RESUMEN
Chaperone-mediated autophagy (CMA) serves as quality control during stress conditions through selective degradation of cytosolic proteins in lysosomes. Humanin (HN) is a mitochondria-associated peptide that offers cytoprotective, cardioprotective, and neuroprotective effects in vivo and in vitro. In this study, we demonstrate that HN directly activates CMA by increasing substrate binding and translocation into lysosomes. The potent HN analogue HNG protects from stressor-induced cell death in fibroblasts, cardiomyoblasts, neuronal cells, and primary cardiomyocytes. The protective effects are lost in CMA-deficient cells, suggesting that they are mediated through the activation of CMA. We identified that a fraction of endogenous HN is present at the cytosolic side of the lysosomal membrane, where it interacts with heat shock protein 90 (HSP90) and stabilizes binding of this chaperone to CMA substrates as they bind to the membrane. Inhibition of HSP90 blocks the effect of HNG on substrate translocation and abolishes the cytoprotective effects. Our study provides a novel mechanism by which HN exerts its cardioprotective and neuroprotective effects.
Asunto(s)
Autofagia , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Chaperonas Moleculares/metabolismo , Animales , Supervivencia Celular , Células Cultivadas , Citosol/metabolismo , Proteínas HSP90 de Choque Térmico/metabolismo , Lisosomas/metabolismo , Masculino , Ratones , Células 3T3 NIH , Ratas , Ratas WistarRESUMEN
BACKGROUND: Monitoring land change at multiple spatial scales is essential for identifying hotspots of change, and for developing and implementing policies for conserving biodiversity and habitats. In the high diversity country of Colombia, these types of analyses are difficult because there is no consistent wall-to-wall, multi-temporal dataset for land-use and land-cover change. METHODOLOGY/PRINCIPAL FINDINGS: To address this problem, we mapped annual land-use and land-cover from 2001 to 2010 in Colombia using MODIS (250 m) products coupled with reference data from high spatial resolution imagery (QuickBird) in Google Earth. We used QuickBird imagery to visually interpret percent cover of eight land cover classes used for classifier training and accuracy assessment. Based on these maps we evaluated land cover change at four spatial scales country, biome, ecoregion, and municipality. Of the 1,117 municipalities, 820 had a net gain in woody vegetation (28,092 km(2)) while 264 had a net loss (11,129 km(2)), which resulted in a net gain of 16,963 km(2) in woody vegetation at the national scale. Woody regrowth mainly occurred in areas previously classified as mixed woody/plantation rather than agriculture/herbaceous. The majority of this gain occurred in the Moist Forest biome, within the montane forest ecoregions, while the greatest loss of woody vegetation occurred in the Llanos and Apure-Villavicencio ecoregions. CONCLUSIONS: The unexpected forest recovery trend, particularly in the Andes, provides an opportunity to expand current protected areas and to promote habitat connectivity. Furthermore, ecoregions with intense land conversion (e.g. Northern Andean Páramo) and ecoregions under-represented in the protected area network (e.g. Llanos, Apure-Villavicencio Dry forest, and Magdalena-Urabá Moist forest ecoregions) should be considered for new protected areas.
Asunto(s)
Conservación de los Recursos Naturales/tendencias , Árboles , Agricultura , Ciudades/estadística & datos numéricos , Colombia , Fenómenos Ecológicos y Ambientales , Análisis Espacio-TemporalRESUMEN
Mutations leading to expansion of a poly-glutamine track in Huntingtin (Htt) cause Huntington's disease (HD). Signs of endoplasmic reticulum (ER) stress have been recently reported in animal models of HD, associated with the activation of the unfolded protein response (UPR). Here we have investigated the functional contribution of ER stress to HD by targeting the expression of two main UPR transcription factors, XBP1 and ATF4 (activating transcription factor 4), in full-length mutant Huntingtin (mHtt) transgenic mice. XBP1-deficient mice were more resistant to developing disease features, associated with improved neuronal survival and motor performance, and a drastic decrease in mHtt levels. The protective effects of XBP1 deficiency were associated with enhanced macroautophagy in both cellular and animal models of HD. In contrast, ATF4 deficiency did not alter mHtt levels. Although, XBP1 mRNA splicing was observed in the striatum of HD transgenic brains, no changes in the levels of classical ER stress markers were detected in symptomatic animals. At the mechanistic level, we observed that XBP1 deficiency led to augmented expression of Forkhead box O1 (FoxO1), a key transcription factor regulating autophagy in neurons. In agreement with this finding, ectopic expression of FoxO1 enhanced autophagy and mHtt clearance in vitro. Our results provide strong evidence supporting an involvement of XBP1 in HD pathogenesis probably due to an ER stress-independent mechanism involving the control of FoxO1 and autophagy levels.
Asunto(s)
Autofagia , Proteínas de Unión al ADN/genética , Factores de Transcripción Forkhead/genética , Enfermedad de Huntington/genética , Proteínas del Tejido Nervioso/genética , Factores de Transcripción/genética , Animales , Cuerpo Estriado/metabolismo , Cuerpo Estriado/patología , Proteínas de Unión al ADN/metabolismo , Modelos Animales de Enfermedad , Proteína Forkhead Box O1 , Factores de Transcripción Forkhead/metabolismo , Humanos , Proteína Huntingtina , Enfermedad de Huntington/metabolismo , Enfermedad de Huntington/patología , Ratones , Ratones Transgénicos , Proteínas del Tejido Nervioso/metabolismo , Neuronas/metabolismo , Empalme del ARN , ARN Mensajero/metabolismo , Factores de Transcripción del Factor Regulador X , Factores de Transcripción/metabolismo , Respuesta de Proteína Desplegada/genética , Proteína 1 de Unión a la X-BoxRESUMEN
Mutations in superoxide dismutase-1 (SOD1) cause familial amyotrophic lateral sclerosis (fALS). Recent evidence implicates adaptive responses to endoplasmic reticulum (ER) stress in the disease process via a pathway known as the unfolded protein response (UPR). Here, we investigated the contribution to fALS of X-box-binding protein-1 (XBP-1), a key UPR transcription factor that regulates genes involved in protein folding and quality control. Despite expectations that XBP-1 deficiency would enhance the pathogenesis of mutant SOD1, we observed a dramatic decrease in its toxicity due to an enhanced clearance of mutant SOD1 aggregates by macroautophagy, a cellular pathway involved in lysosome-mediated protein degradation. To validate these observations in vivo, we generated mutant SOD1 transgenic mice with specific deletion of XBP-1 in the nervous system. XBP-1-deficient mice were more resistant to developing disease, correlating with increased levels of autophagy in motoneurons and reduced accumulation of mutant SOD1 aggregates in the spinal cord. Post-mortem spinal cord samples from patients with sporadic ALS and fALS displayed a marked activation of both the UPR and autophagy. Our results reveal a new function of XBP-1 in the control of autophagy and indicate critical cross-talk between these two signaling pathways that can provide protection against neurodegeneration.