Autophagy Regulates Formation of Primary Cilia in Mefloquine-Treated Cells

Primary cilia formation requires the Leigh syndrome-associated mitochondrial protein NDUFAF2

Mitochondria-related neurodegenerative diseases have been implicated in the disruption of primary cilia function. Mutation in an intrinsic mitochondrial complex I component NDUFAF2 has been identified in Leigh syndrome, a severe inherited mitochondriopathy. Mutations in ARMC9, which encodes a basal body protein, cause Joubert syndrome, a ciliopathy with defects in the brain, kidney, and eye. Here, we report a mechanistic link between mitochondria metabolism and primary cilia signaling. We discovered that loss of NDUFAF2 caused both mitochondrial and ciliary defects in vitro and in vivo and identified NDUFAF2 as a binding partner for ARMC9. We also found that NDUFAF2 was both necessary and sufficient for cilia formation and that exogenous expression of NDUFAF2 rescued the ciliary and mitochondrial defects observed in cells from patients with known ARMC9 deficiency. NAD+ supplementation restored mitochondrial and ciliary dysfunction in ARMC9-deficient cells and zebrafish and ameliorated the ocular motility and motor deficits of a patient with ARMC9 deficiency. The present results provide a compelling mechanistic link, supported by evidence from human studies, between primary cilia and mitochondrial signaling. Importantly, our findings have significant implications for the development of therapeutic approaches targeting ciliopathies.

Palmitic acid control of ciliogenesis modulates insulin signaling in hypothalamic neurons through an autophagy-dependent mechanism

Palmitic acid (PA) is significantly increased in the hypothalamus of mice, when fed chronically with a high-fat diet (HFD). PA impairs insulin signaling in hypothalamic neurons, by a mechanism dependent on autophagy, a process of lysosomal-mediated degradation of cytoplasmic material. In addition, previous work shows a crosstalk between autophagy and the primary cilium (hereafter cilium), an antenna-like structure on the cell surface that acts as a signaling platform for the cell. Ciliopathies, human diseases characterized by cilia dysfunction, manifest, type 2 diabetes, among other features, suggesting a role of the cilium in insulin signaling. Cilium depletion in hypothalamic pro-opiomelanocortin (POMC) neurons triggers obesity and insulin resistance in mice, the same phenotype as mice deficient in autophagy in POMC neurons. Here we investigated the effect of chronic consumption of HFD on cilia; and our results indicate that chronic feeding with HFD reduces the percentage of cilia in hypothalamic POMC neurons. This effect may be due to an increased amount of PA, as treatment with this saturated fatty acid in vitro reduces the percentage of ciliated cells and cilia length in hypothalamic neurons. Importantly, the same effect of cilia depletion was obtained following chemical and genetic inhibition of autophagy, indicating autophagy is required for ciliogenesis. We further demonstrate a role for the cilium in insulin sensitivity, as cilium loss in hypothalamic neuronal cells disrupts insulin signaling and insulin-dependent glucose uptake, an effect that correlates with the ciliary localization of the insulin receptor (IR). Consistently, increased percentage of ciliated hypothalamic neuronal cells promotes insulin signaling, even when cells are exposed to PA. Altogether, our results indicate that, in hypothalamic neurons, impairment of autophagy, either by PA exposure, chemical or genetic manipulation, cause cilia loss that impairs insulin sensitivity.

Autophagy promotes hepatic cystogenesis in polycystic liver disease by depletion of cholangiocyte ciliogenic proteins

BACKGROUNDS AND AIMS

Polycystic liver disease (PLD) is characterized by defective cholangiocyte cilia that regulate progressive growth of hepatic cysts. Because formation of primary cilia is influenced by autophagy through degradation of proteins involved in ciliogenesis, we hypothesized that ciliary defects in PLD cholangiocytes (PLDCs) originate from autophagy-mediated depletion of ciliogenic proteins ADP-ribosylation factor-like protein 3 (ARL3) and ADP-ribosylation factor-like protein 13B (ARL13B) and ARL-dependent mislocation of a ciliary-localized bile acid receptor, Takeda G-protein-coupled receptor 5 (TGR5), the activation of which enhances hepatic cystogenesis (HCG). The aims here were to determine whether: (1) ciliogenesis is impaired in PLDC, is associated with increased autophagy, and involves autophagy-mediated depletion of ARL3 and ARL13B; (2) depletion of ARL3 and ARL13B in PLDC cilia impacts ciliary localization of TGR5; and (3) pharmacological inhibition of autophagy re-establishes cholangiocyte cilia and ciliary localization of ARL3, ARL3B, and TGR5 and reduces HCG.

