ERMA (TMEM94) is a P-type ATPase transporter for Mg2+ uptake in the endoplasmic reticulum

Intracellular Mg2+ (iMg2+) is bound with phosphometabolites, nucleic acids, and proteins in eukaryotes. Little is known about the intracellular compartmentalization and molecular details of Mg2+ transport into/from cellular organelles such as the endoplasmic reticulum (ER). We found that the ER is a major iMg2+ compartment refilled by a largely uncharacterized ER-localized protein, TMEM94. Conventional and AlphaFold2 predictions suggest that ERMA (TMEM94) is a multi-pass transmembrane protein with large cytosolic headpiece actuator, nucleotide, and phosphorylation domains, analogous to P-type ATPases. However, ERMA uniquely combines a P-type ATPase domain and a GMN motif for ERMg2+ uptake. Experiments reveal that a tyrosine residue is crucial for Mg2+ binding and activity in a mechanism conserved in both prokaryotic (mgtB and mgtA) and eukaryotic Mg2+ ATPases. Cardiac dysfunction by haploinsufficiency, abnormal Ca2+ cycling in mouse Erma+/- cardiomyocytes, and ERMA mRNA silencing in human iPSC-cardiomyocytes collectively define ERMA as an essential component of ERMg2+ uptake in eukaryotes.

Modification of a Transvalvular Microaxial Flow Pump for Instantaneous Determination of Native Cardiac Output and Volume

BACKGROUND

The current Impella cardiopulmonary (CP) pump, used for mechanical circulatory support in patients with cardiogenic shock (CS), cannot assess native cardiac output (CO) and left ventricular (LV) volumes. These data are valuable in facilitating device management and weaning. Admittance technology allows for accurate assessment of cardiac chamber volumes.

OBJECTIVES

This study tested the ability to engineer admittance electrodes onto an existing Impella CP pump to assess total and native CO as well as LV chamber volumes in an instantaneous manner.

METHODS

Impella CP pumps were fitted with 4 admittance electrodes and were placed in the LVs of adult swine (n = 9) that were subjected to 3 different hemodynamic conditions, including Impella CP speed adjustments, administration of escalating doses of dobutamine and microsphere injections into the left main artery to result in cardiac injury. CO, according to admittance electrodes, was calculated from LV volumes and heart rate. In addition, CO was calculated in each instance via thermodilution, continuous CO measurement, the Fick principle, and aortic velocity-time integral by means of echocardiography.

RESULTS

Modified Impella CP pumps were placed in swine LVs successfully. CO, as determined by admittance electrodes, was similar by trend to other methods of CO assessment. It was corrected for pump speed to calculate native CO, and calculated LV chamber volumes trended as expected in each experimental protocol.

CONCLUSIONS

We report, for the first time, that an Impella CP pump can be fitted with admittance electrodes and used to determine total and native CO in various hemodynamic situations.

CONDENSED ABSTRACT

Transvalvular mechanical circulatory support devices such as the Impella CP do not have the ability to provide real-time information on native cardiac output (CO) and left ventricular (LV) volumes. This information is critical in device management and in weaning in patients with cardiogenic shock. We demonstrate, for the first time, that Impella CP pumps coupled with admittance electrodes are able to determine native CO and LV chamber volumes in multiple hemodynamic situations such as Impella pump speed adjustments, escalating dobutamine administration and cardiac injury from microsphere injection.

Right Ventricular Sarcomere Contractile Depression and the Role of Thick Filament Activation in Human Heart Failure With Pulmonary Hypertension

BACKGROUND

Right ventricular (RV) contractile dysfunction commonly occurs and worsens outcomes in patients with heart failure with reduced ejection fraction and pulmonary hypertension (HFrEF-PH). However, such dysfunction often goes undetected by standard clinical RV indices, raising concerns that they may not reflect aspects of underlying myocyte dysfunction. We thus sought to characterize RV myocyte contractile depression in HFrEF-PH, identify those components reflected by clinical RV indices, and uncover underlying biophysical mechanisms.

METHODS

Resting, calcium-, and load-dependent mechanics were prospectively studied in permeabilized RV cardiomyocytes isolated from explanted hearts from 23 patients with HFrEF-PH undergoing cardiac transplantation and 9 organ donor controls.

