Novel echocardiographic pixel intensity quantification method for differentiating transthyretin cardiac amyloidosis from light chain cardiac amyloidosis and other phenocopies

AIMS

Differentiating cardiac amyloidosis (CA) subtypes is important considering the significantly different therapies for transthyretin (ATTR)-CA and light chain (AL)-CA. Therefore, an echocardiographic method to distinguish ATTR-CA from AL-CA would provide significant value. We assessed a novel echocardiographic pixel intensity method to quantify myocardial calcification to differentiate ATTR-CA from phenocopies of CA and from AL-CA, specifically.

METHODS AND RESULTS

167 patients with ATTR-CA (n=53), AL-CA (n=32), hypertrophic cardiomyopathy (n=37), and advanced chronic kidney disease (n=45) were retrospectively evaluated. The septal reflectivity ratio (SRR) was measured as the average pixel intensity of the visible anterior septal wall divided by the average pixel intensity of the visible posterior lateral wall. SRR and other myocardial strain-based echocardiographic measures were evaluated with receiver operator characteristic analysis to evaluate accuracy in distinguishing ATTR-CA from AL-CA and other forms of left ventricular hypertrophy. Mean septal reflectivity ratio (SRR) was significantly higher in the ATTR-CA cohort compared to the other cohorts (p <0.001). SRR demonstrated the largest AUC (0.91, p<0.0001) for distinguishing ATTR from all other cohorts and specifically for distinguishing ATTR-CA from AL-CA (AUC=0.90, p<0.0001, specificity 96%, sensitivity 63%). There was excellent inter- and intra-operator reproducibility with an ICC of 0.91 (p <0.001) and 0.89 (p <0.001), respectively.

CONCLUSION

The SRR is a reproducible and robust parameter for differentiating ATTR-CA from other phenocopies of CA and specifically ATTR-CA from AL-CA.

713. The Clinical Impact of Implementation of a Multidisciplinary Endocarditis Team

Background

Infectious endocarditis is associated with substantial in-patient mortality of 15-20%. Effective management requires coordination between multiple medical and surgical subspecialties which can often lead to disjointed care. Previous European studies have identified multidisciplinary endocarditis teams as a tool for reducing endocarditis mortality.

Methods

The University of Michigan Multidisciplinary Endocarditis Team was formed on May 3^rd, 2018. The group developed an evidence-based algorithm for management of endocarditis that was used to provide recommendations for hospitalized patients over a 1-year period. Mortality outcomes were then retroactively assessed and compared to a historical control that was identified using an internal research tool.

Figure 1

Table 1

Results

Between June 14^th, 2018 and June 13^th, 2019 the team provided guideline-based recommendations on 56 patients with Duke Criteria definite endocarditis and at least 1 American Heart Association indication for surgery. The historical control included 68 patients with definite endocarditis and surgical indications admitted between July 1^st, 2014 to June 30^th, 2015. In-hospital mortality decreased significantly from 29.4% in 2014-2015 to 7.1% in 2018-2019 (p< 0.0001). There was a non-significant increase in the rate of surgical intervention after implementation of the team (41.2% vs 55.4%; p=0.12).

Table 2

Table 3

Table 4

Conclusion

Implementation of a multidisciplinary endocarditis team was associated with a significant 1-year decrease in all-cause in-hospital mortality for patients with definite endocarditis and surgical indications. In conjunction with previous studies demonstrating their effectiveness, this data supports that widespread adoption of endocarditis teams in North America has the potential to improve outcomes for this patient population.

Table 5

Disclosures

All Authors: No reported disclosures

Fibroblast growth factor homologous factors tune arrhythmogenic late NaV1.5 current in calmodulin binding-deficient channels

