe a nonsurgical, ultrasound-guided approach for intrathymic injection in the mouse that results in negligible distress to the animal.

Genetic architecture underlying variation in extent and remodeling of the collateral circulation

RATIONALE

Collaterals are arteriole-to-arteriole anastomoses that connect adjacent arterial trees. They lessen ischemic tissue injury by serving as endogenous bypass vessels when the trunk of 1 tree becomes narrowed by vascular disease. The number and diameter ("extent") of native (preexisting) collaterals, plus their amount of lumen enlargement (growth/remodeling) in occlusive disease, show remarkably wide variation among inbred mouse strains (eg, C57BL/6 and BALB/c), resulting in large differences in tissue injury in models of occlusive disease. Evidence suggests similar large differences exist among healthy humans.

OBJECTIVE

To identify candidate loci responsible for genetic-dependent collateral variation.

METHODS AND RESULTS

Cerebral collateral number and diameter were determined in 221 C57BL/6xBALB/c F2 progeny, followed by linkage analysis to identify quantitative trait loci (QTL) for collateral number and diameter. Four QTL were obtained for collateral number, including epistasis between 2 loci. A QTL that was identical to the strongest QTL for collateral number on chromosome 7 (logarithm of the odds [LOD]=29, effect size=37%) was also mapped for collateral diameter (LOD=17, effect size=30%). Chromosome substitution strain analysis confirmed this locus. We also obtained a unique QTL on chromosome 11 for collateral remodeling after middle cerebral artery occlusion. Association mapping within the chromosome 7 QTL interval using collateral traits measured for 15 inbred strains delineated 172-kbp (P=0.00002) and 290-kbp (P=0.0004) regions on chromosome 7 containing 2 and 7 candidate genes, respectively.

CONCLUSIONS

We conclude that collateral extent and remodeling are unique, highly heritable complex traits, with 1 QTL predominantly affecting native collateral number and diameter.

beta-Arrestin-biased agonism of the angiotensin receptor induced by mechanical stress

beta-Arrestins, which were originally characterized as terminators of heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptor (GPCR) signaling, also act as important signal transducers. An emerging concept in GPCR signaling is beta-arrestin-biased agonism, in which specific ligand-activated GPCR conformational states selectively signal through beta-arrestins, rather than through G proteins. Here, we show that mechanical stretch induced beta-arrestin-biased signaling downstream of angiotensin II type I receptors (AT1Rs) in the absence of ligand or G protein activation. Mechanical stretch triggered an AT1R-mediated conformational change in beta-arrestin similar to that induced by a beta-arrestin-biased ligand to selectively stimulate receptor signaling in the absence of detectable G protein activation. Hearts from mice lacking beta-arrestin or AT1Rs failed to induce responses to mechanical stretch, as shown by blunted extracellular signal-regulated kinase and Akt activation, impaired transactivation of the epidermal growth factor receptor, and enhanced myocyte apoptosis. These data show that the heart responds to acute increases in mechanical stress by activating beta-arrestin-mediated cell survival signals.

The C3H/HeJ inbred mouse is a model of vesico-ureteric reflux with a susceptibility locus on chromosome 12

Vesico-ureteric reflux is the most common congenital anomaly of the urinary tract, characterized by a defective uretero-vesical junction with retrograde urine flow from the bladder toward the kidneys. Because there is strong evidence for a genetic basis for some cases of vesico-ureteric reflux, we screened 11 inbred mouse strains for reflux and kidney size and identified one strain, C3H/HeJ, that has a 100 percent incidence of vesico-ureteric reflux with otherwise normal kidneys at birth. These mice are predisposed to reflux as a result of a defective uretero-vesical junction characterized by a short intravesical ureter. This defect results from a delay in urinary tract development initially manifested by a ureteric bud arising from a more caudal location along the mesonephric duct. In contrast, C57BL/6J mice (resistant to reflux at birth) have long intravesical ureters, normally positioned ureteric buds, and no delay in urinary tract development. Genome-wide and additional fine mapping of backcross mice, derived from C3H/HeJ and C57BL/6J crosses, identified a significant reflux susceptibility locus, Vurm1, on chromosome 12 (peak logarithm of the odds=7.39). The C3H/HeJ mouse is a model of vesico-ureteric reflux without renal malformation, and further characterization of this model will allow for the identification of a pathway important for urinary tract development, a finding that will serve as a model for the human disorder.

