Direct evidence for ultrastructures of the α-synuclein-associated synaptic vesicle pool in presynaptic terminals.

SNCA/PARK1 encodes α-synuclein, which is associated with familial Parkinson's disease. Despite its abundance in presynaptic terminals, the aggregation mechanism of α-synuclein and its relationship with Parkinson's disease have not yet been elucidated. Moreover, the ultrastructures of α-synuclein localization sites in neuronal presynaptic terminals remain unclear. Therefore, we herein generated transgenic mice expressing human α-synuclein tagged with mKate2 (hSNCA-mKate2 mice). These mice exhibited normal growth and fertility and had no motor dysfunction relative to their wild-type littermates, even at one year old. α-Synuclein-mKate2 accumulated in presynaptic terminals, particularly between Purkinje cells in the cerebellum and neurons in cerebellar nuclei. α-Synuclein-mKate2 was associated with the presynaptic marker, synaptophysin. In-resin CLEM and immunoelectron or electron microscopy revealed that α-synuclein-mKate2 localized on the surface of synaptic vesicles that were tightly arranged and assembled to form large synaptic pools in the cerebellum with negligible effects on the active zone. These results suggest that α-synuclein-associated ultrastructures in the presynaptic terminals of hSNCA-mKate2 mice reflect the structures of α-synuclein-assembled synaptic vesicle pools, and the size of vesicle pools increased. This transgenic mouse model will be a valuable tool for studying α-synuclein-associated synaptic vesicle pools.

Pneumococcal sialidase promotes bacterial survival by fine-tuning of pneumolysin-mediated membrane disruption.

Pneumolysin (Ply) is an indispensable cholesterol-dependent cytolysin for pneumococcal infection. Although Ply-induced disruption of pneumococci-containing endosomal vesicles is a prerequisite for the evasion of endolysosomal bacterial clearance, its potent activity can be a double-edged sword, having a detrimental effect on bacterial survivability by inducing severe endosomal disruption, bactericidal autophagy, and scaffold epithelial cell death. Thus, Ply activity must be maintained at optimal levels. We develop a highly sensitive assay to monitor endosomal disruption using NanoBiT-Nanobody, which shows that the pneumococcal sialidase NanA can fine-tune Ply activity by trimming sialic acid from cell-membrane-bound glycans. In addition, oseltamivir, an influenza A virus sialidase inhibitor, promotes Ply-induced endosomal disruption and cytotoxicity by inhibiting NanA activity in vitro and greater tissue damage and bacterial clearance in vivo. Our findings provide a foundation for innovative therapeutic strategies for severe pneumococcal infections by exploiting the duality of Ply activity.

TUNEL-positive structures in activated microglia and SQSTM1/p62-positive structures in activated astrocytes in the neurodegenerative brain of a CLN10 mouse model.

Neuronal ceroid lipofuscinosis is a group of pediatric neurodegenerative diseases. One of their causative genes, CLN10/CtsD, encodes cathepsin D, a major lysosomal protease. Central nervous system (CNS)-specific CtsD-deficient mice exhibit a neurodegenerative disease phenotype with accumulation of ceroid lipofuscins, granular osmiophilic deposits, and SQSTM1/p62. We focused on activated astrocytes and microglia in this neurodegenerative mouse brain, since there are few studies on the relationship between these accumulators and lysosomes in these glial cells. Activated microglia and astrocytes in this mouse thalamus at p24 were increased by approximately 2.5- and 4.6-fold compared with the control, while neurons were decreased by approximately half. Granular osmiophilic deposits were detected in microglial cell bodies and extended their processes in the thalamus. LAMP1-positive lysosomes, but not SQSTM1/p62 aggregates, accumulated in microglia of this mouse thalamus, whereas both lysosomes and SQSTM1/p62 aggregates accumulated in its astrocytes. TUNEL-positive signals were observed mainly in microglia, but few were observed in neurons and astrocytes. These signals were fragmented DNA from degenerated neurons engulfed by microglia or in the lysosomes of microglia. Abnormal autophagic vacuoles also accumulated in the lysosomes of microglia. Granular osmiophilic deposit-like structures localized to LAMP1-positive lysosomes in CtsD-deficient astrocytes. SQSTM1/p62-positive but LAMP1-negative membranous structures also accumulated in the astrocytes and were less condensed than typical granular osmiophilic deposits. These results suggest that CtsD deficiency leads to intracellular abnormalities in activated microglia and astrocytes in addition to neuronal degeneration.