The Ca2+-binding protein calmodulin has emerged as a pivotal player in tuning Na+ channel function, although its impact in vivo remains to be resolved. Here, we identify the role of calmodulin and the NaV1.5 interactome in regulating late Na+ current in cardiomyocytes. We created transgenic mice with cardiac-specific expression of human NaV1.5 channels with alanine substitutions for the IQ motif (IQ/AA). The mutations rendered the channels incapable of binding calmodulin to the C-terminus. The IQ/AA transgenic mice exhibited normal ventricular repolarization without arrhythmias and an absence of increased late Na+ current. In comparison, transgenic mice expressing a lidocaine-resistant (F1759A) human NaV1.5 demonstrated increased late Na+ current and prolonged repolarization in cardiomyocytes, with spontaneous arrhythmias. To determine regulatory factors that prevent late Na+ current for the IQ/AA mutant channel, we considered fibroblast growth factor homologous factors (FHFs), which are within the NaV1.5 proteomic subdomain shown by proximity labeling in transgenic mice expressing NaV1.5 conjugated to ascorbate peroxidase. We found that FGF13 diminished late current of the IQ/AA but not F1759A mutant cardiomyocytes, suggesting that endogenous FHFs may serve to prevent late Na+ current in mouse cardiomyocytes. Leveraging endogenous mechanisms may furnish an alternative avenue for developing novel pharmacology that selectively blunts late Na+ current.

Multiparametric assessment of left atrial remodeling using 18F-FDG PET/CT cardiac imaging: A pilot study

BACKGROUND

Left atrial (LA) remodeling is associated with structural, electric, and metabolic LA changes. Integrated evaluation of these features in vivo is lacking.

METHODS

Patients undergoing 18F-fluorodeoxyglucose (FDG) PET-CT during a hyperinsulinemic-euglycemic clamp were classified into sinus rhythm (SR), paroxysmal AF (PAF), and persistent AF (PerAF). The LA was semiautomatically segmented, and global FDG uptake was quantified using standardized uptake values (SUVmax and SUVmean) in gated, attenuation-corrected images and normalized to LA blood pool activity. Regression was used to relate FDG data to AF burden and critical patient factors. Continuous variables were compared using t-tests or Mann-Whitney tests.

RESULTS

117 patients were included (76% men, age 66.4 ± 11.0, ejection fraction (EF) 25[22-35]%) including those with SR (n = 48), PAF (n = 55), and PerAF (n = 14). Patients with any AF had increased SUVmean (2.3[1.5-2.4] vs 2.0[1.5-2.5], P = 0.006), SUVmax (4.4[2.8-6.7] vs 3.2[2.3-4.3], P < 0.001), uptake coefficient of variation (CoV) 0.28[0.22-0.40] vs 0.25[0.2-0.33], P < 0.001), and hypometabolic scar (32%[14%-53%] vs 16.5%[0%-38.5%], P = 0.01). AF burden correlated with increased SUVmean, SUVmax, CoV, and scar independent of age, gender, EF, or LA size (P < 0.03 for all).

CONCLUSIONS

LA structure and metabolism can be assessed using FDG PET/CT. Greater AF burden correlates with the increased LA metabolism and scar.

Myocardial Microvascular Dysfunction in Rheumatoid ArthritisQuantitation by 13N-Ammonia Positron Emission Tomography/Computed Tomography

BACKGROUND

The goal of this study was to assess the prevalence of myocardial microvascular dysfunction in rheumatoid arthritis (RA) patients without clinical cardiovascular disease and its association with RA characteristics and measures of cardiac structure and function.

METHODS

Participants with RA underwent rest and vasodilator stress N-13 ammonia positron emission tomography and echocardiography. Global myocardial blood flow was quantified at rest and during peak hyperemia. Myocardial flow reserve (MFR) was calculated as peak stress myocardial blood flow/rest myocardial blood flow. A small number of asymptomatic and symptomatic non-RA controls were also evaluated.

RESULTS

In RA patients, mean±SD MFR was 2.9±0.8, with 29% having reduced MFR (<2.5). Male sex and higher interleukin-6 were significantly associated with lower MFR, while the use of tumor necrosis factor inhibitors was associated with higher MFR. Lower MFR was associated with higher left ventricle mass index and higher left ventricle volumes but not with ejection fraction or diastolic dysfunction. RA and symptomatic controls had comparable MFR (mean±SD: 2.9±0.8 versus 2.55±0.6; P=0.48). In contrast, MFR was higher in the asymptomatic controls (mean±SD: 3.25±0.7) although not statistically different.

