Biochemistry and physiology of mitochondrial ion channels involved in cardioprotection

Over the past decades there has been considerable progress in understanding the multifunctional roles of mitochondrial ion channels in metabolism, energy transduction, ion transport, signaling, and cell death. Recent data have suggested that some of these channels function under physiological condition, and others may be activated in response to pathological insults and play a key role in cytoprotection. This review outlines our current understanding of the molecular identity and pathophysiological roles of the mitochondrial ion channels in the heart with particular emphasis on cardioprotection against ischemia/reperfusion injury, and future research on mitochondrial ion channels.     

The Role of Cyclophilins in Inflammatory Bowel Disease and Colorectal Cancer

Cyclophilins (Cyps) is a kind of ubiquitous protein family in organisms, which has biological functions such as promoting intracellular protein folding and participating in the pathological processes of inflammation and tumor. Inflammatory bowel disease (IBD) and colorectal cancer (CRC) are two common intestinal diseases, but the etiology and pathogenesis of these two diseases are still unclear. IBD and CRC are closely associated, IBD has always been considered as one of the main risks of CRC. However, the role of Cyps in these two related intestinal diseases is rarely studied and reported. In this review, the expression of CypA, CypB and CypD in IBD, especially ulcerative colitis (UC), and CRC, their relationship with the development of these two intestinal diseases, as well as the possible pathogenesis, were briefly summarized, so as to provide modest reference for clinical researches and treatments in future.     

GD3-7-aldehyde is an apoptosis inducer and interacts with adenine nucleotide translocase

We prepared GD3-7-aldehyde (GD3-7) and determined its apoptotic potential. GD3-7 proved to be more efficient to induce pro-apoptotic mitochondrial alterations than GD3 when tested on mouse liver mitochondria. GD3-7-induced mitochondrial swelling and depolarization was blocked by cyclosporin A (CsA) supporting a critical role of the permeability transition pore complex (PTPC) during GD3-7-mediated apoptosis. In contrast to GD3, GD3-7 was able to induce channel formation in proteoliposomes containing adenine nucleotide translocase (ANT). This suggests that ANT is the molecular target of GD3-7. Using a specific antiserum, GD3-7 was detected in the lipid extract of the myeloid tumor cell line HL-60 after apoptosis induction, but not in living cells. Therefore, GD3-7 might be a novel mediator of PTPC-dependent apoptosis in cancer cells.     

Electrophysiology clarifies the megariddles of the mitochondrial permeability transition pore

After a brief review of the early history of mitochondrial electrophysiology, the contribution of this approach to the study of the mitochondrial permeability transition (MPT) is recapitulated. It has for example provided evidence for a dimeric nature of the MPT pore, allowed the distinction between two levels of control of its activity, and underscored the relevance of redox events for the phenomenon. Single-channel recording provides a means to finally solve the riddle of the biochemical entity underlying it by comparing the characteristics of the pore with those of channels formed by candidate molecules or complexes. The possibility that this entity may be the protein import machinery of the inner mitochondrial membrane is emphasized.     

A possible pivotal role of mitochondrial free calcium in neurotoxicity mediated by N-methyl-d-aspartate receptors in cultured rat hippocampal neurons

We have previously shown that mitochondrial membrane potential disruption is involved in mechanisms underlying differential vulnerabilities to the excitotoxicity mediated by N-methyl-d-aspartate (NMDA) receptors between primary cultured neurons prepared from rat cortex and hippocampus. To further elucidate the role of mitochondria in the excitotoxicity after activation of NMDA receptors, neurons were loaded with the fluorescent dye calcein diffusible in the cytoplasm and organelles for determination of the activity of mitochondrial permeability transition pore (mPTP) responsible for the leakage of different mitochondrial molecules. The addition of CoCl₂ similarly quenched the intracellular fluorescence except mitochondria in both cultured neurons, while further addition of NMDA led to a leakage of the dye into the cytoplasm in hippocampal neurons only. An mPTP inhibitor prevented the NMDA-induced loss of viability in hippocampal neurons, while an activator of mPTP induced a similarly potent loss of viability in cortical and hippocampal neurons. Although NMDA was more effective in increasing rhodamine-2 fluorescence as a mitochondrial calcium indicator in hippocampal than cortical neurons, a mitochondrial calcium uniporter inhibitor significantly prevented the NMDA-induced loss of viability in hippocampal neurons. Expression of mRNA was significantly higher for the putative uniporter uncoupling protein-2 in hippocampal than cortical neurons. These results suggest that mitochondrial calcium uniporter would be at least in part responsible for the NMDA neurotoxicity through a mechanism relevant to promotion of mPTP orchestration in hippocampal neurons.     

