BackgroundAlzheimer's disease (AD) is an age related progressive neurodegenerative disorder. One of the reasons for Alzheimer's neuropathology is the generation of large aggregates of Aß42 that are toxic in nature and induce oxidative stress, aberrant signaling and many other cellular alterations that trigger neuronal cell death. However, the exact mechanisms leading to cell death are not clearly understood.Methodology/Principal FindingsWe employed a Drosophila eye model of AD to study how Aß42 causes cell death. Misexpression of higher levels of Aß42 in the differentiating photoreceptors of fly retina rapidly induced aberrant cellular phenotypes and cell death. We found that blocking caspase-dependent cell death initially blocked cell death but did not lead to a significant rescue in the adult eye. However, blocking the levels of c-Jun NH (2)-terminal kinase (JNK) signaling pathway significantly rescued the neurodegeneration phenotype of Aß42 misexpression both in eye imaginal disc as well as the adult eye. Misexpression of Aß42 induced transcriptional upregulation of puckered (puc), a downstream target and functional read out of JNK signaling. Moreover, a three-fold increase in phospho-Jun (activated Jun) protein levels was seen in Aß42 retina as compared to the wild-type retina. When we blocked both caspases and JNK signaling simultaneously in the fly retina, the rescue of the neurodegenerative phenotype is comparable to that caused by blocking JNK signaling pathway alone.Conclusions/SignificanceOur data suggests that (i) accumulation of Aß42 plaques induces JNK signaling in neurons and (ii) induction of JNK contributes to Aß42 mediated cell death. Therefore, inappropriate JNK activation may indeed be relevant to the AD neuropathology, thus making JNK a key target for AD therapies.

Stem cell based therapy is a promising intervention for ischemic heart diseases. However, the functional integrity of stem cells is impaired in an ischemic environment. Here, we report a novel finding that heat shock significantly improves Sca-1+stem cell survival in an ischemic environment by the regulation of the triangle: Heat Shock Factor 1(HSF1), HSF1/miR-34a, Heat Shock Protein 70(HSP70). Initially we prove that HSP70 is the key chaperone mediating cytoprotective effect of heat shock in Sca-1+cells and then we establish miR-34a as a direct repressor of HSP70. We found that HSP70 was down-regulated in heat shocked Sca-1+ stem cells (HSSca-1+ cells). Intriguingly, we demonstrate that the down-regulation of miR-34a is attributed to HSF1-mediated epigenetic repression through histone H3 Lys27 trimethylation (H3K27me3)on miR-34a promoter. Moreover, we show that heat shock induces exosomal transfer of HSF1 fromSca-1+ cells, which directs ischemic cardiomyocytes towards a prosurvival phenotype by epigenetic repression of miR-34a. In addition, our in vivo study demonstrates that transplantation of HSSca-1+ cells significantly reduces apoptosis, attenuates fibrosis and improves global heart functions in ischemic myocardium. Hence, our study not only provides novel insights into the effects of heat shock on stem cell survival and paracrine behavior but may have therapeutic values for stem cell therapy in ischemic heart diseases.

Alzheimer's disease (AD, OMIM: 104300), a progressive neurodegenerative disorder with no cure to date, is caused by the generation of amyloid-beta-42 (Aβ42) aggregates that trigger neuronal cell death by unknown mechanism(s). We have developed a transgenic Drosophila eye model where misexpression of human Aβ42 results in AD-like neuropathology in the neural retina. We have identified an apical-basal polarity gene crumbs (crb) as a genetic modifier of Aβ42-mediated-neuropathology. Misexpression of Aβ42 caused upregulation of Crb expression, whereas downregulation of Crb either by RNAi or null allele approach rescued the Aβ42-mediated-neurodegeneration. Co-expression of full length Crb with Aβ42 increased severity of Aβ42-mediated-neurodegeneration, due to three fold induction of cell death in comparison to the wild type. Higher Crb levels affect axonal targeting from the retina to the brain. The structure function analysis identified intracellular domain of Crb to be required for Aβ42-mediated-neurodegeneration. We demonstrate a novel neuroprotective role of Crb in Aβ42-mediated-neurodegeneration.