Mitochondrial dysfunction is considered as a crucial contributory factor in cardiac pathology. This has highlighted the therapeutic potential of targeting mitochondria to prevent or treat cardiac disease. Mitochondrial dysfunction is associated with aberrant electron transport chain activity, reduced ATP production, an abnormal shift in metabolic substrates, ROS overproduction and impaired mitochondrial dynamics. This review will cover the mitochondrial functions and how they are altered in various disease conditions. Furthermore, the mechanisms that lead to mitochondrial defects and the protective mechanisms that prevent mitochondrial damage will be discussed. Finally, potential mitochondrial targets for novel therapeutic intervention will be explored. We will highlight the development of small molecules that target mitochondria from different perspectives and their current progress in clinical trials.Linked Articles: This article is part of a themed section on Mitochondrial Pharmacology: Featured Mechanisms and Approaches for Therapy Translation. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.22/issuetoc

Background—: Stress-induced hypertrophic remodeling is a critical pathogenetic process leading to heart failure. Although many signal transduction cascades are demonstrated as important regulators to facilitate the induction of cardiac hypertrophy, the signaling pathways for suppressing hypertrophic remodeling remain largely unexplored. In this study, we identified p21-activated kinase 1 (Pak1) as a novel signaling regulator that antagonizes cardiac hypertrophy. Methods and Results—: Hypertrophic stress applied to primary neonatal rat cardiomyocytes (NRCMs) or murine hearts caused the activation of Pak1. Analysis of NRCMs expressing constitutively active Pak1 or in which Pak1 was silenced disclosed that Pak1 played an antihypertrophic role. To investigate the in vivo role of Pak1 in the heart, we generated mice with a cardiomyocyte-specific deletion of Pak1 (Pak1 ^cko ). When subjected to 2 weeks of pressure overload, Pak1 ^cko mice developed greater cardiac hypertrophy with attendant blunting of JNK activation compared with controls, and these knockout mice underwent the transition into heart failure when prolonged stress was applied. Chronic angiotensin II infusion also caused increased cardiac hypertrophy in Pak1 ^cko mice. Moreover, we discovered that the Pak1 activator FTY720, a sphingosine-like analog, was able to prevent pressure overload-induced hypertrophy in wild-type mice without compromising their cardiac functions. Meanwhile, FTY720 failed to exert such an effect on Pak1 ^cko mice, suggesting that the antihypertrophic effect of FTY720 likely acts through Pak1 activation. Conclusions—: These results, for the first time, establish Pak1 as a novel antihypertrophic regulator and suggest that it may be a potential therapeutic target for the treatment of cardiac hypertrophy and heart failure.

Ferroportin 1 (FPN1) is an iron export protein expressed in liver and duodenum, as well as in reticuloendothelial macrophages. Previously, we have shown that divalent metal transporter 1 (DMT1) is expressed in late endosomes and lysosomes of the kidney proximal tubule (PT), the nephron segment responsible for the majority of solute reabsorption. We suggested that following receptor mediated endocytosis of transferrin filtered by the glomerulus, DMT1 exports iron liberated from transferrin into the cytosol. FPN1 is also expressed in the kidney yet its role remains obscure. As a first step towards determining the role of renal FPN1, we localized FPN1 in the PT. FPN1 was found to be located in association with the basolateral PT membrane and within the cytosolic compartment. FPN1 was not expressed on the apical brush-border membrane of PT cells. These data support a role for FPN1 in vectorial export of iron out of PT cells. Furthermore, under conditions of iron loading of cultured PT cells, FPN1 was trafficked to the plasma membrane suggesting a coordinated cellular response to export excess iron and limit cellular iron concentrations.

We investigated whether plasma long-chain sphingoid base (LCSB) concentrations are altered by transient cardiac ischemia during percutaneous coronary intervention (PCI) in humans and examined the signaling through the sphingosine-1-phosphate (S1P) cascade as a mechanism underlying the S1P cardioprotective effect in cardiac myocytes. Venous samples were collected from either the coronary sinus ( n = 7) or femoral vein ( n = 24) of 31 patients at 1 and 5 min and 12 h, following induction of transient myocardial ischemia during elective PCI. Coronary sinus levels of LCSB were increased by 1,072% at 1 min and 941% at 5 min ( n = 7), while peripheral blood levels of LCSB were increased by 579% at 1 min, 617% at 5 min, and 436% at 12 h ( n = 24). In cultured cardiac myocytes, S1P, sphingosine (SPH), and FTY720, a sphingolipid drug candidate, showed protective effects against CoCl induced hypoxia/ischemic cell injury by reducing lactate dehydrogenase activity. Twenty-five nanomolars of FTY720 significantly increased phospho-Pak1 and phospho-Akt levels by 56 and 65.6% in cells treated with this drug for 15 min. Further experiments demonstrated that FTY720 triggered nitric oxide release from cardiac myocytes is through pertussis toxin-sensitive phosphatidylinositol 3-kinase/Akt/endothelial nitric oxide synthase signaling. In ex vivo hearts, ischemic preconditioning was cardioprotective in wild-type control mice (Pak1^f/f), but this protection appeared to be ineffective in cardiomyocyte-specific Pak1 knockout (Pak1^cko) hearts. The present study provides the first direct evidence of the behavior of plasma sphingolipids following transient cardiac ischemia with dramatic and early increases in LCSB in humans. We also demonstrated that S1P, SPH, and FTY720 have protective effects against hypoxic/ischemic cell injury, likely a Pak1/Akt1 signaling cascade and nitric oxide release. Further study on a mouse model of cardiac specific deletion of Pak1 demonstrates a crucial role of Pak1 in cardiac protection against ischemia/reperfusion injury.

The H⁺-coupled polyligand transport protein divalent metal transporter 1 (DMT1) plays a key role in mammalian iron homeostasis. It has a widespread pattern of expression including tissues associated with iron acquisition and storage. Interestingly, it is also highly expressed in the kidney, yet its function in this tissue is unknown. The aim of this study was to determine the cellular location of DMT1 in proximal tubule cells as a first step to determining the role of this protein in the kidney. To do this we performed RT-PCR and immunostaining experiments using rat kidney and the S1 proximal tubule-derived WKPT-0293 Cl.2 cell line. RT-PCR revealed that mRNAs encoding all four DMT1 splice variants were present in RNA extracted from rat kidney cortex or WKPT-0293 Cl.2 cells. Immunostaining of rat kidney cortex or WKPT-0293 Cl.2 cells showed that DMT1 protein was expressed intracellularly and was not present in the plasma membrane. Expression of DMT1 partially colocalized with the late endosomal/lysosomal proteins LAMP1 and cathepsin-L. Using immunogold labeling, DMT1 was shown to be expressed in the membranes of late endosomes/lysosomes. Uptake of Alexa Fluor 546-transferrin was only observed following application to the apical membrane of WKPT-0293 Cl.2 cells. Within these cells, Alexa Fluor 546-transferrin colocalized with DMT1. In conclusion, renal proximal tubular cells express DMT1 in the membranes of organelles, including late endosomes/lysosomes, associated with processing of apically sequestered transferrin. These findings have implications for renal iron handling and possibly for the handling of nephrotoxic metals that are also DMT1 ligands, including Cd²⁺.