Fighting cancer by triggering non-canonical mitochondrial permeability transition-driven necrosis through reactive oxygen species induction.

Non-apoptotic necrosis shows therapeutic potential for the treatment of various diseases, especially cancer. Mitochondrial permeability transition (MPT)-driven necrosis is a form of non-apoptotic cell death triggered by oxidative stress and cytosolic Ca2+ overload, and relies on cyclophilin D (CypD). Previous reports demonstrated that isobavachalcone (IBC), a natural chalcone, has anticancer effect by apoptosis induction. Here, we found that IBC induced regulated necrosis in cancer cells. IBC triggered non-apoptotic cell death in lung and breast cancer cells mediated by reactive oxygen species (ROS). IBC caused mitochondrial injury and dysfunction as evidenced by mitochondrial Ca2+ overload, the opening of MPT pore, mitochondrial membrane potential collapse, and structural damages. IBC-triggered cell death could be remarkably reversed by the ROS scavengers, cyclosporin A (CsA) and hemin, whereas CypD silence and heme oxygenase-1 overexpression failed to do so. Protein kinase B, dihydroorotate dehydrogenase, and mitogen-activated protein kinases were not involved in IBC-induced necrosis as well. In addition, IBC showed an anticancer effect in a 4T1 breast cancer cell-derived allograft mouse model, and this effect was considerably reversed by CsA. Collectively, our results showed that IBC triggered non-canonical MPT-driven necrosis mediated by ROS in cancer cells, which might provide a novel strategy for fighting against cancer.

Cyclophilin D-mediated angiotensin II-induced NADPH oxidase 4 activation in endothelial mitochondrial dysfunction that can be rescued by gallic acid.

Vascular endothelial dysfunction plays a central role in the most dreadful human diseases, including stroke, tumor metastasis, and the coronavirus disease 2019 (COVID-19). Strong evidence suggests that angiotensin II (Ang II)-induced mitochondrial dysfunction is essential for endothelial dysfunction pathogenesis. However, the precise molecular mechanisms remain obscure. Here, polymerase-interacting protein 2 (Poldip 2) was found in the endothelial mitochondrial matrix and no effects on Poldip 2 and NADPH oxidase 4 (NOX 4) expression treated by Ang II. Interestingly, we first found that Ang II-induced NOX 4 binds with Poldip 2 was dependent on cyclophilin D (CypD). CypD knockdown (KD) significantly inhibited the binding of NOX 4 to Poldip 2, and mitochondrial ROS generation in human umbilical vein endothelial cells (HUVECs). Similar results were also found in cyclosporin A (CsA) treated HUVECs. Our previous study suggested a crosstalk between extracellular regulated protein kinase (ERK) phosphorylation and CypD expression, and gallic acid (GA) inhibited mitochondrial dysfunction in neurons depending on regulating the ERK-CypD axis. Here, we confirmed that GA inhibited Ang II-induced NOX 4 activation and mitochondrial dysfunction via ERK/CypD/NOX 4/Poldip 2 pathway, which provide novel mechanistic insight into CypD act as a key regulator of the NOX 4/Poldip 2 axis in Ang II-induced endothelial mitochondrial dysfunction and GA might be beneficial in the treatment of wide variety of diseases, such as COVID-19, which is worthy further research.

Cyclophilin D Promotes Acute, but Not Chronic, Kidney Injury in a Mouse Model of Aristolochic Acid Toxicity.

The plant-derived toxin, aristolochic acid (AA), is the cause of Chinese Herb Nephropathy and Balkan Nephropathy. Ingestion of high dose AA induces acute kidney injury, while chronic low dose ingestion leads to progressive kidney disease. Ingested AA is taken up by tubular epithelial cells of the kidney, leading to DNA damage and cell death. Cyclophilin D (CypD) participates in mitochondrial-dependent cell death, but whether this mechanism operates in acute or chronic AA-induced kidney injury is unknown. We addressed this question by exposing CypD-/- and wild type (WT) mice to acute high dose, or chronic low dose, AA. Administration of 5 mg/kg AA to WT mice induced acute kidney injury 3 days later, characterised by loss of kidney function, tubular cell damage and death, and neutrophil infiltration. All of these parameters were significantly reduced in CypD-/- mice. Chronic low dose (2 mg/kg AA) administration in WT mice resulted in chronic kidney disease with impaired renal function and renal fibrosis by day 28. However, CypD-/- mice were not protected from AA-induced chronic kidney disease. In conclusion, CypD facilitates AA-induced acute kidney damage, but CypD does not contribute to the transition of acute kidney injury to chronic kidney disease during ongoing AA exposure.

Mutations in the Hsp90 N Domain Identify a Site that Controls Dimer Opening and Expand Human Hsp90α Function in Yeast.

Hsp90 is a highly conserved molecular chaperone important for the activity of many client proteins. Hsp90 has an N-terminal ATPase domain (N), a middle domain (M) that interacts with clients and a C-terminal dimerization domain (C). "Closing" of dimers around clients is regulated by ATP binding, co-chaperones, and post-translational modifications. ATP hydrolysis coincides with release of mature client and resetting the reaction cycle. Humans have two Hsp90s: hHsp90α and hHsp90ß. Although 85% identical, hHsp90ß supports Hsp90 function in yeast much better than hHsp90α. Determining the basis of this difference would provide important insight into functional specificity of seemingly redundant Hsp90s, and the evolution of eukaryotic Hsp90 systems and clientele. Here, we found host co-chaperones Sba1, Cpr6 and Cpr7 inhibited hHsp90α function in yeast, and we identified mutations clustering in the N domain that considerably improved hHsp90α function in yeast. The strongest of these rescuer mutations accelerated nucleotide-dependent lid closing, N-M domain docking, and ATPase. It also disrupted binding to Sba1, which prolongs the closed state, and promoted N-M undocking and lid opening. Our data suggest the rescuer mutations improve function of hHsp90α in yeast by accelerating return to the open state. Our findings imply hHsp90α occupies the closed state too long to function effectively in yeast, and define an evolutionarily conserved region of the N domain involved in resetting the Hsp90 reaction cycle.