Spinal microglial activation promotes perioperative social defeat stress-induced prolonged postoperative pain in a sex-dependent manner.

Prolonged postsurgical pain, which is associated with multiple risk factors in the perioperative stage, is a common medical and social problem worldwide. Suitable animal models should be established to elucidate the mechanisms underlying the perioperative prolonged postsurgical pain. In this study, standard and modified social defeat stress mice models, including chronic social defeat stress (CSDS), chronic nondiscriminatory social defeat stress (CNSDS) and vicarious social defeat stress (VSDS), were applied to explore the effect of perioperative social defeat stress on postsurgical pain in male and female mice. Our results showed that exposure to preoperative CSDS could induce prolonged postsurgical pain in defeated mice regardless of susceptibility or resilience differentiated by the social interaction test. Similar prolongation of incision-induced mechanical hypersensitivity was also observed in both sexes upon exposing to CNSDS or VSDS in the preoperative period. Moreover, we found that using the modified CNSDS or VSDS models at different recovery stages after surgery could still promote abnormal pain without sex differences. Further studies revealed the key role of spinal microglial activation in the stress-induced transition from acute to prolonged postoperative pain in male but not female mice. Together, these data indicate that perioperative social defeat stress is a vital risk factor for developing prolonged postoperative pain in both sexes, but the promotion of stress-induced prolonged postoperative pain by spinal microglial activation is sexually dimorphic in mice.

Death-associated protein kinase 1 is associated with cognitive dysfunction in major depressive disorder.

We previously showed that death-associated protein kinase 1 (DAPK1) expression is increased in hippocampal tissue in a mouse model of major depressive disorde and is related to cognitive dysfunction in Alzheimer's disease. In addition, depression is a risk factor for developing Alzheimer's disease, as well as an early clinical manifestation of Alzheimer's disease. Meanwhile, cognitive dysfunction is a distinctive feature of major depressive disorder. Therefore, DAPK1 may be related to cognitive dysfunction in major depressive disorder. In this study, we established a mouse model of major depressive disorder by housing mice individually and exposing them to chronic, mild, unpredictable stressors. We found that DAPK1 and tau protein levels were increased in the hippocampal CA3 area, and tau was hyperphosphorylated at Thr231, Ser262, and Ser396 in these mice. Furthermore, DAPK1 shifted from axonal expression to overexpression on the cell membrane. Exercise and treatment with the antidepressant drug citalopram decreased DAPK1 expression and tau protein phosphorylation in hippocampal tissue and improved both depressive symptoms and cognitive dysfunction. These results indicate that DAPK1 may be a potential reason and therapeutic target of cognitive dysfunction in major depressive disorder.

Nmnat2 attenuates amyloidogenesis and up-regulates ADAM10 in AMPK activity-dependent manner.

Amyloid-ß (Aß) accumulating is considered as a causative factor for formation of senile plaque in Alzheimer's disease (AD), but its mechanism is still elusive. The Nicotinamide mononucleotide adenylyltransferase 2 (Nmnat2), a key redox cofactor for energy metabolism, is reduced in AD. Accumulative evidence has shown that the decrease of α-secretase activity, a disintegrin and metalloprotease domain 10 (ADAM10), is responsible for the increase of Aß productions in AD patient's brain. Here, we observe that the activity of α-secretase ADAM10 and levels of Nmnat2 are significantly decreased, meanwhile there is a simultaneous elevation of Aß in Tg2576 mice. Over-expression of Nmnat2 increases the mRNA expression of α-secretase ADAM10 and its activity and inhibits Aß production in N2a/APPswe cells, which can be abolished by Compound C, an AMPK antagonist, suggesting that AMPK is involved in over-expression of Nmnat2 against Aß production. The further assays demonstrate that Nmnat2 activates AMPK by up-regulating the ratio of NAD+/NADH, moreover AMPK agonist AICAR can also increase ADAM10 activity and reduces Aß1-40/1-42. Taken together, Nmnat2 suppresses Aß production and up-regulates ADAM10 in AMPK activity-dependent manner, suggesting that Nmnat2 may serve as a new potential target in arresting AD.

