Extended ischemic time (>15 hours) using controlled hypothermic storage in lung transplantation: A multicenter experience

Static ice storage has long been the standard-of-care for lung preservation, although freezing injury limits ischemic time (IT). Controlled hypothermic storage (CHS) at elevated temperature could safely extend IT. This retrospective analysis assesses feasibility and safety of CHS with IT > 15 hours. Three lung transplant (LuTx) centers (April-October 2023) included demographics, storage details, IT, and short-term outcome from 13 LuTx recipients (8 male, 59 years old). Donor lungs were preserved in a portable CHS device at 7 (5-9.3)°C. Indication was overnight bridging and/or long-distance transport. IT of second-implanted lung was 17.3 (15.1-22) hours. LuTx were successful, 4/13 exhibited primary graft dysfunction grade 3 within 72 hours and 0/13 at 72 hours. Post-LuTx mechanical ventilation was 29 (7-442) hours. Intensive care unit stay was 9 (5-28) and hospital stay 30 (16-90) days. Four patients needed postoperative extracorporeal membrane oxygenation (ECMO). One patient died (day 7) following malpositioning of an ECMO cannula. This multicenter experience demonstrates the possibility of safely extending IT > 15 hours by CHS.

Is Transplantation With Coronavirus Disease 2019-Positive Donor Lungs Safe? A US Nationwide Analysis

BACKGROUND

Since the beginning of the pandemic, coronavirus disease 2019 (COVID-19) has caused debilitating lung failure in many patients. Practitioners have understandably been hesitant to use lungs from donors with COVID-19 for transplantation. This study aimed to analyze the characteristics and short-term outcomes of lung transplantation from donors with recent positive COVID-19 testing results.

METHODS

Lung transplantations performed between January 2020 and June 2022 were queried from the United Network for Organ Sharing database. Pediatric, multiorgan, and repeat lung transplantations were excluded. Propensity scoring matched recipients of lungs from donors with recent positive COVID-19 testing results to recipients of lungs from donors with negative COVID-19 testing results, and comparisons of 30-day mortality, 3-month mortality, and perioperative outcomes were performed.

RESULTS

A total of 5270 patients underwent lung transplantation during the study dates, including 51 patients who received lungs from donors with recent positive COVID-19 testing results. Forty-five recipients of lungs from donors with recent positive COVID-19 testing results were matched with 135 recipients of lungs from donors with negative COVID-19 testing results. After matching, there was no difference in 30-day (log-rank P = .42) and 3-month (log-rank P = .42) mortality. The incidence of other perioperative complications was similar between the groups.

CONCLUSIONS

The 30-day and 3-month survival outcomes were similar between recipients of lungs from donors with recent positive COVID-19 testing results and recipients of lungs from donors with negative COVID-19 testing results. This finding suggests that highly selected COVID-19-positive donors without evidence of active infection may be safely considered for lung transplantation. Further studies should explore long-term outcomes to provide reassurance about the safety of this practice.

Preemptive antiviral therapy in lung transplantation from hepatitis C donors results in a rapid and sustained virologic response

Objective

The study objective was to assess the safety and efficacy of a preemptive direct-acting antiviral therapy in lung transplants from hepatitis C virus donors to uninfected recipients.

Methods

This study is a prospective, open-label, nonrandomized, pilot trial. Recipients of hepatitis C virus nucleic acid test positive donor lungs underwent preemptive direct-acting antiviral therapy with glecaprevir 300 mg/pibrentasvir 120 mg for 8 weeks from January 1, 2019, to December 31, 2020. Recipients of nucleic acid test positive lungs were compared with recipients of lungs from nucleic acid test negative donors. Primary end points were Kaplan-Meier survival and sustained virologic response. Secondary outcomes included primary graft dysfunction, rejection, and infection.

