Hippocampal Mechanisms Underlying Impairment in Spatial Learning Long After Establishment of Noise-Induced Hearing Loss in CBA Mice

Sensorineural hearing loss (SNHL) has been demonstrated in many clinical reports as a risk factor that promotes the development of cognitive impairment. However, the underlying neurological mechanisms are not clear. Noise exposure is one of the most common causes of SNHL. Although noise exposure causes relatively less damage to general health as compared with other methods for creating hearing loss (such as ototoxicity), it does impair cognitive function. Many studies have shown that the noise-induced cognitive impairment occur via the oxidative stress induced by the noise. In those studies, the effects of the noise-induced hearing loss induced (NIHL) were not addressed. Previously, we have demonstrated in the CBA/CaJ mouse model that oxidative stress was transient after a brief noise exposure, but the NIHL was permanent. In addition, NIHL was followed by a declined cognitive function and decreased hippocampal neurogenesis that were developed long after the oxidative stress disappeared. Therefore, NIHL can cause cognitive impairment independent of its stress effect and can serve as a model to investigate the relationship between hearing loss and the development of cognitive impairment. In the present study, we further demonstrated that the oxidative stress produced by the brief noise exposure did not damage the stem cell bank of hippocampus that was evaluated shortly after the noise exposure. In addition to the reduction in the rate of cell proliferation in hippocampus that was found previously, we found that the NIHL significantly reduced the promoting effect of learning activity on various stages of hippocampal neurogenesis, accompanied by the reduction in learning-induced expression of immediate early genes (IEGs) in hippocampus. Since the MWM-tested spatial function does not directly require auditory input, the results provide evidence for the maintenance role of auditory input on the cognitive function; the reduction of IEG expression that is required in memory-formation may be the initial step in blocking the effect of learning activity on neurogenesis in subjects with NIHL.

The effect of noise exposure on insulin sensitivity in mice may be mediated by the JNK/IRS1 pathway

Background

Epidemiological studies have suggested that noise exposure may increase the risk of type 2 diabetes mellitus (T2DM), and experimental studies have demonstrated that noise exposure can induce insulin resistance in rodents. The aim of the present study was to explore noise-induced processes underlying impaired insulin sensitivity in mice.

Methods

Male ICR mice were randomly divided into four groups: a control group without noise exposure and three noise groups exposed to white noise at a 95-dB sound pressure level for 4 h/day for 1, 10, or 20 days (N1D, N10D, and N20D, respectively). Systemic insulin sensitivity was evaluated at 1 day, 1 week, and 1 month post-noise exposure (1DPN, 1WPN, and 1MPN) via insulin tolerance tests (ITTs). Several insulin-related processes, including the phosphorylation of Akt, IRS1, and JNK in the animals’ skeletal muscles, were examined using standard immunoblots. Biomarkers of inflammation (circulating levels of TNF-α and IL-6) and oxidative stress (SOD and CAT activities and MDA levels in skeletal muscles) were measured via chemical analyses.

Results

The data obtained in this study showed the following: (1) The impairment of systemic insulin sensitivity was transient in the N1D group but prolonged in the N10D and N20D groups. (2) Noise exposure led to enhanced JNK phosphorylation and IRS1 serine phosphorylation as well as reduced Akt phosphorylation in skeletal muscles in response to exogenous insulin stimulation. (3) Plasma levels of TNF-α and IL-6, CAT activity, and MDA concentrations in skeletal muscles were elevated after 20 days of noise exposure.

Conclusions

Impaired insulin sensitivity in noise-exposed mice might be mediated by an enhancement of the JNK/IRS1 pathway. Inflammation and oxidative stress might contribute to insulin resistance after chronic noise exposure.

Characterization of the Transcriptomes of Lgr5+ Hair Cell Progenitors and Lgr5- Supporting Cells in the Mouse Cochlea

Cochlear supporting cells (SCs) have been shown to be a promising resource for hair cell (HC) regeneration in the neonatal mouse cochlea. Previous studies have reported that Lgr5+ SCs can regenerate HCs both in vitro and in vivo and thus are considered to be inner ear progenitor cells. Lgr5+ progenitors are able to regenerate more HCs than Lgr5- SCs, and it is important to understand the mechanism behind the proliferation and HC regeneration of these progenitors. Here, we isolated Lgr5+ progenitors and Lgr5- SCs from Lgr5-EGFP-CreERT2/Sox2-CreERT2/Rosa26-tdTomato mice via flow cytometry. As expected, we found that Lgr5+ progenitors had significantly higher proliferation and HC regeneration ability than Lgr5- SCs. Next, we performed RNA-Seq to determine the gene expression profiles of Lgr5+ progenitors and Lgr5- SCs. We analyzed the genes that were enriched and differentially expressed in Lgr5+ progenitors and Lgr5- SCs, and we found 8 cell cycle genes, 9 transcription factors, and 24 cell signaling pathway genes that were uniquely expressed in one population but not the other. Last, we made a protein–protein interaction network to further analyze the role of these differentially expressed genes. In conclusion, we present a set of genes that might regulate the proliferation and HC regeneration ability of Lgr5+ progenitors, and these might serve as potential new therapeutic targets for HC regeneration.

Association between the MDR1 gene variant C3435T and risk of leukaemia: a meta-analysis

Although a number of genetic studies have attempted to link the multidrug resistance (MDR1) C3435T polymorphism to risk of leukaemia, the results were often inconsistent. The present study aimed at investigating the pooled association using a meta-analysis on the published studies. 1933 cases and 2215 controls of 11 published studies in English before June 2012 were involved in the updated meta-analysis. Furthermore, subgroup analysis was performed in different ethnic and leukaemia subtype groups. This meta-analysis suggests that the MDR1 C3435T polymorphism associate with risk of leukaemia. The effect of the variant on the expression levels and the possible functional role of the variant in leukaemia should be addressed in further studies.

RBB, a novel transcription repressor, represses the transcription of HDM2 oncogene

The p53 tumor suppressor is important in many aspects of cell biology. Tight regulation of p53 is thus imperative for maintaining cell homeostasis and preventing tumorigenesis. The stabilization and activity of p53 is primarily regulated by MDM2, which is encoded for by HDM2. However, how the expression and activity of MDM2 is regulated remains largely unknown. Here, we report a novel BTB and BEN domains-containing protein, RBB. We demonstrated that RBB is a novel transcriptional repressor binding specific DNA motif via a homodimer and interacting with the nucleosome remodeling and deacetylase (NuRD) complex. Genome wide transcription target analysis by ChIP sequencing revealed that RBB represses the transcription of a series of functionally important genes including HDM2. We showed that RBB recruits the NuRD complex to the internal promoter of HDM2 and inhibits the expression of MDM2 protein, leading to subsequent stabilization of tumor suppressor p53. Significantly, we showed that RBB suppresses cell proliferation and sensitizes cells to DNA damage-induced apoptosis. Our data indicate that RBB is a novel transcriptional repressor and an important regulator of p53 pathway.

Blood compatibility of amorphous titanium oxide films synthesized by ion beam enhanced deposition

Titanium oxide films were synthesized on titanium, cobalt alloy and low-temperature isotropic pryolytic carbon by ion beam enhanced deposition. The non-stoichiometrical titanium oxide films were obtained. Blood compatibility of the films were evaluated by clotting time measurement, platelet adhesion investigation and hemolysis analyses. The results revealed that blood compatibility of the materials was improved by the coating of titanium oxide films. Semiconductor nature of non-stoichiometric titanium oxide films might be responsible for the improvement of blood compatibility.