Search results

There are 39 results for Rapamycin (displaying 31 to 39).

Selective clearance of aberrant tau proteins and rescue of neurotoxicity by transcription factor EB

Accumulating evidence implicates impairment of the autophagy‐lysosome pathway in Alzheimer's disease (AD). Recently discovered, transcription factor EB (TFEB) is a molecule shown to play central roles in cellular degradative processes. Here we investigate the role of TFEB in AD mouse models. In this study, we demonstrate that TFEB effectively reduces neurofibrillary tangle pathology and rescues behavioral and synaptic deficits and neurodegeneration in the rTg4510 mouse model of tauopathy with no detectable adverse effects when expressed in wild‐type mice. TFEB specifically targets hyperphosphorylated and misfolded Tau species present in both soluble and aggregated fractions while leaving normal Tau intact. We provide in vitro evidence that this effect requires lysosomal activity and we identify phosphatase and tensin homolog (PTEN) as a direct target of TFEB that is required for TFEB‐dependent aberrant Tau clearance. The specificity and efficacy of TFEB in mediating the clearance of toxic Tau species makes it an attractive therapeutic target for treating diseases of tauopathy including AD.

… that TFEB targets the detergent‐insoluble pTau for degradation. This assessment is consistent with the TFEB's role in the autophagy‐lysosomal pathway and is in agreement with the published reports that autophagy activators such as rapamycin or trehalose are effective in removing Tau aggregates (Schaeffer et al , ; Ozcelik et al , ). To probe the cellular mechanisms mediating TFEB reduction of soluble pTau, we used a doxycycline inducible cell line expressing the largest human Tau isoform …

Vinicia A Polito et al. EMBO molecular medicine September 2014

MCL‐1 is a stress sensor that regulates autophagy in a developmentally regulated manner

Apoptosis has an important role during development to regulate cell number. In differentiated cells, however, activation of autophagy has a critical role by enabling cells to remain functional following stress. In this study, we show that the antiapoptotic BCL‐2 homologue MCL‐1 has a key role in controlling both processes in a developmentally regulated manner. Specifically, MCL‐1 degradation is an early event not only following induction of apoptosis, but also under nutrient deprivation conditions where MCL‐1 levels regulate activation of autophagy. Furthermore, deletion of MCL‐1 in cortical neurons of transgenic mice activates a robust autophagic response. This autophagic response can, however, be converted to apoptosis by either reducing the levels of the autophagy regulator Beclin‐1, or by a concomitant activation of BAX. Our results define a pathway whereby MCL‐1 has a key role in determining cell fate, by coordinately regulating apoptosis and autophagy.

… function and death of the animals within a few months of life ( ; ). Several studies have also shown that overexpression of autophagy genes or activation of autophagy by rapamycin leads to a reduction in aggregate formation in models of Alzheimer's, Huntington and Parkinson's disease ( ; ; ; ). At the molecular level, autophagy is characterised by the formation of a double‐membrane vesicle, the autophagosome, containing the material to be degraded ( ; ). Autophagosomes subsequently fuse …

Marc Germain et al. The EMBO Journal January 2011

HDAC6 controls autophagosome maturation essential for ubiquitin‐selective quality‐control autophagy

Autophagy is primarily considered a non‐selective degradation process induced by starvation. Nutrient‐independent basal autophagy, in contrast, imposes intracellular QC by selective disposal of aberrant protein aggregates and damaged organelles, a process critical for suppressing neurodegenerative diseases. The molecular mechanism that distinguishes these two fundamental autophagic responses, however, remains mysterious. Here, we identify the ubiquitin‐binding deacetylase, histone deacetylase‐6 (HDAC6), as a central component of basal autophagy that targets protein aggregates and damaged mitochondria. Surprisingly, HDAC6 is not required for autophagy activation; rather, it controls the fusion of autophagosomes to lysosomes. HDAC6 promotes autophagy by recruiting a cortactin‐dependent, actin‐remodelling machinery, which in turn assembles an F‐actin network that stimulates autophagosome–lysosome fusion and substrate degradation. Indeed, HDAC6 deficiency leads to autophagosome maturation failure, protein aggregate build‐up, and neurodegeneration. Remarkably, HDAC6 and F‐actin assembly are completely dispensable for starvation‐induced autophagy, uncovering the fundamental difference of these autophagic modes. Our study identifies HDAC6 and the actin cytoskeleton as critical components that define QC autophagy and uncovers a novel regulation of autophagy at the level of autophagosome–lysosome fusion.