Results

Fifty-nine lung transplantations were included: 16 nucleic acid test positive and 43 nucleic acid test negative. Twelve nucleic acid test positive recipients (75%) developed hepatitis C virus viremia. Median time to clearance was 7 days. All nucleic acid test positive patients had undetectable hepatitis C virus RNA by week 3, and all alive patients (n = 15) remained negative during follow-up with 100% sustained virologic response at 12 months. One nucleic acid test positive patient died of primary graft dysfunction and multiorgan failure. Three of 43 nucleic acid test negative patients (7%) had hepatitis C virus antibody positive donors. None of them developed hepatitis C virus viremia. One-year survival was 94% for nucleic acid test positive recipients and 91% for nucleic acid test negative recipients. There was no difference in primary graft dysfunction, rejection, or infection. One-year survival for nucleic acid test positive recipients was similar to a historical cohort of the Scientific Registry of Transplant Recipients (89%).

Conclusions

Recipients of hepatitis C virus nucleic acid test positive lungs have similar survival as recipients of nucleic acid test negative lungs. Preemptive direct-acting antiviral therapy results in rapid viral clearance and sustained virologic response at 12 months. Preemptive direct-acting antiviral may partially prevent hepatitis C virus transmission.

Impact of Moderate Aortic Stenosis in Patients With Heart Failure With Reduced Ejection Fraction

BACKGROUND

Afterload from moderate aortic stenosis (AS) may contribute to adverse outcomes in patients with heart failure with reduced ejection fraction (HFrEF).

OBJECTIVES

The authors evaluated clinical outcomes in patients with HFrEF and moderate AS relative to those without AS and with severe AS.

METHODS

Patients with HFrEF, defined by left ventricular ejection fraction (LVEF) <50% and no, moderate, or severe AS were retrospectively identified. The primary endpoint, defined as a composite of all-cause mortality and heart failure (HF) hospitalization, was compared across groups and within a propensity score-matched cohort.

RESULTS

We included 9,133 patients with HFrEF, of whom 374 and 362 had moderate and severe AS, respectively. Over a median follow-up time of 3.1 years, the primary outcome occurred in 62.7% of patients with moderate AS vs 45.9% with no AS (P < 0.0001); rates were similar with severe and moderate AS (62.0% vs 62.7%; P = 0.68). Patients with severe AS had a lower incidence of HF hospitalization (36.2% vs 43.6%; P < 0.05) and were more likely to undergo AVR within the follow-up period. Within a propensity score-matched cohort, moderate AS was associated with an increased risk of HF hospitalization and mortality (HR: 1.24; 95% CI: 1.04-1.49; P = 0.01) and fewer days alive outside of the hospital (P < 0.0001). Aortic valve replacement (AVR) was associated with improved survival (HR: 0.60; CI: 0.36-0.99; P < 0.05).

CONCLUSIONS

In patients with HFrEF, moderate AS is associated with increased rates of HF hospitalization and mortality. Further investigation is warranted to determine whether AVR in this population improves clinical outcomes.

Building a successful minimally invasive mitral valve repair program before introducing the robotic approach: The Massachusetts General Hospital experience

Background

Patients with mitral valve prolapse (MVP) requiring surgical repair (MVr) are increasingly operated using minimally invasive strategies. Skill acquisition may be facilitated by a dedicated MVr program. We present here our institutional experience in establishing minimally invasive MVr (starting in 2014), laying the foundation to introduce robotic MVr.

Methods

We reviewed all patients that had undergone MVr for MVP via sternotomy or mini-thoracotomy between January 2013 and December 2020 at our institution. In addition, all cases of robotic MVr between January 2021 and August 2022 were analyzed. Case complexity, repair techniques, and outcomes are presented for the conventional sternotomy, right mini-thoracotomy and robotic approaches. A subgroup analysis comparing only isolated MVr cases via sternotomy vs. right mini-thoracotomy was conducted using propensity score matching.

Results

Between 2013 and 2020, 799 patients were operated for native MVP at our institution, of which 761 (95.2%) received planned MVr (263 [34.6%] via mini-thoracotomy) and 38 (4.8%) received planned MV replacement. With increasing proportions of minimally invasive procedures (2014: 14.8%, 2020: 46.5%), we observed a continuous growth in overall institutional volume of MVP (n = 69 in 2013; n = 127 in 2020) and markedly improved institutional rates of successful MVr, with 95.4% in 2013 vs. 99.2% in 2020. Over this period, a higher complexity of cases were treated minimally-invasively and increased use of neochord implantation ± limited leaflet resection was observed. Patients operated minimally invasively had longer aortic cross-clamp times (94 vs. 88 min, p = 0.001) but shorter ventilation times (4.4 vs. 4.8 h, p = 0.002) and hospital stays (5 vs. 6 days, p < 0.001) than those operated via sternotomy, with no significant differences in other outcome variables. A total of 16 patients underwent robotically assisted MVr with successful repair in all cases.