Application of immuno- and affinity labeling with fluorescent dyes to in-resin CLEM of Epon-embedded cells.

In-resin CLEM (Correlative Light and Electron Microscopy) of Epon-embedded cells involves correlating fluorescence microscopy with electron microscopy in the same Epon-embedded ultrathin section. This method offers the advantage of high positional accuracy compared to standard CLEM. However, it requires the expression of recombinant proteins. In order to detect the localization of endogenous target(s) and their localized ultrastructures of Epon-embedded samples using in-resin CLEM, we investigated whether immunological and affinity-labeling using fluorescent dyes applied to in-resin CLEM of Epon-embedded cells. The orange fluorescent (λem ∼550 nm) and far-red (λem ∼650 nm) fluorescent dyes examined maintained a sufficient level of fluorescent intensity after staining with osmium tetroxide and subsequent dehydration treatment with ethanol. Immunological in-resin CLEM of mitochondria and the Golgi apparatus was achieved using anti-TOM20, anti-GM130 antibodies, and fluorescent dyes. Two-color in-resin CLEM revealed that wheat germ agglutinin-puncta showed the ultrastructures of multivesicular body-like structures. Finally, taking the advantage of high positional accuracy, volume in-resin CLEM of mitochondria in the semi-thin section (2 µm thick) of Epon-embedded cells was performed by focused ion beam scanning electron microscopy. These results suggested that the application of immunological reaction and affinity-labeling with fluorescent dyes to in-resin CLEM of Epon-embedded cells is suitable for analyzing the localization of endogenous targets and their ultrastructures by scanning and transmission electron microscopy.

Recent advances in in-resin correlative light and electron microscopy of Epon-embedded cells.

Correlative fluorescent and electron microscopic images of the same section of epoxy (or other polymer)-embedded samples, hereafter referred to as 'in-resin CLEM', have been developed to improve the positional accuracy and Z-axis resolution limitations of conventional correlative light and electron microscopy (CLEM). High-pressure freezing and quick-freezing substitution result in in-resin CLEM of acrylic-based resin-embedded cells expressing green fluorescent protein, yellow fluorescent protein, mVenus and mCherry, which are sensitive to osmium tetroxide. The identification of osmium-resistant fluorescent proteins leads to the development of in-resin CLEM of Epon-embedded cells. Using subtraction-based fluorescence microscopy with a photoconvertible fluorescent protein, mEosEM-E, its green fluorescence can be observed in thin sections of Epon-embedded cells, and two-color in-resin CLEM using mEosEM-E and mScarlet-H can be performed. Green fluorescent proteins, CoGFP variant 0 and mWasabi, and far-red fluorescent proteins, mCherry2 and mKate2, are available for in-resin CLEM of Epon-embedded cells using the standard procedure for Epon-embedding with additional incubation. Proximity labeling is applied to in-resin CLEM to overcome the limitations of fluorescent proteins in epoxy resin. These approaches will contribute significantly to the future of CLEM analysis.

Monitoring autophagic flux in vivo revealed its physiological response and significance of heterogeneity in pancreatic beta cells.

Autophagy plays an essential role in preserving cellular homeostasis in pancreatic beta cells. However, the extent of autophagic flux in pancreatic islets induced in various physiological settings remains unclear. In this study, we generate transgenic mice expressing pHluorin-LC3-mCherry reporter for monitoring systemic autophagic flux by measuring the pHluorin/mCherry ratio, validating them in the starvation and insulin-deficient model. Our findings reveal that autophagic flux in pancreatic islets enhances after starvation, and suppression of the flux after short-term refeeding needs more prolonged re-starvation in islets than in the other insulin-targeted organs. Furthermore, heterogeneity of autophagic flux in pancreatic beta cells manifests under insulin resistance, and intracellular calcium influx by glucose stimulation increases more in high- than low-autophagic flux beta cells, with differential gene expression, including lipoprotein lipase. Our pHluorin-LC3-mCherry mice enable us to reveal biological insight into heterogeneity in autophagic flux in pancreatic beta cells.