Neonatal macrosomia is an independent risk factor for adult metabolic syndrome

BACKGROUND

Weight in infancy correlates with risk of type 2 diabetes, hypertension, and obesity in adulthood. Clinical observations have been confounded by obesity-prone genotypes and obesity-linked lifestyles.

OBJECTIVES

To define the effects of isolated neonatal macrosomia in isogenic animals, we compared macrosomic and control C57Bl6 mice co-fostered by healthy dams receiving standard laboratory feed.

METHODS

Naturally occurring neonatal macrosomia was identified by a gender-specific weanling weight above the 90th percentile for the colony. Macrosomic and control mice were phenotyped in adulthood by exercise wheel, tail cuff and intraperitoneal insulin or glucose challenge.

RESULTS

Compared to control males, adult males with a history of neonatal macrosomia had significantly increased body weight, reduced voluntary activity, insulin resistance, fasting hyperinsulinemia, and impaired glucose tolerance. In contrast, adult females with neonatal macrosomia had no significant alteration in body weight or endocrine phenotypes, but did have higher blood pressures and lower heart rates than control females. After these baseline studies, all mice were switched to a hypercaloric, high fat diet (5 kcal/g, 45% of energy as fat). Twenty weeks later, male mice had impaired glucose tolerance and insulin resistance, independent of their weanling weight classification. While on high fat feeds, macrosomic males maintained a significantly higher body weight than control males.

CONCLUSIONS

We conclude that (1) in our murine model, neonatal macrosomia is an independent risk factor of adult metabolic syndrome, and (2) neonatal macrosomia accentuates the sexually dimorphic predisposition of C57Bl6 male mice towards glucose intolerance and C57Bl6 female mice towards hypertension.

Physiological and pathophysiological applications of sensitive ELISA methods for urinary deoxycorticosterone and corticosterone in rodents

Deoxycorticosterone (DOC: a weak mineralocorticoid) is the precursor to corticosterone (B: the major glucocorticoid in rodents) and aldosterone (the major mineralocorticoid). The genes Cyp11b1 and Cyp11b2 that encode the enzymes responsible for DOC to B (11beta-hydroxylase) and DOC to aldosterone (aldosterone synthase) conversions are located on the same chromosome. The aim of this study was to develop sensitive and specific ELISA methods to quantify urinary DOC and B concentrations to assess the physiological and genetic control of the Cyp11b1/b2 locus. Antibodies raised in rabbits against DOC and B and horse radish peroxidase-goat anti-rabbit IgG enzyme tracer were used to develop the assays. Urine samples collected from mice held in metabolic cages were extracted with dichloromethane and reconstituted in assay buffer. The assays were validated for specificity, sensitivity, parallelism, accuracy and imprecision. Cross-reactivities with major interfering steroids were minimal: DOC assay (progesterone=0.735% and corticosterone=0.045%), and for B assay (aldosterone=0.14%, 11-dehydro-B=0.006%, cortisol=0.016% and DOC=0.04%) and minimum detection limit for DOC ELISA was 2.2 pg/mL (6.6 pmol/L), and for B ELISA was 6.2 pg/mL (17.9 pmol/L). The validity of urinary DOC and B ELISAs was confirmed by the excellent correlation between the results obtained before and after solvent extraction and HPLC (DOC ELISA: Y=1.092X-0.054, R(2)=0.988; B ELISA: Y=1.047X-0.226, R(2)=0.996). Accuracy studies, parallelism and imprecision data were determined and all found to be satisfactory. The methods were used in a series of metabolic cage studies which demonstrated that (i) females produce more DOC and corticosterone than males; (ii) DOC and corticosterone respond to ACTH treatment but not dietary sodium restriction; (iii) DOC:B ratios in Cyp11b1 null mice were >200-fold greater than wild type.