RESULTS

Unsupervised machine learning using myocyte mechanical data with the highest variance yielded 2 HFrEF-PH subgroups that in turn mapped to patients with decompensated or compensated clinical RV function. This correspondence was driven by reduced calcium-activated isometric tension in decompensated clinical RV function, whereas surprisingly, many other major myocyte contractile measures including peak power and myocyte active stiffness were similarly depressed in both groups. Similar results were obtained when subgroups were first defined by clinical indices, and then myocyte mechanical properties in each group compared. To test the role of thick filament defects, myofibrillar structure was assessed by x-ray diffraction of muscle fibers. This revealed more myosin heads associated with the thick filament backbone in decompensated clinical RV function, but not compensated clinical RV function, as compared with controls. This corresponded to reduced myosin ATP turnover in decompensated clinical RV function myocytes, indicating less myosin in a crossbridge-ready disordered-relaxed (DRX) state. Altering DRX proportion (%DRX) affected peak calcium-activated tension in the patient groups differently, depending on their basal %DRX, highlighting potential roles for precision-guided therapeutics. Last, increasing myocyte preload (sarcomere length) increased %DRX 1.5-fold in controls but only 1.2-fold in both HFrEF-PH groups, revealing a novel mechanism for reduced myocyte active stiffness and by extension Frank-Starling reserve in human heart failure.

CONCLUSIONS

Although there are many RV myocyte contractile deficits in HFrEF-PH, commonly used clinical indices only detect reduced isometric calcium-stimulated force, which is related to deficits in basal and recruitable %DRX myosin. Our results support use of therapies to increase %DRX and enhance length-dependent recruitment of DRX myosin heads in such patients.

The benefits of index telephone consultations in patients referred on the two-week wait colorectal cancer pathway

INTRODUCTION

The coronavirus disease 2019 (COVID-19) pandemic led to hospitals in the UK substituting face-to-face (FtF) clinics with virtual clinic (VC) appointments. We evaluated the use of virtual two-week wait (2-ww) lower gastrointestinal (LGI) clinic appointments, conducted using telephone calls at a district general hospital in England.

METHODS

Patients undergoing index outpatient 2-ww LGI clinic assessment between 1 June 2019 and 31 October 2019 (FtF group) and 1 June 2020 and 31 October 2020 (VC group) were identified. Relevant data were obtained using electronic patient records. Compliance with national cancer waiting time targets was assessed. Environmental and financial impact analyses were performed.

RESULTS

In total, 1,531 patients were analysed (median age=70, male=852, 55.6%). Of these, 757 (49.4%) were assessed virtually via telephone; the remainder were seen FtF (n=774, 50.6%). Ninety-two (6%, VC=44, FtF=48) patients had malignant pathology and 64 (4.2%) had colorectal cancer (CRC); of these, 46 (71.9%, VC=26, FtF=20) underwent treatment with curative intent. The median waiting times to index appointment, investigation and diagnosis were significantly lower following VC assessment (p<0.001). The cancer detection rates (p=0.749), treatments received (p=0.785) and median time to index treatment for CRC patients (p=0.156) were similar. A significantly higher proportion of patients were seen within two weeks of referral in the VC group (p<0.001). VC appointments saved patients a total of 9,288 miles, 0.7 metric tonnes of CO2 emissions and £7,482.97. Taxpayers saved £80,242.00 from VCs. No formal complaints were received from patients or staff in the VC group.

CONCLUSION

Virtual 2-ww LGI clinics were effective, safe and were associated with tangible environmental and financial benefits.

Limiting Mrs2-dependent mitochondrial Mg2+ uptake induces metabolic programming in prolonged dietary stress

The most abundant cellular divalent cations, Mg2+ (mM) and Ca2+ (nM-μM), antagonistically regulate divergent metabolic pathways with several orders of magnitude affinity preference, but the physiological significance of this competition remains elusive. In mice consuming a Western diet, genetic ablation of the mitochondrial Mg2+ channel Mrs2 prevents weight gain, enhances mitochondrial activity, decreases fat accumulation in the liver, and causes prominent browning of white adipose. Mrs2 deficiency restrains citrate efflux from the mitochondria, making it unavailable to support de novo lipogenesis. As citrate is an endogenous Mg2+ chelator, this may represent an adaptive response to a perceived deficit of the cation. Transcriptional profiling of liver and white adipose reveals higher expression of genes involved in glycolysis, β-oxidation, thermogenesis, and HIF-1α-targets, in Mrs2-/- mice that are further enhanced under Western-diet-associated metabolic stress. Thus, lowering mMg2+ promotes metabolism and dampens diet-induced obesity and metabolic syndrome.

