Hena Ramay

CURRENT POSITION : BIOINFORMATICIAN AT BIONFORMATICS CORE FACILITY,SWISS INSTITUTE OF BIOINFORMATICS

 

Email: ramay@sysbio.ioc.ee Phone: +372 620 4162

TRAINING AND EDUCATION Post-doctoral fellowship Mount Sinai School of Medicine, New York Ph.D. (Bioinformatics), George Mason University M Sc. (Comp. Sci.), University of Texas B Sc. (Comp. Sci), New Mexico Tech

Research Projects Miscarriage and MTHFR mutations Nrf2 Knockout mice and ROS Restitution of Ca2+ Sparks Prediction of local Ca dynamics Publications

RESEARCH INTERESTS

My research interest focuses on resolving mechanistic uncertainties in biological systems with the use of computational methods and experimental techniques. Following are the current research projects I am involved in

1.) Miscarriage and MTHFR mutations: A clinical study to determine a link between recurrent embryo loss and Methylenetetrahydrofolate reductase (MTHFR).
The first trimester is the most critical period for a human pregnancy. Our aim in this investigation is to find if there is a link between early miscarriage in Estonian population and polymorphic mutations in MTHFR gene. Our focus is on two mutations, C667->T and A1298 ->C  that are thought to be responsible for massively elevated plasma homocysteine concentrations which can result in homocystinuria and homocysteinemia.
Our clinical study comprises of two group of women; control group with two or more healthy children and a test group of women with two or more miscarriages. Blood samples will be collected from all patients. Biochemical parameters such as folic acid and homocycteine will be compared.  We will perform genotyping on the DNA isolated from blood samples of the patients to look for mutations in MTHFR gene. Analysis of this initial data will guide our research direction.
Collaborators: Dr. Riina Žordania and Dr Kairit Joost from Genetic Center at Tartu University Hospital

2.) Consequences of Elevated reactive oxygen species(ROS) in Nrf2 knockout mice. In NF-E2-related factor 2 (Nrf2) Knockout mice, ROS levels are elevated. As in the development of most cardiovascular disease, increased ROS levels have a role to play, these mice provided a good model to study Ca²⁺ signaling in cardiac myocytes. As a preliminary study, three set of experiments were planned; measurement of Ca²⁺ sparks, Ca²⁺ transients and effects of Antimycin. Our initial results indicate severe differences in Ca²⁺ transient and spark characteristics in control and knockout mice. From this initial data, we hypothesize mishandling of Ca²⁺ removal from the cytosol either by extrusion from the cell or by uptake in the sarcoplasmic reticulum. At the moment, to better understand the differences in these mice, we are conducting extensive gene expression profiling.
Collaborator: Pasi Tavi from University of Eastern Finland

3.) Restitution of Ca²⁺ sparks. The mechanisms responsible for the termination of Ca²⁺ sparks and refractoriness after termination remain a subject of debate. While local depletion of SR Ca²⁺ is clearly important for spark termination, the roles of SR refilling versus time-dependent changes in Ryanodine receptor (RyR2)  gating in refractoriness and recovery are unclear. Using a previous experimental technique (Sobie et al 2005, Journal of Physiology), in this study we are altering RyR2 gating behavior with different drugs such caffeine, tetracaine and isoproterenol and studying characteristics of consecutive Ca²⁺sparks arising from the same RyR2 cluster. The figures below are extreme representations of how consecutive spark delays change with different drugs. Our aim here is to measure spark-to-spark delays and ratios of consecutive spark amplitudes to assess which mechanism might be primary in termination of Ca²⁺ sparks.

4.) Prediction of local calcium dynamics.

Under pathological conditions such as Ca²⁺ overload spontaneous Ca²⁺ sparks can give rise to regenerative Ca²⁺ waves whereby sparks trigger additional sparks from neighboring clusters of sarcoplasmic reticulum (SR) Ca²⁺ release channels (ryanodine receptors; RyR2s). Controversy exists, however, regarding the relative importance of two competing mechanisms where one proposes cytosolic diffusion of Ca²⁺and activation of neighbouring RyR2 clusters through Ca²⁺-induced Ca²⁺ release versus the second that proposes cluster-to-cluster diffusion of Ca²⁺ within the SR network sensitizing RyRs at sites that have not yet been activated (un-activated sites). To address this problem we are  implementing a  computational model of cytosolic and SR [Ca²⁺] during Ca²⁺ waves.

The figure below is of simulations where we investigated how dynamic local changes in SR [Ca²⁺] were influenced by diffusion of Ca²⁺ in the SR.  Image is space-time representation of cytosolic [Ca²⁺] (on a logarithmic scale) during a Ca²⁺ wave (left). The corresponding image of SR [Ca²⁺] is at right. Transverse tubules are indicated by horizontal white lines.  Spatiotemporal changes in [Ca²⁺]_SR within two sarcomeres are displayed for three values of Ca diffusion constant (D_Ca,SR) (B). Slow SR diffusion leads the most dramatic increases in[Ca²⁺]_SR above the baseline value (1500 µM) in unactivated regions. Recovery of total JSR [Ca²⁺] after release at an individual site depends on D_Ca,SR. Time constants range from 53 ms (fast) to 84 ms (slow).

 

PUBLICATIONS:

1. Ramay, H.R., Liu, O., Sobie E.A. (2011) Recovery of cardiac calcium release is controlled by sarcoplasmic reticulum refilling and ryanodine receptor sensitivity. Cardiovascular Research, 91(4):598-605
2. Macquaide, N., Ramay, H.R., Sobie E.A., Smith G.L. (2010). Differential sensitivity of Ca²⁺ wave and Ca²⁺ spark events to ruthenium red in isolated permeabilized rabbit cardiomyocytes. Journal of Physiology, 588(Pt 23):4731-42
3. Ramay, H.R., Jafri M.S., Lederer W.J., Sobie E.A. (2010). Predicting local SR Ca²⁺ dynamics during Ca²⁺ wave propagation in ventricular myocytes. Biophysical Journal, 98(11):2515-23
4. Ramay, H.R., and Vendelin, M. (2009). Diffusion restrictions surrounding mitochondria: a mathematical model of heart muscle fibers. Biophysical Journal, 97, 443 – 452.
5. Sobie, E. A., Ramay, H.R. (2009). Excitation-contraction coupling gain in ventricular myocytes: insights from a parsimonious model. Journal of Physiology, 587(Pt 6):1293-9
6. Sobie, E.A., Ramay, H.R. (2009). Extrasystoles. Lang, Florian (Eds.). Encyclopedia of Molecular Mechanisms of Disease (625 – 626). Berlin: Springer
7. Ramay, H.R., Fabris, F., Noel, O., Sarkar, A. (2008). An il-lumen-ating look at ryanodine receptor modulation by disruption in triadin and calsequestrin interactions in cardiac myocytes. Journal of Physiology-London, 697 – 699.
8. Nguyen, M.T., Ramay, H.R., Dudycha, S.J., Jafri, M.S. (2004). Modeling the cellular basis of cardiac excitation-contraction coupling and energy metabolism. Recent research developments in biophysics (125 – 145). Trivandrum: Transworld Research Network