The Reactive Oxygen Species-Mitophagy Signaling Pathway Regulates Liver Endothelial Cell Survival During Ischemia/Reperfusion Injury.

Ischemia/reperfusion injury (IRI) is the main cause of complications following liver transplantation. Reactive oxygen species (ROS) were thought to be the main regulators of IRI. However, recent studies demonstrate that ROS activate the cytoprotective mechanism of autophagy promoting cell survival. Liver IRI initially damages the liver endothelial cells (LEC), but whether ROS-autophagy promotes cell survival in LEC during IRI is not known. Primary human LEC were isolated from human liver tissue and exposed to an in vitro model of IRI to assess the role of autophagy in LEC. The role of autophagy during liver IRI in vivo was assessed using a murine model of partial liver IRI. During IRI, ROS specifically activate autophagy-related protein (ATG) 7 promoting autophagic flux and the formation of LC3B-positive puncta around mitochondria in primary human LEC. Inhibition of ROS reduces autophagic flux in LEC during IRI inducing necrosis. In addition, small interfering RNA knockdown of ATG7 sensitized LEC to necrosis during IRI. In vivo murine livers in uninjured liver lobes demonstrate autophagy within LEC that is reduced following IRI with concomitant reduction in autophagic flux and increased cell death. In conclusion, these findings demonstrate that during liver IRI ROS-dependent autophagy promotes the survival of LEC, and therapeutic targeting of this signaling pathway may reduce liver IRI following transplantation.

B cells from patients with multiple sclerosis induce cell death via apoptosis in neurons in vitro.

B cells mediate multiple sclerosis (MS) pathogenesis by mechanisms unrelated to immunoglobulin (Ig). We reported that supernatants (Sup) from cultured B cells from blood of relapsing remitting MS (RRMS) patients, but not normal controls (NC), were cytotoxic to rat oligodendrocytes (OL). We now show that RRMS blood B cells, not stimulated in vitro, secrete factor/s toxic to rat and human neurons. Cytotoxicity is independent of Ig and multiple cytokines, not complement-mediated, and involves apoptosis. The factor/s have an apparent mw of >300kDa. B cells could contribute to damage within the central nervous system by secreting molecules toxic to OL and neurons.

Cytokine-Defined B Cell Responses as Therapeutic Targets in Multiple Sclerosis.

Important antibody-independent pathogenic roles of B cells are emerging in autoimmune diseases, including multiple sclerosis (MS). The contrasting results of different treatments targeting B cells in patients (in spite of predictions of therapeutic benefits from animal models) call for a better understanding of the multiple roles that distinct human B cell responses likely play in MS. In recent years, both murine and human B cells have been identified with distinct functional properties related to their expression of particular cytokines. These have included regulatory (Breg) B cells (secreting interleukin (IL)-10 or IL-35) and pro-inflammatory B cells (secreting tumor necrosis factor α, LTα, IL-6, and granulocyte macrophage colony-stimulating factor). Better understanding of human cytokine-defined B cell responses is necessary in both health and diseases, such as MS. Investigation of their surface phenotype, distinct functions, and the mechanisms of regulation (both cell intrinsic and cell extrinsic) may help develop effective treatments that are more selective and safe. In this review, we focus on mechanisms by which cytokine-defined B cells contribute to the peripheral immune cascades that are thought to underlie MS relapses, and the impact of B cell-directed therapies on these mechanisms.

The expression of neuronal sorting nexin 8 (SNX8) exacerbates abnormal cholesterol levels.

SNX8 is a PX-BAR domain sub-family of sorting nexins (SNXs), which is reported as a ß-amyloid (Aß) toxicity enhancer and associated with Alzheimer's disease. We have also described SNX8 as a novel activator of the sterol regulatory element binding protein (SREBP) transcription factor, a major regulator of cholesterol homeostasis. In that study, we have showed that SNX8 reduced an insulin-induced gene (INSIG)-dependent block of SREBP-mediated transcription. Here, for the first time, we investigated the expression and function of SNX8 within the CNS. We found that SNX8 was expressed within neurons, but not astrocytes or microglia, with neuronal localisation primarily in the soma. The protein levels of neuronal SNX8 were unchanged in the presence of moderately high cholesterol but were decreased by mevinolin (a cholesterol-lowering statin) and U18666a (which causes cholesterol to accumulate within the lysosome). To determine if SNX8 overexpression alters the levels of cholesterol, we engineered a GFP-SNX8 lentivirus. The overexpression of GFP-SNX8 had no effect on cholesterol in neurons under control conditions or in already strongly altered cholesterol conditions of mevinolin or U18666a. In contrast, in moderately high cholesterol, the overexpression of GFP-SNX8 caused redistribution of cholesterol within neurons creating a phenotype similar to U18666a treatment. Taken together, these data suggest that extreme changes in cholesterol reduce SNX8 expression and that overexpression of SNX8 exacerbates aberrant handling of neuronal cholesterol. This work further supports the role for SNX8 in regulating cholesterol levels, which could be important in understanding its role as an Aß toxicity enhancer and its association with Alzheimer's disease.