RIG-1 and MDA-5 signaling pathways contribute to IFN-ß production and viral replication in porcine circovirus virus type 2-infected PK-15 cells in vitro.

Type I Interferons (IFNs) is known for its antiviral activity; however, it is surprising that in vitro treatment of IFN-α and IFN-γ enhanced the replication of porcine circovirus type 2 (PCV2), indicating a complex relationship between interferon and PCV2. To date, it remains poorly understood how the interferon is produced during PCV2 infection and whether the interferon induced by PCV2 itself can promote viral replication. In this study, PCV2 induced the up-regulation of IFN-ß in PK-15 cells, while treatment of PCV2-infected cells with the interferon regulatory factor-3 (IRF3) inhibitor, BX795, decreased the expression of IFN-ß, whereas treatment with the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) inhibitor, BAY11-7082, did not. These findings indicate that PCV2 can induce IFN-ß production via the IRF3-mediated rather than the NF-κB-mediated signal pathway. Moreover, PCV2 increased the protein expression levels of phosphorylation-IRF3 (p-IRF3), mitochondria antiviral-signaling protein (MAVS), retinoic acid-inducible gene I (RIG-1) and melanoma differentiation-associated protein 5 (MDA-5), and the knockdown of RIG-1 and MDA-5 decreased the expression level of IFN-ß in PK-15 cells. Therefore, PCV2 induces IFN-ß production via the RIG-1/MDA-5/MAVS/IRF signaling pathway. Furthermore, the PCV2 load and PCV2 infectivity decreased after knockdown of RIG-1 and MDA-5, indicating that RIG-1 and MDA-5 signaling pathways contribute to PCV2 replication. In conclusion, PCV2 induces the production of IFN-ß via the RIG-1 and MDA-5 signaling pathways, and the IFN-ß produced during PCV2 infection facilitates viral replication. These results will help us further understand the pathogenic mechanisms of PCV2.

Apoptosis in response to heat stress is positively associated with heat-shock protein 90 expression in chicken myocardial cells in vitro.

To determine heat-shock protein (Hsp)90 expression is connected with cellular apoptotic response to heat stress and its mechanism, chicken (Gallus gallus) primary myocardial cells were treated with the Hsp90 promoter, aspirin, and its inhibitor, geldanamycin (GA), before heat stress. Cellular viability, heat-stressed apoptosis and reactive oxygen species level under different treatments were measured, and the expression of key proteins of the signaling pathway related to Hsp90 and their colocalization with Hsp90 were detected. The results showed that aspirin treatment increased the expression of protein kinase B (Akt), the signal transducer and activator of transcription (STAT)-3 and p-IKKα/ß and the colocalization of Akt and STAT-3 with Hsp90 during heat stress, which was accompanied by improved viability and low apoptosis. GA significantly inhibited Akt expression and p-IKKα/ß level, but not STAT-3 quantity, while the colocalization of Akt and STAT-3 with Hsp90 was weakened, followed by lower cell viability and higher apoptosis. Aspirin after GA treatment partially improved the stress response and apoptosis rate of tested cells caused by the recovery of Akt expression and colocalization, rather than the level of STAT-3 (including its co-localization with Hsp90) and p-IKKα/ß. Therefore, Hsp90 expression has a positive effect on cellular capacity to resist heat-stressed injury and apoptosis. Moreover, inhibition of Hsp90 before stress partially attenuated its positive effects.

Melamine negatively affects testosterone synthesis in mice.

Several studies have found that melamine causes damage to the testes, epididymis and sperm. However, few studies have investigated the effect of melamine on the synthesis of testosterone, which plays an import role in testicular development and spermatogenesis. In present study, mice were orally administrated with 2, 10 or 50mg/kg of melamine for 28days. In these groups, various abnormalities were observed including disruption of the seminiferous tubule structure, an increased necrotic germ cells and sperm abnormalities, and a reduced sperm count. Melamine exposure also decreased the level of serum testosterone and levels of testicular StAR, P450scc and 17ß-HSD. In addition, melamine exposure reduced the number of Leydig cells. Taken together, these results indicate that melamine exposure reduces the level of testosterone through down-regulation of StAR and testosterone synthetic enzyme expression and also a decreased number of Leydig cells. This may further affect testicular development and lead to sperm damage.

Ovarian Toxicity in Female Rats after Oral Administration of Melamine or Melamine and Cyanuric Acid.

Although the toxicity of melamine to the kidneys and testes is well known, few studies have investigated the effects of melamine on female reproductive organs. Therefore, this study explores the effects of oral administration melamine or melamine and cyanuric acid for 28 days on the ovaries of female rats. Rats that were exposed to the mixture exhibited reduced ovarian and uterine weights, a shorter estrous cycle, and reduced serum estrogen and progesterone levels compared to rats that were exposed to melamine and control rats. Furthermore, morphological analysis revealed pathological changes in the ovaries of rats exposed to melamine or the mixture, such as more atretic follicles and necrosis of oocytes and granulosa cells. TUNEL staining revealed that the exposed groups had a higher proportion of TUNEL-positive granulosa cells than the control group, and the mRNA expressions of SOD1, GPX1, GPX2, P450scc, 17ß-HSD I, and 17ß-HSD II were reduced in the exposure groups compared with the control group. These results indicated that exposure to melamine alone or to the melamine-cyanuric acid mixture could damage the ovaries in rats.