Sufang Yu

Carboxyl-terminus of Hsc70 interacting protein mediates 2,5-hexanedione-induced neurofilament medium chain degradation.

Neurofilaments (NFs), the most abundant cytoskeletal components in large neurons and myelinated axons, are the targets of n-hexane-induced neuropathy, in which a specific loss of NFs protein has been frequently observed. However, the precise mechanisms regulating NFs contents are not well understood. The aim of this study was to elucidate the role of ubiquitin-proteasome system (UPS) in NFs degradation. We first demonstrated that the E3 ligase carboxyl-terminus of Hsc70 interacting protein (CHIP), originally identified as a co-chaperone of Hsc70, directly interacted with NFs medium chain (NF-M) and then enhanced NF-M ubiquitination and degradation after 2,5-hexanedione (HD) treatment. Consistent with this result, the application of proteasome inhibitor MG132 partly reversed HD-induced decrease of NF-M. Finally, we found that other components of UPS system (e.g. ubiquitin-activating enzyme E1, CHIP and proteasome) were significantly increased in sciatic nerve of HD-intoxicated rats. In conclusion, this study indicated that the CHIP ubiquitin ligase complex interacted with and repressed NFs by targeting NFs for ubiquitin-mediated proteolysis, which led to reduction of NFs contents in HD-induced neuropathy.

2,5-hexanedione (HD) treatment alters calmodulin, Ca2+/calmodulin-dependent protein kinase II, and protein kinase C in rats' nerve tissues

Calcium-dependent mechanisms, particularly those mediated by Ca(2+)/calmodulin (CaM)-dependent protein kinase II (CaMKII), have been implicated in neurotoxicant-induced neuropathy. However, it is unknown whether similar mechanisms exist in 2,5-hexanedione (HD)-induced neuropathy. For that, we investigated the changes of CaM, CaMKII, protein kinase C (PKC) and polymerization ratios (PRs) of NF-L, NF-M and NF-H in cerebral cortex (CC, including total cortex and some gray), spinal cord (SC) and sciatic nerve (SN) of rats treated with HD at a dosage of 1.75 or 3.50 mmol/kg for 8 weeks (five times per week). The results showed that CaM contents in CC, SC and SN were significantly increased, which indicated elevation of Ca(2+) concentrations in nerve tissues. CaMKII contents and activities were also increased in CC and were positively correlated with gait abnormality, but it could not be found in SC and SN. The increases of PKC contents and activities were also observed in SN and were positively correlated with gait abnormality. Except for that of NF-M in CC, the PRs of NF-L, NF-M and NF-H were also elevated in nerve tissues, which was consistent with the activation of protein kinases. The results suggested that CaMKII might be partly (in CC but not in SC and SN) involved in HD-induced neuropathy. CaMKII and PKC might mediate the HD neurotoxicity by altering the NF phosphorylation status and PRs.

2,5-Hexanedione induced reduction in protein content and mRNA expression of neurofilament in rat cerebral cortex

Exposure chronically to n-hexane produces central-peripheral axonopathy mediated by 2,5-hexanedione (HD). Studies have shown neurofilament (NF) subunit proteins are decreased substantially in cerebral cortices, optic axons, spinal cords, and sciatic nerves from HD-exposed rats. To deeply investigate the alterations in NF contents in HD neuropathy, the relative levels of NF-L, NF-M, and NF-H in rat cerebral cortex were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. HD was administrated to Wistar rats by intraperitoneal injection at dosage of 200 or 400mg/kg. Rats were sacrificed after 6 weeks of treatment, and cerebral cortices were dissected, homogenized, and used for the determination of NF subunit proteins. The results, except for supernatant NF-L and NF-M that could not be assayed, showed HD intoxication resulted in significant decreases by 32-67% (P<0.01) in NF subunits in both of the pellet and supernatant fractions of cerebral cortex homogenate. As an initial investigation to determine how such changes in NF proteins might occur, the gene expression of NF-L, NF-M, and NF-H subunit mRNA was quantified using reverse transcription-polymerase chain reaction (RT-PCR). Statistical analysis revealed that HD exposure caused a significant reduction in the expression of NF-L and NF-H gene (P<0.05 or P<0.01), while the levels of NF-M mRNA kept unaffected (P>0.05). These suggest that the observed reduction in NF gene expression might be related to diminished levels of subunit proteins, while the actual contribution might be uncertain. The functional significance of the reduced protein contents and the regulation of gene expression remain to be determined.