… disease. Supporting this view, in the Drosophila SBMA model, the neuroprotective effect of rapamycin, which potently activates autophagy, was abrogated in the HDAC6‐mutant background ( ). Instead, we speculate that agents that stimulate autophagosome–lysosome fusion might provide an alternative and effective way to enhance the degradative capacity of autophagy, thereby protecting the neurons. Thus, the autophagosome–lysosome fusion machinery could be an attractive therapeutic target for developing …

Joo‐Yong Lee et al. The EMBO Journal June 2010

Genome‐wide siRNA screen reveals amino acid starvation‐induced autophagy requires SCOC and WAC

Autophagy is a catabolic process by which cytoplasmic components are sequestered and transported by autophagosomes to lysosomes for degradation, enabling recycling of these components and providing cells with amino acids during starvation. It is a highly regulated process and its deregulation contributes to multiple diseases. Despite its importance in cell homeostasis, autophagy is not fully understood. To find new proteins that modulate starvation‐induced autophagy, we performed a genome‐wide siRNA screen in a stable human cell line expressing GFP–LC3, the marker‐protein for autophagosomes. Using stringent validation criteria, our screen identified nine novel autophagy regulators. Among the hits required for autophagosome formation are SCOC (short coiled‐coil protein), a Golgi protein, which interacts with fasciculation and elongation protein zeta 1 (FEZ1), an ULK1‐binding protein. SCOC forms a starvation‐sensitive trimeric complex with UVRAG (UV radiation resistance associated gene) and FEZ1 and may regulate ULK1 and Beclin 1 complex activities. A second candidate WAC is required for starvation‐induced autophagy but also acts as a potential negative regulator of the ubiquitin‐proteasome system. The identification of these novel regulatory proteins with diverse functions in autophagy contributes towards a fuller understanding of autophagosome formation.

… , recycling macromolecules and restoring metabolic functions ( ). Decreased amino acids in the cytosol causes inactivation of mTOR (mammalian target of rapamycin), a major regulator of cell growth, and induces autophagy ( ). Many essential mammalian autophagy (Atg) proteins, most originally discovered in yeast, have been identified, leading to our current basic understanding of the process ( ). A double bi‐layered membrane, the isolation membrane or phagophore, encloses cytoplasmic macromolecules …

Nicole C McKnight et al. The EMBO Journal April 2012

Atg1‐mediated myosin II activation regulates autophagosome formation during starvation‐induced autophagy

Autophagy is a membrane‐mediated degradation process of macromolecule recycling. Although the formation of double‐membrane degradation vesicles (autophagosomes) is known to have a central role in autophagy, the mechanism underlying this process remains elusive. The serine/threonine kinase Atg1 has a key role in the induction of autophagy. In this study, we show that overexpression of Drosophila Atg1 promotes the phosphorylation‐dependent activation of the actin‐associated motor protein myosin II. A novel myosin light chain kinase (MLCK)‐like protein, Spaghetti‐squash activator (Sqa), was identified as a link between Atg1 and actomyosin activation. Sqa interacts with Atg1 through its kinase domain and is a substrate of Atg1. Significantly, myosin II inhibition or depletion of Sqa compromised the formation of autophagosomes under starvation conditions. In mammalian cells, we found that the Sqa mammalian homologue zipper‐interacting protein kinase (ZIPK) and myosin II had a critical role in the regulation of starvation‐induced autophagy and mammalian Atg9 (mAtg9) trafficking when cells were deprived of nutrients. Our findings provide evidence of a link between Atg1 and the control of Atg9‐mediated autophagosome formation through the myosin II motor protein.

