Parvalbumin gene transfer corrects diastolic dysfunction in diseased cardiac myocytes

Abstract

Heart failure frequently involves diastolic dysfunction that is characterized by a prolonged relaxation. This prolonged relaxation is typically the result of a decreased rate of intracellular Ca 2؉ sequestration. No effective treatment for this decreased Ca 2؉ sequestration rate currently exists. As an approach to possibly correct diastolic dysfunction, we hypothesized that expression of the Ca 2؉ binding protein parvalbumin in cardiac myocytes would lead to increased rates of Ca 2؉ sequestration and mechanical relaxation. Parvalbumin, which is normally absent in cardiac tissue, is known to act as a soluble relaxing factor in fast skeletal muscle fibers by acting as a delayed Ca 2؉ sink. As a test of the hypothesis, gene transfer was used to express parvalbumin in isolated adult cardiac myocytes. We report here that expression of parvalbumin dramatically increases the rate of Ca 2؉ sequestration and the relaxation rate in normal cardiac myocytes. Importantly, parvalbumin fully restored the relaxation rate in diseased cardiac myocytes isolated from an animal model of human diastolic dysfunction. These findings indicate that parvalbumin gene transfer offers unique potential as a possible direct treatment for diastolic dysfunction in failing hearts. H eart failure is a leading cause of hospitalization in the U.S., diagnosed in Ϸ700,000 new patients annually (1). About a third of all heart failure involves diastolic dysfunction (2), which frequently is the result of an inappropriate prolongation of the intracellular Ca 2ϩ transients that trigger cardiac muscle contraction (3-6). Consequently, the heart fails to relax appropriately between contractions, leading to an increased stiffness of the myocardium during diastole and thereby generating excessive resistance to filling. Currently there is no clinical treatment that directly ameliorates this prolonged Ca 2ϩ transient. Recent research into alleviating this form of diastolic dysfunction has centered primarily on increasing the rate of Ca 2ϩ uptake by the sarcoplasmic reticulum (SR), either through increased SR Ca 2ϩ pumping rates or increased expression of the SR pump. These are energy-dependent approaches, however, and energy production in failing hearts also is frequently impaired (5, 6). As a different approach, we used adenoviral-mediated gene transfer to express the soluble relaxing factor parvalbumin in cardiac myocytes. Parvalbumin, which is not naturally found in cardiac tissue, is a Ca 2ϩ binding protein whose Ca 2ϩ affinity is intermediate between the thin filament regulatory protein troponin C and the SR Ca 2ϩ pump. This intermediate Ca 2ϩ affinity allows parvalbumin to enhance the rate of relaxation in fast skeletal muscle by acting as a Ca 2ϩ sink to temporarily store Ca 2ϩ before SR uptake (7-9). Relaxation thus becomes dependent on the rate of Ca 2ϩ binding to parvalbumin, independent of energy status, rather than dependent on the slower, energy requiring SR Ca 2ϩ uptake (see Fig. 2 A, Inset). Parvalbumin is thought to be complexed to Mg 2ϩ at rest, ...

Gene Transfer of Parvalbumin Improves Diastolic Dysfunction in Senescent Myocytes

“…In parallel with the improvement in calcium decay rate, we also found that the rate of myocyte relengthening is dramatically increased in senescent myocytes expressing parvalbumin and in fact slightly exceeds the relaxation rate of adult control myocytes. These results are consistent with the findings of Wahr et al, 9 who demonstrated that relaxation parameters in both hypothyroid and healthy myocytes were significantly ameliorated with parvalbumin, with no effect on the rate of cell shortening or the amplitude of peak contraction.…”

“…3 Adenoviral gene transfer of parvalbumin into cardiac myocytes has shown that both the rate of calcium transient decay and the rate of myocyte relaxation are increased by the introduction of parvalbumin, with no decrease in contraction amplitude. 9 This effect is observed both in healthy adult myocytes and in a disease model of diastolic dysfunction (hypothyroidism) in which expression of parvalbumin fully corrected relaxation parameters (t 1/2R and ϪdL/dT) in myocytes from diseased animals back to normal (euthyroid) levels. Further confirmation of the ability of parvalbumin to restore diastolic parameters to normal was obtained in an in vivo setting, in which injection of parvalbumin into the LV free wall both accelerated myocardial relaxation under physiological conditions and improved myocardial twitch relaxation rates and ϪdP/dt in hypothyroid hearts to normal.…”

“…6 -8 Parvalbumin gene transfer is one approach that has recently been used successfully to target prolonged relaxation in a rodent model of diastolic dysfunction. 9 Adenoviral transduction of parvalbumin into the LV free wall has been shown to significantly accelerate LV isovolumic relaxation times in normal animals and also to restore normal relaxation performance in hypothyroidisminduced diastolic dysfunction. 10 In addition, adenoviral gene transfer of parvalbumin into adult myocytes in vitro has been shown to significantly increase the rate of myocyte relaxation (ϪdL/dT max , t 1/2R ) and to decrease the rate of decay of the intracellular calcium transient.…”

Abrogation of ventricular arrhythmias in a model of ischemia and reperfusion by targeting myocardial calcium cycling

“…It has a calcium affinity that is intermediate between troponin and SERCA, allowing it to act as a Ca 2ϩ sink to temporarily bind Ca 2ϩ before SR uptake. PV gene transfer is one approach that has recently been used successfully to target prolonged relaxation in a rodent model of diastolic dysfunction in short term (15). Adenoviral transduction of PV into the LV free wall has been shown to accelerate LV isovolumic relaxation times significantly in normal animals and also to restore normal relaxation performance in hypothyroidism-induced diastolic dysfunction (15).…”

“…PV gene transfer is one approach that has recently been used successfully to target prolonged relaxation in a rodent model of diastolic dysfunction in short term (15). Adenoviral transduction of PV into the LV free wall has been shown to accelerate LV isovolumic relaxation times significantly in normal animals and also to restore normal relaxation performance in hypothyroidism-induced diastolic dysfunction (15). However, overexpression of PV in our model did not mitigate the effects of I͞R on contractile dysfunction in the anterior wall, as evidenced by the echocardiographic data, and did not decrease the incidence of arrhythmias.…”