APPROACH AND RESULTS

By using liver tissue from healthy persons and patients with PLD, in vitro and in vivo models of PLD, and in vitro models of ciliogenesis, we demonstrated that, in PLDCs: ciliogenesis is impaired; autophagy is enhanced; ARL3 and ARL13B are ubiquitinated by HDAC6, depleted in cilia, and present in autophagosomes; depletion of ARL3 and ARL13B impacts ciliary localization of TGR5; and pharmacological inhibition of autophagy with mefloquine and verteporfin re-establishes cholangiocyte cilia and ciliary localization of ARL3, ARL13B, and TGR5 and reduces HCG.

CONCLUSIONS

The intersection between autophagy, defective cholangiocyte cilia, and enhanced HCG contributes to PLD progression and can be considered a target for therapeutic interventions.

Cellular targets of mefloquine

Mefloquine is a quinoline-based compound widely used as an antimalarial drug, particularly in chemoprophylaxis. Although decades of research have identified various aspects of mefloquine's anti-Plasmodium properties, toxic effects offset its robust use in humans. Mefloquine exerts harmful effects in several types of human cells by targeting many of the cellular lipids, proteins, and complexes, thereby blocking a number of downstream signaling cascades. In general, mefloquine modulates several cellular phenomena, such as alteration of membrane potential, induction of oxidative stress, imbalance of ion homeostasis, disruption of metabolism, failure of organelle function, etc., leading to cell cycle arrest and programmed cell death. This review aims to summarize the information on functional and mechanistic findings related to the cytotoxic effects of mefloquine.

Group III phospholipase A2 downregulation attenuated survival and metastasis in ovarian cancer and promotes chemo-sensitization

Background

Aberrant lipogenicity and deregulated autophagy are common in most advanced human cancer and therapeutic strategies to exploit these pathways are currently under consideration. Group III Phospholipase A2 (sPLA2-III/PLA2G3), an atypical secretory PLA2, is recognized as a regulator of lipid metabolism associated with oncogenesis. Though recent studies reveal that high PLA2G3 expression significantly correlates with poor prognosis in several cancers, however, role of PLA2G3 in ovarian cancer (OC) pathogenesis is still undetermined.

Methods

CRISPR-Cas9 and shRNA mediated knockout and knockdown of PLA2G3 in OC cells were used to evaluate lipid droplet (LD) biogenesis by confocal and Transmission electron microscopy analysis, and the cell viability and sensitization of the cells to platinum-mediated cytotoxicity by MTT assay. Regulation of primary ciliation by PLA2G3 downregulation both genetically and by metabolic inhibitor PFK-158 induced autophagy was assessed by immunofluorescence-based confocal analysis and immunoblot. Transient transfection with GFP-RFP-LC3B and confocal analysis was used to assess the autophagic flux in OC cells. PLA2G3 knockout OVCAR5 xenograft in combination with carboplatin on tumor growth and metastasis was assessed in vivo. Efficacy of PFK158 alone and with platinum drugs was determined in patient-derived primary ascites cultures expressing PLA2G3 by MTT assay and immunoblot analysis.