Cardiovascular response to beta-adrenergic blockade or activation in 23 inbred mouse strains

We report the characterisation of 27 cardiovascular-related traits in 23 inbred mouse strains. Mice were phenotyped either in response to chronic administration of a single dose of the β-adrenergic receptor blocker atenolol or under a low and a high dose of the β-agonist isoproterenol and compared to baseline condition. The robustness of our data is supported by high trait heritabilities (typically H²>0.7) and significant correlations of trait values measured in baseline condition with independent multistrain datasets of the Mouse Phenome Database. We then focused on the drug-, dose-, and strain-specific responses to β-stimulation and β-blockade of a selection of traits including heart rate, systolic blood pressure, cardiac weight indices, ECG parameters and body weight. Because of the wealth of data accumulated, we applied integrative analyses such as comprehensive bi-clustering to investigate the structure of the response across the different phenotypes, strains and experimental conditions. Information extracted from these analyses is discussed in terms of novelty and biological implications. For example, we observe that traits related to ventricular weight in most strains respond only to the high dose of isoproterenol, while heart rate and atrial weight are already affected by the low dose. Finally, we observe little concordance between strain similarity based on the phenotypes and genotypic relatedness computed from genomic SNP profiles. This indicates that cardiovascular phenotypes are unlikely to segregate according to global phylogeny, but rather be governed by smaller, local differences in the genetic architecture of the various strains.

Endothelium-specific overexpression of human IC53 downregulates endothelial nitric oxide synthase activity and elevates systolic blood pressure in mice

AIMS

Hypertension is one of the major risk factors for cardiovascular diseases. Endothelial cells (ECs) exert important functions in the regulation of blood pressure. A novel gene, IC53, as an isoform of the cyclin-dependent kinase (CDK)-binding protein gene C53, is mainly expressed in vascular ECs and is upregulated in the failing heart of rats. Overexpression of IC53 promotes proliferation of ECs. To examine whether IC53 plays a role in the regulation of vascular tone and blood pressure, we constructed a transgenic (tg) mouse model of the IC53 gene and studied its phenotypes relevant to vascular function.

METHODS AND RESULTS

IC53 cDNA was cloned from a human aorta cDNA library. Using the endothelium-specific VE-cadherin promoter, we constructed tg mice in which IC53 was specifically overexpressed in vascular endothelia and found that the tg mice exhibit elevated systolic blood pressure (SBP) in contrast to the wild-type (wt) controls. Further studies revealed impaired endothelium-dependent vasodilation, reduced nitric oxide (NO) production and decreased endothelial NO synthase (eNOS) expression, and activity in the tg mice. Inhibition of IC53 in human umbilical vein ECs induces upregulation of eNOS activity.

CONCLUSION

Our results indicate that IC53 participates in the regulation of vascular homeostasis. Endothelium-specific overexpression of IC53 is associated with elevated SBP, which may be in part attributed to the downregulation of eNOS signalling.

Vascular nitric oxide and superoxide anion contribute to sex-specific programmed cardiovascular physiology in mice

Intrauterine environmental pertubations have been linked to the development of adult hypertension. We sought to evaluate the interrelated roles of sex, nitric oxide, and reactive oxygen species (ROS) in programmed cardiovascular disease. Programming was induced in mice by maternal dietary intervention (DI; partial substitution of protein with carbohydrates and fat) or carbenoxolone administration (CX, to increase fetal glucocorticoid exposure). Adult blood pressure and locomotor activity were recorded by radiotelemetry at baseline, after a week of high salt, and after a week of high salt plus nitric oxide synthase inhibition (by l-NAME). In male offspring, DI or CX programmed an elevation in blood pressure that was exacerbated by N(omega)-nitro-l-arginine methyl ester administration, but not high salt alone. Mesenteric resistance vessels from DI male offspring displayed impaired vasorelaxation to ACh and nitroprusside, which was blocked by catalase and superoxide dismutase. CX-exposed females were normotensive, while DI females had nitric oxide synthase-dependent hypotension and enhanced mesenteric dilation. Despite the disparate cardiovascular phenotypes, both male and female DI offspring displayed increases in locomotor activity and aortic superoxide production. Despite dissimilar blood pressures, DI and CX-exposed females had reductions in cardiac baroreflex sensitivity. In conclusion, both maternal malnutrition and fetal glucocorticoid exposure program increases in arterial pressure in male but not female offspring. While maternal DI increased both superoxide-mediated vasoconstriction and nitric oxide mediated vasodilation, the balance of these factors favored the development of hypertension in males and hypotension in females.