Osmium-Resistant Fluorescent Proteins and In-Resin Correlative Light-Electron Microscopy of Epon-Embedded Mammalian Cultured Cells.

Postfixation with osmium tetroxide and Epon embedding are essential for the preservation and visualization of subcellular ultrastructures via electron microscopy. These chemical treatments diminish the fluorescent intensity of most fluorescent proteins in cells, creating a problem for the in-resin correlative light-electron microscopy (CLEM) of Epon-embedded mammalian cultured cells. We found that two green and two far-red fluorescent proteins retain their fluorescence after chemical fixation with glutaraldehyde, osmium tetroxide-staining, dehydration, and polymerization of Epon resins. Consequently, we could observe the fluorescence of fluorescent proteins in ultrathin sections of Epon-embedded cells via fluorescence microscopy, investigate ultrastructures of the cells in the same sections via electron microscopy, and correlate the fluorescent image with the electron microscopic image without chemical or physical distortion of the cells. In other words, referred as "in-resin CLEM" of Epon-embedded samples. This technique also improves the Z-axis resolution of fluorescent images. In this chapter, we introduce the detailed protocol for in-resin CLEM of Epon-embedded mammalian cultured cells using these fluorescent proteins.

Lack of Cathepsin D in the central nervous system results in microglia and astrocyte activation and the accumulation of proteinopathy-related proteins.

Neuronal ceroid lipofuscinosis is one of many neurodegenerative storage diseases characterized by excessive accumulation of lipofuscins. CLN10 disease, an early infantile neuronal ceroid lipofuscinosis, is associated with a gene that encodes cathepsin D (CtsD), one of the major lysosomal proteases. Whole body CtsD-knockout mice show neurodegenerative phenotypes with the accumulation of lipofuscins in the brain and also show defects in other tissues including intestinal necrosis. To clarify the precise role of CtsD in the central nervous system (CNS), we generated a CNS-specific CtsD-knockout mouse (CtsD-CKO). CtsD-CKO mice were born normally but developed seizures and their growth stunted at around postnatal day 23 ± 1. CtsD-CKO did not exhibit apparent intestinal symptoms as those observed in whole body knockout. Histologically, autofluorescent materials were detected in several areas of the CtsD-CKO mouse's brain, including: thalamus, cerebral cortex, hippocampus, and cerebellum. Expression of ubiquitin and autophagy-associated proteins was also increased, suggesting that the autophagy-lysosome system was impaired. Microglia and astrocytes were activated in the CtsD-CKO thalamus, and inducible nitric oxide synthase (iNOS), an inflammation marker, was increased in the microglia. Interestingly, deposits of proteinopathy-related proteins, phosphorylated α-synuclein, and Tau protein were also increased in the thalamus of CtsD-CKO infant mice. Considering these results, we propose thatt the CtsD-CKO mouse is a useful mouse model to investigate the contribution of cathepsin D to the early phases of neurodegenerative diseases in relation to lipofuscins, proteinopathy-related proteins and activation of microglia and astrocytes.

In-resin CLEM of Epon-embedded cells using proximity labeling.

Biotin ligases have been developed as proximity biotinylation enzymes for analyses of the interactome. However, there has been no report on the application of proximity labeling for in-resin correlative light-electron microscopy of Epon-embedded cells. In this study, we established a proximity-labeled in-resin CLEM of Epon-embedded cells using miniTurbo, a biotin ligase. Biotinylation by miniTurbo was observed in cells within 10 min following the addition of biotin to the medium. Using fluorophore-conjugated streptavidin, intracellular biotinylated proteins were labeled after fixation of cells with a mixture of paraformaldehyde and glutaraldehyde. Fluorescence of these proteins was resistant to osmium tetroxide staining and was detected in 100-nm ultrathin sections of Epon-embedded cells. Ultrastructures of organelles were preserved well in the same sections. Fluorescence in sections was about 14-fold brighter than that in the sections of Epon-embedded cells expressing mCherry2 and was detectable for 14 days. When mitochondria-localized miniTurbo was expressed in the cells, mitochondria-like fluorescent signals were detected in the sections, and ultrastructures of mitochondria were observed as fluorescence-positive structures in the same sections by scanning electron microscopy. Proximity labeling using miniTurbo led to more stable and brighter fluorescent signals in the ultrathin sections of Epon-embedded cells, resulting in better performance of in-resin CLEM.

