Palmitic and Stearic Acids Inhibit Chaperone-Mediated Autophagy (CMA) in POMC-like Neurons In Vitro

The intake of food with high levels of saturated fatty acids (SatFAs) is associated with the development of obesity and insulin resistance. SatFAs, such as palmitic (PA) and stearic (SA) acids, have been shown to accumulate in the hypothalamus, causing several pathological consequences. Autophagy is a lysosomal-degrading pathway that can be divided into macroautophagy, microautophagy, and chaperone-mediated autophagy (CMA). Previous studies showed that PA impairs macroautophagy function and insulin response in hypothalamic proopiomelanocortin (POMC) neurons. Here, we show in vitro that the exposure of POMC neurons to PA or SA also inhibits CMA, possibly by decreasing the total and lysosomal LAMP2A protein levels. Proteomics of lysosomes from PA- and SA-treated cells showed that the inhibition of CMA could impact vesicle formation and trafficking, mitochondrial components, and insulin response, among others. Finally, we show that CMA activity is important for regulating the insulin response in POMC hypothalamic neurons. These in vitro results demonstrate that CMA is inhibited by PA and SA in POMC-like neurons, giving an overview of the CMA-dependent cellular pathways that could be affected by such inhibition and opening a door for in vivo studies of CMA in the context of the hypothalamus and obesity.

Chaperone mediated autophagy contributes to the newly synthesized histones H3 and H4 quality control

Although there are several pathways to ensure that proteins are folded properly in the cell, little is known about the molecular mechanisms regulating histone folding and proteostasis. In this work, we identified that chaperone-mediated autophagy (CMA) is the main pathway involved in the degradation of newly synthesized histones H3 and H4. This degradation is finely regulated by the interplay between HSC70 and tNASP, two histone interacting proteins. tNASP stabilizes histone H3 levels by blocking the direct transport of histone H3 into lysosomes. We further demonstrate that CMA degrades unfolded histone H3. Thus, we reveal that CMA is the main degradation pathway involved in the quality control of histone biogenesis, evidencing an additional mechanism in the intricate network of histone cellular proteostasis.

Chaperone Mediated Autophagy Degrades TDP-43 Protein and Is Affected by TDP-43 Aggregation

TAR DNA binding protein 43 kDa (TDP-43) is a ribonuclear protein regulating many aspects of RNA metabolism. Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Lobar Degeneration (FTLD) are fatal neurodegenerative diseases with the presence of TDP-43 aggregates in neuronal cells. Chaperone Mediated Autophagy (CMA) is a lysosomal degradation pathway participating in the proteostasis of several cytosolic proteins including neurodegenerative associated proteins. In addition, protein oligomers or aggregates can affect the status of CMA. In this work, we studied the relationship between CMA and the physiological and pathological forms of TDP-43. First, we found that recombinant TDP-43 was specifically degraded by rat liver’s CMA+ lysosomes and that endogenous TDP-43 is localized in rat brain’s CMA+ lysosomes, indicating that TDP-43 can be a CMA substrate in vivo. Next, by using a previously reported TDP-43 aggregation model, we have shown that wild-type and an aggregate-prone form of TDP-43 are detected in CMA+ lysosomes isolated from cell cultures. In addition, their protein levels increased in cells displaying CMA down-regulation, indicating that these two TDP-43 forms are CMA substrates in vitro. Finally, we observed that the aggregate-prone form of TDP-43 is able to interact with Hsc70, to co-localize with Lamp2A, and to up-regulate the levels of these molecular components of CMA. The latter was followed by an up-regulation of the CMA activity and lysosomal damage. Altogether our data shows that: (i) TDP-43 is a CMA substrate; (ii) CMA can contribute to control the turnover of physiological and pathological forms of TDP-43; and (iii) TDP-43 aggregation can affect CMA performance. Overall, this work contributes to understanding how a dysregulation between CMA and TDP-43 would participate in neuropathological mechanisms associated with TDP-43 aggregation.