Results

Downregulation of PLA2G3 in OVCAR8 and 5 cells inhibited LD biogenesis, decreased growth and sensitized cells to platinum drug mediated cytotoxicity in vitro and in in vivo OVCAR5 xenograft. PLA2G3 knockdown in HeyA8MDR-resistant cells showed sensitivity to carboplatin treatment. We found that both PFK158 inhibitor-mediated and genetic downregulation of PLA2G3 resulted in increased number of percent ciliated cells and inhibited cancer progression. Mechanistically, we found that PFK158-induced autophagy targeted PLA2G3 to restore primary cilia in OC cells. Of clinical relevance, PFK158 also induces percent ciliated cells in human-derived primary ascites cells and reduces cell viability with sensitization to chemotherapy.

Conclusions

Taken together, our study for the first time emphasizes the role of PLA2G3 in regulating the OC metastasis. This study further suggests the therapeutic potential of targeting phospholipases and/or restoration of PC for future OC treatment and the critical role of PLA2G3 in regulating ciliary function by coordinating interface between lipogenesis and metastasis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-01985-9.

The transcriptomic response of cells to a drug combination is more than the sum of the responses to the monotherapies

Our ability to discover effective drug combinations is limited, in part by insufficient understanding of how the transcriptional response of two monotherapies results in that of their combination. We analyzed matched time course RNAseq profiling of cells treated with single drugs and their combinations and found that the transcriptional signature of the synergistic combination was unique relative to that of either constituent monotherapy. The sequential activation of transcription factors in time in the gene regulatory network was implicated. The nature of this transcriptional cascade suggests that drug synergy may ensue when the transcriptional responses elicited by two unrelated individual drugs are correlated. We used these results as the basis of a simple prediction algorithm attaining an AUROC of 0.77 in the prediction of synergistic drug combinations in an independent dataset.

The Autophagy Regulator p62 Controls PTEN-Dependent Ciliogenesis

Autophagy is a catabolic process required for maintaining intracellular energy homeostasis. It eliminates harmful proteins and recycles functional macromolecules back into the cell via cargo breakdown. Autophagy is generally suppressed under fed conditions and induced by serum starvation; therefore, it is considered to be a nutrient-sensing mechanism. Cilia, finger-like organelles harboring multiple receptors along their surface, are energy-sensing structures that are also triggered by serum deprivation. Herein, we verified the effect of autophagy alterations on cilia assembly and the specific underlying mechanisms. Autophagy flux altered either by drugs or autophagy-targeting siRNAs strongly inhibited ciliogenesis, and this inhibition was affected by p62, an autophagy regulator, via Pten/Dvl2/AurKA signaling.

Geniposide alleviates lipopolysaccharide-caused apoptosis of murine kidney podocytes by activating Ras/Raf/MEK/ERK-mediated cell autophagy

Proteinuria is one of the most important clinical features of nephrotic syndrome (NS). Injury of podocyte has been proved to contribute to the occurrence of proteinuria. This study explored the effects of geniposide (GEN) on lipopolysaccharide (LPS)-caused murine kidney podocyte MPC5 apoptosis and autophagy. Viability and apoptosis of MPC5 cells were respectively detected with the help of CCK-8 assay and Guava Nexin assay. 3-Methyladenine (3-MA) was used as an autophagy inhibitor, while rapamycin as autophagy activator. Si-Beclin-1 was transfected in MPC5 cells to down-regulate the expression of Beclin-1. We found that LPS stimulation significantly caused MPC5 cell viability reduction, apoptosis and autophagy (P < .05 or P < .01). GEN treatment remarkably alleviated the LPS-caused MPC5 cell viability reduction and apoptosis, but promoted cell autophagy (P < .05). Moreover, 3-MA incubation or si-Beclin-1 transfection notably weakened the effects of GEN on LPS-caused MPC5 cell apoptosis and autophagy (P < .05), while rapamycin had opposite effects (P < .05). Furthermore, GEN activated Ras/Raf/MEK/ERK pathway in LPS-treated MPC5 cells (P < .05). In conclusion, this research verified the protective effects of GEN on podocytes damage. GEN alleviates LPS-caused apoptosis of murine kidney podocytes by activating Ras/Raf/MEK/ERK-mediated cell autophagy. Highlights: LPS causes podocyte MPC5 apoptosis and autophagy. GEN alleviates LPS-caused MPC5 cell apoptosis, but promotes cell autophagy. 3-MA or si-Beclin-1 weakens the effects of GEN on LPS-treated MPC5 cells. Rapamycin strengthens the effects of GEN on LPS-treated MPC5 cells. GEN activates Ras/Raf/MEK/ERK pathway in LPS-treated MPC5 cells.