CONCLUSIONS

Reduced MFR was observed in a third of RA patients without clinical cardiovascular disease and was associated with a measure of inflammation and with higher left ventricle mass and volumes. MFR in RA patients was similar to controls referred for clinical scans (symptomatic controls). Whether reduced MFR contributes to the increased risk for heart failure in RA remains unknown.

203. Correlating Cardiac PET Results with Intra-Operative Findings in Infectious Endocarditis

Background

Care for patients with infectious endocarditis is complicated by delays in diagnosis and relatively low sensitivity of existing diagnostic algorithms, particularly the Duke Criteria. In recent years, cardiac positron emission tomography (PET) has been identified as a useful tool in detecting occult endocardial infections. Multiple prospective studies have demonstrated that when incorporated with conventional imaging modalities cardiac PET can improve the sensitivity of the Duke Criteria by 27–38 percent. These studies used as their gold standard for diagnosis the consensus opinion of an endocarditis team and were characterized by a relatively low percentage of patients who underwent surgery. We reviewed 4 years of surgically managed IE cases at a tertiary care center where cardiac PET was used to aid diagnosis.

Methods

Between July 1, 2014 and December 31, 2018 we retrospectively reviewed 68 surgically managed cases of endocarditis. Cases were identified using ICD-9 and ICD-10 codes of patients who underwent surgical valve replacement for endocarditis as well as all patients who had cardiac PET scans to rule out endocarditis. Variables including PET results, operative findings, valve culture, pathology and PCR testing were recorded.

Results

14 patients were identified who underwent cardiac PET prior to their surgical intervention. 9 cases were classified as possible endocarditis by Duke Criteria and 10 involved prosthetic valves. 12/14 scans were interpreted as suggestive of or consistent with endocarditis. Twelve positive PETs were associated with either operative findings of infection and/or positive PCR testing on the excised valve (positive predictive value: 100%). The 2 patients with negative scans were found to have noninfectious vegetations intra-operatively, negative valve cultures and negative pathology.

Conclusion

Cardiac PET correlates closely with intra-operative findings in patients with endocarditis. In patients with suspected endocarditis it may help guide surgical decision making. Cardiac PET should be considered for addition to the Modified Duke’s Criteria similar to the European Society of Cardiology guidelines.

Disclosures

All authors: No reported disclosures.

Standardization of 99mTechnetium pyrophosphate imaging methodology to diagnose TTR cardiac amyloidosis

BACKGROUND

Technetium pyrophosphate (99mTc-PYP) imaging to diagnose transthyretin cardiac amyloidosis (ATTR-CA) has been increasingly utilized. The objective of this study is to provide a standardized 99mTc-PYP imaging protocol to diagnose ATTR-CA.

METHODS

104 scans from 45 subjects with biopsy-proven ATTR-CA or light-chain cardiac amyloidosis (AL) were assessed. Multiple scans were obtained using different counts (750 vs 2000 K), times to acquisition (1 vs 2 to 4 hours), processing matrix (256 vs 128), and 99mTc-PYP dose. Image quality and extracardiac activity was assessed. Quantitative methods using heart-to-contralateral ratios (H/CL) and a visual semiquantitative scale were used to diagnose ATTR-CA.19 The correlation between H/CL ratios and reproducibility of semiquantitative visual scores, acquired using various imaging parameters, were evaluated.

RESULTS

All imaging parameters had good to excellent image quality. 750 vs 2000 K counts, 1 hour acquisition and 256 matrix, had lower extracardiac activity (P = .00018). 10 mCi of 99mTc-PYP v. higher doses showed excellent image quality and less extracardiac activity (P = .0015). Correlation of H/CL ratios was strong (r ≥ 0.92) and reproducibility of semiquantitative visual scores was high (Kappa = 95%).

CONCLUSION

An imaging protocol using 750 K counts, 10 mCi of 99mTc-PYP, and a 256 matrix was chosen as the standardized imaging protocol since it provided the shortest overall study time (1 vs 2 to 4 hours) and lowest radiation exposure (3 vs 8 to 10 mSv).