Temporal pattern of neuronal insulin release during Caenorhabditis elegans aging: Role of redox homeostasis

The insulin‐IGF‐1/DAF‐2 pathway has a central role in the determination of aging and longevity in Caenorhabditis elegans and other organisms. In this paper, we measured neuronal insulin secretion (using INS‐22::Venus) during C. elegans lifespan and monitored how this secretion is modified by redox homeostasis. We showed that INS‐22::Venus secretion fluctuates during the organism lifetime reaching maximum levels in the active reproductive stage. We also demonstrate that long‐lived daf‐2 insulin receptor mutants show remarkable low levels of INS‐22::Venus secretion. In contrast, we found that short‐lived mutant worms that lack the oxidation repair enzyme MSRA‐1 show increased levels of INS‐22::Venus secretion, specifically during the reproductive stage. MSRA‐1 is a target of the insulin‐IGF‐1/DAF‐2 pathway, and the expression of this antioxidant enzyme exclusively in the nervous system rescues the mutant insulin release phenotype and longevity. The msra‐1 mutant phenotype can also be reverted by antioxidant treatment during the active reproductive stage. We showed for the first time that there is a pattern of neuronal insulin release with a noticeable increment during the peak of reproduction. Our results suggest that redox homeostasis can modulate longevity through the regulation of insulin secretion, and that the insulin‐IGF‐1/DAF‐2 pathway could be regulated, at least in part, by a feedback loop. These findings highlight the importance of timing for therapeutic interventions aimed at improving health span.

Chaperone Mediated Autophagy in the Crosstalk of Neurodegenerative Diseases and Metabolic Disorders

Chaperone Mediated Autophagy (CMA) is a lysosomal-dependent protein degradation pathway. At least 30% of cytosolic proteins can be degraded by this process. The two major protein players of CMA are LAMP-2A and HSC70. While LAMP-2A works as a receptor for protein substrates at the lysosomal membrane, HSC70 specifically binds protein targets and takes them for CMA degradation. Because of the broad spectrum of proteins able to be degraded by CMA, this pathway has been involved in physiological and pathological processes such as lipid and carbohydrate metabolism, and neurodegenerative diseases, respectively. Both, CMA, and the mentioned processes, are affected by aging and by inadequate nutritional habits such as a high fat diet or a high carbohydrate diet. Little is known regarding about CMA, which is considered a common regulation factor that links metabolism with neurodegenerative disorders. This review summarizes what is known about CMA, focusing on its molecular mechanism, its role in protein, lipid and carbohydrate metabolism. In addition, the review will discuss how CMA could be linked to protein, lipids and carbohydrate metabolism within neurodegenerative diseases. Furthermore, it will be discussed how aging and inadequate nutritional habits can have an impact on both CMA activity and neurodegenerative disorders.

PP32 and SET/TAF-Iβ proteins regulate the acetylation of newly synthesized histone H4

Newly synthesized histones H3 and H4 undergo a cascade of maturation steps to achieve proper folding and to establish post-translational modifications prior to chromatin deposition. Acetylation of H4 on lysines 5 and 12 by the HAT1 acetyltransferase is observed late in the histone maturation cascade. A key question is to understand how to establish and regulate the distinct timing of sequential modifications and their biological significance. Here, we perform proteomic analysis of the newly synthesized histone H4 complex at the earliest time point in the cascade. In addition to known binding partners Hsp90 and Hsp70, we also identify for the first time two subunits of the histone acetyltransferase inhibitor complex (INHAT): PP32 and SET/TAF-Iβ. We show that both proteins function to prevent HAT1-mediated H4 acetylation in vitro. When PP32 and SET/TAF-Iβ protein levels are down-regulated in vivo, we detect hyperacetylation on lysines 5 and 12 and other H4 lysine residues. Notably, aberrantly acetylated H4 is less stable and this reduces the interaction with Hsp90. As a consequence, PP32 and SET/TAF-Iβ depleted cells show an S-phase arrest. Our data demonstrate a novel function of PP32 and SET/TAF-Iβ and provide new insight into the mechanisms regulating acetylation of newly synthesized histone H4.