Cyclophilin D deficiency protects against the development of mitochondrial ROS and cellular inflammation in aorta

Introduction

Inflammation and oxidative stress are closely correlated in the pathology of cardiovascular disease. Mitochondrial cyclophilin D (CypD), the important modulator for mPTP opening, is increasingly recognized as a key regulator of cellular ROS generation. Besides, its association with cell inflammation is also being discovered. However, the effects of CypD in modulating vascular inflammatory response is unknown. We sought to investigate whether CypD deficiency attenutes vascular inflammation under physical conditions.

Targeting post-mitochondrial effectors of apoptosis for neuroprotection

Mitochondrial membrane permeabilization (MMP) is commonly regarded as the “point-of-no-return” in the cascade of events that delineate the intrinsic pathway of apoptosis. MMP leads to the functional impairment of mitochondria and to the release into the cytosol of toxic proteins that are normally confined within the mitochondrial intermembrane space. These include direct activators of caspases and caspase-independent effectors of the cell death program. MMP has been implicated in a plethora of pathophysiological settings. In particular, MMP contributes to both the immediate and delayed phases of cell loss that follow acute neuronal injury by ischemia/reperfusion or trauma. Although preventing MMP a priori would be the most desirable therapeutic choice, prophylactic interventions are rarely (if ever) achievable in the treatment of stroke and trauma patients. Conversely, interventions that block the post-mitochondrial phase of apoptosis (if administered within the first few hours after the accident) hold great promises for the development of novel neuroprotective strategies. In animal models of acute neuronal injury, the inhibition of caspases, apoptosis-inducing factor (AIF) and other apoptotic effectors can confer significant neuroprotection. Our review recapitulates the results of these studies and proposes novel strategies of inhibiting post-mitochondrial apoptosis in neurons.     

Estrogen receptor beta modulates permeability transition in brain mitochondria

Recent evidence highlights a role for sex and hormonal status in regulating cellular responses to ischemic brain injury and neurodegeneration. A key pathological event in ischemic brain injury is the opening of a mitochondrial permeability transition pore (MPT) induced by excitotoxic calcium levels, which can trigger irreversible damage to mitochondria accompanied by the release of pro-apoptotic factors. However, sex differences in brain MPT modulation have not yet been explored. Here, we show that mitochondria isolated from female mouse forebrain have a lower calcium threshold for MPT than male mitochondria, and that this sex difference depends on the MPT regulator cyclophilin D (CypD). We also demonstrate that an estrogen receptor beta (ERβ) antagonist inhibits MPT and knockout of ERβ decreases the sensitivity of mitochondria to the CypD inhibitor, cyclosporine A. These results suggest a functional relationship between ERβ and CypD in modulating brain MPT. Moreover, co-immunoprecipitation studies identify several ERβ binding partners in mitochondria. Among these, we investigate the mitochondrial ATPase as a putative site of MPT regulation by ERβ. We find that previously described interaction between the oligomycin sensitivity-conferring subunit of ATPase (OSCP) and CypD is decreased by ERβ knockout, suggesting that ERβ modulates MPT by regulating CypD interaction with OSCP. Functionally, in primary neurons and hippocampal slice cultures, modulation of ERβ has protective effects against glutamate toxicity and oxygen glucose deprivation, respectively. Taken together, these results reveal a novel pathway of brain MPT regulation by ERβ that could contribute to sex differences in ischemic brain injury and neurodegeneration.     

The properties of the mitochondrial megachannel in mitoplasts from human colon carcinoma cells are not influenced by Bax

This paper explores the relationship between Bax and the mitochondrial permeability transition pore (PTP). Isolated human colon tumor (HCT116) Bax- mitochondria exposed to recombinant Bax exhibited a slow, cyclosporin A-sensitive swelling, but only at [Bax]>200 nM. The amount of Bax incorporated was much higher than that found in organelles isolated from HCT116 Bax+ staurosporine- or etoposide-treated apoptotic cells, casting doubts on the significance of the putative PT induction for apoptosis. Bax did not influence the electrophysiological properties of an approximately 1 nS channel ascribed to the Ca2+-dependent mitochondrial permeability transition pore. These observations indicate that the PTP is independent of Bax.