Ryanodine Receptor Calcium Leak in Circulating B-Lymphocytes As a Biomarker in Heart Failure

Background: Advances in congestive heart failure (CHF) management depend on biomarkers for monitoring disease progression and therapeutic response. During systole, intracellular Ca is released from the sarcoplasmic reticulum into the cytoplasm through type-2 ryanodine receptor/Ca release channels. In CHF, chronically elevated circulating catecholamine levels cause pathological remodeling of type-2 ryanodine receptor/Ca release channels resulting in diastolic sarcoplasmic reticulum Ca leak and decreased myocardial contractility. Similarly, skeletal muscle contraction requires sarcoplasmic reticulum Ca release through type-1 ryanodine receptors (RyR1), and chronically elevated catecholamine levels in CHF cause RyR1-mediated sarcoplasmic reticulum Ca leak, contributing to myopathy and weakness. Circulating B-lymphocytes express RyR1 and catecholamine-responsive signaling cascades, making them a potential surrogate for defects in intracellular Ca handling because of leaky RyR channels in CHF.

Methods: Whole blood was collected from patients with CHF, CHF following left-ventricular assist device implant, and controls. Blood was also collected from mice with ischemic CHF, ischemic CHF+S107 (a drug that specifically reduces RyR channel Ca leak), and wild-type controls. Channel macromolecular complex was assessed by immunostaining RyR1 immunoprecipitated from lymphocyte-enriched preparations. RyR1 Ca leak was assessed using flow cytometry to measure Ca fluorescence in B-lymphocytes in the absence and presence of RyR1 agonists that empty RyR1 Ca stores within the endoplasmic reticulum.

Results: Circulating B-lymphocytes from humans and mice with CHF exhibited remodeled RyR1 and decreased endoplasmic reticulum Ca stores, consistent with chronic intracellular Ca leak. This Ca leak correlated with circulating catecholamine levels. The intracellular Ca leak was significantly reduced in mice treated with the Rycal S107. Patients with CHF treated with left-ventricular assist devices exhibited a heterogeneous response.

Conclusions: In CHF, B-lymphocytes exhibit remodeled leaky RyR1 channels and decreased endoplasmic reticulum Ca stores consistent with chronic intracellular Ca leak. RyR1-mediated Ca leak in B-lymphocytes assessed using flow cytometry provides a surrogate measure of intracellular Ca handling and systemic sympathetic burden, presenting a novel biomarker for monitoring response to pharmacological and mechanical CHF therapy.