Impaired GATE16-mediated exocytosis in exocrine tissues causes Sjögren's syndrome-like exocrinopathy.

Sjögren's syndrome (SjS) is a chronic autoimmune disease characterized by immune cell infiltration of the exocrine glands, mainly the salivary and lacrimal glands. Despite recent advances in the clinical and mechanistic characterization of the disease, its etiology remains largely unknown. Here, we report that mice with a deficiency for either Atg7 or Atg3, which are enzymes involved in the ubiquitin modification pathway, in the salivary glands exhibit a SjS-like phenotype, characterized by immune cell infiltration with autoantibody detection, acinar cell death, and dry mouth. Prior to the onset of the SjS-like phenotype in these null mice, we detected an accumulation of secretory vesicles in the acinar cells of the salivary glands and found that GATE16, an uncharacterized autophagy-related molecule activated by ATG7 (E1-like enzyme) and ATG3 (E2-like enzyme), was highly expressed in these cells. Notably, GATE16 was activated by isoproterenol, an exocytosis inducer, and localized on the secretory vesicles in the acinar cells of the salivary glands. Failure to activate GATE16 was correlated with exocytosis defects in the acinar cells of the salivary glands in Atg7 and Atg3 cKO mice. Taken together, our results show that GATE16 activation regulated by the autophagic machinery is crucial for exocytosis and that defects in this pathway cause SjS.

Membranous Structures Directly Come in Contact With p62/SQSTM1 Bodies.

During autophagy, autophagosomes are formed to engulf cytoplasmic contents. p62/SQSTM-1 is an autophagic adaptor protein that forms p62 bodies. A unique feature of p62 bodies is that they seem to directly associate with membranous structures. We first investigated the co-localization of mKate2-p62 bodies with phospholipids using click chemistry with propargyl-choline. Propargyl-choline-labeled phospholipids were detected inside the mKate2-p62 bodies, suggesting that phospholipids were present inside the bodies. To clarify whether or not p62 bodies come in contact with membranous structures directly, we investigated the ultrastructures of p62 bodies using in-resin correlative light and electron microscopy of the Epon-embedded cells expressing mKate2-p62. Fluorescent-positive p62 bodies were detected as uniformly lightly osmificated structures by electron microscopy. Membranous structures were detected on and inside the p62 bodies. In addition, multimembranous structures with rough endoplasmic reticulum-like structures that resembled autophagosomes directly came in contact with amorphous-shaped p62 bodies. These results suggested that p62 bodies are unique structures that can come in contact with membranous structures directly.

Structural basis of antiviral activity of caffeic acid against severe fever with thrombocytopenia syndrome virus.

Caffeic acid (CA), a coffee-related natural compound, has various beneficial biological effects, including antiviral effects. Our former studies demonstrated that the CA dose-dependently inhibited the in vitro infection with Dabie bandavirus, which was previously named as severe fever with thrombocytopenia syndrome virus (SFTSV), mainly at the step of virus attachment. Therefore, we studied the structural basis of CA for conferring anti-SFTSV activity to clarify the mechanism of action of CA against SFTSV. In this study, the anti-SFTSV activity of nine CA analogs were examined. The treatment of SFTSV with the 3,4-dihydroxyhydrocinnamic acid (DHCA) as well as CA inhibited the SFTSV infection in a dose-dependent manner, whereas other CA analogs did not. Both CA and DHCA only possessed the o-dihydroxybenzene backbone. When SFTSV was treated with catechol (o-dihydroxybenzene), SFTSV infection was also dose-dependently inhibited. Additionally, four compounds having the o-dihydroxybenzene backbone; CA phenethyl ester, methyl CA, 3,4-dihydroxyphenylacetic acid, and 3,4-dihydroxybenzoic acid, dose-dependently inhibited the viral infection, although these compounds were more toxic or less effective than CA. In conclusion, the o-dihydroxybenzene backbone in CA and its analogs was a critical structure for the anti-SFTSV activity. Based on these findings, modifications of the o-dihydroxybenzene backbone with various other residues might improve the antiviral effect and cytotoxicity for SFTSV.

