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The use of doxorubicin (Dox) in cancer patients carries the risk of cardiotoxicity which is associated with an excessive production of reactive oxygen species as well as an imbalance in the redox state affecting mitochondrial functioning, ER homeostasis and protein folding. An accumulation of misfolded proteins triggers the unfolded protein response (UPR) known as ER stress. Subsequently ER-stress induced apoptosis results in loss of cardiomyocytes. Despite clinical trials indicating the benefits of an antidiabetic drug, Empagliflozin (EMPA) in reducing cardiovascular deaths and hospitalization rate in heart failure patients, it remains uncertain whether EMPA exerts a cardioprotective effect on Dox-induced cardiomyopathy (DIC). Herein, we aimed to investigate the effects of EMPA on Dox-induced ER stress and cardiomyopathy. In isolated adult rat cardiomyocytes, Dox (10μM, 24hrs) induced oxidative stress causing the activation of inflammation markers as well as ER-stress markers. Interestingly, EMPA (500nM, 24hrs) treatment prior to Dox was able to reduce oxidative stress; inflammatory markers (IL-1β, TNFα, and TGFβ), and significantly increased the expression of STAT-3. Dox-induced ER-stress activated ER transmembrane proteins and upregulated the expression of various genes, including X-box binding protein 1 (XBP1). The splicing of XBP1 mRNA on Dox treatment generated spliced XBP1 and subsequently up-regulated chaperones like glucose regulated protein 94 (GRP94), glucose regulated protein 78 (GRP78), and/or protein disulfide-isomerase (PDI). These Dox-induced changes in the upregulation of ER stress proteins were blunted by EMPA. EMPA also promoted expression of inositol requiring kinase 1α (IRE1α) which helped in maintaining ER homeostasis. Additionally, EMPA treatment, down-regulated caspase-12 and caspase-3 activation as well as phosphorylation of c-JUN NH2-terminal kinase (JNK), thereby promoting cardiomyocyte survival. These cardioprotective effects of EMPA on the reduction of ER stress in an in-vitro DIC model suggests its therapeutic potential that can occur independent of the effects related to diabetes. Thus, EMPA may contribute to improvements in cardiac damage during Dox mediated stress and inflammation. The recognition of Dox-induced cardiotoxicity as well as a dire need for a cardioprotective agent to be administered in conjunction with Dox is evident and EMPA may prove to be such an agent. Supported by CANUSA grant. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Rationale: The vascular adventitia is a complex layer of the vessel wall consisting of vasa vasorum microvessels, nerves, fibroblasts, immune cells, and resident progenitor cells. Adventitial progenitors express the stem cell markers, Sca1 and CD34 (adventitial sca1-positive progenitor cells [AdvSca1]), have the potential to differentiate in vitro into multiple lineages, and potentially contribute to intimal lesions in vivo. Objective: Although emerging data support the existence of AdvSca1 cells, the goal of this study was to determine their origin, degree of multipotency and heterogeneity, and contribution to vessel remodeling. Methods and Results: Using 2 in vivo fate-mapping approaches combined with a smooth muscle cell (SMC) epigenetic lineage mark, we report that a subpopulation of AdvSca1 cells is generated in situ from differentiated SMCs. Our data establish that the vascular adventitia contains phenotypically distinct subpopulations of progenitor cells expressing SMC, myeloid, and hematopoietic progenitor-like properties and that differentiated SMCs are a source to varying degrees of each subpopulation. SMC-derived AdvSca1 cells exhibit a multipotent phenotype capable of differentiating in vivo into mature SMCs, resident macrophages, and endothelial-like cells. After vascular injury, SMC-derived AdvSca1 cells expand in number and are major contributors to adventitial remodeling. Induction of the transcription factor Klf4 in differentiated SMCs is essential for SMC reprogramming in vivo, whereas in vitro approaches demonstrate that Klf4 is essential for the maintenance of the AdvSca1 progenitor phenotype. Conclusions: We propose that generation of resident vascular progenitor cells from differentiated SMCs is a normal physiological process that contributes to the vascular stem cell pool and plays important roles in arterial homeostasis and disease.