… ( ; ). It seems that for this formation to begin, the PAS must be targeted by Atg proteins. The molecular mechanism underlying this process is not known, though the Atg1 complex may be involved in the recruitment of Atg proteins to PAS ( ). The serine/threonine protein kinase Atg1 acts as an important link between the nutrient‐sensing target of rapamycin (TOR) kinase signalling and autophagy. It has been shown that Atg1 associates with Atg13 and Atg17 in response to TOR regulation ( ). Moreover, Atg1 …

Hong‐Wen Tang et al. The EMBO Journal February 2011

Impairment of chaperone‐mediated autophagy leads to selective lysosomal degradation defects in the lysosomal storage disease cystinosis

Metabolite accumulation in lysosomal storage disorders ( LSD s) results in impaired cell function and multi‐systemic disease. Although substrate reduction and lysosomal overload‐decreasing therapies can ameliorate disease progression, the significance of lysosomal overload‐independent mechanisms in the development of cellular dysfunction is unknown for most LSD s. Here, we identify a mechanism of impaired chaperone‐mediated autophagy ( CMA ) in cystinosis, a LSD caused by defects in the cystine transporter cystinosin ( CTNS ) and characterized by cystine lysosomal accumulation. We show that, different from other LSD s, autophagosome number is increased, but macroautophagic flux is not impaired in cystinosis while mTOR activity is not affected. Conversely, the expression and localization of the CMA receptor LAMP 2A are abnormal in CTNS ‐deficient cells and degradation of the CMA substrate GAPDH is defective in Ctns −/− mice. Importantly, cysteamine treatment, despite decreasing lysosomal overload, did not correct defective CMA in Ctns −/− mice or LAMP 2A mislocalization in cystinotic cells, which was rescued by CTNS expression instead, suggesting that cystinosin is important for CMA activity. In conclusion, CMA impairment contributes to cell malfunction in cystinosis, highlighting the need for treatments complementary to current therapies that are based on decreasing lysosomal overload.

… of rapamycin ( mTOR) signaling pathway represents the major regulatory hub at the interface between cell growth and starvation (Zoncu et al , ). Amino acids and cell nutrients can activate the mTOR kinase complex, whose activity is responsible for phosphorylation of different substrates important in the promotion of cell growth and suppression of autophagy (Zoncu et al , ). Conversely, starvation inactivates mTOR, thereby inhibiting anabolic processes and liberating nutrient reserves by activating …

Gennaro Napolitano et al. EMBO molecular medicine February 2015

Impaired GAPDH‐induced mitophagy contributes to the pathology of Huntington's disease

Mitochondrial dysfunction is implicated in multiple neurodegenerative diseases. In order to maintain a healthy population of functional mitochondria in cells, defective mitochondria must be properly eliminated by lysosomal machinery in a process referred to as mitophagy. Here, we uncover a new molecular mechanism underlying mitophagy driven by glyceraldehyde‐3‐phosphate dehydrogenase ( GAPDH ) under the pathological condition of Huntington's disease ( HD ) caused by expansion of polyglutamine repeats. Expression of expanded polyglutamine tracts catalytically inactivates GAPDH ( iGAPDH ), which triggers its selective association with damaged mitochondria in several cell culture models of HD . Through this mechanism, iGAPDH serves as a signaling molecule to induce direct engulfment of damaged mitochondria into lysosomes (micro‐mitophagy). However, abnormal interaction of mitochondrial GAPDH with long polyglutamine tracts stalled GAPDH ‐mediated mitophagy, leading to accumulation of damaged mitochondria, and increased cell death. We further demonstrated that overexpression of inactive GAPDH rescues this blunted process and enhances mitochondrial function and cell survival, indicating a role for GAPDH ‐driven mitophagy in the pathology of HD.

