Mitochondrial DNA enhance innate immune responses in neuromyelitis optica by monocyte recruitment and activation.

Although recent studies indicate the involvement of monocytes in accelerating the lesion formation of neuromyelitis optica spectrum disorder (NMOSD), the precise mechanism of the innate immune system activation remains elusive. Thus, in this study, we aimed to clarify the mechanisms of NMOSD pathogenesis from the viewpoint of innate immunity activation. We established anti-AQP4 recombinant autoantibodies (Ab) from plasmablasts in NMOSD patient's CSF. Human astrocytes treated with anti-AQP4 Ab produced a significant amount of CCL2 and contributed to the efficient recruitment of monocytes. Moreover, mitochondrial DNA (mtDNA), which activated monocytes via Toll-like receptor 9 (TLR9), was released from astrocytes treated with anti-AQP4 Ab. MtDNA further enhanced CCL2 production by monocytes, and it was demonstrated that mtDNA concentration correlated with the efficiency of monocyte recruitment in the CSF of NMOSD patients. In conclusion, these observations highlight that mtDNA which was released from astrocytes damaged by anti-AQP4 Ab has a central role in establishing the inflammatory loop of monocyte recruitment and activation via an innate immunity pathway.

Sema4A is implicated in the acceleration of Th17 cell-mediated neuroinflammation in the effector phase.

BACKGROUND: Sema4A is a regulator of helper T cell (Th) activation and differentiation in the priming phase, which plays an important role in the pathogenesis of experimental autoimmune encephalomyelitis (EAE) and multiple sclerosis (MS). However, the role of Sema4A in the effector phase remains elusive. We aimed to investigate the role of Sema4A at the effector phase in adoptively transferred EAE model. Clinical features and cytokine profiles of MS patients with high Sema4A levels were also examined in detail to clarify the correlation between Sema4A levels and disease activity of patients with MS. METHODS: We adoptively transferred encephalitogenic Th1 or Th17 cells to wild type (WT) or Sema4A-deficient (Sema4A KO) mice and assessed severity of symptoms and cellular infiltration within the central nervous system (CNS). In addition, we analyzed clinical and radiological features (n = 201), levels of serum IFN-γ and IL-17A (n = 86), complete remission ratio by IFN-ß (n = 38) in all of relapsing-remitting multiple sclerosis (RRMS) patients enrolled in this study. RESULTS: Sema4A KO recipient mice receiving Th17-skewed WT myelin oligodendrocyte glycoprotein (MOG)-specific encephalitogenic T cells showed a significant reduction in the clinical score compared to the WT recipient mice. However, Sema4A KO recipient mice showed similar disease activity to the WT recipient mice when transferred with Th1-skewed encephalitogenic T cells. Bone marrow chimeric study indicated that Sema4A expressed on hematopoietic cells, but not the CNS resident cells, are responsible for augmenting Th17-mediated neuroinflammation. Additionally, in contrast to comparable IFN-γ levels, IL-17A is significantly higher in RRMS patients with high Sema4A level than those with low Sema4A patients with high Sema4A levels showed earlier disease onset, more severe disease activity and IFN-ß unresponsiveness than those with low Sema4A levels. CONCLUSIONS: Sema4A is involved not only in the Th cell priming but also in the acceleration of Th17 cell-mediated neuroinflammation in the effector phase, which could contribute to the higher disease activity observed in RRMS patients with high serum Sema4A levels.

Phospholipid methylation controls Atg32-mediated mitophagy and Atg8 recycling.

Degradation of mitochondria via selective autophagy, termed mitophagy, contributes to mitochondrial quality and quantity control whose defects have been implicated in oxidative phosphorylation deficiency, aberrant cell differentiation, and neurodegeneration. How mitophagy is regulated in response to cellular physiology remains obscure. Here, we show that mitophagy in yeast is linked to the phospholipid biosynthesis pathway for conversion of phosphatidylethanolamine to phosphatidylcholine by the two methyltransferases Cho2 and Opi3. Under mitophagy-inducing conditions, cells lacking Opi3 exhibit retardation of Cho2 repression that causes an anomalous increase in glutathione levels, leading to suppression of Atg32, a mitochondria-anchored protein essential for mitophagy. In addition, loss of Opi3 results in accumulation of phosphatidylmonomethylethanolamine (PMME) and, surprisingly, generation of Atg8-PMME, a mitophagy-incompetent lipid conjugate of the autophagy-related ubiquitin-like modifier. Amelioration of Atg32 expression and attenuation of Atg8-PMME conjugation markedly rescue mitophagy in opi3-null cells. We propose that proper regulation of phospholipid methylation is crucial for Atg32-mediated mitophagy.

Receptor-mediated mitophagy in yeast and mammalian systems.

