Stress‐activated protein kinase‐3 (SAPK3), a recently described MAP kinase family member with a widespread tissue distribution, was transfected into several mammalian cell lines and shown to be activated in response to cellular stresses, interleukin‐1 (IL‐1) and tumour necrosis factor (TNF) in a similar manner to SAPK1 (also termed JNK) and SAPK2 (also termed p38, RK, CSBP and Mxi2). SAPK3 and SAPK2 were activated at similar rates in vitro by SAPKK3 (also termed MKK6), and SAPKK3 was the only activator of SAPK3 that was induced when KB or 293 cells were exposed to cellular stresses or stimulated with IL‐1 or TNF. Co‐transfection with SAPKK3 induced SAPK3 activity and greatly enhanced activation in response to osmotic shock. These experiments indicate that SAPKK3 mediates the activation of SAPK3 in several mammalian cells. SAPK3 and SAPK2 phosphorylated a number of proteins at similar rates, including the transcription factors ATF2, Elk‐1 and SAP1, but SAPK3 was far less effective than SAPK2 in activating MAPKAP kinase‐2 and MAPKAP kinase‐3. Unlike SAPK2, SAPK3 was not inhibited by the drug SB 203580. SAPK3 phosphorylated ATF2 at Thr69, Thr71 and Ser90, the same residues phosphorylated by SAPK1, whereas SAPK2 only phosphorylated Thr69 and Thr71. Our results suggest that cellular functions previously attributed to SAPK1 and/or SAPK2 may be mediated by SAPK3.

Background: There is a growing interest in the involvement of anesthetic agents in the etiology of postoperative cognitive dysfunction. Recent animal studies suggest that acute anesthesia induces transient hyperphosphorylation of tau, an effect essentially ascribed to hypothermia. The main aim of the present study was to investigate effects, in normothermic conditions, of acute or repeated exposure to sevoflurane, a halogenated anesthetic agent, on hippocampal tau phosphorylation and spatial memory in adult mice. Methods: 5 to 6-month-old C57Bl6/J mice were submitted to acute (1 h) or repeated (five exposures of 1h every month) anesthesia using 1.5 or 2.5% sevoflurane, in normothermic conditions. In the acute protocol, animals were sacrificed 1 and 24 h after exposure. In the chronic protocol, spatial memory was evaluated using the Morris water maze following the fourth exposure, and tau phosphorylation evaluated 1 month following the last exposure using bi- and mono-dimensional electrophoresis. Results: Acute sevoflurane anesthesia in normothermic conditions led to a significant dose-dependent and reversible hippocampal tau phosphorylation, 1 h following the end of exposure (P < 0.001). Conversely, repeated anesthesia led to persistent tau hyperphosphorylation and significant memory impairments, as seen in the retention phase of the Morris water maze in sevoflurane-anesthesized animals. These pathologic features may be related to the activation of both Akt and Erk pathways. Conclusions: The present study demonstrates, in mice, that sevoflurane exposure is associated with increased tau phosphorylation through specific kinases activation and spatial memory deficits. These data support a correlation between exposures to this anesthetic agent and cognitive decline.

Synaptic dysfunction plays a central role in Alzheimer’s disease (AD), since it drives the cognitive decline. An association between a polymorphism of the adenosine A_2A receptor (A_2AR) encoding gene—ADORA2A, and hippocampal volume in AD patients was recently described. In this study, we explore the synaptic function of A_2AR in age-related conditions. We report, for the first time, a significant overexpression of A_2AR in hippocampal neurons of aged humans, which is aggravated in AD patients. A similar profile of A_2AR overexpression in rats was sufficient to drive age-like memory impairments in young animals and to uncover a hippocampal LTD-to-LTP shift. This was accompanied by increased NMDA receptor gating, dependent on mGluR5 and linked to enhanced Ca²⁺ influx. We confirmed the same plasticity shift in memory-impaired aged rats and APP/PS1 mice modeling AD, which was rescued upon A_2AR blockade. This A_2AR/mGluR5/NMDAR interaction might prove a suitable alternative for regulating aberrant mGluR5/NMDAR signaling in AD without disrupting their constitutive activity.

Mechanisms for selective targeting to unique subcellular sites play an important role in determining the substrate specificities of protein kinases. Here we show that stress-activated protein kinase-3 (SAPK3, also called ERK6 and p38γ), a member of the mitogen-activated protein kinase family that is abundantly expressed in skeletal muscle, binds through its carboxyl-terminal sequence -KETXL to the PDZ domain of α1-syntrophin. SAPK3 phosphorylates α1-syntrophin at serine residues 193 and 201 in vitro and phosphorylation is dependent on binding to the PDZ domain of α1-syntrophin. In skeletal muscle SAPK3 and α1-syntrophin co-localize at the neuromuscular junction, and both proteins can be co-immunoprecipitated from transfected COS cell lysates. Phosphorylation of a PDZ domain-containing protein by an associated protein kinase is a novel mechanism for determining both the localization and the substrate specificity of a protein kinase.