Conclusion

A focused approach towards minimally invasive MVr has transformed the overall MVr strategy (incision; repair techniques) at our institution, leading to a growth in MVr volume and improved repair rates without significant complications. On this foundation, robotic MVr was first introduced at our institution in 2021 with excellent outcomes. This emphasizes the importance of building a competent team to perform these challenging operations, especially during the initial learning curve.

Induction therapy in lung transplantation: A contemporary analysis of trends and outcomes

OBJECTIVES

We provide a contemporary consideration of long-term outcomes and trends of induction therapy use following lung transplantation in the United States.

METHODS

We reviewed the United Network for Organ Sharing registry from 2006 to 2018 for first-time, adult, lung-only transplant recipients. Long-term survival was compared between induction classes (Interleukin-2 inhibitors, monoclonal or polyclonal cell-depleting agents, and no induction therapy). A 1:1 propensity score match was performed, pairing patients who received basiliximab with similar risk recipients who did not receive induction therapy. Outcomes in matched populations were compared using Cox, Kaplan-Meier and Logistic regression modeling.

MEASUREMENTS AND MAIN RESULTS

22 025 recipients were identified; 8003 (36.34%) were treated with no induction therapy, 11 045 (50.15%) with basiliximab, 1556 (7.06%) with alemtuzumab and 1421 (6.45%) with anti-thymocyte globulin. Compared with those who received no induction, patients receiving basiliximab, alemtuzumab or anti-thymocyte globulin were found on multivariable Cox-regression analyses to have lower long-term mortality (all p < .05). Following propensity score matching of basiliximab and no induction populations, analyses demonstrated a statistically significant association between basiliximab use and long- term survival (p < .001). Basiliximab was also associated with a lower risk of acute rejection (p < .001) and renal failure (p = .002).

CONCLUSION

Induction therapy for lung transplant recipients-specifically basiliximab-is associated with improved long-term survival and a lower risk of renal failure or acute rejection.

Patient- and Process-Related Contributors to the Underuse of Aortic Valve Replacement and Subsequent Mortality in Ambulatory Patients With Severe Aortic Stenosis

Background

Many patients with severe aortic stenosis (AS) and an indication for aortic valve replacement (AVR) do not undergo treatment. The reasons for this have not been well studied in the transcatheter AVR era. We sought to determine how patient‐ and process‐specific factors affected AVR use in patients with severe AS.

Methods and Results

We identified ambulatory patients from 2016 to 2018 demonstrating severe AS, defined by aortic valve area ≤1.0 cm². Propensity scoring analysis with inverse probability of treatment weighting was used to evaluate associations between predictors and the odds of undergoing AVR at 365 days and subsequent mortality at 730 days. Of 324 patients with an indication for AVR (79.3±9.7 years, 57.4% men), 140 patients (43.2%) did not undergo AVR. The odds of AVR were reduced in patients aged >90 years (odds ratio [OR], 0.24 [95% CI, 0.08–0.69]; P=0.01), greater comorbid conditions (OR, 0.88 per 1‐point increase in Combined Comorbidity Index [95% CI, 0.79–0.97]; P=0.01), low‐flow, low‐gradient AS with preserved left ventricular ejection fraction (OR, 0.11 [95% CI, 0.06–0.21]), and low‐gradient AS with reduced left ventricular ejection fraction (OR, 0.18 [95% CI, 0.08–0.40]) and were increased if the transthoracic echocardiogram ordering provider was a cardiologist (OR, 2.46 [95% CI, 1.38–4.38]). Patients who underwent AVR gained an average of 85.8 days of life (95% CI, 40.9–130.6) at 730 days.