Arterial Inflammation Detected With 18 F-Fluorodeoxyglucose-Positron Emission Tomography in Rheumatoid Arthritis

OBJECTIVE

In addition to traditional risk factors, excess cardiovascular disease (CVD) in rheumatoid arthritis (RA) is attributed to enhanced vascular and/or systemic inflammation. In several small studies using ¹⁸ F-fluorodeoxyglucose-positron emission tomography/computed tomography (¹⁸ F-FDG-PET/CT) to directly assess vascular inflammation, FDG uptake was higher in RA patients than in controls. Using a substantially larger sample of RA patients, we sought to identify RA disease characteristics independently associated with vascular FDG uptake.

METHODS

RA patients underwent cardiac FDG-PET/CT, with aortic inflammation assessed by quantification of FDG uptake in the ascending aorta, calculated as the mean and maximum (max) standardized uptake value (SUV) of the entire ascending aorta and of its most diseased segment (SUV MDS). Univariate and multivariable regression models were constructed to model the associations of patient characteristics with aortic FDG uptake.

RESULTS

Ninety-one RA patients were scanned. In multivariable models, in addition to the independent associations of hypertension and body mass index with increased aortic FDG uptake, the prevalence of rheumatoid nodules correlated with the SUV mean and SUV MDS mean measures, while anti-cyclic citrullinated peptide (anti-CCP) antibodies correlated inversely with these measures and with the SUV max and SUV MDS max (P < 0.05). A significant association of RA disease activity with aortic FDG uptake was observed but was restricted to anti-CCP seropositivity.

CONCLUSION

Traditional CV risk factors and RA disease characteristics (rheumatoid nodules and the Disease Activity Score in 28 joints using the C-reactive protein level in anti-CCP antibody-positive individuals) were independently associated with ascending aortic FDG uptake in RA patients without clinical CVD.

Relation of Coronary Flow Reserve to Other Findings on Positron Emission Tomography Myocardial Perfusion Imaging and Left Heart Catheterization in Patients With End-stage Renal Disease Being Evaluated for Kidney Transplant

Cardiovascular disease is the leading cause of death in patients with end-stage renal disease (ESRD) and often goes undetected. Abnormal coronary flow reserve (CFR), which predicts increased risk of cardiac death, may be present in patients with ESRD without other evidence of coronary artery disease (CAD). We prospectively studied 131 patients who had rest and dipyridamole pharmacologic stress N¹³-ammonia positron emission tomography myocardial perfusion imaging (PET MPI) for kidney transplant evaluation. Thirty-four patients also had left heart catheterization. Abnormal PET MPI was defined as qualitative ischemia or infarct, stress electrocardiogram ischemia, or transient ischemic dilation. CFR was calculated as the ratio of stress to rest coronary blood flow. Global CFR < 2 was defined as abnormal. Of 131 patients who had PET MPI (66% male, 55.6 ± 12.1 years), 30% (39 of 131) had abnormal PET MPI and 59% (77 of 131) had abnormal CFR. In a subset of 34 patients who had left heart catheterization (66% male, 61.0 ± 12.1 years), 68% (23 of 34) had abnormal CFR on PET MPI, and 68% (23 of 34) had ≥70% obstruction on left heart catheterization. Abnormal CFR was not significantly associated with abnormal PET MPI (p = 0.13) or obstructive CAD on left heart catheterization (p = 0.26). In conclusion, in the first prospective study of PET MPI in patients with ESRD, abnormal CFR is highly prevalent and is independent of abnormal findings on PET MPI or obstructive CAD on left heart catheterization.

Plasminogen promotes cholesterol efflux by the ABCA1 pathway

Using genetic and biochemical approaches, we investigated proteins that regulate macrophage cholesterol efflux capacity (CEC) and ABCA1-specific CEC (ABCA1 CEC), 2 functional assays that predict cardiovascular disease (CVD). Macrophage CEC and the concentration of HDL particles were markedly reduced in mice deficient in apolipoprotein A-I (APOA1) or apolipoprotein E (APOE) but not apolipoprotein A-IV (APOA4). ABCA1 CEC was markedly reduced in APOA1-deficient mice but was barely affected in mice deficient in APOE or APOA4. High-resolution size-exclusion chromatography of plasma produced 2 major peaks of ABCA1 CEC activity. The early-eluting peak, which coeluted with HDL, was markedly reduced in APOA1- or APOE-deficient mice. The late-eluting peak was modestly reduced in APOA1-deficient mice but little affected in APOE- or APOA4-deficient mice. Ion-exchange chromatography and shotgun proteomics suggested that plasminogen (PLG) accounted for a substantial fraction of the ABCA1 CEC activity in the peak not associated with HDL. Human PLG promoted cholesterol efflux by the ABCA1 pathway, and PLG-dependent efflux was inhibited by lipoprotein(a) [Lp(a)]. Our observations identify APOA1, APOE, and PLG as key determinants of CEC. Because PLG and Lp(a) associate with human CVD risk, interplay among the proteins might affect atherosclerosis by regulating cholesterol efflux from macrophages.

