Project Grant R01HL179092

ROLE OF STRESS SIGNALS IN THE PATHOGENESIS OF PULMONARY VENO-OCCLUSIVE DISEASE - PROJECT SUMMARY/ABSTRACT PULMONARY VENO-OCCLUSIVE DISEASE (PVOD) IS A SUBCLASS OF PULMONARY HYPERTENSION CHARACTERIZED BY PREFERENTIAL REMODELING OF THE PULMONARY VENULES AND CAPILLARIES, AND CURRENTLY, THERE ARE NO EFFICACIOUS DRUG THERAPIES. THE CLINICAL PRESENTATIONS AND THE RADIOGRAPHIC FINDINGS OF PVOD ARE INDISTINGUISHABLE FROM PAH, AND THEREFORE, IT IS OFTEN MISCLASSIFIED AS PAH. HOWEVER, THE APPLICATION OF PAH THERAPEUTICS TO PVOD PATIENTS LEADS TO LIFE-THREATENING PULMONARY EDEMA, THUS, THERE IS A CRITICAL NEED FOR DIAGNOSTIC METHODS THAT ACCURATELY DIFFERENTIATE PVOD FROM PAH. GENETICALLY, PVOD IS ASSOCIATED WITH BIALLELIC LOSS OF FUNCTION (LOF) MUTATIONS IN THE EIF2AK4 GENE ENCODING GCN2. GCN2 PHOSPHORYLATES THE ALPHA SUBUNIT OF EUKARYOTIC INITIATION FACTOR 2 (EIF2A), SHUTS DOWN PROTEIN SYNTHESIS, AND ACTIVATES THE INTEGRATED STRESS RESPONSE (ISR). HOWEVER, THE MOLECULAR MECHANISMS CONNECTING THE LOSS OF GCN2 WITH PULMONARY VASCULAR REMODELING ARE POORLY UNDERSTOOD. RECENT STUDIES FIND THAT BIALLELIC EIF2AK4 MUTATIONS ARE IDENTIFIED IN ~9% OF PAH PATIENTS. CONVERSELY, HETEROZYGOUS MUTATIONS IN THE BMPR2 GENE, A LEADING CAUSE OF PAH, HAVE BEEN REPORTED IN PVOD PATIENTS. THESE RESULTS SUGGEST THAT (I) PVOD AND PAH SHARE SOME OF THE PATHOPHYSIOLOGICAL MECHANISMS, AND (II) THE PRESENCE OF EIF2AK4 OR BMPR2 MUTATIONS DOES NOT PROVIDE AN ACCURATE GENETIC DIAGNOSIS FOR PVOD. THE LONG-TERM GOAL OF THIS PROPOSAL IS TO ELUCIDATE THE PATHOPHYSIOLOGICAL MECHANISMS INVOLVED IN REMODELING NOT ONLY PULMONARY ARTERIOLES BUT ALSO VENULES AND CAPILLARIES AND DEVELOP THOSE PATHWAYS AS POTENTIAL THERAPIES FOR POVD. IT HAS BEEN OBSERVED THAT CANCER PATIENTS ADMINISTERED WITH THE CHEMOTHERAPEUTIC AGENT MITOMYCIN-C (MMC) RAPIDLY DEVELOP PVOD. RATS ADMINISTERED WITH MMC DEVELOP PVOD-LIKE PHENOTYPES, INCLUDING RIGHT VENTRICULAR (RV) HYPERTROPHY, INCREASED RV SYSTOLIC PRESSURE, AND PULMONARY VASCULAR LESIONS IN ARTERIES AND VEINS. WE FOUND THAT RAD51, AN ESSENTIAL ENZYME FOR DOUBLE-STRAND DNA BREAK REPAIR, ASSOCIATES WITH VE-CAD IN THE VASCULAR ENDOTHELIUM; HOWEVER, UPON MMC TREATMENT, RAD51 AND VE-CAD COMPLEX (VRC) WERE RELEASED INTO THE CIRCULATION, RESULTING IN INCREASED VASCULAR PERMEABILITY AND REDUCED BARRIER INTEGRITY. MMC TREATMENT ALSO MEDIATES THE DEPLETION OF GCN2, WHICH RECAPITULATES THE GENETIC CAUSE OF PVOD (LOF EIF2AK4 MUTATIONS). BASED ON THESE DATA, THIS PROPOSAL WILL TEST THE HYPOTHESIS THAT THE VASCULAR REMODELING IN PVOD INVOLVES (I) THE RELEASE OF VRC, (II) THE ABERRANT PROTEIN SYNTHESIS DUE TO THE ACTIVATION OF ISR, AND (III) THE MECHANISM OF MALADAPTIVE ISR ACTIVATION. FINALLY, WE WILL EXPLORE THE POTENTIAL APPLICATION OF THE CIRCULATING VRC AS A BLOOD BIOMARKER FOR PVOD.