636 LOOKING AT THE BIGGER PICTURE: FROM ACUTE MYOCARDITIS TO THE DIAGNOSIS OF A MULTISYSTEMIC DISEASE

A 49-year-old man without cardiovascular risk factors, recently diagnosed of asthma and rino-sinusal polyposis, entered the Emergency Department for chest pain, shortness of breath and non-productive cough. The patient was in stable conditions. Laboratory exams showed eosinophilic leucocytosis (WBC 33.000/sqmm, 60% eosinophils) and a mild elevation of C-reactive protein (CRP 2,2 mg/dL). ECG showed a sinus rhythm with flat T-waves in the antero-lateral leads. Troponin values were high but not suggestive of acute myocardial damage (9900 - 9700 ng/L). Echocardiography showed normal biventricular volumes with moderately depressed left ventricular ejection fraction (40%), hypokinesia of the antero-lateral wall in the mid-apical segments and mild pericardial effusion.

During the hospital stay he developed progressive respiratory failure, and he was transferred to a tertiary center to perform an endomyocardial biopsy (EMB) in the suspicion of acute myocarditis. EMB showed multifocal interstitial and sub-endocardial inflammatory infiltrates (predominantly eosinophils) with foci of myocellular damage, small vessels wall inflammation with hypertrophy of the muscular tunica. The overall picture was consistent with diffuse moderate eosinophilic myocarditis with small vessels vasculitis. The right heart cath performed in the same procedure and during diuretic therapy showed a normal hemodynamic profile (RAP 5 mmHg, PCWP 13 mmHg, CI 3,7 L/min/sqm). The patient was treated with high dose steroids, first intravenously (methylprednisolone 125 mg/day for three days), then orally (prednisone 80 mg/day) in slow decalage until a maintenance dose of 12.5 mg daily.

The recent-onset of asthma with hyper-eosinophilia and rhino-sinus-bronchial syndrome in the light of the present cardiac condition was consistent with eosinophilic granulomatosis with polyangiitis (EGPA). Chest CT showed two areas of ground glass at the left superior and right superior lobes. Other potential haematological and infective causes of hyper eosinophilia and viral causes of myocarditis were ruled out.

After the treatment, his clinical conditions improved, ECG was completely normalized, left ventricular systolic function improved (LVEF 50%) and eosinophil count was significantly reduced (Eosinophils 830/sqmm, 8,9%), whereas CT showed resolution of the lung infiltrates.

One month after discharge, the patient was still asymptomatic. Cardiac MRI showed normal biventricular ejection fraction (LVEF 55%) with circumferential subendocardial fibrosis involving only the left ventricle. EMB showed a complete resolution of the inflammatory infiltrates and of the vasculitic aspects. Eosinophil count was elevated (5660/sqmm, 36%). Therefore, steroidal dose was raised to 50 mg/day. After rheumatologic evaluation, a steroidal sparing strategy with cyclophosphamide and anti-IL5 antibody Mepolizumab was adopted, with good laboratory response. Three months later, cardiac MRI showed no signs of active disease. No further EMB was scheduled.

Through the presentation of this unusual cause of acute myocarditis, we want to underscore the importance of an early referral to a tertiary level center of patients with suspected myocarditis and reduced systolic function and the usefulness of histology to guide medical therapy in specific forms of myocarditis that can lead to a potential complete recovery.

Fluorescence correlation spectroscopy analysis of the hydrophobic interactions of protein 4.1 with phosphatidyl serine liposomes

Fluorescence correlation spectroscopy (FCS) was applied to examine the interactions between a protein and a membrane lipid. The protein 4.1-phosphatidyl serine (PS) interactions served as the model system to demonstrate the membrane lipid-protein interactions. This protein was labeled with rhodamine and its interactions with PS-liposomes were measured by FCS. The present results clearly demonstrated that a small protein molecule, protein 4.1, interacts specifically with a large particle, a PS-liposome. This interaction appears to be hydrophobic and not electrostatic, since the bound protein 4.1 did not dissociate in solution and was specifically released from PS-liposomes by treatment with phospholipase A(2) (PLA(2)). In the present study, using FCS we could demonstrate that the serine residue of PS is required for protein 4.1 to bind to PS-liposomes and that the bound protein 4.1 is closely associated with the fatty acid of the PS molecule in the liposomes.

