Differential accumulation of human ß-amyloid and tau from enriched extracts in neuronal and endothelial cells.

While Aß and Tau cellular distribution has been largely studied, the comparative internalization and subcellular accumulation of Tau and Aß isolated from human brain extracts in endothelial and neuronal cells has not yet been unveiled. We have previously demonstrated that controlled enrichment of Aß from human brain extracts constitutes a valuable tool to monitor cellular internalization in vitro and in vivo. Herein, we establish an alternative method to strongly enrich Aß and Tau aggregates from human AD brains, which has allowed us to study and compare the cellular internalization, distribution and toxicity of both proteins within brain barrier endothelial (bEnd.3) and neuronal (Neuro2A) cells. Our findings demonstrate the suitability of human enriched brain extracts to monitor the intracellular distribution of human Aß and Tau, which, once internalized, show dissimilar sorting to different organelles within the cell and differential toxicity, exhibiting higher toxic effects on neuronal cells than on endothelial cells. While tau is strongly concentrated preferentially in mitochondria, Aß is distributed predominantly within the endolysosomal system in endothelial cells, whereas the endoplasmic reticulum was its preferential location in neurons. Altogether, our findings display a picture of the interactions that human Aß and Tau might establish in these cells.

The new truncated somatostatin receptor variant sst5TMD4 is associated to poor prognosis in breast cancer and increases malignancy in MCF-7 cells.

Somatostatin receptors (sst1-5) are present in different types of tumors, where they inhibit key cellular processes such as proliferation and invasion. Although ssts are densely expressed in breast cancer, especially sst2, their role and therapeutic potential remain uncertain. Recently, we identified a new truncated sst5 variant, sst5TMD4, which is related to the abnormal response of certain pituitary tumors to treatment with somatostatin analogs. Here, we investigated the possible role of sst5TMD4 in breast cancer. This study revealed that sst5TMD4 is absent in normal mammary gland, but is abundant in a subset of poorly differentiated human breast tumors, where its expression correlated to that of sst2. Moreover, in the MCF-7 breast cancer model cell, sst5TMD4 expression increased malignancy features such as invasion and proliferation abilities (both in cell cultures and nude mice). This was likely mediated by sst5TMD4-induced increase in phosphorylated extracellular signal-regulated kinases 1 and 2 and p-Akt levels, and cyclin D3 and Arp2/3 complex expression, which also led to mesenchymal-like phenotype. Interestingly, sst5TMD4 interacts physically with sst2 and thereby alters its signaling, enabling disruption of sst2 inhibitory feedback and providing a plausible basis for our findings. These results suggest that sst5TMD4 could be involved in the pathophysiology of certain types of breast tumors.

New insights in the mechanism by which SRIF influences GH secretion.

Once thought to act only as a somatotropin release-inhibiting factor (SRIF), SRIF is currently viewed as a pleiotropic neuroendocrine factor controlling secretion, gene expression, apoptosis and signalling in many different targets. Actually, despite the numerous studies that have characterized SRIF action on somatotropes, new facets are continuously being discovered which help enlightening the biology of this cell type. As an example, ten years ago we demonstrated that SRIF exerts a dual, inhibitory/stimulatory effect on GH release from cultured pig somatotropes, which depends on the concentration of the peptide and on a divergent responsiveness of the two main cell subsets comprising the somatotrope population. Specifically, very low, picomolar doses of SRIF were found to stimulate GH release in vitro from intact cultures of dispersed pig pituitary cells and from purified somatotrope subpopulations. Conversely, higher (10(-7)M) SRIF concentrations inhibited, as expected, GHRH-induced GH release from intact pituitary cells and from one of the somatotrope subtypes; yet, at this same dose, it stimulated GH release from the other somatotrope subset. Analysis of second messenger pathways revealed that cAMP is the main signal conveying the stimulatory effects of low-dose SRIF. This peptide also exerts a distinct, dose-dependent regulation of the expression of three of its receptor subtypes (sst1, sst2 and sst5) at the pituitary. Indeed, acute in vitro treatment with a high SRIF dose increased mRNA levels of all three subtypes, whereas a low SRIF concentration only increased that of sst5. Interestingly, short term treatment with GHRH or ghrelin reduced the expression of sst5, and not that of sst1 and sst2. Hopefully, ongoing studies on cloning and individual characterization of porcine sst will help to unravel the complex and exciting response of somatotropes to SRIF.