Abstract17Correspondence should be addressed to G.K. (e-mail: E-mail: kroemer@igr.fr). 16 These authors contributed equally to this paper. AUTHOR CONTRIBUTIONS E.T., M.C.M., L.G. and I.V. conducted experiments, prepared figures and analysed data; M.D.-M., M.D.'A., A.C., E.M., C.Z., F.H., U.N., C.S., P.P., J.M.V, R.C., F.M., P.P.B, G.S., G.P., K.B., N.T., P.C. and F.C. performed experiments; E.T. and G.K. planned the project; G.K. supervised the project and wrote the manuscript.Note: Supplementary Information is available on the Nature Cell Biology website. COMPETING FINANCIAL INTERESTSThe authors declare no competing financial interests. NIH Public Access Author ManuscriptNat Cell Biol. Author manuscript; available in PMC 2009 May 4. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptMultiple cellular stressors, including activation of the tumour suppressor p53, can stimulate autophagy. Here we show that knockout, knockdown or pharmacological inhibition of p53 can induce autophagy in human, mouse and nematode cells. Enhanced autophagy improved the survival of p53-deficient cancer cells under conditions of hypoxia and nutrient depletion, allowing them to maintain high ATP levels. Inhibition of p53 led to autophagy in enucleated cells, and cytoplasmic, not nuclear, p53 was able to repress the enhanced autophagy of p53 -/-cells. Many different inducers of autophagy (for example, starvation, rapamycin and toxins affecting the endoplasmic reticulum) stimulated proteasome-mediated degradation of p53 through a pathway relying on the E3 ubiquitin ligase HDM2. Inhibition of p53 degradation prevented the activation of autophagy in several cell lines, in response to several distinct stimuli. These results provide evidence of a key signalling pathway that links autophagy to the cancer-associated dysregulation of p53.Autophagy (`self-eating') is an important eukaryotic response to cellular stress. During autophagy, portions of the cytosol and cytoplasmic organelles are sequestered within characteristic double-or multi-membraned autophagosomes and delivered to lysosomes for bulk degradation. By promoting catabolic reactions, autophagy generates new metabolic substrates that meet the bioenergetic needs of cells and allows for adaptive protein synthesis. Autophagy also constitutes a homeostatic `clean-up' process to rid cells of intracellular parasites, damaged organelles and potentially toxic, aggregate-prone proteins. Finally, autophagy has been viewed as a self-destructive process in which stressed cells succumb to the so-called autophagic cell death 1 .Autophagy is essential for the long-term survival of mammalian cells and a partial reduction in the autophagic capacity may constitute an oncogenic event. At least one of the phylogenetically conserved autophagy genes, atg6/beclin 1, is frequently inactivated at one locus in human cancers, and mouse studies have confirmed that beclin 1 is a haploinsufficient tumour suppressor 2 . There are two non-exclusive hypotheses to explain how inhibition of autoph...
Pain perception has evolved as a warning mechanism to alert organisms to tissue damage and dangerous environments. In humans, however, undesirable, excessive or chronic pain is a common and major societal burden for which available medical treatments are currently suboptimal. New therapeutic options have recently been derived from studies of individuals with congenital insensitivity to pain (CIP). Here we identified 10 different homozygous mutations in PRDM12 (encoding PRDI-BF1 and RIZ homology domain-containing protein 12) in subjects with CIP from 11 families. Prdm proteins are a family of epigenetic regulators that control neural specification and neurogenesis. We determined that Prdm12 is expressed in nociceptors and their progenitors and participates in the development of sensory neurons in Xenopus embryos. Moreover, CIP-associated mutants abrogate the histone-modifying potential associated with wild-type Prdm12. Prdm12 emerges as a key factor in the orchestration of sensory neurogenesis and may hold promise as a target for new pain therapeutics.