Right Ventricular Sarcomere Contractile Depression and the Role of Thick Filament Activation in Human Heart Failure with Pulmonary Hypertension

Rationale

Right ventricular (RV) contractile dysfunction commonly occurs and worsens outcomes in heart failure patients with reduced ejection fraction and pulmonary hypertension (HFrEF-PH). However, such dysfunction often goes undetected by standard clinical RV indices, raising concerns that they may not reflect aspects of underlying myocyte dysfunction.

Objective

To determine components of myocyte contractile depression in HFrEF-PH, identify those reflected by clinical RV indices, and elucidate their underlying biophysical mechanisms.

Methods and Results

Resting, calcium- and load-dependent mechanics were measured in permeabilized RV cardiomyocytes isolated from explanted hearts from 23 HFrEF-PH patients undergoing cardiac transplantation and 9 organ-donor controls. Unsupervised machine learning using myocyte mechanical data with the highest variance yielded two HFrEF-PH subgroups that in turn mapped to patients with depressed (RVd) or compensated (RVc) clinical RV function. This correspondence was driven by reduced calcium-activated isometric tension in RVd, while surprisingly, many other major myocyte contractile measures including peak power, maximum unloaded shortening velocity, and myocyte active stiffness were similarly depressed in both groups. Similar results were obtained when subgroups were first defined by clinical indices, and then myocyte mechanical properties in each group compared. To test the role of thick-filament defects, myofibrillar structure was assessed by X-ray diffraction of muscle fibers. This revealed more myosin heads associated with the thick filament backbone in RVd but not RVc, as compared to controls. This corresponded to reduced myosin ATP turnover in RVd myocytes, indicating less myosin in a cross-bridge ready disordered-relaxed (DRX) state. Altering DRX proportion (%DRX) affected peak calcium-activated tension in the patient groups differently, depending on their basal %DRX, highlighting potential roles for precision-guided therapeutics. Lastly, increasing myocyte preload (sarcomere length) increased %DRX 1.5-fold in controls but only 1.2-fold in both HFrEF-PH groups, revealing a novel mechanism for reduced myocyte active stiffness and by extension Frank-Starling reserve in human HF.

Conclusions

While there are multiple RV myocyte contractile deficits In HFrEF-PH, clinical indices primarily detect reduced isometric calcium-stimulated force related to deficits in basal and recruitable %DRX myosin. Our results support use of therapies to increase %DRX and enhance length-dependent recruitment of DRX myosin heads in such patients.

Myofibril orientation as a metric for characterizing heart disease

Myocyte disarray is a hallmark of many cardiac disorders. However, the relationship between alterations in the orientation of individual myofibrils and myofilaments to disease progression has been largely underexplored. This oversight has predominantly been because of a paucity of methods for objective and quantitative analysis. Here, we introduce a novel, less-biased approach to quantify myofibrillar and myofilament orientation in cardiac muscle under near-physiological conditions and demonstrate its superiority as compared with conventional histological assessments. Using small-angle x-ray diffraction, we first investigated changes in myofibrillar orientation at increasing sarcomere lengths in permeabilized, relaxed, wild-type mouse myocardium from the left ventricle by assessing the angular spread of the 1,0 equatorial reflection (angle σ). At a sarcomere length of 1.9 μm, the angle σ was 0.23 ± 0.01 rad, decreased to 0.19 ± 0.01 rad at a sarcomere length of 2.1 μm, and further decreased to 0.15 ± 0.01 rad at a sarcomere length of 2.3 μm (p < 0.0001). Angle σ was significantly larger in R403Q, a MYH7 hypertrophic cardiomyopathy model, porcine myocardium (0.24 ± 0.01 rad) compared with wild-type myocardium (0.14 ± 0.005 rad; p < 0.0001), as well as in human heart failure tissue (0.19 ± 0.006 rad) when compared with nonfailing samples (0.17 ± 0.007 rad; p = 0.01). These data indicate that diseased myocardium suffers from greater myofibrillar disorientation compared with healthy controls. Finally, we showed that conventional, histology-based analysis of disarray can be subject to user bias and/or sampling error and lead to false positives. Our method for directly assessing myofibrillar orientation avoids the artifacts introduced by conventional histological approaches that assess myocyte orientation and only indirectly evaluate myofibrillar orientation, and provides a precise and objective metric for phenotypically characterizing myocardium. The ability to obtain excellent x-ray diffraction patterns from frozen human myocardium provides a new tool for investigating structural anomalies associated with cardiac diseases.

