Muscle RING Finger-1 Promotes a Maladaptive Phenotype in Chronic Hypoxia-Induced Right Ventricular Remodeling

Exposure to chronic hypoxia (CH) induces elevated pulmonary artery pressure/resistance, leading to an eventual maladaptive right ventricular hypertrophy (RVH). Muscle RING finger-1 (MuRF1) is a muscle-specific ubiquitin ligase that mediates myocyte atrophy and has been shown to play a role in left ventricular hypertrophy and altered cardiac bioenergetics in pressure overloaded hearts. However, little is known about the contribution of MuRF1 impacting RVH in the setting of CH. Therefore, we hypothesized that MuRF1 deletion would enhance RVH compared to their wild-type littermates, while cardiac-specific overexpression would reduce hypertrophy following CH-induced pulmonary hypertension. We assessed right ventricular systolic pressure (RVSP), right ventricle to left ventricle plus septal weight ratio (RV/LV+S) and hematocrit (Hct) following a 3-wk isobaric CH exposure. Additionally, we conducted dual-isotope SPECT/CT imaging with cardiac function agent 201Tl-chloride and cell death agent 99mTc-annexin V. Predictably, CH induced pulmonary hypertension, measured by increased RVSP, RV/LV+S and Hct in WT mice compared to normoxic WT mice. Normoxic WT and MuRF1-null mice exhibited no significant differences in RVSP, RV/LV+S or Hct. CH-induced increases in RVSP were also similar between WT and MuRF1-null mice; however, RV/LV+S and Hct were significantly elevated in CH-exposed MuRF1-null mice compared to WT. In cardiac-specific MuRF1 overexpressing mice, RV/LV+S increased significantly due to CH exposure, even greater than in WT mice. This remodeling appeared eccentric, maladaptive and led to reduced systemic perfusion. In conclusion, these results are consistent with an atrophic role for MuRF1 regulating the magnitude of right ventricular hypertrophy following CH-induction of pulmonary hypertension

Assessing antibody pharmacokinetics in mice with in vivo imaging

Recent advances in small-animal molecular imaging instrumentation combined with well characterized antibody-labeling chemistry have enabled detailed in vivo measurements of antibody distribution in mouse models. This article reviews the strengths and limitations of in vivo antibody imaging methods with a focus on positron emission tomography and single-photon emission computed tomography and a brief discussion of the role of optical imaging in this application. A description of the basic principles behind the imaging techniques is provided along with a discussion of radiolabeling methods relevant to antibodies. Practical considerations of study design and execution are presented through a discussion of sensitivity and resolution tradeoffs for these techniques as defined by modality, signaling probe (isotope or fluorophore) selection, labeling method, and radiation dosimetry. Images and analysis results from a case study are presented with a discussion of output data content and relevant informatics gained with this approach to studying antibody pharmacokinetics

High-Resolution Computed Tomography of Single Breast Cancer Microcalcifications in Vivo

Microcalcification is a hallmark of breast cancer and a key diagnostic feature for mammography. We recently described the first robust animal model of breast cancer microcalcification. In this study, we hypothesized that high-resolution computed tomography (CT) could potentially detect the genesis of a single microcalcification in vivo and quantify its growth over time. Using a commercial CT scanner, we systematically optimized acquisition and reconstruction parameters. Two ray-tracing image reconstruction algorithms were tested: a voxel-driven “fast” cone beam algorithm (FCBA) and a detector-driven “exact” cone beam algorithm (ECBA). By optimizing acquisition and reconstruction parameters, we were able to achieve a resolution of 104 μm full width at half-maximum (FWHM). At an optimal detector sampling frequency, the ECBA provided a 28 μm (21%) FWHM improvement in resolution over the FCBA. In vitro, we were able to image a single 300 μm X 100 μm hydroxyapatite crystal. In a syngeneic rat model of breast cancer, we were able to detect the genesis of a single microcalcification in vivo and follow its growth longitudinally over weeks. Taken together, this study provides an in vivo “gold standard” for the development of calcification-specific contrast agents and a model system for studying the mechanism of breast cancer microcalcification

Muscle RING finger-1 promotes a maladaptive phenotype in chronic hypoxia-induced right ventricular remodeling.