Autophagy is the main process for bulk protein and organelle recycling in cells under extracellular or intracellular stress. Deregulation of autophagy has been associated with pathological conditions such as cancer, muscular disorders and neurodegeneration. Necrotic cell death underlies extensive neuronal loss in acute neurodegenerative episodes such as ischemic stroke. We find that excessive autophagosome formation is induced early during necrotic cell death in C. elegans. In addition, autophagy is required for necrotic cell death. Impairment of autophagy by genetic inactivation of autophagy genes or by pharmacological treatment suppresses necrosis. Autophagy synergizes with lysosomal catabolic mechanisms to facilitate cell death. Our findings demonstrate that autophagy contributes to cellular destruction during necrosis. Thus, interfering with the autophagic process may protect neurons against necrotic damage in humans.
Discovery of molecular mechanisms and chemical compounds that enhance neuronal regeneration can lead to development of therapeutics to combat nervous system injuries and neurodegenerative diseases. By combining high-throughput microfluidics and femtosecond laser microsurgery, we demonstrate for the first time largescale in vivo screens for identification of compounds that affect neurite regeneration. We performed thousands of microsurgeries at single-axon precision in the nematode Caenorhabditis elegans at a rate of 20 seconds per animal. Following surgeries, we exposed the animals to a hand-curated library of approximately one hundred small molecules and identified chemicals that significantly alter neurite regeneration. In particular, we found that the PKC kinase inhibitor staurosporine strongly modulates regeneration in a concentration-and neuronal type-specific manner. Two structurally unrelated PKC inhibitors produce similar effects. We further show that regeneration is significantly enhanced by the PKC activator prostratin. C. elegans | chemical screen | microfluidicsT he ability of neurons in the adult mammalian central nervous system to regenerate their axons after injury is extremely limited, which has been attributed to both extrinsic signals of the inhibitory glial environment (1) as well as intrinsic neuronal factors (2-4). The discovery of cell-permeable small molecules that modulate axon regrowth can potentiate the development of efficient therapeutic treatments for spinal cord injuries, brain trauma, stroke, and neurodegenerative diseases. Identification of such molecules can also provide valuable tools for fundamental investigations of the mechanisms involved in the regeneration process. Currently, small-molecule screens for neuronal regeneration are performed in simple in vitro cell culture systems. Such screens have already revealed large numbers of chemicals that enhance regeneration and/or affect cellular morphogenesis, yet many of these hits still remain untested in vivo. In addition, most in vitro studies do not translate to animal models and also fail to reveal off-target, toxic, or lethal effects. Thus, a thorough investigation of neuronal regeneration mechanisms requires in vivo neuronal injury models.In vivo investigation of neuronal regeneration has been performed mainly in mice and rats. However, their long developmental periods, complicated genetics and biology, and expensive maintenance prevent large-scale studies on these animals. The nematode Caenorhabditis elegans is a simple, well-studied, invertebrate model-organism with a fully mapped neuronal network comprising 302 neurons. Its short developmental cycle, simple and low-cost laboratory maintenance, and genetic amenability make it an ideal model for large-scale screens, rapid identification of the molecular targets of screened compounds, and discovery of novel signaling pathways implicated in regeneration.Until recently however, the small size of C. elegans (∼50 μm in diameter) prevented its use for investigation of neuronal re...
Numerous studies implicate necrotic cell death in devastating human pathologies such as stroke and neurodegenerative diseases. Investigations in both nematodes and mammals converge to implicate specific calpain and aspartyl proteases in the execution of necrotic cell death. It is believed that these proteases become activated under conditions that inflict necrotic cell death. However, the factors that modulate necrosis and govern the erroneous activation of these otherwise benign enzymes are largely unknown. Here we show that the function of the vacuolar H(+)-ATPase, a pump that acidifies lysosomes and other intracellular organelles, is essential for necrotic cell death in C. elegans. Cytoplasmic pH drops in dying cells. Intracellular acidification requires the vacuolar H(+)-ATPase, whereas alkalization of endosomal and lysosomal compartments by weak bases protects against necrosis. In addition, we show that vacuolar H(+)-ATPase activity is required downstream of cytoplasmic calcium overload during necrosis. Thus, intracellular pH is an important modulator of necrosis in C. elegans. We propose that vacuolar H(+)-ATPase activity is required to establish necrosis-promoting, acidic intracellular conditions that augment the function of executioner aspartyl proteases in dying cells. Similar mechanisms may contribute to necrotic cell death that follows extreme acidosis-for example, during stroke-in humans.
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