CHIP phosphorylation by protein kinase G enhances protein quality control and attenuates cardiac ischemic injury

Proteotoxicity from insufficient clearance of misfolded/damaged proteins underlies many diseases. Carboxyl terminus of Hsc70-interacting protein (CHIP) is an important regulator of proteostasis in many cells, having E3-ligase and chaperone functions and often directing damaged proteins towards proteasome recycling. While enhancing CHIP functionality has broad therapeutic potential, prior efforts have all relied on genetic upregulation. Here we report that CHIP-mediated protein turnover is markedly post-translationally enhanced by direct protein kinase G (PKG) phosphorylation at S20 (mouse, S19 human). This increases CHIP binding affinity to Hsc70, CHIP protein half-life, and consequent clearance of stress-induced ubiquitinated-insoluble proteins. PKG-mediated CHIP-pS20 or expressing CHIP-S20E (phosphomimetic) reduces ischemic proteo- and cytotoxicity, whereas a phospho-silenced CHIP-S20A amplifies both. In vivo, depressing PKG activity lowers CHIP-S20 phosphorylation and protein, exacerbating proteotoxicity and heart dysfunction after ischemic injury. CHIP-S20E knock-in mice better clear ubiquitinated proteins and are cardio-protected. PKG activation provides post-translational enhancement of protein quality control via CHIP.

Identification of high-risk Dukes B colorectal cancer by microRNA expression profiling: a preliminary study

AIM

MicroRNAs (miRNAs) from tumour tissue and common gene mutations were studied to determine whether they predict the development of metastasis in patients with Dukes B colorectal cancer.

METHOD

Patients who underwent curative resection for Dukes B colorectal cancer who subsequently developed distant metastatic disease at some stage in the following 5 years ('high-risk B') were compared with case-matched controls of Dukes A, Dukes B (no metastases, 'low-risk B') and Dukes C patients without any detectable metastasis at 5 years of follow-up. MiRNAs from tumour and adjacent normal tissue and common gene mutations (KRAS, BRAF, PIK3CA) in primary cancer tissue were analysed to identify prognostic tissue markers for the development of metastasis in patients with Dukes B colorectal cancer.

RESULTS

Expression of miR-15b and miR-135b was significantly downregulated (P < 0.001) in 'high-risk B' tumours compared with Dukes A, 'low-risk B' and C without metastasis. No significant differences were noted for mutation status and the development of metastasis.

CONCLUSION

The study suggests that the development of metastasis in Dukes B tumours may be predictable based on the miRNA expression of miR-15b and miR-135b. This requires further study on a much larger cohort.

Cell-cycle dependent expression of a translocation-mediated fusion oncogene mediates checkpoint adaptation in rhabdomyosarcoma

Rhabdomyosarcoma is the most commonly occurring soft-tissue sarcoma in childhood. Most rhabdomyosarcoma falls into one of two biologically distinct subgroups represented by alveolar or embryonal histology. The alveolar subtype harbors a translocation-mediated PAX3:FOXO1A fusion gene and has an extremely poor prognosis. However, tumor cells have heterogeneous expression for the fusion gene. Using a conditional genetic mouse model as well as human tumor cell lines, we show that that Pax3:Foxo1a expression is enriched in G₂ and triggers a transcriptional program conducive to checkpoint adaptation under stress conditions such as irradiation in vitro and in vivo. Pax3:Foxo1a also tolerizes tumor cells to clinically-established chemotherapy agents and emerging molecularly-targeted agents. Thus, the surprisingly dynamic regulation of the Pax3:Foxo1a locus is a paradigm that has important implications for the way in which oncogenes are modeled in cancer cells.

