The complex effect of granulocyte colony-stimulating factor on human granulopoiesis analyzed by a new physiologically-based mathematical model

Neutropenia, frequently a side effect of chemo- and radiotherapy, increases susceptibility to microbial infections and is a life-threatening condition. For realistically predicting drug treatment effects on granulopoiesis, we have constructed a new mathematical model of granulopoiesis in the bone marrow and in the peripheral blood, featuring cell cycle phase transition and detailed granulocyte-colony stimulating factor (G-CSF) pharmacokinetics (PK) and pharmacodynamics (PD), including intracellular second messenger. Using this model, in conjunction with clinical results, we evaluated the system parameters, implemented those in the model and successfully retrieved the results of several independent clinical experiments under a wide range of G-CSF regimens. Our results show that the introduction of G-CSF-controlled intracellular second messenger is indispensable for precise retrieval of the clinical results, and suggest that the half-life of this messenger varies between a single and multiple G-CSF administration schedules. In addition, our model provided reliable steady-state, as well as dynamic, estimations of human granulopoiesis parameters. These included an estimation of apoptosis index in the post-mitotic compartment, which corroborates previous results. At present the model is used for suggesting improved drug regimens.     

Mapping the DNA- and zinc-binding domains of ASR1 (abscisic acid stress ripening), an abiotic-stress regulated plant specific protein

Abscisic acid stress ripening (ASR1) is a highly charged low molecular weight plant specific protein that is regulated by salt- and water-stresses. The protein possesses a zinc-dependent DNA-binding activity (Kalifa et al., Biochem. J. 381 (2004) 373) and overexpression in transgenic plants results in an increased salt-tolerance (Kalifa et al., Plant Cell Environ. 27 (2004) 1459). There are no structure homologs of ASR1, thus the structural and functional domains of the protein cannot be predicted. Here, we map the protein domains involved in the binding of Zn(2+) and DNA. Using mild acid hydrolysis, and a series of ASR1 carboxy-terminal truncations we show that the zinc-dependent DNA-binding could be mapped to the central/carboxy-terminal domain. In addition, using MALDI-TOF-MS with a non-acidic matrix, we show that two zinc ions are bound to the amino-terminal domain. Other zinc ion(s) bind the DNA-binding domain. Binding of zinc to ASR1 induces conformational changes resulting in a decreased sensitivity to proteases.     

Can the Error Detection Mechanism Benefit from Training the Working Memory? A Comparison between Dyslexics and Controls — An ERP Study

Background

Based on the relationship between working memory and error detection, we investigated the capacity of adult dyslexic readers'' working memory to change as a result of training, and the impact of training on the error detection mechanism.

Methodology

27 dyslexics and 34 controls, all university students, participated in the study. ERP methodology and behavioral measures were employed prior to, immediately after, and 6 months after training. The CogniFit Personal Coach Program, which consists of 24 sessions of direct training of working memory skills, was used.

Findings

Both groups of readers gained from the training program but the dyslexic readers gained significantly more. In the dyslexic group, digit span increased from 9.84±3.15 to 10.79±3.03. Working memory training significantly increased the number of words per minute read correctly by 14.73%. Adult brain activity changed as a result of training, evidenced by an increase in both working memory capacity and the amplitude of the Error-related Negativity (ERN) component (24.71%). When ERN amplitudes increased, the percentage of errors on the Sternberg tests decreased.

Conclusions

We suggest that by expanding the working memory capacity, larger units of information are retained in the system, enabling more effective error detection. The crucial functioning of the central-executive as a sub-component of the working memory is also discussed.     