Serial scanning with technetium pyrophosphate (99mTc-PYP) in advanced ATTR cardiac amyloidosis

BACKGROUND

Development of noninvasive imaging modalities to quantify amyloid burden over time is an unmet clinical need. Technetium pyrophosphate (99mTc-PYP) scintigraphy is a simple and widely available radiotracer useful to differentiate transthyretin from light-chain amyloidosis in patients with advanced cardiac amyloidosis. We examined the utility of serial 99mTc-PYP scanning to quantify amyloid burden over time in TTR cardiac amyloidosis (ATTR-CA).

METHODS AND RESULTS

Twenty subjects with ATTR-CA (10 wild type, 10 mutant) underwent serial 99mTc-PYP planar cardiac imaging. Cardiac retention was assessed both semiquantitatively (visual score 0, no uptake to 3, uptake greater than bone) and quantitatively (region of interest drawn over the heart, copied, and mirrored over the contralateral chest) to calculate a heart-to-contralateral (H/CL) ratio. Index scan mean visual score and H/CL were 3.0 ± 0.2 and 1.79 ± 0.2, respectively, and after an average 1.5 ± 0.5 years follow-up, did not differ, 3.0 ± 0.2, P = .33 and 1.76 ± 0.2, P = .44. H/CL change was minimal, 0.03 ± 0.17, did not correlate with time between scans, r = 0.19, P = .43, and was observed despite obvious clinical progression (increase in troponin ≥ 0.1 ng/mL, BNP ≥ 400 pg/mL, NYHA class, and/or death).

CONCLUSIONS

Serial 99mTc-PYP scanning in subjects with advanced ATTR-CA does not show significant changes over an average 1.5 years of follow-up despite obvious clinical progression.

β-adrenergic regulation of the L-type Ca2+ channel does not require phosphorylation of α1C Ser1700

RATIONALE

Sympathetic nervous system triggered activation of protein kinase A, which phosphorylates several targets within cardiomyocytes, augments inotropy, chronotropy, and lusitropy. An important target of β-adrenergic stimulation is the sarcolemmal L-type Ca(2+) channel, CaV1.2, which plays a key role in cardiac excitation-contraction coupling. The molecular mechanisms of β-adrenergic regulation of CaV1.2 in cardiomyocytes, however, are incompletely known. Recently, it has been postulated that proteolytic cleavage at Ala(1800) and protein kinase A phosphorylation of Ser(1700) are required for β-adrenergic modulation of CaV1.2.

OBJECTIVE

To assess the role of Ala(1800) in the cleavage of α1C and the role of Ser(1700) and Thr(1704) in mediating the adrenergic regulation of CaV1.2 in the heart.

METHODS AND RESULTS

Using a transgenic approach that enables selective and inducible expression in mice of FLAG-epitope-tagged, dihydropyridine-resistant CaV1.2 channels harboring mutations at key regulatory sites, we show that adrenergic regulation of CaV1.2 current and fractional shortening of cardiomyocytes do not require phosphorylation of either Ser(1700) or Thr(1704) of the α1C subunit. The presence of Ala(1800) and the (1798)NNAN(1801) motif in α1C is not required for proteolytic cleavage of the α1C C-terminus, and deletion of these residues did not perturb adrenergic modulation of CaV1.2 current.

CONCLUSIONS

These results show that protein kinase A phosphorylation of α1C Ser(1700) does not have a major role in the sympathetic stimulation of Ca(2+) current and contraction in the adult murine heart. Moreover, this new transgenic approach enables functional and reproducible screening of α1C mutants in freshly isolated adult cardiomyocytes in a reliable, timely, cost-effective manner.