Interplay Between Primary Cilia and Autophagy and Its Controversial Roles in Cancer

Primary cilia and autophagy are two distinct nutrient-sensing machineries required for maintaining intracellular energy homeostasis, either via signal transduction or recycling of macromolecules from cargo breakdown, respectively. Potential correlations between primary cilia and autophagy have been recently suggested and their relationship may increase our understanding of the pathogenesis of human diseases, including ciliopathies and cancer. In this review, we cover the current issues concerning the bidirectional interaction between primary cilia and autophagy and discuss its role in cancer with cilia defect.

Primary cilia and autophagy interaction is involved in mechanical stress mediated cartilage development via ERK/mTOR axis

AIMS

Biomechanical reactivity is a special property of chondrocytes and mechanical stress can affect the development of cartilage. Primary cilia have been proved a cellular sensory which can detect physical and chemical stimuli extracellular and initiate multiple signaling transduction. Autophagy is an important environmental adaptive mechanism for cells maintenance of homeostasis. The aims of this study were to detect whether there is an interaction between primary cilia and autophagy in the regulation of mechanical stress-mediated cartilage development and to explore the underlying mechanism.

MAIN METHODS

In this study, chondrocytes were treated with cyclic tensile strain (CTS) by the four-point bending system. Chondrocytes viability, proliferation and differentiation capacities were analyzed by western blot and live/dead assays after CTS of different intensities. Meanwhile, primary cilia incidence and length changes, and autophagy expression were detected by immunofluorescence staining. The primary cilia and autophagy interaction regulation and the underlying mechanism were detected by immunofluorescence double staining and western blot.

KEY FINDINGS

Mechanical stress could affect chondrocytes proliferation, phenotype and viability in an intensity dependent manner. The incidence and length of primary cilia as well as autophagy expression could be regulated by CTS. The integrity of primary cilia structure is vital for mechanical stress regulated ERK/mTOR signaling transduction and autophagy expression in chondrocyte.

SIGNIFICANCE

These findings indicate that mechanical stress could affect the interaction between primary cilia and autophagy and help to reveal the underlying mechanism of stress regulated cartilage development.

Intermittent high glucose-induced oxidative stress modulates retinal pigmented epithelial cell autophagy and promotes cell survival via increased HMGB1

Background

In this study, we evaluated the effects of intermittent high glucose on oxidative stress production in retinal pigmented epithelial (RPE) cells and explored whether the mechanisms of autophagy and apoptosis in oxidative stress are associated with high-mobility group box 1 (HMGB1) protein.

Methods

Cultured human RPE cell line ARPE-19 cells were exposed to intermittent high glucose-induced oxidative stress. Reactive oxygen species (ROS) was determined by 2′, 7′-dichlorofluorescin diacetate (DCFH-DA); and malonyldialdehyde (MDA), superoxide dismutase (SOD) by commercial kits. Transmission electron microscopy was used to observe the generation of autophagosome. And MTT assay was used to examine the effect of autophagy on cell viability. For the inhibition experiments, cells were pre-incubated with lysosomal inhibitors NH4Cl or N-acetyl cysteine (NAC).Western blot was used to measure the expression patterns of autophagic markers, including LC3 and p62. The expression of HMGB1 was detected by immunohistochemistry.Cells were pre-incubated with HMGB1 inhibitor ethyl pyruvate (EP) ,then detected the expression pattern of autophagic markers and level of cellular ROS.

Results

We found that intermittent high glucose significantly increased oxidative stress levels (as indicated by ROS, MDA, SOD), increased in the generation of autophagosome, decreased the level of p62, induced conversion of LC3 I to LC3 II. We further demonstrated that the NH4Cl/NAC inhibited intermittent high glucose-induced autophage by altered level of LC3 and p62. Intermittent high glucose-induced autophagy is independent of HMGB1 signaling, inhibition of HMGB1 release by EP decreased expression pattern of autophagic markers and level of cellular viability.

