Mitophagy reporter mouse analysis reveals increased mitophagy activity in disuse-induced muscle atrophy.

Muscle disuse induces atrophy through increased reactive oxygen species (ROS) released from damaged mitochondria. Mitophagy, the autophagic degradation of mitochondria, is associated with increased ROS production. However, the mitophagy activity status during disuse-induced muscle atrophy has been a subject of debate. Here, we developed a new mitophagy reporter mouse line to examine how disuse affected mitophagy activity in skeletal muscles. Mice expressing tandem mCherry-EGFP proteins on mitochondria were then used to monitor the dynamics of mitophagy activity. The reporter mice demonstrated enhanced mitophagy activity and increased ROS production in atrophic soleus muscles following a 14-day hindlimb immobilization. Results also showed an increased expression of multiple mitophagy genes, including Bnip3, Bnip3l, and Park2. Our findings thus conclude that disuse enhances mitophagy activity and ROS production in atrophic skeletal muscles and suggests that mitophagy is a potential therapeutic target for disuse-induced muscle atrophy.

Standalone cell culture microfluidic device-based microphysiological system for automated cell observation and application in nephrotoxicity tests.

Microphysiological systems (MPS) offer an alternative method for culturing cells on microfluidic platforms to model organ functions in pharmaceutical and medical sciences. Although MPS hardware has been proposed to maintain physiological organ function through perfusion culture, no existing MPS can automatically assess cell morphology and conditions online to observe cellular dynamics in detail. Thus, with this study, we aimed to establish a practical strategy for automating cell observation and improving cell evaluation functions with low temporal resolution and throughput in MPS experiments. We developed a versatile standalone cell culture microfluidic device (SCCMD) that integrates microfluidic chips and their peripherals. This device is compliant with the ANSI/SLAS standards and has been seamlessly integrated into an existing automatic cell imaging system. This integration enables automatic cell observation with high temporal resolution in MPS experiments. Perfusion culture of human kidney proximal tubule epithelial cells using the SCCMD improves cell function. By combining the proximal tubule MPS with an existing cell imaging system, nephrotoxicity studies were successfully performed to automate morphological and material permeability evaluation. We believe that the concept of building the ANSI/SLAS-compliant-sized MPS device proposed herein and integrating it into an existing automatic cell imaging system for the online measurement of detailed cell dynamics information and improvement of throughput by automating observation operations is a novel potential research direction for MPS research.

Cytokine receptor-like factor 1 is highly expressed in damaged human knee osteoarthritic cartilage and involved in osteoarthritis downstream of TGF-beta.

Osteoarthritis (OA) is the most prevalent joint disease and is characterized by pain and functional loss of the joint. However, the pathogenic mechanism of OA remains unclear, and no drug therapy for preventing its progress has been established. To identify genes related to the progress of OA, the gene expression profiles of paired intact and damaged cartilage obtained from OA patients undergoing joint substitution were compared using oligo microarrays. Using functional categorization combined with gene ontology and a statistical analysis, five genes were found to be highly expressed in damaged cartilage (HBEGF, ASUS, CRLF1, LOX, CDA), whereas three genes were highly expressed in intact tissues (CHST2, PTPRD, CPAN6). Among these genes, the upregulated expression of CRLF1 was reconfirmed using real-time PCR, and the in vivo expression of CRLF1 was detected in clusters of chondrocytes and fibrocartilage-like cells in damaged OA cartilages using in situ hybridization. In vitro, the transcriptional level of CRLF1 was positively regulated by TGF-beta1 in the mouse chondrogenic cell line ATDC5. Additionally, the CRLF1/CLC complex promoted the proliferation of ATDC5 cells and suppressed the expression level of aggrecan and type II collagen. Our data suggest that the CRLF1/CLC complex disrupts cartilage homeostasis and promotes the progress of OA by enhancing the proliferation of chondrocytes and suppressing the production of cartilage matrix. A component of the complex, CRLF1, may be useful as a biomarker of OA; and the corresponding receptor is a potential new drug target for OA.

Phenotypic analysis of Meltrin alpha (ADAM12)-deficient mice: involvement of Meltrin alpha in adipogenesis and myogenesis.

Meltrin alpha (ADAM12) is a metalloprotease-disintegrin whose specific expression patterns during development suggest that it is involved in myogenesis and the development of other organs. To determine the roles Meltrin alpha plays in vivo, we generated Meltrin alpha-deficient mice by gene targeting. Although the number of homozygous embryos are close to the expected Mendelian ratio at embryonic days 17 to 18, ca. 30% of the null pups born die before weaning, mostly within 1 week of birth. The viable homozygous mutants appear normal and are fertile. Most of the muscles in the homozygous mutants appear normal, and regeneration in experimentally damaged skeletal muscle is unimpeded. In some Meltrin alpha-deficient pups, the interscapular brown adipose tissue is reduced, although the penetrance of this phenotype is low. Impaired formation of the neck and interscapular muscles is also seen in some homozygotes. These observations suggest Meltrin alpha may be involved in regulating adipogenesis and myogenesis through a linked developmental pathway. Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a candidate substrate of Meltrin alpha, and we found that TPA (12-O-tetradecanoylphorbol-13-acetate)-induced ectodomain shedding of HB-EGF is markedly reduced in embryonic fibroblasts prepared from Meltrin alpha-deficient mice. We also report here the chromosomal locations of Meltrin alpha in the mouse and rat.

