Oxidative and energetic stresses mediate beta-cell dysfunction induced by PGC-1α.

AIM: Alteration of functional beta-cell mass in adults can be programmed by adverse events during fetal life. Previously, it was demonstrated that high glucocorticoid (GC) levels during fetal life participate in this programming by inhibition of beta-cell development. More specifically, GC levels stimulate expression of peroxisome proliferator-activated receptor-gamma coactivator 1-alpha (PGC-1α), a transcriptional co-regulator of the GC receptor (GR), which per se impairs beta-cell mass and function when overexpressed. As PGC-1α is also a potent inducer of mitochondrial biogenesis, our study aimed to determine how PGC-1α modifies mitochondrial function in beta cells and how it might regulate insulin secretion. METHODS: Beta-cell function was studied in mice overexpressing PGC-1α specifically in beta cells and in MIN6 cells overexpressing PGC-1α in vitro. RESULTS: PGC-1α overexpression in beta cells in vivo leads to a reduced beta-cell mass early in fetal life, whereas PGC-1α overexpression in vitro stimulates mitochondrial biogenesis and respiratory activity without improving ATP production, while increasing oxidative stress and impairing insulin secretion in response to glucose. While oxidative stress with PGC-1α overexpression in beta cells activates AMPK, it has also been revealed that blocking such oxidative stress or AMPK activation restores insulin secretion. CONCLUSION: PGC-1α induces oxidative stress, which disrupts insulin secretion by AMPK activation. Thus, control of oxidative or energetic stress in beta cells may help to restore insulin secretion.

Protection from articular damage by passive or active anti-tumour necrosis factor (TNF)-α immunotherapy in human TNF-α transgenic mice depends on anti-TNF-α antibody levels.

Active anti-tumour necrosis factor (TNF)-α immunization with the kinoid of TNF-α (TNF-K) induces polyclonal anti-TNF-α antibodies and ameliorates arthritis in human TNF-α (hTNF-α) transgenic mice (TTg). We compared the efficacy of TNF-K to that of infliximab (IFX) and of TNF-K and IFX co-administration, and evaluated whether the titres of anti-hTNF-α antibodies induced by immunization were a determinant of TNF-K efficacy. Forty-eight TTg mice received one of the following treatments: TNF-K immunization (TNF-K group); weekly IFX throughout the study duration (IFXw0-15); TNF-K plus weekly IFX for 4 weeks (TNF-K + IFX); and weekly IFX for 4 weeks (IFXw0-4); PBS. Animals were killed at week 16. Anti-hTNF-α antibody titres and clinical and histological scores were compared. All TNF-K immunized mice (TNF-K and TNF-K + IFX) produced anti-hTNF-α antibodies. Titres were higher in TNF-K versus TNF-K + IFX (P < 0·001) and correlated inversely with histological inflammation (R = -0·78; P = 0·0001) and destruction (R = -0·67; P = 0·001). TNF-K + IFX had higher histological inflammation and destruction versus TNF-K (P < 0·05). A receiver operating characteristic (ROC) analysis of anti-hTNF-α antibody titres identified the criterion cut-off value to discriminate most effectively between the TNF-K and TNF-K + IFX groups. Mice with high versus low titres had less histological inflammation and destruction (P < 0·05). In a model of TNF-α-dependent arthritis, protection from articular damage by TNF-K correlates with the titres of induced anti-hTNF-α antibodies. The co-administration of TNF-K and a short course of infliximab does not result in less articular damage versus solely TNF-K, due probably to lower anti-hTNF-α antibody production. These results are relevant for future development of active anti-TNF-α immunization in human disease.

AIF-mediated caspase-independent necroptosis requires ATM and DNA-PK-induced histone H2AX Ser139 phosphorylation.

