Abstract 88: Small Molecule Inhibition of Mixed Lineage Kinase 3 Attenuates Cardiac Fibroblast Activation and Pathologic Cardiac Remodeling

Abstract

Heart failure (HF) is a manifestation of most cardiovascular diseases whose increasing prevalence highlights the need for novel therapeutics. The extent of pathologic cardiac remodeling is correlated with clinical outcome. Importantly, cardiac injury enhances cardiac fibroblast (CF) activation, producing myofibroblasts that release pro-fibrotic/inflammatory mediators which target cardiomyocytes (CM), CFs, and local inflammatory cells to exacerbate remodeling. Mixed Lineage Kinases (MLKs) are a family of stress-activated MAPKKKs whose functional role(s) in the heart remain largely unknown. MLK3 has been implicated in HIV-associated neurocognitive disorder (HAND), where it mediates deleterious cross-talk between microglia and neurons, suggesting an analogous mechanism of pathologic intercellular CF-CM communication in HF. We hypothesize that MLK3 exacerbates cardiac remodeling through enhanced CF activation that contributes to pathologic cardiac intercellular communication. We have synthesized a series of MLK3-specific small molecule inhibitors, one of which (URMC-099) was found to attenuate microglial-mediated neurotoxicity in murine models of HAND. To investigate the role of MLK3 in CF activation, neonatal rat ventricular CFs were stimulated with isoproterenol (Iso) or angiotensin II (AngII). Concurrent treatment with URMC-099 attenuated both α-smooth muscle actin expression, indicative of myofibroblast transition, and proinflammatory cytokine production. Further, therapeutic efficacy and specificity of URMC-099 were tested in iso-infused and myocardial infarction (MI) models of HF using wild-type (WT) and MLK3-/- mice (shown to have no overt cardiac phenotype). URMC-099 significantly attenuated cardiac hypertrophy (HW:BW) and reduced interstitial fibrosis (assessed by Masson's Trichrome staining) in an acute iso-pump model of HF in WT mice. Current echocardiographic data post-MI suggest cardioprotection in the MLK3-/- and URMC-099 treated mice. In conclusion, our collaborative data not only suggest a role for MLK3 in cardiac remodeling through pathologic CF activation but indicate a possibly novel paradigm of pathologic intercellular communication in multiple disease states.