The underlying cellular mechanism in the effect of tetramethylpyrazine on the anion secretion of colonic mucosa.

The present study investigated the underlying cellular mechanism in the effect of ligustrazine (tetramethylpyrazine, TMP) on the anion secretion of colonic mucosa in rats using a short-circuit current (I(sc)) technique in conjunction with "tool drugs." (i) After a pretreatment of the tissues by bathing the bilateral surface with Cl(-)-free Krebs-Henseleit (K-H) solution for over an hour, a basolateral application of 1 mmol/l TMP produced an increase in I(sc), and the total charges transported for 30 min were about 8.7 +/- 1.4 mC/cm(2); an apical pretreatment of DPC and a basolateral addition of acetazolamide decreased the TMP-induced I(sc) by about 60% (P < 0.01) and 45% (P < 0.05), respectively; a basolateral application of 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), the inhibitor of Na(+)-HCO(3)(-) cotransporter (NBC), did not alter the TMP-induced I(sc). (ii) After the bilateral surface of mucosa was bathed with HCO(3)(-)-free K-H solution for over an hour, a basolateral application of 1 mmol/l TMP produced an increase in I(sc), and the total charges transported in 30 min were about 8.3 +/- 1.9 mC/cm(2); an apical pretreatment of DPC (1 mmol/l), the inhibitor of Cl(-) channels, decreased the TMP-induced Isc by about 84% (P < 0.01). The basolateral presence of bumetanide (0.1 mmol/l), the inhibitor of Na(+)-K(+)-Cl(-) cotransporter (NKCC), significantly reduced the TMP-evoked I(sc) by about 86% (P < 0.01). In conclusion, (i) ligustrazine could promote colonic mucosa secretion Cl(-) via apical Cl(-) channels and basolateral NKCC; (ii) ligustrazine could promote colonic mucosa secretion HCO(3)(-) via apical Cl(-) channels and the basolateral diffusion of CO(2).

Humanin attenuates Alzheimer-like cognitive deficits and pathological changes induced by amyloid ß-peptide in rats.

Amyloid ß-peptide (Aß) has been implicated as a key molecule in the neurodegenerative cascades of Alzheimer's disease (AD). Humanin (HN) is a secretory peptide that inhibits the neurotoxicity of Aß. However, the mechanism(s) by which HN exerts its neuroprotection against Aß-induced AD-like pathological changes and memory deficits are yet to be completely defined. In the present study, we provided evidence that treatment of rats with HN increases the number of dendritic branches and the density of dendritic spines, and upregulates pre- and post-synaptic protein levels; these effects lead to enhanced long-term potentiation and amelioration of the memory deficits induced by Aß(1-42). HN also attenuated Aß(1-42)-induced tau hyperphosphorylation, apparently by inhibiting the phosphorylation of Tyr307 on the inhibitory protein phosphatase-2A (PP2A) catalytic subunit and thereby activating PP2A. HN also inhibited apoptosis and reduced the oxidative stress induced by Aß(1-42). These findings provide novel mechanisms of action for the ability of HN to protect against Aß(1-42)-induced AD-like pathological changes and memory deficits.

Nmnat2 attenuates Tau phosphorylation through activation of PP2A.