AglP is a S‐adenosyl‐L‐methionine‐dependent methyltransferase that participates in the N‐glycosylation pathway of Haloferax volcanii

While pathways for N‐glycosylation in Eukarya and Bacteria have been solved, considerably less is known of this post‐translational modification in Archaea. In the halophilic archaeon Haloferax volcanii, proteins encoded by the agl genes are involved in the assembly and attachment of a pentasaccharide to select asparagine residues of the S‐layer glycoprotein. AglP, originally identified based on the proximity of its encoding gene to other agl genes whose products were shown to participate in N‐glycosylation, was proposed, based on sequence homology, to serve as a methyltransferase. In the present report, gene deletion and mass spectrometry were employed to reveal that AglP is responsible for adding a 14 Da moiety to a hexuronic acid found at position four of the pentasaccharide decorating the Hfx. volcanii S‐layer glycoprotein. Subsequent purification of a tagged version of AglP and development of an in vitro assay to test the function of the protein confirmed that AglP is a S‐adenosyl‐L‐methionine‐dependent methyltransferase.     

The universal properties of stem cells as pinpointed by a simple discrete model

The ability of a few stem-cells to repopulate a severely damaged bone marrow (BM) guarantees the stability of our physical existence, and facilitates successful BM transplantations. What are the basic properties of stem cells that enable the maintenance of the system's homeostasis? In the present work we attempt to answer this question by investigating a discrete (in time and phase-space) dynamical system. The model we present is shown to retrieve the essential properties of homeostasis, as reflected in BM functioning, namely, (a) to produce a constant amount of mature cells, and (b) to be capable of returning to this production after very large perturbations. The mechanism guaranteeing the fulfillment of these properties is extrinsic--negative feedback control in the micro-environment--and does not need additional stochastic assumptions. Nevertheless, the existence of a simple intrinsic control mechanism, a clock which determines the switch to differentiation, ascertains that the system does not admit non-trivial extinction states. This result may help clarifying some of the controversy about extrinsic versus intrinsic control over stem cell fate. It should be stressed that all conclusions are valid for any system containing progenitor and maturing cells.     

An integrated disease/pharmacokinetic/pharmacodynamic model suggests improved interleukin-21 regimens validated prospectively for mouse solid cancers

Interleukin (IL)-21 is an attractive antitumor agent with potent immunomodulatory functions. Yet thus far, the cytokine has yielded only partial responses in solid cancer patients, and conditions for beneficial IL-21 immunotherapy remain elusive. The current work aims to identify clinically-relevant IL-21 regimens with enhanced efficacy, based on mathematical modeling of long-term antitumor responses. For this purpose, pharmacokinetic (PK) and pharmacodynamic (PD) data were acquired from a preclinical study applying systemic IL-21 therapy in murine solid cancers. We developed an integrated disease/PK/PD model for the IL-21 anticancer response, and calibrated it using selected "training" data. The accuracy of the model was verified retrospectively under diverse IL-21 treatment settings, by comparing its predictions to independent "validation" data in melanoma and renal cell carcinoma-challenged mice (R(2)>0.90). Simulations of the verified model surfaced important therapeutic insights: (1) Fractionating the standard daily regimen (50 μg/dose) into a twice daily schedule (25 μg/dose) is advantageous, yielding a significantly lower tumor mass (45% decrease); (2) A low-dose (12 μg/day) regimen exerts a response similar to that obtained under the 50 μg/day treatment, suggestive of an equally efficacious dose with potentially reduced toxicity. Subsequent experiments in melanoma-bearing mice corroborated both of these predictions with high precision (R(2)>0.89), thus validating the model also prospectively in vivo. Thus, the confirmed PK/PD model rationalizes IL-21 therapy, and pinpoints improved clinically-feasible treatment schedules. Our analysis demonstrates the value of employing mathematical modeling and in silico-guided design of solid tumor immunotherapy in the clinic.     

Evidence for the Circulation of Equine Encephalosis Virus in Israel since 2001

Equine encephalosis virus (EEV) distribution was thought to be limited to southern Africa until 2008 when we reported EEV in Israel. It was then assumed that the clinical presentation resembled the initial incursion in Israel. To investigate further we conducted a retrospective analysis of equine sera, which had been collected for diagnosis of other suspected diseases, via serum neutralisation test. The data demonstrated that EEV was circulating as early as 2001 with incidence ranging from 20–100% for time period 2001–2008. As the symptoms of EEV can be similar to other equine notifiable diseases this is a significant finding which highlights the need for vigilance and education to accurately diagnose new and emerging diseases.