Wnt5a inhibits K(+) currents in hippocampal synapses through nitric oxide production

Hippocampal synapses play a key role in memory and learning processes by inducing long-term potentiation and depression. Wnt signaling is essential in the development and maintenance of synapses via several mechanisms. We have previously found that Wnt5a induces the production of nitric oxide (NO), which modulates NMDA receptor expression in the postsynaptic regions of hippocampal neurons. Here, we report that Wnt5a selectively inhibits a voltage-gated K(+) current (Kv current) and increases synaptic activity in hippocampal slices. Further supporting a specific role for Wnt5a, the soluble Frizzled receptor protein (sFRP-2; a functional Wnt antagonist) fully inhibits the effects of Wnt5a. We additionally show that these responses to Wnt5a are mediated by activation of a ROR2 receptor and increased NO production because they are suppressed by the shRNA-mediated knockdown of ROR2 and by 7-nitroindazole, a specific inhibitor of neuronal NOS. Together, our results show that Wnt5a increases NO production by acting on ROR2 receptors, which in turn inhibit Kv currents. These results reveal a novel mechanism by which Wnt5a may regulate the excitability of hippocampal neurons.

Role of the androgen receptor in breast cancer and preclinical analysis of enzalutamide

Introduction

The androgen receptor (AR) is widely expressed in breast cancers and has been proposed as a therapeutic target in estrogen receptor alpha (ER) negative breast cancers that retain AR. However, controversy exists regarding the role of AR, particularly in ER + tumors. Enzalutamide, an AR inhibitor that impairs nuclear localization of AR, was used to elucidate the role of AR in preclinical models of ER positive and negative breast cancer.

Methods

We examined nuclear AR to ER protein ratios in primary breast cancers in relation to response to endocrine therapy. The effects of AR inhibition with enzalutamide were examined in vitro and in preclinical models of ER positive and negative breast cancer that express AR.

Results

In a cohort of 192 women with ER + breast cancers, a high ratio of AR:ER (≥2.0) indicated an over four fold increased risk for failure while on tamoxifen (HR = 4.43). The AR:ER ratio had an independent effect on risk for failure above ER % staining alone. AR:ER ratio is also an independent predictor of disease-free survival (HR = 4.04, 95% CI: 1.68, 9.69; p = 0.002) and disease specific survival (HR = 2.75, 95% CI: 1.11, 6.86; p = 0.03). Both enzalutamide and bicalutamide inhibited 5-alpha-dihydrotestosterone (DHT)-mediated proliferation of breast cancer lines in vitro; however, enzalutamide uniquely inhibited estradiol (E2)-mediated proliferation of ER+/AR + breast cancer cells. In MCF7 xenografts (ER+/AR+) enzalutamide inhibited E2-driven tumor growth as effectively as tamoxifen by decreasing proliferation. Enzalutamide also inhibited DHT- driven tumor growth in both ER positive (MCF7) and negative (MDA-MB-453) xenografts, but did so by increasing apoptosis.

Conclusions

AR to ER ratio may influence breast cancer response to traditional endocrine therapy. Enzalutamide elicits different effects on E2-mediated breast cancer cell proliferation than bicalutamide. This preclinical study supports the initiation of clinical studies evaluating enzalutamide for treatment of AR⁺ tumors regardless of ER status, since it blocks both androgen- and estrogen- mediated tumor growth.

Enzalutamide, an androgen receptor signaling inhibitor, induces tumor regression in a mouse model of castration-resistant prostate cancer

BACKGROUND

Enzalutamide (formerly MDV3100 and available commercially as Xtandi), a novel androgen receptor (AR) signaling inhibitor, blocks the growth of castration-resistant prostate cancer (CRPC) in cellular model systems and was shown in a clinical study to increase survival in patients with metastatic CRPC. Enzalutamide inhibits multiple steps of AR signaling: binding of androgens to AR, AR nuclear translocation, and association of AR with DNA. Here, we investigate the effects of enzalutamide on AR signaling, AR-dependent gene expression and cell apoptosis.