Calpeptin is neuroprotective against acrylamide-induced neuropathy in rats.

The aim of this study is to explore the potent neuroprotective effect of calpeptin (CP) on neuron damage induced by acrylamide (ACR) and its mechanism. Behavioural indicators such as hind limb splay, rota-rod performance, and gait analysis were assessed weekly to evaluate neurobehavioural changes after ACR and/or CP administration. The histopathological alterations and the changes of μ-calpain, m-calpain, microtubule-associated protein 2 (MAP2), and α-tubulin and β-tubulin protein levels in spinal cord were determined. Results showed that after administration of 30 mg/kg ACR, decreased body weight, attenuated neurobehavioural function, injury of motor neuron, increased protein levels of m-calpain and β-tubulin, suppressed MAP2 protein level, and no significant changes of μ-calpain and α-tubulin protein levels were observed compared with the control group rats. After administration of 200 μg/kg CP, partially restored body weight and neurobehavioural function, improvement of motor neuron injury, decreased protein levels of m- calpain and β-tubulin, and reversed effects of MAP2 protein level were observed compared with the ACR group rats. Our results suggested that CP alleviates neuropathy induced by ACR in rats. The calpains overactivation causes the degrading of MAP2 and eventually leads to the destruction of microtubules (MTs), which may be one of the mechanisms of cytoskeletal damage induced by ACR.

Low back pain among taxi drivers: a cross-sectional study

Background Low back pain (LBP) is a common occupational problem for drivers all over the world. However, few epidemiological studies have investigated LBP among taxi drivers. Aims To investigate the prevalence of LBP and associated work-related factors among Chinese taxi drivers. Methods A cross-sectional survey was administered to all participants. Using cluster sampling, questionnaires were collected from taxi drivers of three major taxi companies in Jinan, China. Univariate and multivariate logistic regressions were used to estimate the odd ratios (ORs) and 95% confidence intervals (CIs) among participants. Results A total of 800 taxi drivers were invited to take part, with a participation rate of 90%. The 1-year period prevalence of LBP was 54%. Multivariate logistic regression analysis revealed that longer daily driving duration (OR 3.3, 95% CI 1.9-5.9), night shifts (OR 1.9, 95% CI 1.2-3.1) and increasing work years as a taxi driver (OR 1.7, 95% CI 1.2-2.5) were associated with increased risk of reporting LBP; while increased rest days per month (OR 0.8, 95% CI 0.7-0.9), longer sleep duration (OR 0.7, 95% CI 0.5-0.9) and more physical activity (OR 0.5, 95% CI 0.3-0.8) were significantly associated with decreased risk of reporting LBP. Conclusions The prevalence of LBP among professional taxi drivers in China was associated with a number of occupational features.

Protective effect of calpeptin on acrylamide-induced microtubule injury in sciatic nerve

The present study aimed to investigate the protective effect and mechanism of calpeptin (CP) on acrylamide (ACR)-induced microtubule (MT) injury in the sciatic nerve of rats. All rats were divided into four groups (control, CP, ACR, and ACR + CP):1 ml/kg saline, 200 μg/kg CP, 30 mg/kg ACR, and 30 mg/kg ACR plus 200 μg/kg CP were administered to the corresponding rats for 4 weeks through intraperitoneal injection. Body weight and neurobehavioral indicators were measured weekly and α-tubulin, β-tubulin, and other concerned proteins were estimated by western blotting and immunohistochemistry. At 4 weeks, decreased body weight, increased gait scores, increased hindlimb splay, and decreased time of fall of ACR rats were observed compared with those of control rats. All these mentioned changes were restored in the ACR + CP group compared with the ACR group. After 4 weeks of administration, western blotting and immunohistochemistry revealed significant increase in the protein levels of β-tubulin, calpain I, calpain II, Tau, microtubule-associated protein 2 (MAP2), protein kinase C, and cyclin-dependent kinase 5 in the ACR group compared with the control group; these increases were significantly lower in the ACR + CP group than in the ACR group. Furthermore, histopathological examination revealed loose arrangement, disorganised structure, uneven density, and exfoliated perineurium in the ACR group, and CP administration improved these changes significantly. The present results suggest that CP has an intervening effect on ACR-induced MT injury. A possible mechanism is that calpain maintains the stability of MTs by regulating the metabolism of Tau and MAP2.