Identification of diverse nerve growth factor-regulated genes by serial analysis of gene expression (SAGE) profiling

Neurotrophic factors such as nerve growth factor (NGF) promote a wide variety of responses in neurons, including differentiation, survival, plasticity, and repair. Such actions often require changes in gene expression. To identify the regulated genes and thereby to more fully understand the NGF mechanism, we carried out serial analysis of gene expression (SAGE) profiling of transcripts derived from rat PC12 cells before and after NGF-promoted neuronal differentiation. Multiple criteria supported the reliability of the profile. Approximately 157,000 SAGE tags were analyzed, representing at least 21,000 unique transcripts. Of these, nearly 800 were regulated by 6-fold or more in response to NGF. Approximately 150 of the regulated transcripts have been matched to named genes, the majority of which were not previously known to be NGF-responsive. Functional categorization of the regulated genes provides insight into the complex, integrated mechanism by which NGF promotes its multiple actions. It is anticipated that as genomic sequence information accrues the data derived here will continue to provide information about neurotrophic factor mechanisms.

Improved NlaIII digestion of PAGE-purified 102 bp ditags by addition of a single purification step in both the SAGE and microSAGE protocols

Despite the success of microarray technologies, serial analysis of gene expression (SAGE) still remains the only technique that allows an accurate quantitative and qualitative analysis of cell transcription in a variety of physiological and pathological conditions. Nevertheless, the efficiency of SAGE is limited by the numerous gel purification steps required and these increase the possibility of contamination and reduce or inhibit the activity of the enzymes used in the protocol. In order to eliminate this problem, we have modified the original protocol by adding a single purification step before NLA:III digestion of the ditags. This allows us to increase the yield of digested ditags without reducing the amount of DNA or affecting the subsequent concatemerization.

Endogenous APP derivatives oppositely modulate apoptosis through an autocrine loop

We have recently shown that, in rat cerebellar granule cells, apoptosis triggered by KCl deprivation is associated with an amyloidogenic shift in the processing of amyloid precursor protein (APP) resulting in an increase of amyloid beta-protein (A beta) secretion. To further investigate this issue we studied the relationship between secretion of APP metabolites (A beta, APPs) and neuronal degeneration. We postulated that the endogenous products of the APP metabolism may modulate neuronal survival by an autocrine loop. Treatment of cerebellar granule cells with various antibodies raised against different epitopes of APPs and A beta oppositely modulates low potassium apoptotic cell death. Antibodies specific for the N-terminal of A beta (4G8, 6E10, R3659) increased neuronal survival by 30% over controls. On the contrary, treatment of cultures undergoing apoptosis with the monoclonal antibody 22C11 directed against the APP N-terminus reduced neuronal survival by 53%, suggesting that endogenous alpha-APPs contribute to neuronal survival. Moreover low KCl culture medium, conditioned by cerebellar granule cells, attenuated the apoptotic process. This anti-apoptotic effect was abolished by removal of APPs from the conditioned medium. Western blotting of APPs removed from the conditioned medium confirmed the presence of alpha-APPs. These data indicate that APP cleavage products oppositely modulate neuronal survival through an autocrine loop and further strengthen an Alzheimer's disease pathogenetic scheme based on altered metabolism of APP.

Adenosine and ADP prevent apoptosis in cultured rat cerebellar granule cells

Cerebellar granule cells (CGCs) explanted in vitro undergo death via apoptosis when the concentration of potassium is shifted from 25 mM to 5 mM. We report that adenosine and ADP, which act as neurotransmitters and neuromodulators in the brain, exert in cultured cerebellar granule cells a specific and marked antiapoptotic action with half-maximal effect in the 10-100 microM range. The action of adenosine is partly inhibited by the A1AR antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) and is mimicked by the A1AR agonist 2-chloro-N6-cyclopentyladenosine (CCPA), while ADP effect, that is completely blocked by the P2x, P2y receptors noncompetitive antagonist suramine, is restored in the presence of the selective P2x purinoceptors agonist beta, gamma-methylene-L-ATP. These findings demonstrate that adenosine and ADP markedly inhibit the program of cell death in cerebellar granule cells and suggest that such an action is mediated via interaction with, respectively, A1 and P2x receptors.