METHODS

The expression of AR target gene prostate-specific antigen (PSA) was measured in LnCaP and C4-2 cells. AR nuclear translocation was assessed in HEK-293 cells stably transfected with AR-yellow fluorescent protein. The in vivo effects of enzalutamide were determined in a mouse xenograft model of CRPC. Differential gene expression in LNCaP cells was measured using Affymetrix human genome microarray technology.

RESULTS

We found that unlike bicalutamide, enzalutamide lacked AR agonistic activity at effective doses and did not induce PSA expression or AR nuclear translocation. Additionally, it is more effective than bicalutamide at inhibiting agonist-induced AR nuclear translocation. Enzalutamide induced the regression of tumor volume in a CRPC xenograft model and apoptosis in AR-over-expressing prostate cancer cells. Finally, gene expression profiling in LNCaP cells indicated that enzalutamide opposes agonist-induced changes in genes involved in processes such as cell adhesion, angiogenesis, and apoptosis.

CONCLUSIONS

These results indicate that enzalutamide efficiently inhibits AR signaling, and we suggest that its lack of AR agonist activity may be important for these effects.

Latrepirdine stimulates autophagy and reduces accumulation of α-synuclein in cells and in mouse brain

Latrepirdine (Dimebon; dimebolin) is a neuroactive compound that was associated with enhanced cognition, neuroprotection and neurogenesis in laboratory animals, and has entered phase II clinical trials for both Alzheimer's disease and Huntington's disease (HD). Based on recent indications that latrepirdine protects cells against cytotoxicity associated with expression of aggregatable neurodegeneration-related proteins, including Aβ42 and γ-synuclein, we sought to determine whether latrepirdine offers protection to Saccharomyces cerevisiae. We utilized separate and parallel expression in yeast of several neurodegeneration-related proteins, including α-synuclein (α-syn), the amyotrophic lateral sclerosis-associated genes TDP43 and FUS, and the HD-associated protein huntingtin with a 103 copy-polyglutamine expansion (HTT gene; htt-103Q). Latrepirdine effects on α-syn clearance and toxicity were also measured following treatment of SH-SY5Y cells or chronic treatment of wild-type mice. Latrepirdine only protected yeast against the cytotoxicity associated with α-syn, and this appeared to occur via induction of autophagy. We further report that latrepirdine stimulated the degradation of α-syn in differentiated SH-SY5Y neurons, and in mouse brain following chronic administration, in parallel with elevation of the levels of markers of autophagic activity. Ongoing experiments will determine the utility of latrepirdine to abrogate α-syn accumulation in transgenic mouse models of α-syn neuropathology. We propose that latrepirdine may represent a novel scaffold for discovery of robust pro-autophagic/anti-neurodegeneration compounds, which might yield clinical benefit for synucleinopathies including Parkinson's disease, Lewy body dementia, rapid eye movement (REM) sleep disorder and/or multiple system atrophy, following optimization of its pro-autophagic and pro-neurogenic activities.

Latrepirdine improves cognition and arrests progression of neuropathology in an Alzheimer's mouse model