Mitophagy, or mitochondria autophagy, plays a critical role in selective removal of damaged or unwanted mitochondria. Several protein receptors, including Atg32 in yeast, NIX/BNIP3L, BNIP3 and FUNDC1 in mammalian systems, directly act in mitophagy. Atg32 interacts with Atg8 and Atg11 on the surface of mitochondria, promoting core Atg protein assembly for mitophagy. NIX/BNIP3L, BNIP3 and FUNDC1 also have a classic motif to directly bind LC3 (Atg8 homolog in mammals) for activation of mitophagy. Recent studies have shown that receptor-mediated mitophagy is regulated by reversible protein phosphorylation. Casein kinase 2 (CK2) phosphorylates Atg32 and activates mitophagy in yeast. In contrast, in mammalian cells Src kinase and CK2 phosphorylate FUNDC1 to prevent mitophagy. Notably, in response to hypoxia and FCCP treatment, the mitochondrial phosphatase PGAM5 dephosphorylates FUNDC1 to activate mitophagy. Here, we mainly focus on recent advances in our understanding of the molecular mechanisms underlying the activation of receptor-mediated mitophagy and the implications of this catabolic process in health and disease.

Sexual fusion of protoplasts in a marine green alga, Bryopsis plumosa.

We isolated protoplasts from male and female gametophytes of a strictly dioecious strain of the coenocytic marine green alga Bryopsis plumosa. The protoplasts successfully developed into macrothalli. These in turn produced swimming cells, which appeared similar to biflagellated gametes even when the mixed protoplasts were comprised of protoplasm from male and female gametophytes. We found that swimming cell sizes depended on the male/female protoplasm ratio; macrothalli successfully produced swimming cells with male/female protoplasm ratios of 10:0; 9:1; 7:3; 5:5; 1:9; and 0:10. In male/female protoplasm ratios ranging from equal to strongly female biased (5:5; 3:7; 1:9), swimming cells exhibited normal behaviors of gametes and resultant zygotes, displaying positive and negative phototaxis, respectively. Negatively phototactic swimming cells were quadriflagellated and had two nuclei, apparently as a result of fusion, but never developed into microthalli. Thus, these swimming cells might lack functionality essential for normal gametes. Our findings suggested that natural monoecy observed in this genus did not originate from hybridization of protoplasm between the sexes.

NF-kappaB activation stimulates transcription and replication of retrovirus XMRV in human B-lineage and prostate carcinoma cells.

Xenotropic murine leukemia virus-related virus (XMRV) is a gammaretrovirus linked to prostate carcinoma and chronic fatigue syndrome. Here we report that NF-κB activation can markedly increase XMRV production. The inflammatory cytokine tumor necrosis factor alpha (TNF-α), which activates NF-κB, significantly augmented viral Gag protein production in XMRV-infected cells. Reporter assays showed that TNF-α and Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1), an intrinsic NF-κB activator, increased long terminal repeat (LTR)-dependent XMRV transcription. We identified two NF-κB binding sites (designated κB-1 and κB-2) in the LTR U3 region of XMRV and demonstrated that both sites bind to the NF-κB component p65/RelA. Mutation of the κB-1 site, but not the κB-2 site, impaired responsiveness to TNF-α and LMP1 in reporter assays. A mutant XMRV with a mutation at the κB-1 site replicated significantly less efficiently than the wild-type XMRV in the prostate carcinoma LNCaP, DU145, and PC-3 cell lines, HEK293 cells, the EBV-immortalized cell line IB4, and the Burkitt's lymphoma cell line BJAB. These results demonstrate that TNF-α and EBV LMP1 enhance XMRV replication in prostate carcinoma and B-lineage cells through the κB-1 site in the XMRV LTR, suggesting that inflammation, EBV infection, and other conditions leading to NF-κB activation may promote XMRV spread in humans.

Constitutive reductions in mTOR alter cell size, immune cell development, and antibody production.

Mammalian TOR (mTOR) regulates cell growth, proliferation, and migration. Because mTOR knock-outs are embryonic lethal, we generated a viable hypomorphic mouse by neo-insertion that partially disrupts mTOR transcription and creates a potential physiologic model of mTORC1/TORC2 inhibition. Homozygous knock-in mice exhibited reductions in body, organ, and cell size. Although reductions in most organ sizes were proportional to decreased body weight, spleens were disproportionately smaller. Decreases in the total number of T cells, particularly memory cells, and reduced responses to chemokines suggested alterations in T-cell homing/homeostasis. T-cell receptor-stimulated T cells proliferated less, produced lower cytokine levels, and expressed FoxP3. Decreased neutrophil numbers were also observed in the spleen, despite normal development and migration in the bone marrow. However, B-cell effects were most pronounced, with a partial block in B-cell development in the bone marrow, altered splenic populations, and decreases in proliferation, antibody production, and migration to chemokines. Moreover, increased AKT(Ser473) phosphorylation was observed in activated B cells, reminiscent of cancers treated with rapamycin, and was reduced by a DNA-pk inhibitor. Thus, mTOR is required for the maturation and differentiation of multiple immune cell lineages. These mice provide a novel platform for studying the consequences of constitutively reduced mTORC1/TORC2 activity.