Rare childhood cancers can be paradigms from which important new principles can be discerned. The childhood muscle cancer rhabdomyosarcoma is no exception, having been the focus of the original 1969 description by Drs. Li and Fraumeni of a syndrome now know to be commonly caused by underlying p53 tumor suppressor loss-of-function. In our studies using a conditional genetic mouse model of alveolar rhabdomyosarcoma in conjunction with human tumor cell lines, we have uncovered that the expression level of a translocation-mediated fusion gene, Pax3:Foxo1a, is dynamic and varies during the cell cycle. Our studies support that Pax3:Foxo1a facilitate the yeast-related process of checkpoint adaptation under stresses such as irradiation. The broader implication of our studies is that distal cis elements (promoter-influencing regions of DNA) may be critical to fully understanding the function of cancer-associated translocations.

Use of Peptide Thrombopoietin Receptor Agonist Romiplostim (Nplate) in a Case of Primary HIV-Associated Thrombocytopenia

Thrombocytopenia is frequently encountered in HIV-infected patients, and the predominant cause is primary HIV-associated thrombocytopenia (PHAT). Standard treatment regimens include optimization of antiretroviral therapy, intravenous immunoglobulin, anti-D, and corticosteroids. Retreatment due to the inability to sustain remission or inferior responses is common, and investigation into the safety and efficacy of alternative therapies is warranted. We describe novel and effective treatment of PHAT with the peptide thrombopoietin receptor agonist romiplostim in a patient with a minimal response to conventional therapy.

Dynamic and nuclear expression of PDGFRα and IGF-1R in alveolar Rhabdomyosarcoma

Since the advent of tyrosine kinase inhibitors as targeted therapies in cancer, several receptor tyrosine kinases (RTK) have been identified as operationally important for disease progression. Rhabdomyosarcoma (RMS) is a malignancy in need of new treatment options; therefore, better understanding of the heterogeneity of RTKs would advance this goal. Here, alveolar RMS (aRMS) tumor cells derived from a transgenic mouse model expressing two such RTKs, platelet-derived growth factor (PDGFR)α and insulin-like growth factor (IGF)-1R, were investigated by fluorescence-activated cell sorting (FACS). Sorted subpopulations that were positive or negative for PDGFRα and IGF-1R dynamically altered their cell surface RTK expression profiles as early as the first cell division. Interestingly, a difference in total PDGFRα expression and nuclear IGF-1R expression was conserved in populations. Nuclear IGF-1R expression was greater than cytoplasmic IGF-1R in cells with initially high cell surface IGF-1R, and cells with high nuclear IGF-1R established tumors more efficiently in vivo. RNA interference-mediated silencing of IGF-1R in the subpopulation of cells initially harboring higher cell surface and total IGF-1R resulted in significantly reduced anchorage-independent colony formation as compared with cells with initially lower cell surface and total IGF-1R expression. Finally, in accordance with the findings observed in murine aRMS, human aRMS also had robust expression of nuclear IGF-1R.

IMPLICATIONS

RTK expression status and subcellular localization dynamics are important considerations for personalized medicine.

Abstract 1747: The Pax3:Foxo1a translocation product is a cell cycle-specific modifier of the alveolar rhabdomyosarcoma tumor phenotype

BACKGROUND: Rhabdomyosarcoma is the most common soft-tissue sarcoma in childhood, which falls into one of two biologically distinct subtypes, alveolar (aRMS) or embryonal rhabdomyosarcoma. aRMS harbors a translocation-mediated PAX3:FOXO1A fusion gene and has an extremely poor prognosis.

MATERIALS AND METHODS: Primary murine aRMS cultures were obtained from the Myf6Cre, Pax3:Foxo1a, p53 conditional mouse aRMS model, in which eYFP is expressed as a second cistron in the targeted Pax3:Foxo1a-ires-eYFP allele. Limited dilution transplantation experiments were performed using Pax3:Foxo1a knockdown by siRNA of eYFP or control aRMS primary cultures. To elucidate the dynamical function of Pax3:Foxo1a, time-lapse confocal microscopy experiments, cell cycle analysis, quantitative RT-PCR, western blotting, immunohistochemistry and mRNA array were performed using murine aRMS primary cell cultures with or without Pax3:Foxo1a knockdown treated by 6 Gy irradiation, or selected for ploidy using hoechst33342 sorted cell cycle-specific cells.