Structural and functional characterization of protein 4.1R-phosphatidylserine interaction: potential role in 4.1R sorting within cells

Erythrocyte protein 4.1R is a multifunctional protein that binds to various membrane proteins and to phosphatidylserine. In the present study, we report two important observations concerning 4.1R-phosphatidylserine interaction. Biochemically, a major finding of the present study is that 4.1R binding to phosphatidylserine appears to be a two-step process in which 4.1R first interacts with serine head group of phosphatidylserine through the positively charged amino acids YKRS and subsequently forms a tight hydrophobic interaction with fatty acid moieties. 4.1R failed to dissociate from phosphatidylserine liposomes under high ionic strength but could be released specifically by phospholipase A(2) but not by phospholipase C or D. Biochemical analyses showed that acyl chains were associated with 4.1R released by phospholipase A(2). Importantly, the association of acyl chains with 4.1R impaired its ability to interact with calmodulin, band 3, and glycophorin C. Removal of acyl chains restored 4.1R binding. These data indicate that acyl chains of phosphatidylserine play an important role in its interaction with 4.1R and on 4.1R function. In terms of biological significance, we have obtained evidence that 4.1R-phosphatidylserine interaction may play an important role in cellular sorting of 4.1R.

Regulation of erythrocyte ghost membrane mechanical stability by chlorpromazine

Chlorpromazine (CPZ), a widely used tranquilizer, is known to induce stomatocytic shape changes in human erythrocytes. However, the effect of CPZ on membrane mechanical properties of erythrocyte membranes has not been documented. In the present study we show that CPZ induces a dose-dependent increase in mechanical stability of erythrocyte ghost membrane. Furthermore, we document that spectrin specifically binds to CPZ intercalated into inside-out vesicles depleted of all peripheral proteins. These findings imply that CPZ-induced mechanical stabilization of the erythrocyte ghost membranes may be mediated by direct binding of spectrin to the bilayer. Membrane active drugs that partition into lipid bilayer can thus induce cytoskeletal protein interactions with the membrane and modulate membrane material properties.

A cysteine protease activity from Plasmodium falciparum cleaves human erythrocyte ankyrin

The malaria parasite Plasmodium falciparum undergoes distinct morphologic changes during its 48-h life cycle inside human red blood cells. Parasite proteinases appear to play important roles at all stages of the erythrocytic cycle of human malaria. Proteases involved in erythrocyte rupture and invasion are possibly required to breakdown erythrocyte membrane skeleton. To identify such proteases, soluble cytosolic extract of isolated trophozoites/schizonts was incubated with erythrocyte membrane ghosts or spectrin-actin depleted inside-out vesicles, which were then analyzed by SDS-PAGE. In both cases, a new protein band of 155 kDa was detected. The N-terminal peptide sequencing established that the 155 kDa band represents truncated ankyrin. Immunoblot analysis using defined monoclonal antibodies confirmed that ankyrin was cleaved at the C-terminus. While the enzyme preferentially cleaved ankyrin, degradation of protein 4.1 was also observed at high concentrations of the enzyme. The optimal activity of the purified enzyme, using ankyrin as substrate, was observed at pH 7.0-7.5, and the activity was strongly inhibited by standard inhibitors of cysteine proteinases (cystatin, NEM, leupeptin, E-64 and MDL 28 170), but not by inhibitors of aspartic (pepstatin) or serine (PMSF, DFP) proteinases. Furthermore, we demonstrate that protease digestion of ankyrin substantially reduces its interaction with ankyrin-depleted membrane vesicles. Ektacytometric measurements showed a dramatic increase in the rate of fragmentation of ghosts after treatment with the protease. Although the role of ankyrin cleavage in vivo remains to be determined, based on our findings we postulate that the parasite-derived cysteine protease activity cleaves host ankyrin thus weakening the ankyrin-band 3 binding interactions and destabilizing the erythrocyte membrane skeleton, which, in turn, facilitates parasite release. Further characterization of the enzyme may lead to the development of novel antimalarial drugs.

Modulation of band 3-ankyrin interaction by protein 4.1. Functional implications in regulation of erythrocyte membrane mechanical properties

Protein 4.1 is an important structural component of the erythrocyte membrane. In contrast to our detailed understanding of the role of protein 4.1 in regulating membrane mechanical properties through modulation of spectrin-actin interaction, very little is known regarding the functional implications of protein 4.1 interaction with band 3. In the present study, we explored the potential role of protein 4.1-band 3 interaction in modulating membrane mechanical properties. Based on recent studies which identified the sequence motif IRRRY in band 3 as the protein 4.1 interacting domain, we studied the functional consequences of specific dissociation of band 3-protein 4.1 interaction by the synthetic peptide IRRRY. We show that protein 4.1 bound to the inside-out vesicles could be dissociated from band 3 but not from glycophorin C by IRRRY. Furthermore, incorporation of IRRRY into resealed ghosts resulted in decreased membrane deformability and increased membrane mechanical stability. The observed alterations in membrane properties appears to result from increased band 3-ankyrin interaction following dissociation of protein 4.1 from band 3. These studies have enabled us to identify an important functional role for band 3-protein 4.1 interaction in modulating erythrocyte membrane properties.