… therapeutic approach to treat HD and maybe other neurodegenerative diseases. Because of the complexity of the disease, a comprehensive treatment, including a selective inhibitor of mitochondrial fission protein (Drp1) and a pharmacological activator of the macro‐autophagic pathway (Nixon, ) such as mTOR‐inhibiting drug, rapamycin, may provide the greatest therapeutic potential. Antibodies used in this study were principally purchased from Santa Cruz Biotechnology (Tom20: SC‐11415, enolase: SC‐15343 …

Sunhee Hwang et al. EMBO molecular medicine October 2015

Activation of serum/glucocorticoid‐induced kinase 1 (SGK1) is important to maintain skeletal muscle homeostasis and prevent atrophy

Maintaining skeletal muscle mass is essential for general health and prevention of disease progression in various neuromuscular conditions. Currently, no treatments are available to prevent progressive loss of muscle mass in any of these conditions. Hibernating mammals are protected from muscle atrophy despite prolonged periods of immobilization and starvation. Here, we describe a mechanism underlying muscle preservation and translate it to non‐hibernating mammals. Although Akt has an established role in skeletal muscle homeostasis, we find that serum‐ and glucocorticoid‐inducible kinase 1 (SGK1) regulates muscle mass maintenance via downregulation of proteolysis and autophagy as well as increased protein synthesis during hibernation. We demonstrate that SGK1 is critical for the maintenance of skeletal muscle homeostasis and function in non‐hibernating mammals in normal and atrophic conditions such as starvation and immobilization. Our results identify a novel therapeutic target to combat loss of skeletal muscle mass associated with muscle degeneration and atrophy.

… rodent. We analysed the 13‐lined ground squirrel ( Ictidomys tridecemlineatus ), a naturally occurring, hibernating animal (Vaughan et al, ). These rodents spend approximately half of the year in hibernation. Bradycardia, hypothermia, episodic ventilation, lack of food and water intake, and immobility characterize the torpor state. While the molecular mechanisms determining the hibernator's marked resilience against atrophy have not been elucidated, changes in mammalian target of rapamycin (mTOR …

Eva Andres‐Mateos et al. EMBO molecular medicine January 2013

Hrr25 kinase promotes selective autophagy by phosphorylating the cargo receptor Atg19

Autophagy is the major pathway for the delivery of cytoplasmic material to the vacuole or lysosome. Selective autophagy is mediated by cargo receptors, which link the cargo to the scaffold protein Atg11 and to Atg8 family proteins on the forming autophagosomal membrane. We show that the essential kinase Hrr25 activates the cargo receptor Atg19 by phosphorylation, which is required to link cargo to the Atg11 scaffold, allowing selective autophagy to proceed. We also find that the Atg34 cargo receptor is regulated in a similar manner, suggesting a conserved mechanism.

GFP‐Atg11 Ape1‐mRuby atg19Δ cells containing myc‐Atg19 as indicated and Cup1‐Ape1 were grown to log phase. Overexpression of Ape1 was induced by addition of 250 μM copper sulfate for 3 h, and autophagy was induced by treating cells for 1 h with rapamycin. Scale bar, 5 μm. Ape1‐mRuby atg19Δ cells containing GFP‐Atg19 wild‐type or GFP‐Atg19‐3A were analyzed in log phase. Scale bar, 5 μm. GFP‐Atg8 Ape1‐mRuby atg19Δ cells containing myc‐Atg19 as indicated and Cup1‐Ape1 were analyzed as in (A). Scale bar, 5 μm.

Comparison of Atg19 and Atg34 domain structures and C‐terminal amino acid sequences. Green: Atg11 binding region. Serine residues S390, S391, and S396, which are phosphorylated in Atg19, and the conserved sites in Atg34 are shown enlarged. atg34Δ yeast cells containing HTB‐Atg34 were grown to mid‐log phase and treated with rapamycin. Atg34 was affinity purified and subjected to mass spectrometric phosphorylation mapping. Phosphorylation sites: enlarged; Atg11 binding region: green; lysine …

Thaddaeus Pfaffenwimmer et al. EMBO Reports August 2014