Fad104, a positive regulator of adipogenesis, negatively regulates osteoblast differentiation

Fad104 (factor for adipocyte differentiation 104) is a novel gene expressed temporarily in the early stages of adipocyte differentiation. Previously, we showed that fad104 promotes adipocyte differentiation in mouse 3T3-L1 cells and mouse embryonic fibroblasts (MEFs). Furthermore, we reported that implanted wild-type MEFs could develop into adipocytes, whereas fad104-deficient MEFs could not. Interestingly, bone-like tissues were only observed in the implants derived from fad104-deficient MEFs. This result implies that fad104 is involved in osteoblast differentiation. However, the functions of fad104 during osteogenesis are unknown. In this paper, we show that fad104 negatively regulates osteoblast differentiation. During the differentiation process, the level of fad104 expression decreased. Deletion of fad104 facilitated osteoblast differentiation in MEFs, and elevated the level of runx2, a master regulator of osteoblast differentiation. Disruption of fad104 suppressed BMP-2-mediated adipocyte differentiation in MEFs. In conclusion, we demonstrate that fad104 reciprocally regulates differentiation of adipocytes and osteoblast; functions as a positive regulator in adipocyte differentiation and as a negative regulator in osteoblast differentiation.     

Genetic characterization of mutants resistant to the antiauxin p-chlorophenoxyisobutyric acid reveals that AAR3, a gene encoding a DCN1-like protein, regulates responses to the synthetic auxin 2,4-dichlorophenoxyacetic acid in Arabidopsis roots

To isolate novel auxin-responsive mutants in Arabidopsis (Arabidopsis thaliana), we screened mutants for root growth resistance to a putative antiauxin, p-chlorophenoxyisobutyric acid (PCIB), which inhibits auxin action by interfering the upstream auxin-signaling events. Eleven PCIB-resistant mutants were obtained. Genetic mapping indicates that the mutations are located in at least five independent loci, including two known auxin-related loci, TRANSPORT INHIBITOR RESPONSE1 and Arabidopsis CULLIN1. antiauxin-resistant mutants (aars) aar3-1, aar4, and aar5 were also resistant to 2,4-dichlorophenoxyacetic acid as shown by a root growth assay. Positional cloning of aar3-1 revealed that the AAR3 gene encodes a protein with a domain of unknown function (DUF298), which has not previously been implicated in auxin signaling. The protein has a putative nuclear localization signal and shares homology with the DEFECTIVE IN CULLIN NEDDYLATION-1 protein through the DUF298 domain. The results also indicate that PCIB can facilitate the identification of factors involved in auxin or auxin-related signaling.     

Important role of apoptosis signal-regulating kinase 1 in ischemic acute kidney injury

We investigated the role of apoptosis signal-regulating kinase 1 (ASK1) in ischemia/reperfusion (I/R)-induced acute kidney injury (AKI). Blood urea nitrogen (BUN) and serum creatinine were significantly higher in ASK1+/+ mice than in ASK1−/− mice after I/R injury. Renal histology of ASK1+/+ mice showed significantly greater tubular necrosis and degradation. In ASK1−/− mice, phosphorylation of ASK1, JNK, and p38K, and the number of TUNEL-positive cells and infiltrated leukocytes decreased after I/R injury. Apoptotic changes were significantly decreased in cultured renal tubular epithelial cells (TECs) from ASK1−/− mice under hypoxic condition. Transfection with dominant-active ASK1 induced apoptosis in TECs. Protein expression of monocyte chemoattractant protein-1 (MCP-1) was significantly weaker in ASK1−/− mice after I/R injury. Transfection with dominant negative-ASK1 significantly decreased MCP-1 production in TECs. These results demonstrated that ASK1 is activated in I/R-induced AKI, and blockage of ASK1 attenuates renal tubular apoptosis, MCP-1 expression, and renal function.     

Lysophosphatidylcholine induces delayed myelination in the juvenile ventral hippocampus and behavioral alterations in adulthood

Maternal virus infection or maternal polyinosinic-polycytidilic acid injection confers behavioral alterations including deficit in prepulse inhibition on the offspring. We previously found delayed myelination specifically in the early postnatal hippocampus in the polyinosinic–polycytidilic acid-injection model. To test whether the transient delay in myelination in the juvenile hippocampus leads to abnormal behaviors after adolescence, we injected lysophosphatidylcholine, a potent demyelinating agent, into the ventral hippocampus of the 10-day-old rat. The lysophosphatidylcholine treatment yielded hypomyelination at postnatal day 16, but myelination reverted to normal level in the adult rat. Neuronal arrays and morphology were not disturbed in this model. We then performed a battery of behavioral tests on the lysophosphatidylcholine-treated and control PBS-injected rats. The lysophosphatidylcholine-treated rats showed deficit in prepulse inhibition, motor hyperactivity in response to methamphetamine and anxiety-related behaviors, all of which are typical behaviors observed in the maternal infection models. These findings suggest that the timing of myelination in the early postnatal hippocampus is crucial for the proper development of sensorimotor and emotional functions. The lysophosphatidylcholine-treated rat without a gross anatomical defect is useful as a model for psychotic disorders.     