Conclusions

The proportion of ambulatory patients with severe AS and an indication for AVR who do not receive AVR remains significant. Efforts are needed to maximize the recognition of severe AS, especially low‐gradient subtypes, and to encourage patient referral to multidisciplinary heart valve teams.

Trends in Utilization of Aortic Valve Replacement for Severe Aortic Stenosis

BACKGROUND

Despite the rapid growth of aortic valve replacement (AVR) for aortic stenosis (AS), limited data suggest symptomatic severe AS remains undertreated.

OBJECTIVES

This study sought to investigate temporal trends in AVR utilization among patients with a clinical indication for AVR.

METHODS

Patients with severe AS (aortic valve area <1 cm²) on transthoracic echocardiograms from 2000 to 2017 at 2 large academic medical centers were classified based on clinical guideline indications for AVR and divided into 4 AS subgroups: high gradient with normal left ventricular ejection fraction (LVEF) (HG-NEF), high gradient with low LVEF (HG-LEF), low gradient with normal LVEF (LG-NEF), and low gradient with low LVEF (LG-LEF). Utilization of AVR was examined and predictors identified.

RESULTS

Of 10,795 patients, 6,150 (57%) had an indication or potential indication for AVR, of whom 2,977 (48%) received AVR. The frequency of AVR varied by AS subtype with LG groups less likely to receive an AVR (HG-NEF: 70%, HG-LEF: 53%, LG-NEF: 32%, LG-LEF: 38%, P < 0.001). AVR volumes grew over the 18-year study period but were paralleled by comparable growth in the number of patients with an indication for AVR. In patients with a Class I indication, younger age, coronary artery disease, smoking history, higher hematocrit, outpatient index transthoracic echocardiogram, and LVEF ≥0.5 were independently associated with an increased likelihood of receiving an AVR. AVR was associated with improved survival in each AS-subgroup.

CONCLUSIONS

Over an 18-year period, the proportion of patients with an indication for AVR who did not receive AVR has remained substantial despite the rapid growth of AVR volumes.

Ascending aorta, aortic arch and supra-aortic vessels rupture in blunt thoracic trauma

Surgical strategy and long-term outcomes of patients with rupture of the ascending aorta, aortic arch and supra-aortic vessels following blunt thoracic trauma have been rarely reported. We reviewed our institutional experience between 1995 and 2016. We identified 2 patients with an innominate artery ruptures, 2 with an aortic arch ruptures and 1 with an ascending aorta rupture; all were induced by the posterior displacement of the anterior chest wall. All patients underwent open surgical repair. Cardiopulmonary bypass with antegrade cerebral perfusion was required in 2 cases. All patients were alive at the end of the follow-up (median 18 months; from 3 to 180 months) including 1 patient with cortical blindness.

Minimally Invasive Cardiovascular Surgery: Incisions and Approaches

Throughout the modern era of cardiac surgery, most operations have been performed via median sternotomy with cardiopulmonary bypass. This paradigm is changing, however, as cardiovascular surgery is increasingly adopting minimally invasive techniques. Advances in patient evaluation, instrumentation, and operative technique have allowed surgeons to perform a wide variety of complex operations through smaller incisions and, in some cases, without cardiopulmonary bypass. With patients desiring less invasive operations and the literature supporting decreased blood loss, shorter hospital length of stay, improved postoperative pain, and better cosmesis, minimally invasive cardiac surgery should be widely practiced. Here, we review the incisions and approaches currently used in minimally invasive cardiovascular surgery.

Injuries to the Aorta, Aortic Annulus, and Left Ventricle During Transcatheter Aortic Valve Replacement

The experience with transcatheter aortic valve replacement is increasing worldwide; however, the incidence of potentially catastrophic cardiac or aortic complications has not decreased. In most cases, significant injuries to the aorta, aortic valve annulus, and left ventricle require open surgical repair. However, the transcatheter aortic valve replacement patient presents a unique challenge as many patients are at high or prohibitive surgical risk and, therefore, an open surgical procedure may not be feasible or appropriate. Consequently, prevention of these potentially catastrophic injuries is vital, and practitioners need to understand when open surgical repair is required and when alternative management strategies can be used. The goal of this article is to provide an overview of current management and prevention strategies for major complications involving the aorta, aortic valve annulus, and left ventricle.