Systemic first-line phenotyping

With the completion of the mouse genome sequence an essential task for biomedical sciences in the twenty-first century will be the generation and functional analysis of mouse models for every gene in the mammalian genome. More than 30,000 mutations in ES cells will be engineered and thousands of mouse disease models will become available over the coming years by the collaborative effort of the International Mouse Knockout Consortium. In order to realize the full value of the mouse models proper characterization, archiving and dissemination of mouse disease models to the research community have to be performed. Phenotyping centers (mouse clinics) provide the necessary capacity, broad expertise, equipment, and infrastructure to carry out large-scale systemic first-line phenotyping. Using the example of the German Mouse Clinic (GMC) we will introduce the reader to the different aspects of the organization of a mouse clinic and present selected methods used in first-line phenotyping.

Characterization of a novel gain of function glucocorticoid receptor knock-in mouse

Glucocorticoids (GCs) exert profound influences on many physiologic functions by virtue of their diverse roles in growth, development, and maintenance of homeostasis. We previously created a novel gain of function in the human glucocorticoid receptor (hGR), hGRM604L, which is active at GC concentrations 5-10-fold lower than wild-type GR. To gain a greater insight into GC physiology in vivo, we inserted this mutant GR (GRM610L in mice) into mice via homologous recombination. Mice expressing the allele are phenotypically normal with respect to GC function. However, corticosterone levels, ACTH levels, and adrenocortical size are markedly reduced, suggesting they are phenotypically normal because the mutant GR alters the basal regulation of the hypothalamic-pituitary-adrenal axis. We demonstrate via physiologic and immunologic studies that GRM610L mice have increased sensitivity to GCs in vivo. Sensitivity to the actions of endogenous GCs may be an important factor underlying the development of many human diseases including hypertension, obesity, and diabetes. Our model may provide a new and powerful tool for the study of GC physiological and pathological processes in vivo.

Cardiac phenotype of mitochondrial creatine kinase knockout mice is modified on a pure C57BL/6 genetic background

Discrepant results for the phenotype of mitochondrial creatine kinase knockout mice (Mt-CK(-/-)) could be due to mixed genetic background and use of non-littermate controls. We therefore backcrossed with C57BL/6J for >8 generations, followed by extensive in vivo cardiac phenotyping. Echocardiography and in vivo LV haemodynamics were performed in independent cohorts at 20-40 weeks and 1 year. No significant differences were observed for ECG, LV volumes, pressures, and systolic or diastolic function compared to littermate controls. Furthermore, responses to dobutamine were not different, indicating preserved contractile reserve. Contrary to published reports using Mt-CK(-/-) on a mixed background, we observed normal LV weights even in year old mice, and gene expression of common hypertrophic markers were not elevated. However, previously undetected adaptations were observed: an increase in activity of the cytosolic MM-CK isoenzyme (+20% vs WT, P=0.0009), and of citrate synthase (+18% vs WT, P=0.0007), a marker for mitochondrial volume. In a 3-week voluntary wheel running protocol, Mt-CK(-/-) ran significantly less per day (P=0.009) and attained lower maximum speed compared to controls (P=0.0003), suggesting impaired skeletal muscle function. MM-CK isoenzyme activity was significantly elevated in soleus but not gastrocnemius muscle of KO mice, and citrate synthase activities were normal in both, suggesting compensatory mechanisms are incomplete in skeletal muscle.