Hydroxyl-radical production and ethanol oxidation by liver microsomes isolated from ethanol-treated rats.

In order to distinguish between the mechanism of microsomal ethanol oxidation and hydroxyl-radical formation, the rate of cytochrome P-450 (P-450)-dependent oxidation of dimethyl sulphoxide (Me2SO) was determined in the presence and in the absence of iron-chelating compounds, in liver microsomes from control, ethanol- and phenobarbital-treated rats. Ethanol treatment resulted in a specific increase (3-fold) of the microsomal ethanol oxidation and NADPH consumption per nmol of P-450. A form of P-450 was purified to apparent homogeneity from the ethanol-treated rats and characterized with respect of amino acid composition and N-terminal amino acid sequence. Specific ethanol induction of a cytochrome P-450 species having a catalytic-centre activity of 20/min for ethanol and consuming 30 nmol of NADPH/min could account for the results observed with microsomes. Phenobarbital treatment caused 50% decrease in the rate of ethanol oxidation and NADPH oxidation per nmol of P-450. The rate of oxidation of the hydroxyl-radical scavenger Me2SO was increased 3-fold by ethanol or phenobarbital treatment when expressed on a per-mg-of-microsomal-protein basis, but the rate of Me2SO oxidation expressed on a per-nmol-of-P-450 basis was unchanged. Addition of iron-chelating agents to the three different types of microsomal preparations caused an 'uncoupling' of the electron-transport chain accompanied by a 4-fold increase of the rate of Me2SO oxidation. It is concluded that ethanol treatment results in the induction of P-450 forms specifically effective in ethanol oxidation and NADPH oxidation, but not in hydroxyl-radical production, as detected by the oxidation of Me2SO.     

Complement C1q activates canonical Wnt signaling and promotes aging-related phenotypes

Wnt signaling plays critical roles in development of various organs and pathogenesis of many diseases, and augmented Wnt signaling has recently been implicated in mammalian aging and aging-related phenotypes. We here report that complement C1q activates canonical Wnt signaling and promotes aging-associated decline in tissue regeneration. Serum C1q concentration is increased with aging, and Wnt signaling activity is augmented during aging in the serum and in multiple tissues of wild-type mice, but not in those of C1qa-deficient mice. C1q activates canonical Wnt signaling by binding to Frizzled receptors and subsequently inducing C1s-dependent cleavage of the ectodomain of Wnt coreceptor low-density lipoprotein receptor-related protein 6. Skeletal muscle regeneration in young mice is inhibited by exogenous C1q treatment, whereas aging-associated impairment of muscle regeneration is restored by C1s inhibition or C1qa gene disruption. Our findings therefore suggest the unexpected role of complement C1q in Wnt signal transduction and modulation of mammalian aging.     

PDK1 is required for the hormonal signaling pathway leading to meiotic resumption in starfish oocytes

Meiotic resumption is generally under the control of an extracellular maturation-inducing hormone. It is equivalent to the G2-M phase transition in somatic cell mitosis and is regulated by cyclin B-Cdc2 kinase. However, the complete signaling pathway from the hormone to cyclin B-Cdc2 is yet unclear in any organism. A model system to analyze meiotic resumption is the starfish oocyte, in which Akt/protein kinase B (PKB) plays a key mediator in hormonal signaling that leads to cyclin B-Cdc2 activation. Here we show in starfish oocytes that when PDK1 activity is inhibited by a neutralizing antibody, maturation-inducing hormone fails to induce cyclin B-Cdc2 activation at the meiotic G2-M phase transition, even though PDK2 activity becomes detectable. These observations assign a novel role to PDK1 for a hormonal signaling intermediate toward meiotic resumption. They further support that PDK2 is a molecule distinct from PDK1 and Akt, and that PDK2 activity is not sufficient for the full activation of Akt in the absence of PDK1 activity.     

1α,25-dihydroxyvitamin D₃ enhances fast-myosin heavy chain expression in differentiated C2C12 myoblasts

We investigated the effect of VD3 (1α,25-dihydroxyvitamin D3) on the proliferating, differentiating and differentiated phases of C2C12 myoblasts, a mouse skeletal muscle cell line. VD3 treatment in 10% FBS (fetal bovine serum) inhibited the proliferation and viability of the cells in a dose-dependent manner. It also dose-dependently increased the percentage of cells in the G0/G1 phase as shown by flow cytometry. In the differentiating phase, VD3 treatment inhibited the formation of myotubes and the expression of total myosin heavy chain at both the mRNA and protein levels. In the differentiated phase, treatment had no significant effect on the amount of total myosin heavy chain, as Western blot analysis with MF20 antibody [DSHB (Developmental Studies Hybridoma Bank)] showed. However, significantly greater expression of fast myosin heavy chain in 1 nM VD3 was found by Western blot analysis with MY-32 (Sigma). Thus VD3 inhibited the proliferation of myoblasts during proliferating and differentiating phases, whereas it increased the expression of the fast myosin heavy chain isoform in the differentiated phase. The data indicate that an adequate concentration of VD3 might have an anabolic effect on differentiated skeletal muscle.