[Structure of erythrocyte membrane skeleton]

Underlying the human erythrocyte membrane is a self-assembled network of proteins termed the membrane skeleton. This network plays a major role in conferring a biconcave shape on the normal erythrocyte and maintaining mechanical properties of the human erythrocyte membrane. Spectrin, actin, protein 4.1, adducin, tropomyosin, dematin and p55 are the principal components of the membrane skeleton. Lateral interactions among these proteins constitute the spectrin-based composite structure that is anchored to the bilayer through vertical interactions, one involving beta-spectrin, ankyrin and band 3, and the other through an interaction between protein 4.1 and glycophorin C. In this article reviewed are biochemical structure of the skeletal proteins, their interactions and regulations by various constituents based on recent studies.

Defective anion transport and marked spherocytosis with membrane instability caused by hereditary total deficiency of red cell band 3 in cattle due to a nonsense mutation

We studied bovine subjects that exhibited a moderate uncompensated anemia with hereditary spherocytosis inherited in an autosomal incompletely dominant mode and retarded growth. Based on the results of SDS-PAGE, immunoblotting, and electron microscopic analysis by the freeze fracture method, we show here that the proband red cells lacked the band 3 protein completely. Sequence analysis of the proband band 3 cDNA and genomic DNA showed a C --> T substitution resulting in a nonsense mutation (CGA --> TGA; Arg --> Stop) at the position corresponding to codon 646 in human red cell band 3 cDNA. The proband red cells were deficient in spectrin, ankyrin, actin, and protein 4.2, resulting in a distorted and disrupted membrane skeletal network with decreased density. Therefore, the proband red cell membranes were extremely unstable and showed the loss of surface area in several distinct ways such as invagination, vesiculation, and extrusion of microvesicles, leading to the formation of spherocytes. Total deficiency of band 3 also resulted in defective Cl-/HCO3- exchange, causing mild acidosis with decreases in the HCO3- concentration and total CO2 in the proband blood. Our results demonstrate that band 3 indeed contributes to red cell membrane stability, CO2 transport, and acid-base homeostasis, but is not always essential to the survival of this mammal.

Modulation of erythrocyte membrane mechanical function by beta-spectrin phosphorylation and dephosphorylation

The mechanical properties of human erythrocyte membrane are largely regulated by submembranous protein skeleton whose principal components are alpha- and beta-spectrin, actin, protein 4.1, adducin, and dematin. All of these proteins, except for actin, are phosphorylated by various kinases present in the erythrocyte. In vitro studies with purified skeletal proteins and various kinases has shown that while phosphorylation of these proteins can modify some of the binary and ternary protein interactions, it has no effect on certain other interactions between these proteins. Most importantly, at present there is no direct evidence that phosphorylation of skeletal protein(s) alters the function of the intact membrane. To explore this critical issue, we have developed experimental strategies to determine the functional consequences of phosphorylation of beta-spectrin on mechanical properties of intact erythrocyte membrane. We have been able to document that membrane mechanical stability is exquisitely regulated by phosphorylation of beta-spectrin by membrane-bound casein kinase I. Increased phosphorylation of beta-spectrin decreases membrane mechanical stability while decreased phosphorylation increases membrane mechanical stability. Our data for the first time demonstrate that phosphorylation of a skeletal protein in situ can modulate physiological function of native erythrocyte membrane.

Factors of the shape change of human erythrocytes induced with lidocaine

We studied the molecular mechanism of the shape change of erythrocytes with a local anesthetic, lidocaine. The shape of human erythrocytes changed from discocytes to stomatocytes in the presence of lidocaine when ATP was present. But, the shape of resealed cells which were prepared with 10 mM Tris-HCl buffer (pH 7.4) containing 2 mM ATP-MgCl2 and various substances was not changed from discocytes to stomatocytes with lidocaine. When intact cells and resealed cells which were prepared with various concentrations of Tris-HCl buffer (pH 7.4) were incubated with various concentrations of lidocaine and their membrane proteins were analyzed by SDS-PAGE, the densities of bands 62K, 28K and 22K depended on lidocaine concentration: in particular, that of band 28K changed remarkably. These membranous 62K-, 28K- and 22K-proteins agreed with cytoplasmic 62K-, 28K- and 22K-proteins in molecular weight. We propose that not only ATP but also the 62K-, 28K- and 22K-proteins in the cytoplasm are concerned with the shape change of human erythrocytes induced with lidocaine.