CONCLUSIONS

in contrast to previous reports using a mixed genetic background, Mt-CK(-/-) on a C57BL/6 background do not develop LV hypertrophy or dysfunction even up to 1 year, and this may be explained by a compensatory increase in MM-CK activity and mitochondrial volume.

Chronic oxidative stress induces a tissue-specific reduction in telomere length in CAST/Ei mice

We examine whether increased oxidative stress in vivo promotes telomere shortening in CAST/Ei mice. We explored the effects of L-buthionine sulfoximine treatment (BSO) on telomere length. BSO shortened telomere length in white fat, brown fat, skin, tail, and testis in concert with diminished tissue glutathione content, increased tissue carbonyl content, and increased plasma advanced oxidized protein products. Telomerase activity was mainly detected in testis but no reduction of telomerase activity was observed in response to BSO. In conclusion, BSO-mediated increase in systemic oxidative stress shortens telomeres in several tissues of the mouse. The variable effect of BSO treatment on telomere length in different tissue may result from their different adaptive antioxidative capacity.

Endothelial dysfunction and elevated blood pressure in MAS gene-deleted mice

Mas codes for a G protein-coupled receptor that is implicated in angiotensin-(1-7) signaling. We studied the cardiovascular phenotype of Mas-deficient mice backcrossed onto the FVB/N genetic background using telemetry and found that they exhibit higher blood pressures compared with controls. These Mas(-/-) mice also had impaired endothelial function, decreased NO production, and lower endothelial NO synthase expression. Reduced nicotinamide-adenine dinucleotide phosphate oxidase catalytic subunit gp91(phox) protein content determined by Western blotting was higher in Mas(-/-) mice than in controls, whereas superoxide dismutase and catalase activities were reduced. The superoxide dismutase mimetic, Tempol, decreased blood pressure in Mas(-/-) mice but had a minimal effect in control mice. Our results show a major cardiovascular phenotype in Mas(-/-) mice. Mas-deletion results in increased blood pressure, endothelial dysfunction, and an imbalance between NO and reactive oxygen species. Our animals represent a promising model to study angiotensin-(1-7)-mediated cardiovascular effects and to evaluate Mas agonistic compounds as novel cardioprotective and antihypertensive agents based on their beneficial effects on endothelial function.

Naturally occurring perinatal growth restriction in mice programs cardiovascular and endocrine function in a sex- and strain-dependent manner

Perinatal growth restriction (PGR) is associated with type 2 diabetes and hypertension. Identification of an isogenic mouse model of fetal programming will facilitate mechanistic understanding. We sought to test the hypotheses that 1) PGR impairs glucose tolerance and induces hypertension; and 2) the programming phenotype is more severe in an inbred mouse strain susceptible to diabetes (C57BL/6) than in a strain without such genetic predisposition (DBA/2). PGR pups were paired at weaning with same sex normally grown littermates. Glucose and insulin tolerance tests were performed at 17 wk, and systolic blood pressure (SBP) was measured at 20 wk. Impaired glucose tolerance was evident only among female PGR mice from both strains. While PGR did not alter insulin sensitivity in either strain, female DBA/2 mice had significantly decreased insulin levels during glucose tolerance testing. SBP was increased in PGR male C57BL/6 mice (p<0.01), while heart rate was decreased in PGR male DBA/2 mice (p<0.05). These studies indicate that in isogenic mice, PGR alters endocrine and cardiovascular physiology in female and male mice, respectively. Strain-and sex-specific genetic susceptibilities emphasize the need to consider genetic predisposition when evaluating the role of the perinatal environmental in the inception of adult disease.

