The spine apparatus is an essential component of dendritic spines of cortical and hippocampal neurons, yet its functions are still enigmatic. Synaptopodin (SP), an actin-binding protein, is tightly associated with the spine apparatus and it may play a role in synaptic plasticity, but it has not yet been linked mechanistically to synaptic functions. We studied endogenous and transfected SP in dendritic spines of cultured hippocampal neurons and found that spines containing SP generate larger responses to flash photolysis of caged glutamate than SP-negative ones. An NMDA-receptor-mediated chemical long-term potentiation caused the accumulation of GFP-GluR1 in spine heads of control but not of shRNA-transfected, SP-deficient neurons. SP is linked to calcium stores, because their pharmacological blockade eliminated SP-related enhancement of glutamate responses, and release of calcium from stores produced an SP-dependent increase of GluR1 in spines. Thus, SP plays a crucial role in the calcium store-associated ability of neurons to undergo long-term plasticity.

Hypoxia-inducible factors (HIFs) provoke adaptation to hypoxic stress occurring in rapidly growing tumor tissues. Therefore, overexpression of HIF-1 or HIF-2 is a common feature in hepatocellular carcinoma but their specific function is still controversially discussed. To analyze HIF function in hypoxia-induced cell death we created a stable knockdown of HIF-1a and HIF-2a in HepG2 cells and generated tumor spheroids as an in vitro hepatocellular carcinoma model. Knockdown of HIF-1a enhanced expression of HIF-2a and vice versa. Unexpectedly, knockdown of HIF-1a or HIF-2a increased cell viability as well as spheroid size and decreased caspase-3 activity. Antiapoptotic Bcl-X L expression increased in both knockdown spheroids, whereas proapoptotic Bax was only reduced in HIF-1a-knockdown cells. Furthermore, an HIF-2a-knockdown significantly increased Bcl-2/adenovirus E1B 19 kDa-interacting protein 3 (BNIP3) expression in an HIF-1a-dependent manner. Concomitantly, electron microscopy revealed a substantial increase in autophagosomal structures in HIF-2a-knockdown spheroids and mito-/lysotracker costaining confirmed lysosomal activity of these autophagosomes. Blocking autophagosome maturation using 3-methyladenine restored cell death in HIF-2a-knockdown clones comparable to wildtype cells. Conclusion: An HIF-1a-knockdown increases HIF-2a expression and shifts the balance of Bcl-2 family members toward survival. The knockdown of HIF-2a raises autophagic activity and attenuates apoptosis by enhancing HIF-1a expression. Our data indicate that enhanced expression of one HIF-isoform causes a survival advantage in hepatocellular carcinoma development. (HEPATOLOGY 2010;51:2183-2192

Summary Gradual changes in steady-state levels of beta amyloid peptides (Aβ) in brain are considered an initial step in the amyloid cascade hypothesis of Alzheimer's disease. Aβ is a product of the secretase cleavage of amyloid precursor protein (APP). There is evidence that the membrane lipid environment may modulate secretase activity and alters its function. Cleavage of APP strongly depends on membrane properties. Since Aβ perturbs cell membrane fluidity, the cell membrane may be the location where the neurotoxic cascade of Aβ is initiated. Therefore, we tested effects of oligomeric Aβ on membrane fluidity of whole living cells, the impact of exogenous and cellular Aβ on the processing of APP and the role of GM-1 ganglioside. We present evidence that oligoAβ(1-40) stimulates the amyloidogenic processing of APP by reducing membrane fluidity and complexing with GM-1 ganglioside. This dynamic action of Aβ may start a vicious circle, where endogenous Aβ stimulates its own production. Based on our novel findings, we propose that oligoAβ(1-40) accelerates the proteolytic cleavage of APP by decreasing membrane fluidity.

No abstract

Our results show compelling evidence that STAT3 is a key driver of diffuse infiltration and glioma growth and might therefore represent a promising target for an anti-invasive therapy.

The fluidity of neuronal membranes plays a pivotal role in brain aging and neurodegeneration. In this study, we investigated the role of the omega-3 fatty acid docosahexaenoic acid (DHA) in modulation of membrane fluidity, APP processing, and protection from cytotoxic stress. To this end, we applied unilamellar transfer liposomes, which provided protection from oxidation and effective incorporation of DHA into cell membranes. Liposomes transferring docosanoic acid (DA), the completely saturated form of DHA, to the cell cultures served as controls. In HEK-APP cells, DHA significantly increased membrane fluidity and non-amyloidogenic processing of APP, leading to enhanced secretion of sAPPα. This enhanced secretion of sAPPα was associated with substantial protection against apoptosis induced by ER Ca(2+) store depletion. sAPPα-containing supernatants obtained from HEK-APP cells exerted similar protective effects as DHA in neuronal PC12 cells and HEK293 control cells. Correlating to further increased sAPPα levels, supernatants obtained from DHA-treated HEK-APP cells enhanced protection, whereas supernatants obtained from DHA-treated HEK293 control cells did not inhibit apoptosis, likely due to the low expression of endogenous APP and negligible sAPPα secretion in these cells. Further experiments with the small molecule inhibitors LY294002 and SP600125 indicated that sAPPα-induced cytoprotection relied on activation of the anti-apoptotic PI3K/Akt pathway and inhibition of the stress-triggered JNK signaling pathway in PC12 cells. Our data suggest that liposomal DHA is able to restore or maintain physiological membrane properties, which are required for neuroprotective sAPPα secretion and autocrine modulation of neuronal survival.

No abstract

The amyloid precursor protein (APP) has been suggested to regulate gene expression. GeneChip s analysis and in vitro kinase assays revealed potent APP-dependent repression of c-Jun, its target gene SPARC and reduced basal c-Jun Nterminal kinase (JNK) activity in PC12 cells overexpressing APP. UV-induced activation of the JNK signalling pathway and subsequent apoptosis were likewise reduced by APP and this effect could be mimicked by the indirect JNK inhibitor CEP-11004. Treatment with a c-secretase inhibitor did not affect APP-mediated downmodulation of the JNK signalling pathway, suggesting that the effects might be mediated via asecretase processing of APP. In support of these data, overexpression of the Swedish mutant of APP did not inhibit SPARC expression, UV-induced JNK activation and cell death. Our data suggest an important physiological role of APP and a-secretase activity in the control of JNK/c-Jun signalling, target gene expression and cell death activation in response to cytotoxic stress.