Selective loss of nigral dopamine neurons induced by overexpression of truncated human alpha-synuclein in mice.

Parkinson's disease is characterized by loss of nigral dopaminergic neurons and presence of Lewy bodies, whose major component is alpha-synuclein. In the present study, we generated transgenic mice termed Syn130m that express truncated human alpha-synuclein (amino acid residue number: 1-130) in dopaminergic neurons. Notably, dopaminergic neurons were selectively diminished in the substantia nigra pars compacta of Syn130m, while transgenic mice that expressed comparable amount of full-length human alpha-synuclein did not develop such pathology. Therefore, the truncation of human alpha-synuclein seems to be primarily responsible for the loss of nigral dopaminergic neurons. The nigral pathology resulted in impairment of axon terminals in the striatum and concomitant decrease in striatal dopamine content. Behaviorally, spontaneous locomotor activities of Syn130m were reduced, but the abnormality was ameliorated by treatment with L-DOPA. The loss of nigral dopaminergic neurons was not progressive and seemed to occur during embryogenesis along with the onset of expression of the transgene. Our results indicate that truncated human alpha-synuclein is deleterious to the development and/or survival of nigral dopaminergic neurons.

Accumulation of phosphorylated alpha-synuclein in dopaminergic neurons of transgenic mice that express human alpha-synuclein.

Parkinson's disease is neuropathologically characterized by the presence of Lewy bodies, whose major component is alpha-synuclein. We had previously generated transgenic mice that expressed human alpha-synuclein carrying an Ala53Thr point mutation (halpha-syn140m) under the control of the rat tyrosine hydroxylase promoter and found that halpha-syn140m was localized not only in the cytoplasm but also in the nuclei of mesencephalic dopaminergic neurons. In the present study, we carried out immunohistochemical analysis of the brain of Tg mice using anti-PSer129, an antibody that specifically recognizes alpha-synuclein phosphorylated at Ser129. The antibody detected only phosphorylated halpha-syn140m, whereas phosphorylation of endogenous alpha-synuclein, if any, was below the detection limit of the method employed. The analysis showed that approximately one-third of the halpha-syn140m-positive neurons in the midbrain of heterozygous Tg mice were concomitantly reactive to anti-PSer129. The ratio almost doubled in homozygotes, indicating that the phosphorylation level depends directly on the amount of substrate. In addition, the ratio did not change at least up to 48 weeks of age. These data strongly suggest that halpha-syn140m underwent constitutive phosphorylation and that the phosphorylation level was maintained to a certain level until the aged stages. Remarkably, halpha-syn140m localized in the nuclei seemed to be preferentially phosphorylated compared with that in the cytoplasm. Among kinases that have been reported to be involved in the phosphorylation of alpha-synuclein, the beta subunit of casein kinase-2 was detected in the nuclei by immunohistochemistry. These data imply that at least casein kinase-2 is involved in the phosphorylation of halpha-syn140m in the Tg mice.

Increase in hepatic NKT cells in leukocyte cell-derived chemotaxin 2-deficient mice contributes to severe concanavalin A-induced hepatitis.

Leukocyte cell-derived chemotaxin 2 (LECT2) was originally identified for its possible chemotactic activity against human neutrophils in vitro. It is a 16-kDa protein that is preferentially expressed in the liver. Its homologues have been widely identified in many vertebrates. Current evidence suggests that LECT2 may be a multifunctional protein like cytokines. However, the function of LECT2 in vivo remains unclear. To elucidate the role of this protein in vivo, we have generated LECT2-deficient (LECT2(-/-)) mice. We found that the proportion of NKT cells in the liver increased significantly in LECT2(-/-) mice, although those of conventional T cells, NK cells, and other cell types were comparable with those in wild-type mice. Consistent with increased hepatic NKT cell number, the production of IL-4 and IFN-gamma was augmented in LECT2(-/-) mice upon stimulation with alpha-galactosylceramide, which specifically activates Valpha14 NKT cells. In addition, NKT cell-mediated cytotoxic activity against syngeneic thymocytes increased in hepatic mononuclear cells obtained from LECT2(-/-) mice in vitro. Interestingly, the hepatic injury was exacerbated in LECT2(-/-) mice upon treatment with Con A, possibly because of the significantly higher expression of IL-4 and Fas ligand. These results suggest that LECT2 might regulate the homeostasis of NKT cells in the liver and might be involved in the pathogenesis of hepatitis.

Mice deficient in nervous system-specific carbohydrate epitope HNK-1 exhibit impaired synaptic plasticity and spatial learning.

The HNK-1 carbohydrate epitope, a sulfated glucuronic acid at the non-reducing terminus of glycans, is expressed characteristically on a series of cell adhesion molecules and is synthesized through a key enzyme, glucuronyltransferase (GlcAT-P). We generated mice with a targeted deletion of the GlcAT-P gene. The GlcAT-P -/- mice exhibited normal development of gross anatomical features, but the adult mutant mice exhibited reduced long term potentiation at the Schaffer collateral-CA1 synapses and a defect in spatial memory formation. This is the first evidence that the loss of a single non-reducing terminal carbohydrate residue attenuates brain higher functions.