CARDIAC PATHOLOGIC EFFECTS OF UREMIC TOXINS IN CARDIORENAL SYNDROME

Chronic kidney disease is characterized by the progressive accumulation of protein-bound uremic toxins such as indoxyl sulfate (IS) and p-cresyl sulfate (PCS), which contribute to the development of cardiovascular complications and cardiorenal syndrome type 4. Clinical evidence links these toxins to oxidative stress, electrical remodelling, and impaired cardiac function. However, most mechanistic insights derive from animal models, which limits their translational relevance to human disease. This doctoral research aims to define the cellular and molecular effects of IS and PCS on human cardiomyocytes and to investigate the mechanisms through which toxin accumulation may contribute to cardiomyocytes dysfunction and stress-related cardiomyopathy. To this end, the study employs human induced pluripotent stem cell–derived cardiomyocytes (hiPSC-CMs) as an in vitro model of acute and chronic toxin exposure. hiPSC-CMs were treated with clinically relevant concentrations of IS (0.1 mM, 0.5 mM and 1 mM) and PCS (0.1 mM and 0.5 mM) over short- and long-term exposure periods. The study evaluates oxidative stress, cell viability, proliferative capacity, DNA damage responses, senescence, and apoptotic signalling using complementary biochemical and imaging-based assays. In parallel, the work examines calcium-handling properties through live-cell calcium imaging and investigates the expression, activation state, and post-translational modifications of Ca2+/ Calmodulin dependent kinase II delta (CaMKIIδ) and Ca²⁺-regulatory proteins, including the voltage dependent L- type calcium channel (Cav1.2), the ryanodine receptor 2 (RyR2), phospholamban (PLN) and sarco- endoplasmic reticulum calcium ATPase 2a (SERCA2a). By integrating functional, molecular, and signalling analyses in a human-based cellular model, this project seeks to clarify how uremic toxins affect cardiomyocytes homeostasis and excitation–contraction coupling. Overall, the study aims to provide mechanistic insights that bridge clinical observations of cardiovascular risk in CKD patients with toxin-mediated cellular dysfunction, offering a translationally relevant framework for understanding uremic cardiomyopathy.