K+ efflux in deoxygenated sickle cells in the presence or absence of DIOA, a specific inhibitor of the [K+, Cl-] cotransport system

The ouabain bumetanide resistant (OBR) K+ efflux was investigated in deoxygenated sickle cells in comparison to oxygenated ones, by using a specific inhibitor of the [K+, Cl-] co-transport system, [(DihydroIndenyl)Oxy] Alkanoic acid (DIOA). A DIOA sensitive and a DIOA resistant K+ efflux were measured in deoxygenated sickle cells. The DIOA sensitive K+ efflux shared the properties of the [K+, Cl-] co-transport system, being stimulated by decreased pH and hypoosmolarity. This DIOA sensitive K+ efflux represented 70% of the total K+ efflux at pH 7.0 and at low pO2 (10-15 mmHg). Thus, a small reduction in Ph effectively stimulated the [K+, Cl-] co-transport system in deoxygenated condition, and this may contribute significantly to the sickle cell dehydration. We conclude that at pH lower than 7.4, the [K+, Cl-] co-transport system is permanently activated in sickle cells and leads to sickle cell dehydration in both oxygenated and deoxygenated conditions.     

Failure of recombinant human interleukin-3 therapy to induce erythropoiesis in patients with refractory Diamond-Blackfan anemia [see comments]

In two previous studies, we observed that recombinant human interleukin- 3 (IL-3) induced an increase in marrow burst-forming unit-erythroid- derived colonies in vitro in some patients with Diamond-Blackfan anemia (DBA). To determine whether a similar erythropoietic response could be induced in vivo, we treated 13 patients with DBA (aged 4 to 19 years) with two preparations of IL-3. All patients had absent absolute reticulocyte counts and markedly reduced to absent recognizable bone marrow erythroid elements; patients with circulating reticulocytes in the previous 12 months were excluded from study. All patients except 1 had failed steroid therapy and had been transfusion-dependent since infancy; 1 patient was maintained on high-dose prednisone at the time of enrollment. On the first arm of the study, IL-3 (Immunex Corp, Seattle, WA) was administered subcutaneously using a dose escalation regimen of 125 to 500 micrograms/m2/day in divided dosage at 12-hour intervals, coadministered with 1.5 mg/kg/d of oral ferrous sulphate. Of the 13 patients that entered the trial, 4 stopped prematurely because of adverse side effects. In the other 9 evaluable cases, reticulocytes increased transiently in 1 patient from 0 to 65 x 10(9)/L after 35 days of IL-3 therapy at 250 micrograms/m2, but transfusion dependency persisted. One transient peak in absolute reticulocyte count was noted in 6 other patients, but no erythroid response was observed after completion of a full course of IL-3. Oral prednisone at 0.5 mg/kg/d was then coadministered with IL-3 at 500 micrograms/m2 to 5 of the patients without effect, and treatment was stopped. In 2 patients, a second preparation of IL-3 (Sandoz Canada Inc, Dorval, Quebec, Canada) was initiated in a dose escalation regimen of 2.5 to 10 micrograms/kg and was coadministered with ferrous sulphate. No erythroid response was observed in either patient, and in one of the two, alternate-day subcutaneous recombinant erythropoietin at 300 U/kg was administered for 3 weeks in combination with daily IL-3 at 10 micrograms/kg, but no increased erythropoiesis was seen. Significant increases in white blood cell and eosinophil counts during administration of both preparations of IL-3 were observed in all patients. These data show that the response of DBA patients to IL-3 in vivo is heterogeneous and cannot be predicted from in vitro studies. The absence of a corrective effect of IL-3 in these patients with DBA indicates that a deficiency of the cytokine is not central in the pathogenesis of the disorder.     

Mutation in Osteoactivin Decreases Bone Formation in Vivo and Osteoblast Differentiation in Vitro

