[Effect of electroacupuncture on the P35/P25-cyclin-dependent kinase 5-Tau pathway in hippocampus of rats with Alzheimer's disease]

OBJECTIVE

To investigate the effect of electroacupuncture on the P35/P25-cyclin-dependent kinase 5 (CDK5)-Tau pathway in rats with Alzheimer's disease (AD), as well as the mechanism of electroacupuncture in the prevention and treatment of AD.

METHODS

Sprague-Dawley rats were randomly divided into control group, sham-operation group, model group, and electroacupuncture treatment group, with 12 rats in each group. A rat model of AD was established by injection of Aβ_25-35 into the bilateral hippocampus. The rats in the electroacupuncture treatment group were given electroacupuncture at "Baihui" (GV20) and "Shenshu" (BL23) once a day, 15 min each time, for 10 days. Morris water maze was used to evaluate learning and memory abilities, immunohistochemistry was used to measure the distribution and expression of P35/P25, CDK5, and Tau5 in the hippocampus, and Western blot was used to measure the expression of the above mentioned proteins, phosphory-lated Tau(Ser199, Ser202).

RESULTS

In the visual platform test, there were no significant differences in escape latency and search path between groups (P>0.05). In the hidden platform test, there were no significant differences in escape latency and search path between the control group and the sham-operation group (P>0.05); the model group had significantly longer escape latency and search path than the control group and the sham-operation group (P<0.05). Compared with the model group, the electroacupuncture treatment group had significantly shorter escape latency and search path (P<0.05). In the spatial exploration test, there was no significant difference in the number of platform crossings between the control group and the sham-operation group (P<0.05). The model group had a significantly lower number of platform crossings than the control group and the sham-operation group (P<0.01, P<0.05). The electroacupuncture treatment group had a significantly higher number of platform crossings than the model group (P<0.05). Compared with the control group and the sham-operation group, the model group had significant increases in the protein expression of P35/P25 and CDK5 (P<0.001), and the electroacupuncture treatment group had significant reductions compared with the model group (P<0.001). There was no significant difference in the protein expression of Tau5 between groups (P>0.05). The model group had significantly higher protein expression of phosphorylated Tau(Ser199, Ser202) in the hippocampus than the control group and the sham-operation group (P<0.01, P<0.05). The electroacupuncture treatment group had significantly lower protein expression of phosphorylated Tau(Ser199，Ser202) than the model group (P<0.05, P<0.01).

CONCLUSION

Electroacupuncture may delay the progression of AD by affecting the expression of proteins involved in the P35/P25-CDK5-Tau pathway in the hippocampus of rats.

Upregulation and lysosomal degradation of AQP4 in rat brains with bacterial meningitis

Brain edema is among the major complications in children with bacterial meningitis. Aquaporins are integral membrane pore proteins that form channels to regulate cellular water content. Aquaporin-4 (AQP4), which is enriched in parts of astrocytic membranes that are apposed to pial or perivascular basal laminae, is the predominant aquaporin in the central nervous system. Dystroglycan is among the proteins that are responsible for the site-specific anchorage of AQP4. To elucidate the role of AQP4 in the development of brain edema induced by meningitis, a model of bacterial meningitis was established by injecting group B β-hemolytic Streptococci into the cerebrospinal fluid of three-week-old rats. The brain water content increased in this model compared with that in the control group. The expression of AQP4 and dystroglycan was examined by Western blot and the degradation route of AQP4 was investigated by double immunofluorescence labeling. Western blot results showed that the expression of AQP4 and dystroglycan in rat brain increased in the meningitis model. Meanwhile, AQP4 was co-localized with the marker of lysosome in this model, indicating that the lysosome is involved in AQP4 degradation.

The internalization and lysosomal degradation of brain AQP4 after ischemic injury

The membrane-bound water channel aquaporin-4 (AQP4) plays a significant role in maintaining brain water homeostasis. In ischemic brain, changes in the expression level of AQP4 have been reported. Previous studies suggest that the internalization of several membrane-bound proteins, including AQP4, may occur with or without lysosomal degradation. In this study, the internalization of AQP4 was detected in the ischemic rat brain via double immunofluorescence labeling. Specifically, AQP4 and early endosome antigen-1 (EEA1) co-localized after 1 h post-ischemic injury. Moreover, the co-expression of AQP4 and lysosomal-associated membrane protein-1 (LAMP1) was observed after 3 h post-ischemia. These findings suggest that AQP4 is internalized and the lysosome is involved in degrading the internalized AQP4 in the ischemic brain. AQP4 is known to be downregulated by the protein kinase C activator phorbol 12-myristate 13-acetate (PMA) in vivo and in vitro. The results in this study displayed that PMA infusion could decrease brain edema accompanied by AQP4 downregulation in ischemic brain. However, compared with vehicle infusion, PKC activator infusion did not increase the ratio of internalized or lysosomal degraded AQP4. That is, we have not found out evidence to prove protein kinase C activator PMA can promote the internalization or lysosomal degradation of AQP4 in the ischemic brain.

Hyperosmotic induction of aquaporin expression in rat astrocytes through a different MAPK pathway

Water homeostasis of the nervous system is important during neural signal transduction. Astrocytes are crucial in water transport in the central nervous system under both physiological and pathological conditions. To date, five aquaporins (AQP) have been found in rat brain astrocytes. Most studies have focused on AQP4 and AQP9, however, little is known about the expression of AQP3, -5, and -8 as well as their regulating mechanism in astrocytes. The expression patterns of AQP3, -5, and -8 in astrocytes exposed to hyperosmotic solutions were examined to clarify the roles of AQP3, -5, and -8 in astrocyte water movement. The expression of AQP4 and AQP9 under the same hyperosmotic conditions was also investigated. The AQP4 and AQP9 expressions continuously increased until 12 h after hyperosmotic solution exposure, whereas the AQP3, -5, and -8 expressions continued to increase until 6 h after hyperosmotic solution exposure. The different AQPs decreased at corresponding time points (24 h for AQP4 and AQP9; 12 h for AQP3, -5, and -8 after hyperosmotic solution exposure). The ERK inhibitor can attenuate the expression of AQP3, -5, and -8 after hyperosmotic solution exposure. The p38 inhibitor can inhibit the AQP4 and AQP9 expressions in cultured astrocytes. AQP expression is directly related to the extracellular hyperosmotic stimuli. Moreover, different AQPs can be regulated by a distinct MAPK signal transduction pathway.

Immunolocalization of aquaporins in rat brain

The aquaporins (AQPs) are a family of homologous water channels expressed in many tissues. In this study, the expression and immunolocalization of different AQP subtypes in rat brains were investigated by RT-PCR, immunohistochemistry and immunofluorescence. The data showed that AQP1 was expressed in the subpial processes of astrocytes, choroid plexus and ependyma. AQP3, AQP5 and AQP8 had similar distribution patterns in piriform cortex, choroid plexus, hippocampus and dorsal thalamus. AQP4 and AQP9 were widely expressed in the rat brain and distributed in the subpial processes of astrocytes, ependyma, dorsal thalamus, hippocampus, white matter, suprachiasmatic nucleus (SCN) and supraoptic nucleus. AQP3, AQP4, AQP5, AQP8 and AQP9 were found in the Bergmann glial cells of cerebellum, cochlear nucleus and trapezoid nuclei. The distinct localization of various AQPs in cerebrum and the similarities of distribution patterns within cerebellum, cochlear nucleus and trapezoid nuclei suggest that AQPs may play an important role in maintaining the specific microenvironments of the brain.