Abnormal pulmonary endothelial cells may underlie the enigmatic pathogenesis of chronic thromboembolic pulmonary hypertension

BACKGROUND

Chronic thromboembolic pulmonary hypertension results from chronic mechanical obstruction of the pulmonary arteries after acute venous thromboembolism. However, the mechanisms that result in the progression from unresolved thrombus to fibrotic vascular remodeling are unknown. We hypothesized that pulmonary artery endothelial cells contribute to this phenomenon via paracrine growth factor and cytokine signaling.

METHODS

Using enzyme-linked immunosorbent assay and cell migration assays, we investigated the circulating growth factors and cytokines of chronic thromboembolic pulmonary hypertension patients as well as the cross talk between pulmonary endothelial cells and pulmonary artery smooth muscle cells and monocytes from patients with chronic thromboembolic pulmonary hypertension in vitro.

RESULTS

Culture medium from the pulmonary endothelial cells of chronic thromboembolic pulmonary hypertension patients contained higher levels of growth factors (fibroblast growth factor 2), inflammatory cytokines (interleukin 1β, interleukin 6, monocyte chemoattractant protein 1), and cell adhesion molecules (vascular cell adhesion molecule 1 and intercellular adhesion molecule 1). Furthermore, exposure to the culture medium of pulmonary endothelial cells from patients with chronic thromboembolic pulmonary hypertension elicited marked pulmonary artery smooth muscle cell growth and monocyte migration.

CONCLUSIONS

These findings implicate pulmonary endothelial cells as key regulators of pulmonary artery smooth muscle cell and monocyte behavior in chronic thromboembolic pulmonary hypertension and suggest a potential mechanism for the progression from unresolved thrombus to fibrotic vascular remodeling.

Outcomes After Resection of T4 Non-Small Cell Lung Cancer Using Cardiopulmonary Bypass

BACKGROUND

Complete, en bloc resection offers the greatest chance of long-term survival in T4 non-small cell lung cancer (NSCLC). The use of cardiopulmonary bypass (CPB) to achieve an en bloc resection is controversial because of potentially increased bleeding, lung dysfunction, and tumor dissemination. We reviewed our institutional experience to assess CPB's effect on survival.

METHODS

All patients who underwent resection for T4 NSCLC at our institution between 1980 and 2013 were retrospectively reviewed and stratified according to whether they did (CPB group, n = 20) or did not (No CPB group, n = 355) undergo CPB. Primary outcomes of interest were overall and disease-free survival and perioperative complications.

RESULTS

Baseline characteristics and medical therapy were similar between the groups. Median overall survival for all patients was 31 months, with 1-, 3-, 5-, and 10-year survival of 73%, 47%, 40%, and 26%, respectively. Median disease-free survival for all patients was 19 months, with 1-, 3-, 5-, and 10-year disease-free survival of 61%, 40%, 33%, and 21%, respectively. No difference was found in overall or disease-free survival at 1, 3, 5, and 10 years between the No CPB and CPB groups (p = 0.89 and p = 0.88). In addition, no differences were found in the rates of major perioperative complications.

CONCLUSIONS

The use of CPB allows for complete, en bloc resection in otherwise inoperable patients with T4 NSCLC and offers similar overall and disease-free survival to patients resected without CPB. All thoracic surgeons who manage T4 NSCLC should consider the use of CPB if it is necessary to achieve a complete, en bloc resection.