Latrepirdine (Dimebon) is a pro-neurogenic, antihistaminic compound that has yielded mixed results in clinical trials of mild to moderate Alzheimer's disease, with a dramatically positive outcome in a Russian clinical trial that was unconfirmed in a replication trial in the United States. We sought to determine whether latrepirdine (LAT)-stimulated amyloid precursor protein (APP) catabolism is at least partially attributable to regulation of macroautophagy, a highly conserved protein catabolism pathway that is known to be impaired in brains of patients with Alzheimer's disease (AD). We utilized several mammalian cellular models to determine whether LAT regulates mammalian target of rapamycin (mTOR) and Atg5-dependent autophagy. Male TgCRND8 mice were chronically administered LAT prior to behavior analysis in the cued and contextual fear conditioning paradigm, as well as immunohistological and biochemical analysis of AD-related neuropathology. Treatment of cultured mammalian cells with LAT led to enhanced mTOR- and Atg5-dependent autophagy. Latrepirdine treatment of TgCRND8 transgenic mice was associated with improved learning behavior and with a reduction in accumulation of Aβ42 and α-synuclein. We conclude that LAT possesses pro-autophagic properties in addition to the previously reported pro-neurogenic properties, both of which are potentially relevant to the treatment and/or prevention of neurodegenerative diseases. We suggest that elucidation of the molecular mechanism(s) underlying LAT effects on neurogenesis, autophagy and behavior might warranty the further study of LAT as a potentially viable lead compound that might yield more consistent clinical benefit following the optimization of its pro-neurogenic, pro-autophagic and/or pro-cognitive activities.

Effect of MDV3100, a novel androgen receptor signaling inhibitor, on cell proliferation and tumor size in an apocrine breast cancer xenograft model

3072

Background: MDV3100, a new androgen receptor (AR) signaling inhibitor, has demonstrated therapeutic effects in men with post-docetaxel prostate cancer (AFFIRM). AR is also expressed in the majority of breast cancers. Molecular profiling of estrogen receptor negative (ER-) breast cancer classifies this disease into basal and molecular apocrine subtypes. Apocrine breast cancer represents ~50% of ER- tumors and is characterized by a steroid response gene signature that includes AR expression. Here we report the effects of MDV3100 on the growth of the ER-/AR+ breast cancer cell line MDA-MB-453 in tissue culture and in an in vivo xenograft mouse model. Methods: MDA-MB-453 cells were maintained in 5% complete or 5% charcoal-stripped serum supplemented with dihydrotestosterone (CSS-DHT). The DHT induced nuclear translocation of AR was determined by subcellular fractionation followed by western blot. AR target gene expression was measured by qPCR. To generate a mouse xenograft model, 5-6 wk old female NOD-SCID-IL2Rgc–/– mice were injected ortotopically with 6x106 MDA-MB-453 cells into the fourth inguinal gland and were administered exogenous DHT (12.5 mg in a 60 day release pellet) or control pellets. When tumor size reached 100 mm3, mice were treated with 10 mg/kg/day MDV3100 or vehicle (0.5% methocel solution) by oral gavage for 33 days. Results: Viability of MDA-MB-453 cells treated with 10 uM MDV3100 was reduced by 10% after 3 days and 27% after 6 days. Treatment with 25 uM MDV3100 reduced cell viability by 27% after 3 days and 36% after 6 days. Similar results were obtained when cells maintained in CSS-DHT were treated with MDV3100. Treatment with MDV3100 blocked DHT-induced nuclear translocation and concordantly reduced the expression of AR-targets fatty acid synthase, prolactin receptor, and gross cystic disease protein-15. In the xenograft model, MDV3100 inhibited tumor growth by 78% as compared to tumors treated with vehicle. Conclusions: MDV3100 reduced cell proliferation in apocrine cell lines. MDV3100 also suppressed exogenous DHT-induced growth of ER-/AR+ tumors in vivo. These results support the evaluation of MDV3100 as a treatment for apocrine tumors.

Cognition-enhancing properties of Dimebon in a rat novel object recognition task are unlikely to be associated with acetylcholinesterase inhibition or N-methyl-D-aspartate receptor antagonism