Two-color in-resin CLEM of Epon-embedded cells using osmium resistant green and red fluorescent proteins.

In-resin CLEM of Epon embedded samples can greatly simplify the correlation of fluorescent images with electron micrographs. The usefulness of this technique is limited at present by the low number of fluorescent proteins that resist CLEM processing. Additionally, no study has reported the possibility of two-color in-resin CLEM of Epon embedded cells. In this study, we screened for monomeric green and red fluorescent proteins that resist CLEM processing. We identified mWasabi, CoGFP variant 0, and mCherry2; two green and one red fluorescent proteins as alternatives for in-resin CLEM. We expressed mitochondria-localized mCherry2 and histone H2B tagged with CoGFP variant 0 in cells. Green and red fluorescence was detected in 100 nm-thin sections of the Epon-embedded cells. In the same thin sections, we correlated the fluorescent signals to mitochondria and the nucleus using a scanning electron microscope. Similar results were obtained when endoplasmic reticulum-localized mCherry2 and histone H2B tagged with CoGFP variant 0 were expressed in the cells. Two-color in-resin CLEM of two cytoplasmic organelles, mitochondria and endoplasmic reticulum, was also achieved using mitochondria-localized mCherry2 and endoplasmic reticulum-localized mWasabi. In summary, we report three new fluorescent protein-alternatives suitable for in-resin CLEM of Epon-embedded samples, and achieved Epon-based two-color in-resin CLEM.

Visualization of cytoplasmic organelles via in-resin CLEM using an osmium-resistant far-red protein.

Post-fixation with osmium tetroxide staining and the embedding of Epon are robust and essential treatments that are used to preserve and visualize intracellular membranous structures during electron microscopic analyses. These treatments, however, can significantly diminish the fluorescent intensity of most fluorescent proteins in cells, which creates an obstacle for the in-resin correlative light-electron microscopy (CLEM) of Epon-embedded cells. In this study, we used a far-red fluorescent protein that retains fluorescence after osmium staining and Epon embedding to perform an in-resin CLEM of Epon-embedded samples. The fluorescence of this protein was detected in 100 nm thin sections of the cells in Epon-embedded samples after fixation with 2.5% glutaraldehyde and post-fixation with 1% osmium tetroxide. We performed in-resin CLEM of the mitochondria in Epon-embedded cells using a mitochondria-localized fluorescent protein. Using this protein, we achieved in-resin CLEM of the Golgi apparatus and the endoplasmic reticulum in thin sections of the cells in Epon-embedded samples. To our knowledge, this is the first reported use of a far-red fluorescent protein retains its fluorescence after osmium staining and Epon-embedding, and it represents the first achievement of in-resin CLEM of both the Golgi apparatus and the endoplasmic reticulum in Epon-embedded samples.

Characterization of starvation-induced autophagy in cerebellar Purkinje cells of pHluorin-mKate2-human LC3B transgenic mice.

We generated a new transgenic mouse model that expresses a pHluorin-mKate2 fluorescent protein fused with human LC3B (PK-LC3 mice) for monitoring autophagy activity in neurons of the central nervous system. Histological analysis revealed fluorescent puncta in neurons of the cerebral cortex, hippocampus, cerebellar Purkinje cells, and anterior spinal regions. Using CLEM analysis, we confirmed that PK-LC3-positive puncta in the perikarya of Purkinje cells correspond to autophagic structures. To validate the usability of PK-LC3 mice, we quantified PK-LC3 puncta in Purkinje cells of mice kept in normal feeding conditions and of mice starved for 24 hours. Our results showed a significant increase in autophagosome number and in individual puncta areal size following starvation. To confirm these results, we used morphometry at the electron microscopic level to analyze the volume densities of autophagosomes and lysosomes/autolysosomes in Purkinje cells of PK-LC3 mice. The results revealed that the volume densities of autophagic structures increase significantly after starvation. Together, our data show that PK-LC3 mice are suitable for monitoring autophagy flux in Purkinje cells of the cerebellum, and potentially other areas in the central nervous system.