Conclusions

Under intermittent high glucose condition, autophagy may be required for preventing oxidative stress-induced injury in RPE. HMGB1 plays important roles in signaling for both autophagy and oxidative stress.

TSC1 and TSC2 regulate cilia length and canonical Hedgehog signaling via different mechanisms

Primary cilia are sensory organelles that coordinate multiple cellular signaling pathways, including Hedgehog (HH), Wingless/Int (WNT) and Transforming Growth Factor-β (TGF-β) signaling. Similarly, primary cilia have been implicated in regulation of mTOR signaling, in which Tuberous Sclerosis Complex proteins 1 and 2 (TSC1/2) negatively regulate protein synthesis by inactivating the mTOR complex 1 (mTORC1) at energy limiting states. Here we report that TSC1 and TSC2 regulate Smoothened (SMO)-dependent HH signaling in mouse embryonic fibroblasts (MEFs). Reduced SMO-dependent expression of Gli1 was demonstrated in both Tsc1-/- and Tsc2-/- cells, and we found that Tsc1 is required for TGF-β induced phosphorylation of SMAD2/3 and subsequent expression of the HH signaling effector and transcription factor GLI2. Hedgehog signaling was restored in Tsc1-/- cells after exogenous expression of Gli2, whereas rapamycin restored HH signaling in Tsc2-/- cells. Furthermore, we observed that Tsc1-/- MEFs display significantly elongated cilia, whereas cilia in Tsc2-/- MEFs were shorter than normal. The elongated cilium phenotype of Tsc1-/- MEFs is likely due to increased mTORC1-dependent autophagic flux observed in these cells, as both the autophagic flux and the cilia length phenotype was restored by rapamycin. In addition, ciliary length control in Tsc1-/- MEFs was also influenced by reduced expression of Gli2, which compromised expression of Wnt5a that normally promotes cilia disassembly. In summary, our results support distinct functions of Tsc1 and Tsc2 in cellular signaling as the two genes affect ciliary length control and HH signaling via different mechanisms.

The ciliary protein RPGRIP1L governs autophagy independently of its proteasome-regulating function at the ciliary base in mouse embryonic fibroblasts

Previously, macroautophagy/autophagy was demonstrated to be regulated inter alia by the primary cilium. Mutations in RPGRIP1L cause ciliary dysfunctions resulting in severe human diseases summarized as ciliopathies. Recently, we showed that RPGRIP1L deficiency leads to a decreased proteasomal activity at the ciliary base in mice. Importantly, the drug-induced restoration of proteasomal activity does not rescue ciliary length alterations in the absence of RPGRIP1L indicating that RPGRIP1L affects ciliary function also via other mechanisms. Based on this knowledge, we analyzed autophagy in Rpgrip1l-negative mouse embryos. In these embryos, autophagic activity was decreased due to an increased activation of the MTOR complex 1 (MTORC1). Application of the MTORC1 inhibitor rapamycin rescued dysregulated MTORC1, autophagic activity and cilia length but not proteasomal activity in Rpgrip1l-deficient mouse embryonic fibroblasts demonstrating that RPGRIP1L seems to regulate autophagic and proteasomal activity independently from each other.

Autophagy and primary cilia: dual interplay

Primary cilia are microtubule-based organelles for sensing of the extracellular milieu and transducing this information into the cell through a variety of molecular signaling pathways. Functioning of the primary cilium has been recently connected to autophagy, a pathway for degradation of cellular components in lysosomes. Autophagy regulates the length of the cilia by removing proteins required for ciliogenesis, a phenomenon that is molecularly different if performed by basal autophagy or when autophagy is induced in response to various stressors. Here we review the current knowledge about the dual interaction between autophagy and ciliogenesis, and discuss the potential role that deregulated ciliary autophagy could have in pathologies with alterations in autophagy and ciliogenesis.