UPR-mediated TRIB3 expression correlates with reduced AKT phosphorylation and inability of interleukin 6 to overcome palmitate-induced apoptosis in RINm5F cells

Unfolded protein response (UPR)-mediated pancreatic β-cell death has been described as a common mechanism by which palmitate (PA) and pro-inflammatory cytokines contribute to the development of diabetes. There are evidences that interleukin 6 (IL6) has a protective action against β-cell death induced by pro-inflammatory cytokines; the effects of IL6 on PA-induced apoptosis have not been investigated yet. In the present study, we have demonstrated that PA selectively disrupts IL6-induced RAC-alpha serine/threonine-protein kinase (AKT) activation without interfering with signal transducer and activator of transcription 3 phosphorylation in RINm5F cells. The inability of IL6 to activate AKT in the presence of PA correlated with an inefficient protection against PA-induced apoptosis. In contrast to PA, IL6 efficiently reduced apoptosis induced by pro-inflammatory cytokines. In addition, we have demonstrated that IL6 is unable to overcome PA-stimulated UPR, as assessed by activating transcription factor 4 (ATF4) and C/EBP homologous protein (CHOP) expression, X-box binding protein-1 gene mRNA splicing, and pancreatic eukaryotic initiation factor-2α kinase phosphorylation, whereas no significant induction of UPR by pro-inflammatory cytokines was detected. This unconditional stimulation of UPR and apoptosis by PA was accompanied by the stimulation of CHOP and tribble3 (TRIB3) expression, irrespective of the presence of IL6. These findings suggest that IL6 is unable to protect pancreatic β-cells from PA-induced apoptosis because it does not repress UPR activation. In this way, CHOP and ATF4 might mediate PA-induced TRIB3 expression and, by extension, the suppression of IL6 activation of pro-survival kinase AKT.

Changes in motor responses induced by cerebellar stimulation during classical forelimb flexion conditioning in cat

1. The ability of somaesthetic sensory inputs to produce structural changes in the connectivities of the central nervous structures involved in motor activity was tested with an alpha type of classical conditioning in chronically prepared adult cats. Repetitive sensory stimulation was applied at constant intervals after the activation of the motor circuits originating in the neurons or efferent axons of the cerebellar nuclei. A conditional stimulation (CS) applied to interpositus neurons was consistently paired with an unconditional stimulation (UCS) applied to the dorsal skin of the forelimb extremity to induce associative sensorimotor conditioning. The sites at which the conditional and unconditional stimuli were applied set up a simplified sensorimotor circuit including pathways transmitting both these stimuli and others mediating the expression of the conditioned responses. 2. To test the changes resulting from the conditioning, electrodes were implanted into the various relay structures on the cerebellar efferent pathways (ventrolateral nucleus motor cortex). The forelimb motor responses elicited by stimulating these relay structures were recorded with a potentiometer placed at the elbow joint. The angular displacement (amplitude) and latency of the responses and the percentage response rates were systematically quantified throughout the conditioning procedure and at test sessions carried out after the daily conditioning routines. 3. It was observed that daily repetition of paired CS-UCS led to an increase in the response rates and amplitudes of the forelimb flexions, which already began to occur very slightly on the first 4 or 5 days in response to the alpha conditioning, whereas the CS when applied alone failed to produce any changes in this initial response. Likewise, after the acquisition phase, repeated presentation of either the CS alone or the CS preceded by the UCS led to the extinction of the conditioned response, thus indicating that the observed changes were of an associative nature and that they depended on interactions between the motor and sensory inputs occurring somewhere in the CNS. In fact, the effects of conditioning were not generalized, but involved only a circumscribed circuit originating in the cerebellar neurons stimulated by the CS, which were activated concomitantly with the sensory pathways. 4. The conditioned response amplitudes were enhanced by 2.5–3 times their initial value. This enhancement persisted at the end of acquisition or after several days of consolidation, even when the paired CS-UCS sessions were interrupted for a period of 15 days to 2 mo.(ABSTRACT TRUNCATED AT 400 WORDS)