Blood group P1 antigen-bearing glycoproteins are functional but less efficient receptors of Shiga toxin than conventional glycolipid-based receptors.

Shiga toxin (STx) is a virulence factor produced by enterohemorrhagic Escherichia coli. STx is taken up by mammalian host cells by binding to the glycosphingolipid (GSL) globotriaosylceramide (Gb3; Galα1-4Galß1-4Glc-ceramide) and causes cell death after its retrograde membrane transport. However, the contribution of the hydrophobic portion of Gb3 (ceramide) to STx transport remains unclear. In pigeons, blood group P1 glycan antigens (Galα1-4Galß1-4GlcNAc-) are expressed on glycoproteins that are synthesized by α1,4-galactosyltransferase 2 (pA4GalT2). To examine whether these glycoproteins can also function as STx receptors, here we constructed glycan-remodeled HeLa cell variants lacking Gb3 expression but instead expressing pA4GalT2-synthesized P1 glycan antigens on glycoproteins. We compared STx binding and sensitivity of these variants with those of the parental, Gb3-expressing HeLa cells. The glycan-remodeled cells bound STx1 via N-glycans of glycoproteins and were sensitive to STx1 even without Gb3 expression, indicating that P1-containing glycoproteins also function as STx receptors. However, these variants were significantly less sensitive to STx than the parent cells. Fluorescence microscopy and correlative light EM revealed that the STx1 B subunit accumulates to lower levels in the Golgi apparatus after glycoprotein-mediated than after Gb3-mediated uptake but instead accumulates in vacuole-like structures probably derived from early endosomes. Furthermore, coexpression of Galα1-4Gal on both glycoproteins and GSLs reduced the sensitivity of cells to STx1 compared with those expressing Galα1-4Gal only on GSLs, probably because of competition for STx binding or internalization. We conclude that lipid-based receptors are much more effective in STx retrograde transport and mediate greater STx cytotoxicity than protein-based receptors.

Streptococcus pneumoniae triggers hierarchical autophagy through reprogramming of LAPosome-like vesicles via NDP52-delocalization.

In innate immunity, multiple autophagic processes eliminate intracellular pathogens, but it remains unclear whether noncanonical autophagy and xenophagy are coordinated, and whether they occur concomitantly or sequentially. Here, we show that Streptococcus pneumoniae, a causative of invasive pneumococcal disease, can trigger FIP200-, PI3P-, and ROS-independent pneumococcus-containing LC3-associated phagosome (LAPosome)-like vacuoles (PcLVs) in an early stage of infection, and that PcLVs are indispensable for subsequent formation of bactericidal pneumococcus-containing autophagic vacuoles (PcAVs). Specifically, we identified LC3- and NDP52-delocalized PcLV, which are intermediates between PcLV and PcAV. Atg14L, Beclin1, and FIP200 were responsible for delocalizing LC3 and NDP52 from PcLVs. Thus, multiple noncanonical and canonical autophagic processes are deployed sequentially against intracellular S. pneumoniae. The Atg16L1 WD domain, p62, NDP52, and poly-Ub contributed to PcLV formation. These findings reveal a previously unidentified hierarchical autophagy mechanism during bactericidal xenophagy against intracellular bacterial pathogens, and should improve our ability to control life-threating pneumococcal diseases.

Autophagy Deficiency in Renal Proximal Tubular Cells Leads to an Increase in Cellular Injury and Apoptosis under Normal Fed Conditions.