Iron regulatory protein-1 protects against mitoferrin-1-deficient porphyria

Mitochondrial iron is essential for the biosynthesis of heme and iron-sulfur ([Fe-S]) clusters in mammalian cells. In developing erythrocytes, iron is imported into the mitochondria by MFRN1 (mitoferrin-1, SLC25A37). Although loss of MFRN1 in zebrafish and mice leads to profound anemia, mutant animals showed no overt signs of porphyria, suggesting that mitochondrial iron deficiency does not result in an accumulation of protoporphyrins. Here, we developed a gene trap model to provide in vitro and in vivo evidence that iron regulatory protein-1 (IRP1) inhibits protoporphyrin accumulation. Mfrn1(+/gt);Irp1(-/-) erythroid cells exhibit a significant increase in protoporphyrin levels. IRP1 attenuates protoporphyrin biosynthesis by binding to the 5'-iron response element (IRE) of alas2 mRNA, inhibiting its translation. Ectopic expression of alas2 harboring a mutant IRE, preventing IRP1 binding, in Mfrn1(gt/gt) cells mimics Irp1 deficiency. Together, our data support a model whereby impaired mitochondrial [Fe-S] cluster biogenesis in Mfrn1(gt/gt) cells results in elevated IRP1 RNA-binding that attenuates ALAS2 mRNA translation and protoporphyrin accumulation.

ATP-binding cassette B10 regulates early steps of heme synthesis

RATIONALE

Heme plays a critical role in gas exchange, mitochondrial energy production, and antioxidant defense in cardiovascular system. The mitochondrial transporter ATP-binding cassette (ABC) B10 has been suggested to export heme out of the mitochondria and is required for normal hemoglobinization of erythropoietic cells and protection against ischemia-reperfusion injury in the heart; however, its primary function has not been established.

OBJECTIVE

The aim of this study was to identify the function of ABCB10 in heme synthesis in cardiac cells.

METHODS AND RESULTS

Knockdown of ABCB10 in cardiac myoblasts significantly reduced heme levels and the activities of heme-containing proteins, whereas supplementation with δ-aminolevulinic acid reversed these defects. Overexpression of mitochondrial δ-aminolevulinic acid synthase 2, the rate-limiting enzyme upstream of δ-aminolevulinic acid export, failed to restore heme levels in cells with ABCB10 downregulation. ABCB10 and heme levels were increased by hypoxia, and reversal of ABCB10 upregulation caused oxidative stress and cell death. Furthermore, ABCB10 knockdown in neonatal rat cardiomyocytes resulted in a significant delay of calcium removal from the cytoplasm, suggesting a relaxation defect. Finally, ABCB10 expression and heme levels were altered in failing human hearts and mice with ischemic cardiomyopathy.

CONCLUSIONS

ABCB10 plays a critical role in heme synthesis pathway by facilitating δ-aminolevulinic acid production or export from the mitochondria. In contrast to previous reports, we show that ABCB10 is not a heme exporter and instead is required for the early mitochondrial steps of heme biosynthesis.

Mitochondrial Atpif1 regulates haem synthesis in developing erythroblasts

Defects in the availability of haem substrates or the catalytic activity of the terminal enzyme in haem biosynthesis, ferrochelatase (Fech), impair haem synthesis and thus cause human congenital anaemias. The interdependent functions of regulators of mitochondrial homeostasis and enzymes responsible for haem synthesis are largely unknown. To investigate this we used zebrafish genetic screens and cloned mitochondrial ATPase inhibitory factor 1 (atpif1) from a zebrafish mutant with profound anaemia, pinotage (pnt (tq209)). Here we describe a direct mechanism establishing that Atpif1 regulates the catalytic efficiency of vertebrate Fech to synthesize haem. The loss of Atpif1 impairs haemoglobin synthesis in zebrafish, mouse and human haematopoietic models as a consequence of diminished Fech activity and elevated mitochondrial pH. To understand the relationship between mitochondrial pH, redox potential, [2Fe-2S] clusters and Fech activity, we used genetic complementation studies of Fech constructs with or without [2Fe-2S] clusters in pnt, as well as pharmacological agents modulating mitochondrial pH and redox potential. The presence of [2Fe-2S] cluster renders vertebrate Fech vulnerable to perturbations in Atpif1-regulated mitochondrial pH and redox potential. Therefore, Atpif1 deficiency reduces the efficiency of vertebrate Fech to synthesize haem, resulting in anaemia. The identification of mitochondrial Atpif1 as a regulator of haem synthesis advances our understanding of the mechanisms regulating mitochondrial haem homeostasis and red blood cell development. An ATPIF1 deficiency may contribute to important human diseases, such as congenital sideroblastic anaemias and mitochondriopathies.