Abstract 4: Apolipoprotein A-iv Enhances Triglyceride Secretion and Reduces Hepatic Lipid Content by Promoting Apob Containing-lipoprotein Particle Expansion in Livers of Steatotic Mice

Apolipoprotein A-IV (apoA-IV) is a lipid binding protein expressed in mammalian intestine, as well as rodent liver. While previous in vitro studies demonstrated that apoA-IV promotes cellular triglyceride (TG) secretion by modulating apoB secretory trafficking and lipoprotein size, evidence that apoA-IV affects TG secretion in vivo is lacking. To explore the possible role of apoA-IV in controlling hepatic VLDL-mediated lipid efflux we assessed whether apoA-IV is regulated by liver lipid accumulation and if its deficiency or overexpression affects hepatic TG secretion. Under conditions of high fat diet-induced hepatic steatosis and steatosis caused by transgenic overexpression of SREBP-1a (SREBP-1aTg), a ~40-fold induction of hepatic apoA-IV mRNA and protein was observed. In both systems there was a linear correlation between hepatic TG content and apoA-IV mRNA abundance (r2 = 0.8965). To establish whether the induction of apoA-IV impacted TG secretion, SREBP-1aTg mice were crossed with apoA-IV knock out mice (A4-KO). Based on the Triton block method, SREBP1aTg/A4-KO mice demonstrated a 24% reduction in hepatic TG secretion rate, relative to SREBP1aTg controls. The basis for the decrease in TG secretion was not due to decreased particle number, as apoB production was unaffected; however, negative stain electron microscopy revealed a 33% decrease in the abundance of large diameter (>120 nm) VLDL particles. To explore the impact of human apoA-IV overexpression, a recombinant apoA-IV adenovirus (AdA4) was developed. Mice infected with AdA4 demonstrated abundant hepatic expression of human apoA-IV, and a 50% increase in hepatic TG secretion rate, relative to the LacZ control. In addition, after only three days of expression AdA4 reduced liver TG content by 40%. Although again, apoA-IV expression did not impact apoB secretion, negative stain electron microscopy revealed a 1.8-fold increase in the abundance of large diameter VLDL particles. In conclusion, we demonstrate that in steatotic mice, hepatic apoA-IV expression increases TG secretion by promoting lipoprotein particle expansion, thereby dramatically reducing hepatic lipid burden without increasing atherogenic lipoprotein particle number.

Integrating palliative care into the outpatient, private practice oncology setting

CONTEXT

Quality care for patients with cancer is a national priority-for those with noncurable cancer, the stakes are even higher. Strategies to promote integration of palliative care into oncology practice may enhance quality. We have developed a model in which palliative care services are integrated into the private, office-based oncology practice setting. We have evaluated the feasibility and assessed outcomes for both the oncologists and the patients they serve. To our knowledge, an embedded clinic in an outpatient, private practice oncology clinic has not been described previously.

OBJECTIVE

The primary outcomes assessed were 1) quality care outcomes through assessment of symptom burden and relief achieved through palliative care consultation, 2) provider satisfaction, 3) volume determined by number of palliative care consultations over time, and 4) time saved for the oncologist as a surrogate for the bottom line of the cancer practice.

METHODS

Measurement of: symptom burden and relief with the Edmonton Symptom Assessment System (ESAS), physician acceptance of palliative care services through a provider satisfaction survey and volume of referrals, and billing data to determine potential oncologists' time saved.

RESULTS

Palliative care consultation was associated with a reduction in symptom burden by 21%, evidenced by decrease in average total ESAS score from 49.3 to 39. Median provider satisfaction scores rating components of palliative care ranged from 8.5 to 9/10, with an overall provider satisfaction of 9/10. Over the study period, the "embedded" oncology group consultation requests increased 87% (67-120), with each individual oncology provider nearly doubled. The total time saved for the oncology practice in Year 2 was just over four weeks (9720 minutes; 162 hours).

CONCLUSION

An embedded palliative care clinic integrated into an office-based oncology practice is feasible and may improve the quality of care. Formal study of this service delivery model is warranted.