The alkylating DNA-damage agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) induces a form of caspase-independent necroptosis implicating the mitochondrial flavoprotein apoptosis-inducing factor (AIF). Following the activation of PARP-1 (poly(ADP-ribose) polymerase-1), calpains, BID (BH3 interacting domain death agonist), and BAX (Bcl-2-associated X protein), the apoptogenic form of AIF (tAIF) is translocated to the nucleus where, associated with Ser139-phosphorylated histone H2AX (γH2AX), it creates a DNA-degrading complex that provokes chromatinolysis and cell death by necroptosis. The generation of γH2AX is crucial for this form of cell death, as mutation of H2AX Ser139 to Ala or genetic ablation of H2AX abolish both chromatinolysis and necroptosis. On the contrary, reintroduction of H2AX-wt or the phosphomimetic H2AX mutant (H2AX-S139E) into H2AX(-/-) cells resensitizes to MNNG-triggered necroptosis. Employing a pharmacological approach and gene knockout cells, we also demonstrate in this paper that the phosphatidylinositol-3-OH kinase-related kinases (PIKKs) ATM (ataxia telangiectasia mutated) and DNA-dependent protein kinase (DNA-PK) mediate γH2AX generation and, consequently, MNNG-induced necroptosis. By contrast, H2AX phosphorylation is not regulated by ATR or other H2AX-related kinases, such as JNK. Interestingly, ATM and DNA-PK phosphorylate H2AX at Ser139 in a synergistic manner with different kinetics of activation. Early after MNNG treatment, ATM generates γH2AX. Further, DNA-PK contributes to H2AX Ser139 phosphorylation. In revealing the pivotal role of PIKKs in MNNG-induced cell death, our data uncover a milestone in the mechanisms regulating AIF-mediated caspase-independent necroptosis.

BID regulates AIF-mediated caspase-independent necroptosis by promoting BAX activation.

Alkylating DNA-damage agents such as N-methyl-N'-nitro-N'-nitrosoguanidine (MNNG) trigger necroptosis, a newly defined form of programmed cell death (PCD) managed by receptor interacting protein kinases. This caspase-independent mode of cell death involves the sequential activation of poly(ADP-ribose) polymerase-1 (PARP-1), calpains, BAX and AIF, which redistributes from mitochondria to the nucleus to promote chromatinolysis. We have previously demonstrated that the BAX-mediated mitochondrial release of AIF is a critical step in MNNG-mediated necroptosis. However, the mechanism regulating BAX activation in this PCD is poorly understood. Employing mouse embryonic knockout cells, we reveal that BID controls BAX activation in AIF-mediated necroptosis. Indeed, BID is a link between calpains and BAX in this mode of cell death. Therefore, even if PARP-1 and calpains are activated after MNNG treatment, BID genetic ablation abolishes both BAX activation and necroptosis. These PCD defects are reversed by reintroducing the BID-wt cDNA into the BID(-/-) cells. We also demonstrate that, after MNNG treatment, BID is directly processed into tBID by calpains. In this way, calpain non-cleavable BID proteins (BID-G70A or BID-Δ68-71) are unable to promote BAX activation and necroptosis. Once processed, tBID localizes in the mitochondria of MNNG-treated cells, where it can facilitate BAX activation and PCD. Altogether, our data reveal that, as in caspase-dependent apoptosis, BH3-only proteins are key regulators of caspase-independent necroptosis.

Early and long-lasting protection from arthritis in tumour necrosis factor alpha (TNFalpha) transgenic mice vaccinated against TNFalpha.

OBJECTIVE: To evaluate the effect in mice with arthritis of active anti-tumour necrosis factor (TNF)alpha immunotherapy based on a keyhole limpet haemocyanin-human TNFalpha heterocomplex (hTNFalpha kinoid or TNFK) adjuvanted in incomplete Freund adjuvant. Immunotherapy was evaluated also with methotrexate. METHODS: Human TNFalpha-transgenic mice received TNFK with or without methotrexate. Follow-up ranged from 6 weeks (short term) to 17 weeks (long term). Arthritis was evaluated clinically and histologically. Monitoring included titration of anti-hTNFalpha antibodies by ELISA and neutralisation assay. RESULTS: Vaccination with TNFK was associated with rapid-onset, long-lasting protection. Long-term results showed significantly milder arthritis in vaccinated animals than in control animals at the peak of the disease. Vaccination was followed by resolution of the clinical evidence of arthritis, contrasting with severe progressive arthritis in the control group. Histological improvements with decreased inflammation and destruction were noted in all immunised groups, even after the shortest follow-up (6 weeks). High titres of neutralising anti-hTNFalpha antibodies were detected as early as the fifth week post immunisation and persisted over time. Methotrexate given concomitantly with the vaccine did not influence either the effect on arthritis or the anti-hTNFalpha antibody titres. CONCLUSION: Anti-cytokine induction of autoimmune protection against chronic hTNFalpha overproduction is an efficient alternative to TNFalpha blockade in experimental arthritis and can be achieved using a TNFK vaccine.