Cardiac response to pressure overload in 129S1/SvImJ and C57BL/6J mice: temporal- and background-dependent development of concentric left ventricular hypertrophy

Left ventricular hypertrophy (LVH), a risk factor for cardiovascular morbidity and mortality, is commonly caused by essential hypertension. Three geometric patterns of LVH can be induced by hypertension: concentric remodeling, concentric hypertrophy, and eccentric hypertrophy. Clinical studies suggest that different underlying etiologies, genetic modifiers, and risk of mortality are associated with LVH geometric patterns. Since pressure overload-induced LVH can be modeled experimentally using transverse aortic constriction (TAC) and since C57BL/6J (B6) and 129S1/SvImJ (129S1) strains, which have different baseline cardiovascular phenotypes, are commonly used, we conducted serial echocardiographic studies to assess cardiac function up to 8 wk of post-TAC in male B6, 129S1, and B6129F1 (F1) mice. B6 mice had an earlier onset and more pronounced impairment in contractile function, with corresponding left and right ventricular dilatation, fibrosis, change in expression of hypertrophy marker, and increased liver weights at 5 wk of post-TAC. These observations suggest that B6 mice had eccentric hypertrophy with systolic dysfunction and right-sided heart failure. In contrast, we found that 129S1 and F1 mice delayed transition to decompensated heart failure, with 129S1 mice exhibiting preserved systolic function until 8 wk of post-TAC and relatively mild alterations in histology and markers of hypertrophy at 5 wk post-TAC. Consistent with concentric hypertrophy, our results show that these strains manifest different cardiac responses to pressure overload in a time-dependent manner and that genetic susceptibility to initial concentric hypertrophy is dominant to eccentric hypertrophy. These results also imply that genetic background differences can complicate interpretation of TAC studies when using mixed genetic backgrounds.

Mouse inbred strain differences in ethanol drinking to intoxication

Recently, we described a simple procedure, Drinking in the Dark (DID), in which C57BL/6J mice self-administer ethanol to a blood ethanol concentration (BEC) above 1 mg/ml. The test consists of replacing the water with 20% ethanol in the home cage for 4 h early during the dark phase of the light/dark cycle. Three experiments were conducted to explore this high ethanol drinking model further. In experiment 1, a microanalysis of C57BL/6J behavior showed that the pattern of ethanol drinking was different from routine water intake. In experiment 2, drinking impaired performance of C57BL/6J on the accelerating rotarod and balance beam. In experiment 3, 12 inbred strains were screened to estimate genetic influences on DID and correlations with other traits. Large, reliable differences in intake and BEC were detected among the strains, with C57BL/6J showing the highest values. Strain means were positively correlated with intake and BEC in the standard (24 h) and a limited (4 h) two-bottle ethanol vs. water test, but BECs reached higher levels for DID. Strain mean correlations with other traits in the Mouse Phenome Project database supported previously reported genetic relationships of high ethanol drinking with low chronic ethanol withdrawal severity and low ethanol-conditioned taste aversion. We extend these findings by showing that the correlation estimates remain relatively unchanged even after correcting for phylogenetic relatedness among the strains, thus relaxing the assumption that the strain means are statistically independent. We discuss applications of the model for finding genes that predispose pharmacologically significant drinking in mice.

Comparison of contractile responses in isolated mouse aorta and pulmonary artery: Influence of strain and sex

Transgenic mice are often used to study the physiologic role of a known gene. The design of experiments with transgenic mice usually does not take into account strain and sex differences, at least in isolated vessels. Therefore, we have compared the contractile response of isolated aortae and isolated pulmonary arteries of male and female mice of different strains (CD1, BL6, and DBA). Contractile stimulation was achieved by depolarization due to KCl, alpha1-adrenoceptor stimulation by phenylephrine and inhibition of protein phosphatase activity by cantharidin. In isolated aorta, strain-specific differences in contractility and sex-specific differences could be observed. The concentration of phenylephrine (PE) inducing half maximal contraction (EC50) was different between aortae from DBA male mice and the other strains tested. Phasic contractions of isolated aortic rings due to PE were seen in all mice except DBA male. In isolated pulmonary arteries, strain-specific differences and sex-specific differences could be observed. The EC50-values of PE were not different between all groups. Phasic contractions due to PE were only seen in pulmonary arteries from CD1 male and BL6 female. In conclusion, strain- and sex-specific differences should be considered in selecting mice used for transgenesis or gene targeting experiments.