We have previously identified osteoactivin (OA), encoded by Gpnmb, as an osteogenic factor that stimulates osteoblast differentiation in vitro. To elucidate the importance of OA in osteogenesis, we characterized the skeletal phenotype of a mouse model, DBA/2J (D2J) with a loss-of-function mutation in Gpnmb. Microtomography of D2J mice showed decreased trabecular mass, compared to that in wild-type mice [DBA/2J-Gpnmb⁺/SjJ (D2J/Gpnmb⁺)]. Serum analysis showed decreases in OA and the bone-formation markers alkaline phosphatase and osteocalcin in D2J mice. Although D2J mice showed decreased osteoid and mineralization surfaces, their osteoblasts were increased in number, compared to D2J/Gpnmb⁺ mice. We then examined the ability of D2J osteoblasts to differentiate in culture, where their differentiation and function were decreased, as evidenced by low alkaline phosphatase activity and matrix mineralization. Quantitative RT-PCR analyses confirmed the decreased expression of differentiation markers in D2J osteoblasts. In vitro, D2J osteoblasts proliferated and survived significantly less, compared to D2J/Gpnmb⁺ osteoblasts. Next, we investigated whether mutant OA protein induces endoplasmic reticulum stress in D2J osteoblasts. Neither endoplasmic reticulum stress markers nor endoplasmic reticulum ultrastructure were altered in D2J osteoblasts. Finally, we assessed underlying mechanisms that might alter proliferation of D2J osteoblasts. Interestingly, TGF-β receptors and Smad-2/3 phosphorylation were up-regulated in D2J osteoblasts, suggesting that OA contributes to TGF-β signaling. These data confirm the anabolic role of OA in postnatal bone formation.Osteoporosis is a growing public health problem, in part because of the increasing numbers of people living beyond the age of 65 years.¹ It is characterized by low bone mass due to increased bone resorption by osteoclasts and decreased bone formation by osteoblasts, with significant deterioration in the bone microarchitecture leading to high bone fragility and increased fracture risk.^1,2 The net effect of osteoporosis is low bone mass.¹ There is an increasing demand for identifying novel bone anabolic factors with potential therapeutic benefits in treating generalized bone loss, such as osteoporosis and/or major skeletal fracture.Osteoactivin is a novel glycoprotein first identified in natural mutant osteopetrotic rats.³ The same protein has been identified and named separately in several other species: as dendritic cell heparan sulfate proteoglycan integrin dependent ligand (DCHIL) in mouse dendritic cells,⁴ as transmembrane glycoprotein NMB (GPNMB) in human melanoma cell lines and melanocytes,⁵ and as hematopoietic growth factor inducible neurokinin (HGFIN) in human tumor cells.⁶ The current recommended name for the protein encoded by Gpnmb in mouse is transmembrane glycoprotein NMB (http://www.ncbi.nlm.nih.gov/protein/Q99P91.2); here, we continue to use osteoactivin (OA) for the protein and Gpnmb for the gene. OA is a type I transmembrane protein that consists of multiple domains, including an extracellular domain, transmembrane domain, and protein sorting signal sequence.⁷ Within the C-terminal domain, OA has an RGD motif, predicting an integrin attachment site.^3,7–9Our research group initially reported on the novel role of OA in osteoblast differentiation and function.^7–10 We demonstrated that OA expression has a temporal pattern during osteoblast differentiation, being highest during matrix maturation and culture mineralization in vitro.^7–11 Using loss-of–function and gain-of–function approaches in osteoblasts, we reported that OA overexpression increases osteoblast differentiation and function and that OA down-regulation decreases nodule formation, alkaline phosphatase (ALP) activity, osteocalcin (OC) production, and matrix mineralization in vitro.⁷ We also reported on the positive role of OA in mesenchymal stem cell (MSCs) differentiation into osteoblasts in vitro.¹² In another study, we showed that recombinant OA protein induces higher osteogenic potential of fetal-derived MSCs, compared with bone marrow–derived MSCs¹³ and its osteogenic effects in the mouse C3H10T1/2 MSC cell line were similar to those of recombinant BMP-2.¹² We also localized OA protein as associated predominately with osteoblasts lining trabecular bones in vivo,¹¹ and showed that local injection of recombinant OA increased bone mass in a rat model.¹⁴ Moreover, in a fracture repair model OA expression increased over time, reaching a maximum 2 weeks after fracture.¹¹ In a parallel study, recombinant OA supported bone regeneration and formation in a rat critical-size calvarial defect model.¹⁵ Others have shown that OA is highly expressed by osteoclasts in vitro, suggesting that it may regulate osteoclast formation and activity.¹⁶There is urgent need for an animal model to fully examine the role of OA in osteogenesis. Interestingly, a natural mutation of the Gpnmb gene has been identified in the DBA/2J (D2J) mouse strain.¹⁷ These mice exhibit high-frequency hearing loss, which begins at the time of weaning and becomes severe by 2 to 3 months of age.^18,19 Aged D2J mice also develop progressive eye abnormalities that closely mimic human hereditary glaucoma. The onset of disease symptoms falls roughly between 3 and 4 months of age, and disease becomes severe by 6 months of age.^5,20 D2J mice are homozygous for a nonsense mutation in the Gpnmb gene sequence that induces an early stop codon, generating a truncated protein sequence of 150 amino acids (aa) instead of the full-length 562-aa OA protein.⁵ The control for the D2J mouse is the wild-type DBA/2J-Gpnmb⁺/SjJ mouse (D2J/Gpnmb⁺), homozygous for the wild-type Gpnmb gene.²¹ These Gpnmb wild-type mice do not develop glaucoma, as D2J mice do, although they exhibit mild iris stromal atrophy.²¹In the present study, we used Gpnmb mutant (D2J) and Gpnmb wild-type (D2J/Gpnmb⁺) mice to gain insight into the role of OA in osteogenesis and in osteoblast differentiation and function. Here, we report that loss-of–function mutation of Gpnmb suppresses bone formation by directly affecting osteoblast proliferation and survival, leading to a decreased number of differentiated osteoblasts with suppressed activity in bone mineralization. Thus, our data point to OA as a novel and positive regulator of postnatal bone formation.     