Location of modulatory beta subunits in BK potassium channels

Large-conductance voltage- and calcium-activated potassium (BK) channels contain four pore-forming α subunits and four modulatory β subunits. From the extents of disulfide cross-linking in channels on the cell surface between cysteine (Cys) substituted for residues in the first turns in the membrane of the S0 transmembrane (TM) helix, unique to BK α, and of the voltage-sensing domain TM helices S1–S4, we infer that S0 is next to S3 and S4, but not to S1 and S2. Furthermore, of the two β1 TM helices, TM2 is next to S0, and TM1 is next to TM2. Coexpression of α with two substituted Cys’s, one in S0 and one in S2, and β1 also with two substituted Cys’s, one in TM1 and one in TM2, resulted in two αs cross-linked by one β. Thus, each β lies between and can interact with the voltage-sensing domains of two adjacent α subunits.

Breast Cancer Stem Cells and the Epithelial-Mesenchymal Transition

The acquisition of highly malignant traits by carcinoma cells is often associated with the activation of a transdifferentiation program termed the epithelial-mesenchymal transition (EMT). The EMT program is deployed in a variety of steps of embryonic morphogenesis, enabling the interconversion of epithelial and mesenchymal cell types. When both normal and neoplastic epithelial cells undergo an EMT, they acquire addition changes in addition to expressing characteristic mesenchymal cell markers. In particular, they acquire motility, an increased resistance to apoptosis and, in the case of carcinoma cells, invasiveness. The motility and invasiveness components associated with the EMT would appear to empower many types of cancer cells to metastasize. An interesting question is how the resulting disseminated cancer cells are able to spawn a macroscopic tumor mass at distant anatomical sites, since this clonal expansion would appear to require an ability to self-renew. Recently, we have examined the cellular products of an EMT. Contrary to our expectations, the resulting cells acquired many of the attributes of stem cells, including the expression of stem cell-associated cell-surface markers. Conversely, mammary epithelial cells that naturally express these markers also express greatly elevated levels of at least four pleiotropically acting transcription factors that have been found able to induce an EMT. More recent studies have confirmed that the product of an EMT in mouse mammary epithelial cells is a cell that has a greatly increased ability to generate an entire mammary ductal epithelial tree. Moreover, we find that cells with the attributes of stem cells exist naturally as minor subpopulations in cultured human mammary epithelial cells. These cells can differentiate spontaneously into non-stem cells and, conversely, the non-stem cells appear capable of dedifferentiating spontaneously into cells with progenitor or stem-cell phenotypes. Hence, the study of certain aspects of mammary epithelial cell biology, including the biology of mammary carcinoma stem cells, may be feasible with cultured cells.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr A1-1.

A critical role for myosin IIb in dendritic spine morphology and synaptic function

Dendritic spines show rapid motility and plastic morphology, which may mediate information storage in the brain. It is presently believed that polymerization/depolymerization of actin is the primary determinant of spine motility and morphogenesis. Here, we show that myosin IIB, a molecular motor that binds and contracts actin filaments, is essential for normal spine morphology and dynamics and represents a distinct biophysical pathway to control spine size and shape. Myosin IIB is enriched in the postsynaptic density (PSD) of neurons. Pharmacologic or genetic inhibition of myosin IIB alters protrusive motility of spines, destabilizes their classical mushroom-head morphology, and impairs excitatory synaptic transmission. Thus, the structure and function of spines is regulated by an actin-based motor in addition to the polymerization state of actin.

Biochemical and morphological characterization of an intracellular membrane compartment containing AMPA receptors

AMPA receptors cycle rapidly in and out of the postsynaptic membrane, while NMDA receptors are relatively immobile. Changing the distribution of AMPA receptors between intracellular and surface synaptic pools is an important means of controlling synaptic strength. However, little is known about the intracellular membrane compartments of neurons that contain AMPA receptors. Here we describe biochemical and morphological characteristics of an intracellular pool of AMPA receptors in rat brain. By velocity gradient centrifugation of microsomal light membranes from rat brain, we identified a membrane fraction enriched for AMPA receptor subunits GluR2/3 but lacking NMDA receptors. This membrane compartment sedimented more slowly than synaptosomes but faster than synaptic vesicles and cofractionated with GRIP, PICK-1 and syntaxin-13. Morphological examination of this fraction revealed round and tubular vesicles ranging from approximately 50 to 300 nm in diameter. Immunocytochemistry of cultured hippocampal neurons showed that a significant portion of AMPA receptors colocalized with syntaxin-13 (a SNARE protein associated with tubulovesicular recycling endosomes) and with transferrin receptors. Taken together, these results suggest that a pool of intracellular GluR2/3 resides in a syntaxin 13-positive tubulovesicular membrane compartment, which might serve as a reservoir for the dendritic recycling of AMPA receptors.