Exposure to chronic hypoxia (CH) induces elevated pulmonary artery pressure/resistance, leading to an eventual maladaptive right ventricular hypertrophy (RVH). Muscle RING finger-1 (MuRF1) is a muscle-specific ubiquitin ligase that mediates myocyte atrophy and has been shown to play a role in left ventricular hypertrophy and altered cardiac bioenergetics in pressure overloaded hearts. However, little is known about the contribution of MuRF1 impacting RVH in the setting of CH. Therefore, we hypothesized that MuRF1 deletion would enhance RVH compared to their wild-type littermates, while cardiac-specific overexpression would reduce hypertrophy following CH-induced pulmonary hypertension. We assessed right ventricular systolic pressure (RVSP), right ventricle to left ventricle plus septal weight ratio (RV/LV+S) and hematocrit (Hct) following a 3-wk isobaric CH exposure. Additionally, we conducted dual-isotope SPECT/CT imaging with cardiac function agent 201Tl-chloride and cell death agent 99mTc-annexin V. Predictably, CH induced pulmonary hypertension, measured by increased RVSP, RV/LV+S and Hct in WT mice compared to normoxic WT mice. Normoxic WT and MuRF1-null mice exhibited no significant differences in RVSP, RV/LV+S or Hct. CH-induced increases in RVSP were also similar between WT and MuRF1-null mice; however, RV/LV+S and Hct were significantly elevated in CH-exposed MuRF1-null mice compared to WT. In cardiac-specific MuRF1 overexpressing mice, RV/LV+S increased significantly due to CH exposure, even greater than in WT mice. This remodeling appeared eccentric, maladaptive and led to reduced systemic perfusion. In conclusion, these results are consistent with an atrophic role for MuRF1 regulating the magnitude of right ventricular hypertrophy following CH-induction of pulmonary hypertension

Monocrotaline induced significant changes in right ventricular systolic (A) and mean (B) pressure, which were alleviated by late treatment with resveratrol in the drinking water.

<p>Right-sided cardiac contractility, as assessed by +<i>d</i>P/<i>d</i>t_max from the RV pressure wave, was significantly elevated in the MCT-treated rats, and again reduced to control levels by resveratrol (C). No heart rate (HR) differences among the groups were noted, confirming a consistent level of anesthetic depth between groups during hemodynamic assessment (D). Asterisks indicate significant (P<0.05) elevation over other groups by ANOVA with Newman-Keuls Posthoc Comparison Test.</p

Global cardiac perfusion, as assessed by 201Thallium detection, showed no significant differences between groups or trends across the 42-day imaging period.

<p>Global cardiac perfusion, as assessed by 201Thallium detection, showed no significant differences between groups or trends across the 42-day imaging period.</p

Right ventricular remodeling following MCT injection was evident from the ratio of right ventricular mass to left ventricular plus septal mass (RV/LVS); this effect was diminished by resveratrol treatment (A).

<p>No obvious effect on lung remodeling or edema formation was noted at 42 days post-MCT injection (B). Right ventricular enlargement was evident at 3–4 weeks in MCT/water-treated rats (M/W), with some resolution in MCT/resveratrol rats (M/R) from SPECT images of ²⁰¹Thallium (C). No apparent changes were noted in saline/water (S/W) or saline/resveratrol (S/R) control rats. Notably, septal indentation, a result of increased right ventricular pressure, was evident as early as 2 weeks post-MCT (D). Asterisks indicate significant (P<0.05) elevation over other groups by ANOVA with Newman-Keuls Posthoc Comparison Test.</p

Representative SPECT/CT images of lung ⁹⁹Tc-annexin at day 0 and day 42 from one subject per group.

<p>CT images include the ECG wires in various positions. Quantitative assessments of ⁹⁹Tc energy from the lung region, with cardiac region subtracted out, are shown graphically, below. Asterisks indicate significant (P<0.05) elevation in the MCT-only group compared to other groups by 2-way (time, treatment) ANOVA.</p

Quantitative assessments of ⁹⁹Tc-annexin energy from the cardiac region, without consideration of pulmonary signals, are shown graphically.

<p>A severe induction of cardiac apoptosis was observed in one MCT-only rat, depicted from two positions in the figure to the right. Asterisks indicate significant (P<0.05) elevation in the MCT-only group compared to other groups by 2-way (time, treatment) ANOVA.</p