Renal proximal tubular epithelial cells are significantly damaged during acute kidney injury. Renal proximal tubular cell-specific autophagy-deficient mice show increased sensitivity against renal injury, while showing few pathological defects under normal fed conditions. Considering that autophagy protects the proximal tubular cells from acute renal injury, it is reasonable to assume that autophagy contributes to the maintenance of renal tubular cells under normal fed conditions. To clarify this possibility, we generated a knock out mouse model which lacks Atg7, a key autophagosome forming enzyme, in renal proximal tubular cells (Atg7flox/flox;KAP-Cre+). Analysis of renal tissue from two months old Atg7flox/flox;KAP-Cre+ mouse revealed an accumulation of LC3, binding protein p62/sequestosome 1 (a selective substrate for autophagy), and more interestingly, Kim-1, a biomarker for early kidney injury, in the renal proximal tubular cells under normal fed conditions. TUNEL (TdT-mediated dUTP Nick End Labeling)-positive cells were also detected in the autophagy-deficient renal tubular cells. Analysis of renal tissue from Atg7flox/flox;KAP-Cre+ mice at different age points showed that tubular cells positive for p62 and Kim-1 continually increase in number in an age-dependent manner. Ultrastructural analysis of tubular cells from Atg7flox/flox;KAP-Cre+ revealed the presence of intracellular inclusions and abnormal structures. These results indicated that autophagy-deficiency in the renal proximal epithelial tubular cells leads to an increase in injured cells in the kidney even under normal fed conditions.

Establishment of a system for screening autophagic flux regulators using a modified fluorescent reporter and CRISPR/Cas9.

Autophagy is a mechanism of bulk protein degradation that plays an important role in regulating homeostasis in many organisms. Among several methods for evaluating its activity, a fluorescent reporter GFP-LC3-RFP-LC3ΔG, in which GFP-LC3 is cleaved by ATG4 following autophagic induction and degraded in lysosome, has been used for monitoring autophagic flux, which is the amount of lysosomal protein degradation. In this study, we modified this reporter by exchanging GFP for pHluorin, which is more sensitive to low pH, and RFP to mCherry, to construct pHluorin-LC3-mCherry reporter. Following starvation or mTOR inhibition, the increase of autophagic flux was detected by a decrease of the fluorescent ratio of pHluorin to mCherry; our reporter was also more sensitive to autophagy-inducing stimuli than the previous one. To establish monitoring cells for mouse genome-wide screening of regulators of autophagic flux based on CRISPR/Cas9 system, after evaluating knockout efficiency of clones of Cas9-expressing MEFs, we co-expressed our reporter and confirmed that autophagic flux was impaired in gRNA-mediated knockout of canonical autophagy genes. Finally, we performed genome-wide gRNA screening for genes inhibiting starvation-mediated autophagic flux and identified previously reported genes such as Atgs. Thus, we have successfully established a system for screening of genes regulating autophagic flux with our pHluorin-LC3-mCherry reporter in mice.

Cerebellar Neurodegeneration and Neuronal Circuit Remodeling in Golgi pH Regulator-Deficient Mice.

The Golgi apparatus plays an indispensable role in posttranslational modification and transport of proteins to their target destinations. Although it is well established that the Golgi apparatus requires an acidic luminal pH for optimal activity, morphological and functional abnormalities at the neuronal circuit level because of perturbations in Golgi pH are not fully understood. In addition, morphological alteration of the Golgi apparatus is associated with several neurodegenerative diseases, including Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis. Here, we used anatomical and electrophysiological approaches to characterize morphological and functional abnormalities of neuronal circuits in Golgi pH regulator (GPHR) conditional knock-out mice. Purkinje cells (PCs) from the mutant mice exhibited vesiculation and fragmentation of the Golgi apparatus, followed by axonal degeneration and progressive cell loss. Morphological analysis provided evidence for the disruption of basket cell (BC) terminals around PC soma, and electrophysiological recordings showed selective loss of large amplitude responses, suggesting BC terminal disassembly. In addition, the innervation of mutant PCs was altered such that climbing fiber (CF) terminals abnormally synapsed on the somatic spines of mutant PCs in the mature cerebellum. The combined results describe an essential role for luminal acidification of the Golgi apparatus in maintaining proper neuronal morphology and neuronal circuitry.