A severe case of cefoxitin-induced immune hemolytic anemia

Drug-induced immune hemolytic anemia is a rare but underdiagnosed and potentially fatal condition. We report a case of severe hemolytic anemia induced by cefoxitin in a 45-year-old woman admitted with menometrorrhagia. Hemoglobin levels reached a nadir of 4.7 g/dl approximately 72 h after cefoxitin initiation, and hemolysis resolved when cefoxitin was discontinued and prednisone 1 mg/kg was initiated. A transfusion reaction workup revealed no abnormalities. Direct antiglobulin testing was weakly positive with anti-C3. The patient's plasma and RBC eluate reacted with cefoxitin-treated RBCs but not with untreated RBCs in the presence or absence of cefoxitin.

In vivo inactivation of MASTL kinase results in thrombocytopenia

OBJECTIVE

A missense mutation in the microtubule-associated serine/threonine-like kinase gene (MASTL, FLJ14813) on human chromosome 10 was previously linked to a novel form of autosomal dominant inherited thrombocytopenia in a single pedigree. The mutation results in an amino acid change from glutamic acid at position 167 to aspartic acid and segregates perfectly with thrombocytopenic individuals within this extended family. The phenotype is characterized by mild thrombocytopenia with an average platelet count of 60,000 platelets per microliter of blood. We wanted to determine the expression and localization of MASTL, as well as its role in developing thrombocytes using an in vivo model system.

MATERIALS AND METHODS

Northern blot analysis allowed us to examine expression patterns. Morpholino knockdown assays in zebrafish (Danio rerio) were employed to determine in vivo contribution to thrombocyte development. Transient expression in baby hamster kidney cells resulted in localization of both the wild-type and E167D mutant forms of MASTL kinase to the nucleus.

RESULTS

Northern blot analysis indicates that MASTL messenger RNA is restricted in its expression to hematopoietic and cancer cell lines. A transient knockdown of MASTL in zebrafish results in deficiency of circulating thrombocytes. Transient expression of recombinant MASTL kinase in vitro demonstrates localization to the nucleus.

CONCLUSIONS

Functional studies presented here demonstrate a direct relationship between transient knockdown of MASTL kinase gene expression and reduction of circulating thrombocytes in zebrafish. This transient knockdown of MASTL in zebrafish correlates with a decrease in the expression of the thrombopoietin receptor, c-mpl, and the CD41 platelet adhesion protein, GpIIb, but has no effect on essential housekeeping zebrafish gene, EF1alpha.

montalcino, A zebrafish model for variegate porphyria

OBJECTIVE

Inherited or acquired mutations in the heme biosynthetic pathway leads to a debilitating class of diseases collectively known as porphyrias, with symptoms that can include anemia, cutaneous photosensitivity, and neurovisceral dysfunction. In a genetic screen for hematopoietic mutants, we isolated a zebrafish mutant, montalcino (mno), which displays hypochromic anemia and porphyria. The objective of this study was to identify the defective gene and characterize the phenotype of the zebrafish mutant.

MATERIALS AND METHODS

Genetic linkage analysis was utilized to identify the region harboring the mno mutation. Candidate gene analysis together with reverse transcriptase polymerase chain reaction was utilized to identify the genetic mutation, which was confirmed via allele-specific oligo hybridizations. Whole mount in situ hybridizations and o-dianisidine staining were used to characterize the phenotype of the mno mutant. mRNA and morpholino microinjections were performed to phenocopy and/or rescue the mutant phenotype.

RESULTS

Homozygous mno mutant embryos have a defect in the protoporphyrinogen oxidase (ppox) gene, which encodes the enzyme that catalyzes the oxidation of protoporphyrinogen. Homozygous mutant embryos are deficient in hemoglobin, and by 36 hours post-fertilization are visibly anemic and porphyric. The hypochromic anemia of mno embryos was partially rescued by human ppox, providing evidence for the conservation of function between human and zebrafish ppox.

CONCLUSION

In humans, mutations in ppox result in variegate porphyria. At present, effective treatment for acute attacks requires the administration intravenous hemin and/or glucose. Thus, mno represents a powerful model for investigation, and a tool for future screens aimed at identifying chemical modifiers of variegate porphyria.