RESULTS: Pax3:Foxo1a is not required for tumor repopulating ability in mouse limiting-dilution transplantation experiments. The expression level of Pax3:Foxo1a was discovered to be dynamic and varied during the cell cycle in murine aRMS primary cell cultures and human aRMS cell lines. Pax3:Foxo1a is enriched in G2 and triggers a transcriptional program conducive to checkpoint adaptation in genome-wide expression analysis and quantitative RT-PCR. Radiation resulted in a higher fraction of DNA breaks amongst mitotic cells (as represented by dual pHH3 positive, H2AX positive cells) under conditions of Pax3:Foxo1a expression compared with knockdown, suggesting that Pax3:Foxo1a facilitates G2/M transit, consistent with checkpoint adaptation.

CONCLUSION: We demonstrated that Pax3:Foxo1a does not function in tumor cell maintenance, the expression level of Pax3:Foxo1a is dynamic and varies during the cell cycle, and Pax3:Foxo1a facilitates checkpoint adaptation under stress conditions such as irradiation. Furthermore, the surprisingly dynamic regulation of the Pax3:Foxo1a locus is a paradigm that has important implications for the way in which oncogenes are modeled in cancer biology.

Citation Format: Ken Kikuchi, Simone Hettmer, M. Imran Aslam, Joel E. Michalek, Wolfram Laub, Brian P. Rubin, Amy J. Wagers, Charles Keller. The Pax3:Foxo1a translocation product is a cell cycle-specific modifier of the alveolar rhabdomyosarcoma tumor phenotype. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1747. doi:10.1158/1538-7445.AM2013-1747

Does liquid tissue adhesive increase satisfaction with wound and stoma management after surgery?

OBJECTIVE

This pilot study reviews the impact of tissue adhesive to seal skin wounds in elective large bowel resections where a stoma is fashioned.

METHOD

Patients undergoing elective colorectal resection over six-month period were prospectively evaluated for wound infections rates, length of inpatient stay and patient satisfaction with their wound and stoma management. The wounds were observed for 30 days in both inpatient and outpatient settings. A patient satisfaction questionnaire was used with respect to the stoma and wound management.

RESULTS

Fifty patients undergoing elective colorectal resection over a six-month period were prospectively evaluated. The median patient ages were 63.5 years (40-83) for males and 60 years (33-85) for females. Ninety-two per cent of the patients found their wound management satisfactory (overall satisfaction score >5, where 5 represents 'high satisfaction'). Eighty-six per cent reported a stoma management satisfaction score of >4 (where for 4 represents 'satisfaction'). Stoma site leakage was reported by 16%, but none of these developed a SSI. Two patients who had laboratory-confirmed SSI; they had an average length of inpatient stay of 18 days compared with 6.5 days for patients without SSI. .

CONCLUSION

Liquid tissue adhesive provides a flexible, water-resistant and protective coating which increases the satisfaction and ease of surgical wound and stoma management. We recommend a randomised controlled trial be conducted to evaluate these results in larger cohorts.

MicroRNAs are novel biomarkers of colorectal cancer

BACKGROUND

Recent studies have identified unique small ribonucleic acids called microRNAs (miRNAs) in colonic tumour tissue and blood that may accurately diagnose the presence of colorectal cancer and help predict disease recurrence. This review explores the potential role of these biomarkers.

METHODS

A literature search identified studies describing miRNAs in colorectal cancers. The outcomes of interest included diagnosis, progression and recurrence of disease, and future therapy.

RESULTS

Overexpression and silencing of specific miRNAs are associated with the development and progression of colorectal cancer. Such a role in oncogenesis suggest that miRNAs may be important targets for gene therapies. Differential expression of specific miRNAs in tissues and blood offers the prospect of their use in early detection and screening for colorectal cancer. MiRNAs are implicated in metastasis and cytotoxic drug resistance. Their manipulation has potential in both prevention of recurrence and palliation.

CONCLUSION

The miRNAs expression profile in tissue and blood has potential for their use in the detection, screening and surveillance of colorectal cancer. Furthermore, miRNAs may be targeted by gene therapy to treat colorectal cancer.