The Effects of Optic Atrophy Protein (OPA)-1 Deletion on Platelet Function Is Regulated By the Hormonal Milieu
Authors: Souvenir Rhonda , Jensen Melissa J , Fidler Trevor P.L. , Volker Joshua A , Dayal Sanjana , Weyrich Andrew S. , Abel E Dale 
Published: October 2019

Abstract
Cardiovascular diseases (CVD) are the leading cause of death in the United States. Thrombosis represents one of the most common underlying pathologies in CVD and disproportionately plagues females. Analyses of transcripts from the Framingham offspring cohort, revealed enrichment in transcripts encoding for the mitochondrial dynamics protein: optic atrophy-1 in females that positively correlated with coronary heart disease and diabetes. Optic atrophy (OPA)-1 regulates mitochondrial fusion, electron transport chain (ETC), complex assembly and apoptosis. The correlation suggests that altered mitochondrial dynamics may contribute to platelet dysfunction. Thus, to determine whether the enrichment in OPA1 transcripts in females that correlates with increased CVD risk represents a physiological adaptation or a pathophysiological response, mice with platelet-specific deletion of OPA1 (pOPA-1 KO) were generated. Male pOPA-1 KO mice exhibited compromised cristae morphology and a 50% reduction in mitochondrial DNA. Additionally, mitochondrial function assessed by an extracellular flux analyzer (XF24 Seahorse biosciences) was reduced by 50%. Mitochondrial dysfunction in male pOPA-1 KO mice was associated with heightened agonist-mediated platelet activation (a hyperactive phenotype). Male pOPA-1 KO mice had a shortened time to stable occlusion of the carotid artery as assessed in vivo by (rose Bengal) photochemical injury (~25 min knockout vs ~ 35 min control), and were more prone to develop a thrombus (14/15 knockouts vs. 4/8 controls) following permanent ligation of the inferior vena cava. In contrast, cristae morphology was normal and mitochondrial DNA unchanged in females. Females revealed no evidence of heightened agonist response or increased incidence of thrombus formation. In contrast, female pOPA-1 KO mice had increased time to stable occlusion of the carotid artery as assessed by photochemical injury (~75 min knockout vs ~35 min control). Additionally, when platelets from pOPA-1 KO or control males were transferred into female mice harboring the human interleukin 4 receptor (HIL4R) transgene that were depleted of their native platelets by HIL4R antibodies, the reconstituted male platelets acquired the phenotype of female pOPA-1 KO mice. Thus, the time to stable occlusion of the carotid artery following photochemical injury was increased. In parallel, gonadectomized pOPA-1 KO male mice were protected from the prothrombotic phenotype. Additionally, gonadectomized female pOPA-1 KO no longer exhibited increased time to stable carotid artery occlusion. These findings suggest a direct interaction between platelet genotype and the systemic milieu, which determines platelet function in pOPA-1 KO mice and the modulation by gonadectomy suggests a role for sex steroids. Thus, whereas preserving OPA-1 expression might be a protective adaptation in males, OPA-1 induction in platelets of females that correlates with CVD in humans, might promote platelet hyper-activation.

Disclosures
No relevant conflicts of interest to declare.