Acute alcoholic hepatitis,end stage alcoholic liver disease and liver transplantation: An Italian position statement

Alcoholic liver disease encompasses a broad spectrum of diseases ranging from steatosis steatohepatitis, fibrosis, and cirrhosis to hepatocellular carcinoma. Forty-four per cent of all deaths from cirrhosis are attributed to alcohol. Alcoholic liver disease is the second most common diagnosis among patients undergoing liver transplantation (LT). The vast majority of transplant programmes (85%) require 6 mo of abstinence prior to transplantation; commonly referred to as the “6-mo rule”. Both in the case of progressive end-stage liver disease (ESLD) and in the case of severe acute alcoholic hepatitis (AAH), not responding to medical therapy, there is a lack of evidence to support a 6-mo sobriety period. It is necessary to identify other risk factors that could be associated with the resumption of alcohol drinking. The “Group of Italian Regions” suggests that: in a case of ESLD with model for end-stage liver disease < 19 a 6-mo abstinence period is required; in a case of ESLD, a 3-mo sober period before LT may be more ideal than a 6-mo period, in selected patients; and in a case of severe AAH, not responding to medical therapies (up to 70% of patients die within 6 mo), LT is mandatory, even without achieving abstinence. The multidisciplinary transplant team must include an addiction specialist/hepato-alcohologist. Patients have to participate in self-help groups.     

Chlamydophila pneumoniae phospholipase D (CpPLD) drives Th17 inflammation in human atherosclerosis

Phospholipases are produced from bacterial pathogens causing very different diseases. One of the most intriguing aspects of phospholipases is their potential to interfere with cellular signaling cascades and to modulate the host-immune response. Here, we investigated the role of the innate and acquired immune responses elicited by Chlamydophila pneumoniae phospholipase D (CpPLD) in the pathogenesis of atherosclerosis. We evaluated the cytokine and chemokine production induced by CpPLD in healthy donors' monocytes and in vivo activated T cells specific for CpPLD that infiltrate atherosclerotic lesions of patients with C. pneumoniae antibodies. We also examined the helper function of CpPLD-specific T cells for monocyte matrix metalloproteinase (MMP)-9 and tissue factor (TF) production as well as the CpPLD-induced chemokine expression by human venular endothelial cells (HUVECs). We report here that CpPLD is a TLR4 agonist able to induce the expression of IL-23, IL-6, IL-1β, TGF-β, and CCL-20 in monocytes, as well as CXCL-9, CCL-20, CCL-4, CCL-2, ICAM-1, and VCAM-1 in HUVECs. Plaque-derived T cells produce IL-17 in response to CpPLD. Moreover, CpPLD-specific CD4(+) T lymphocytes display helper function for monocyte MMP-9 and TF production. CpPLD promotes Th17 cell migration through the induction of chemokine secretion and adhesion molecule expression on endothelial cells. These findings indicate that CpPLD is able to drive the expression of IL-23, IL-6, IL-1β, TGF-β, and CCL-20 by monocytes and to elicit a Th17 immune response that plays a key role in the genesis of atherosclerosis.     

Intramembrane proteolysis of Toxoplasma apical membrane antigen 1 facilitates host-cell invasion but is dispensable for replication

Apical membrane antigen 1 (AMA1) is a conserved transmembrane adhesin of apicomplexan parasites that plays an important role in host-cell invasion. Toxoplasma gondii AMA1 (TgAMA1) is secreted onto the parasite surface and subsequently released by proteolytic cleavage within its transmembrane domain. To elucidate the function of TgAMA1 intramembrane proteolysis, we used a heterologous cleavage assay to characterize the determinants within the TgAMA1 transmembrane domain (ALIAGLAVGGVLLLALLGGGCYFA) that govern its processing. Quantitative analysis revealed that the TgAMA1(L/G) mutation enhanced cleavage by 13-fold compared with wild type. In contrast, the TgAMA1(AG/FF) mutation reduced cleavage by 30-fold, whereas the TgAMA1(GG/FF) mutation had a minor effect on proteolysis; mutating both motifs in a quadruple mutant blocked cleavage completely. We then complemented a TgAMA1 conditional knockout parasite line with plasmids expressing these TgAMA1 variants. Contrary to expectation, variants that increased or decreased TgAMA1 processing by >10-fold had no phenotypic consequences, revealing that the levels of rhomboid proteolysis in parasites are not delicately balanced. Only parasites transgenically expressing or carrying a true knock-in allele of the uncleavable TgAMA1(AG/FF+GG/FF) mutant showed a growth defect, which resulted from inhibiting invasion without perturbing intracellular replication. These data demonstrate that TgAMA1 cleavage plays a role in invasion, but refute a recently proposed model in which parasite replication within the host cell is regulated by intramembrane proteolysis of TgAMA1.