The activity of protein phosptase-2A (PP2A) is significantly decreased in the brains of Alzheimer's disease (AD) patients, but the upstream effectors for regulating PP2A activity are not fully understood. Nicotinamide mononucleotide adenylyltransferase 2 (Nmnat2) is a key enzyme involved in energy metabolism and its gene expression level is reduced in AD brain specimens. Whether Nmnat2 can activate PP2A deserves to be explored. Here, we first measured the level of Nmnat2, Tyr307-phosphorylation of PP2A, and tau phosphorylation in Tg2576 mice. We observed that the mRNA and protein levels of Nmnat2 were significantly decreased with a simultaneous elevation of p-Tyr307-PP2A and tau phosphorylation in Tg2576 mice. Further studies in HEK293 cells with stable expression of human tau441 (HEK293/tau) demonstrated that simultaneous inhibition of PP2A by okadaic acid abolished the Nmnat2-induced tau dephosphorylation. Moreover, we further demonstrated that overexpression of Nmnat2 could activate PP2A with attenuation of tau phosphorylation, whereas downregulation of Nmnat2 by shRNA inhibited PP2A with tau hyperphosphorylation at multiple AD-associated sites. Our data provide the first evidence that Nmnat2 affects tau phosphorylation by regulating PP2A activity, suggesting that Nmnat2 may serve as a potential target in arresting AD-like tau pathologies.

Phosphorylation of tau by death-associated protein kinase 1 antagonizes the kinase-induced cell apoptosis.

The intracellular accumulation of hyperphosphorylated tau plays a crucial role in neurodegeneration of Alzheimer's disease (AD), but the mechanism is not fully understood. From the observation that tau hyperphosphorylation renders cells more resistant to chemically-induced cell apoptosis, we have proposed that tau-involved apoptotic abortion may be the trigger of neurodegeneration. Here, we further studied whether this phenomenon is also applicable for the cell death induced by constitutively expressed factors, such as death-associated protein kinase 1 (DAPK1). We found that DAPK1 was upregulated and accumulated in the brain of human tau transgenic mice. Overexpression of DAPK1 in HEK293 and N2a cells decreased cell viability with activation of caspase-3, whereas simultaneous expression of tau antagonized DAPK1-induced apoptotic cell death. Expression of DAPK1 induced tau hyperphosphorylation at Thr231, Ser262, and Ser396 with no effects on protein phosphatase 2A, glycogen synthase kinase-3ß, protein kinase A, calcium/calmodulin dependent protein kinase II, cell division cycle 2, or cyclin dependent protein kinase 5. The phosphorylation level of microtubule affinity-regulating kinase 2 (MARK2) was increased by expression of DAPK1, but simultaneous downregulation of MARK2 did not affect the DAPK1-induced tau hyperphosphorylation. DAPK1 was co-immunoprecipitated with tau proteins both in vivo and in vitro, and expression of the kinase domain-truncated DAPK1 did not induce tau hyperphosphorylation. These data suggest that tau hyperphosphorylation at Thr231, Ser262, and Ser396 by DAPK1 renders the cells more resistant to the kinase-induced apoptotic cell death, providing new insights into the tau-involved apoptotic abortion in the course of chronic neurodegeneration.

MicroRNA-195 downregulates Alzheimer's disease amyloid-ß production by targeting BACE1.

Alzheimer's disease (AD) is a progressive neurodegenerative disease, characterized by amyloid-beta (Aß) deposition and neurofibrillary tangles. Numerous microRNAs have been found to play crucial roles in regulating Aß production in the process of AD. Previous investigations have reported lower levels of many microRNAs in AD patients and animal models. Here, we examined the role of miR-195 in the process of Aß formation. Bioinformatics' algorithms predicted miR-195 binding sites within the beta-site APP cleaving enzyme 1 (BACE1) 3'-untranslated region (3'-UTR), and we found the level of miR-195 to be negatively related to the protein level of BACE1 in SAMP8 mice. We confirmed the target site in HEK293 cells by luciferase assay. Overexpression of miR-195 in N2a/WT cells decreased the BACE1 protein level, and inhibition of miR-195 resulted in increase of BACE1 protein level. Furthermore, overexpression of miR-195 in N2a/APP decreased the level of Aß, while inhibition of miR-195 resulted in an increase of Aß. Thus, we demonstrated that miR-195 could downregulate the level of Aß by inhibiting the translation of BACE1. We conclude that miR-195 might provide a therapeutic strategy for AD.