Is the oxidation of high-density lipoprotein lipids different than the oxidation of low-density lipoprotein lipids?

This article gives detailed insight into the kinetics of high-density lipoprotein (HDL) oxidation catalyzed by azobis(2-amidinopropane).dihydrochloride (ABAP) or by copper. ABAP initialized oxidation of human HDL 3-4 times faster than non-human primate HDL with a similar composition. The oxidizability of non-human primate HDL was 1000 times lower than the oxidizability calculated from rate constants derived from liposome oxidation, suggesting that there is a slow step in HDL oxidation not present in liposomes. Saturable binding of copper to HDL was a significant feature of copper-catalyzed oxidation. Binding constants (K(m)) for non-human primate HDL were 2-3-fold lower than those for human HDL. Copper-catalyzed oxidation of non-human primate HDL was slower than that of human HDL, but human HDL(2) and HDL(3) oxidized at about the same rate. Overall, the kinetics describing the oxidation of HDL were mechanistically similar to those reported for LDL, suggesting that HDL lipids were as easily oxidized as LDL lipids and that HDL will be easily oxidized in vivo when exposed to agents that oxidize LDL.

Cyclin D2 is essential for BCR-mediated proliferation and CD5 B cell development

Progression into G(1) in B lymphocytes is regulated by cyclins D2 and D3, components of the cell cycle machinery currently believed to have overlapping and potentially redundant roles in cell cycle control. To study the specific role of cyclin D2 in B lymphocyte proliferation, we examined B cells from cyclin D2(-/-) mice and demonstrate a specific requirement for cyclin D2 in BCR- but not CD40- or lipopolysaccharide-induced proliferation. Furthermore, conventional B cell development proceeds normally in the mutant mice; however, the CD5 B cell compartment is dramatically reduced, suggesting that cyclin D2 is important in CD5 B cell development as well as antigen-dependent B cell clonal expansion.

Association of AMPA receptors with a subset of glutamate receptor-interacting protein in vivo

The NMDA and AMPA classes of ionotropic glutamate receptors are concentrated at postsynaptic sites in excitatory synapses. NMDA receptors interact via their NR2 subunits with PSD-95/SAP90 family proteins, whereas AMPA receptors bind via their GluR2/3 subunits to glutamate receptor-interacting protein (GRIP), AMPA receptor-binding protein (ABP), and protein interacting with C kinase 1 (PICK1). We report here a novel cDNA (termed ABP-L/GRIP2) that is virtually identical to ABP except for additional GRIP-like sequences at the N-terminal and C-terminal ends. Like GRIP (which we now term GRIP1), ABP-L/GRIP2 contains a seventh PDZ domain at its C terminus. Using antibodies that recognize both these proteins, we examined the subcellular localization of GRIP1 and ABP-L/GRIP2 (collectively termed GRIP) and their biochemical association with AMPA receptors. Immunogold electron microscopy revealed the presence of GRIP at excitatory synapses and also at nonsynaptic membranes and within intracellular compartments. The association of native GRIP and AMPA receptors was confirmed biochemically by coimmunoprecipitation from rat brain extracts. A majority of detergent-extractable GluR2/3 was complexed with GRIP in the brain. However, only approximately half of GRIP was associated with AMPA receptors. Unexpectedly, immunocytochemistry of cultured hippocampal neurons and rat brain at the light microscopic level showed enrichment of GRIP in GABAergic neurons and in GABAergic nerve terminals. Thus GRIP is associated with inhibitory as well as excitatory synapses. Collectively, these findings support a role for GRIP in the synaptic anchoring of AMPA receptors but also suggest that GRIP has additional functions unrelated to the binding of AMPA receptors.