Current and future approaches using genetically modified mice in endocrine research

Genetically modified mouse models have been used widely to advance our knowledge in the field of endocrinology and metabolism. A number of different approaches to generate genetically modified mice are now available, which provide the power to analyze the role of individual proteins in vivo. However, there are a number of points to be considered in the use and interpretation of these models. This review discusses the advantages and disadvantages involved in the generation and use of different genetically modified mouse models in endocrine research, including conventional techniques (e.g., overexpression, knockout, and knock-in models), tissue- and/or time-specific deletion of target genes [e.g., Cre-loxP and short interfering (si)RNA transgenic approaches], and gene-trap approaches to undertake functional genomics. This review also highlights the many factors that should be considered when assessing the phenotype of these mouse models, many of which are relevant to all murine physiological studies. These approaches are a powerful means by which to dissect the function of genes and are revolutionizing our understanding of endocrine physiology and metabolism.

Strain-dependent differences in responses to exercise training in inbred and hybrid mice

The aim of this study was to characterize the response to exercise training in several mouse strains and estimate the genetic contribution to phenotypic variation in the responses to exercise training. Male mice from three inbred strains [C57Bl/6J (BL6), FVB/NJ (FVB), and Balb/cJ (Balb/c)] and three hybrid F(1) strains [CB6F1/J (CB6 = female Balb/c x male BL6), B6F F(1) (female BL6 x male FVB), and FB6 F(1) (female FVB x male BL6)] completed an exercise performance test before and after a 4-wk treadmill running program. Distance was used as the primary estimate of endurance exercise performance. FVB mice showed the greatest response to training, with five- to sevenfold greater increases in distance run compared with BL6 and Balb/c strains. Specifically, BL6, FVB, and Balb/c strains increased distance by 33, 172, and 23%, respectively. A similar pattern of changes across strains was observed for run time (17, 87, and 11%) and work (99, 287, and 57%). As a group, F(1) hybrid mice derived from BL6 and FVB strains showed an intermediate response to training (61%). However, further analysis indicated that training responses in FB6 F(1) mice (80%) were approximately 2.5-fold greater than responses in B6F F(1) mice (33%, P = 0.08). A similar pattern of changes between FB6 and B6F F(1) mice was observed for run time (44.5 and 17%) and work (141 and 59%). These data demonstrate that there are large strain-dependent differences in training responses among inbred mouse strains, suggesting that genetic background contributes significantly to adaptation to exercise. Furthermore, the contrasting responses in B6F and FB6 F(1) strains show that a maternal component strongly influences strain-dependent differences in training responses.

Osteogenic Differentiation of Recombinant Adeno-Associated Virus 2-Transduced Murine Mesenchymal Stem Cells and Development of an Immunocompetent Mouse Model forEx VivoOsteoporosis Gene Therapy

Gene therapy for osteopenic conditions including osteoporosis is a potential alternative to pharmacotherapy for cost effectiveness, long-term viability, and the ability to enhance bone mass by anabolic approaches. Increased understanding of mesenchymal stem cell (MSC) lineage differentiation during osteogenesis, and of the molecular pathways involved in bone cell production, provides an opportunity for the advancement of gene therapy approaches for osteopenic conditions. The potential of MSCs in osteoblast differentiation and the relative ease of MSC isolation and culturing offer a promising resource for the development of ex vivo gene therapy for bone defects. In an effort to develop ex vivo gene therapy for osteoporosis, we used gene-modified MSCs in a preclinical mouse model to determine the efficiency of transduction of murine MSCs by recombinant adeno-associated virus 2 (AAV) vectors carrying reporter genes and determined their osteogenic potential after recombinant AAV-mediated expression of bone morphogenic protein 2, known to induce osteoblast differentiation. Although surgical ovariectomy is believed to induce progressive bone loss in mouse models, similar to an osteoporosis-like phenotype in humans, several factors, including hormonal alteration and dietary habits, significantly affect both the onset and progression of the disease. Thus, in the present study, we determined the influence of these factors and developed an immunocompetent mouse model of osteoporosis with degenerative bone loss as in the human pathology.