Dimebon (dimebolin) treatment enhances cognition in patients with Alzheimer's disease (AD) or Huntington's disease. Although Dimebon was originally thought to improve cognition and memory through inhibition of acetylcholinesterase (AChE) and the N-methyl-d-aspartate (NMDA) receptor, the low in vitro affinity for these targets suggests that these mechanisms may not contribute to its clinical effects. To test this hypothesis, we assessed whether Dimebon enhances cognition in rats and if such an action is related to either mechanism or additional candidate mechanisms. Acute oral administration of Dimebon to rats (0.05, 0.5, and 5 mg/kg) enhanced cognition in a novel object recognition task and produced Dimebon brain concentrations of 1.7 +/- 0.43, 14 +/- 5.1, and 172 +/- 94 nM, respectively. At these concentrations, Dimebon did not alter the activity of recombinant human or rat brain AChE. Unlike the AChE inhibitors donepezil and galantamine, Dimebon did not change acetylcholine levels in the hippocampus or prefrontal cortex of freely moving rats. Dimebon displays affinity for the NMDA receptor (K(i) = 105 +/- 18 microM) that is considerably higher than brain concentrations associated with cognition enhancement in the novel object recognition task and 200-fold weaker than that of memantine (K(i) = 0.54 +/- 0.05 microM). Dimebon did not block NMDA-induced calcium influx in primary neuronal cells (IC(50) > 50 microM), consistent with a lack of significant effect on this pathway. The cognition-enhancing effects of Dimebon are unlikely to be mediated by AChE inhibition or NMDA receptor antagonism, and its mechanism of action appears to be distinct from currently approved medications for AD.

Role of the Wnt receptor Frizzled-1 in presynaptic differentiation and function

BACKGROUND

The Wnt signaling pathway regulates several fundamental developmental processes and recently has been shown to be involved in different aspects of synaptic differentiation and plasticity. Some Wnt signaling components are localized at central synapses, and it is thus possible that this pathway could be activated at the synapse.

RESULTS

We examined the distribution of the Wnt receptor Frizzled-1 in cultured hippocampal neurons and determined that this receptor is located at synaptic contacts co-localizing with presynaptic proteins. Frizzled-1 was found in functional synapses detected with FM1-43 staining and in synaptic terminals from adult rat brain. Interestingly, overexpression of Frizzled-1 increased the number of clusters of Bassoon, a component of the active zone, while treatment with the extracellular cysteine-rich domain (CRD) of Frizzled-1 decreased Bassoon clustering, suggesting a role for this receptor in presynaptic differentiation. Consistent with this, treatment with the Frizzled-1 ligand Wnt-3a induced presynaptic protein clustering and increased functional presynaptic recycling sites, and these effects were prevented by co-treatment with the CRD of Frizzled-1. Moreover, in synaptically mature neurons Wnt-3a was able to modulate the kinetics of neurotransmitter release.

CONCLUSION

Our results indicate that the activation of the Wnt pathway through Frizzled-1 occurs at the presynaptic level, and suggest that the synaptic effects of the Wnt signaling pathway could be modulated by local activation through synaptic Frizzled receptors.

Wnt-5a/JNK signaling promotes the clustering of PSD-95 in hippocampal neurons

During the formation of synapses, specific regions of pre- and postsynaptic cells associate to form a single functional transmission unit. In this process, synaptogenic factors are necessary to modulate pre- and postsynaptic differentiation. In mammals, different Wnt ligands operate through canonical and non-canonical Wnt pathways, and their precise functions to coordinate synapse structure and function in the mature central nervous system are still largely unknown. Here, we studied the effect of different Wnt ligands on postsynaptic organization. We found that Wnt-5a induces short term changes in the clustering of PSD-95, without affecting its total levels. Wnt-5a promotes the recruitment of PSD-95 from a diffuse dendritic cytoplasmic pool to form new PSD-95 clusters in dendritic spines. Moreover, Wnt-5a acting as a non-canonical ligand regulates PSD-95 distribution through a JNK-dependent signaling pathway, as demonstrated by using the TAT-TI-JIP peptide in mature hippocampal neurons. Finally, using adult rat hippocampal slices, we found that Wnt-5a modulates glutamatergic synaptic transmission through a postsynaptic mechanism. Our studies indicate that the Wnt-5a/JNK pathway modulates the postsynaptic region of mammalian synapse directing the clustering and distribution of the physiologically relevant scaffold protein, PSD-95.