White adipocytes act as lipid storage, and play an important role in energy homeostasis. The small GTPase Rac1 has been implicated in the regulation of insulin-stimulated glucose uptake in white ...adipocytes. Adipocyte-specific
-knockout (adipo-
-KO) mice exhibit atrophy of subcutaneous and epididymal white adipose tissue (WAT); white adipocytes in these mice are significantly smaller than controls. Here, we aimed to investigate the mechanisms underlying the aberrations in the development of Rac1-deficient white adipocytes by employing in vitro differentiation systems. Cell fractions containing adipose progenitor cells were obtained from WAT and subjected to treatments that induced differentiation into adipocytes. In concordance with observations in vivo, the generation of lipid droplets was significantly attenuated in Rac1-deficient adipocytes. Notably, the induction of various enzymes responsible for de novo synthesis of fatty acids and triacylglycerol in the late stage of adipogenic differentiation was almost completely suppressed in Rac1-deficient adipocytes. Furthermore, the expression and activation of transcription factors, such as the CCAAT/enhancer-binding protein (C/EBP) β, which is required for the induction of lipogenic enzymes, were largely inhibited in Rac1-deficient cells in both early and late stages of differentiation. Altogether, Rac1 is responsible for adipogenic differentiation, including lipogenesis, through the regulation of differentiation-related transcription.
Mammalian target of rapamycin (mTOR) is a central regulator of cellular metabolism. The importance of mTORC1 signaling in neuronal development and functions has been highlighted by its strong ...relationship with many neurological and neuropsychiatric diseases. Previous studies demonstrated that hyperactivation of mTORC1 in forebrain recapitulates tuberous sclerosis and neurodegeneration. In the mouse cerebellum, Purkinje cell-specific knockout of Tsc1/2 has been implicated in autistic-like behaviors. However, since TSC1/2 activity does not always correlate with clinical manifestations as evident in some cases of tuberous sclerosis, the intriguing possibility is raised that phenotypes observed in Tsc1/2 knockout mice cannot be attributable solely to mTORC1 hyperactivation. Here we generated transgenic mice in which mTORC1 signaling is directly hyperactivated in Purkinje cells. The transgenic mice exhibited impaired synapse elimination of climbing fibers and motor discoordination without affecting social behaviors. Furthermore, mTORC1 hyperactivation induced prominent apoptosis of Purkinje cells, accompanied with dysregulated cellular homeostasis including cell enlargement, increased mitochondrial respiratory activity, and activation of pseudohypoxic response. These findings suggest the different contributions between hyperactivated mTORC1 and Tsc1/2 knockout in social behaviors, and reveal the perturbations of cellular homeostasis by hyperactivated mTORC1 as possible underlying mechanisms of neuronal dysfunctions and death in tuberous sclerosis and neurodegenerative diseases.
SETD1A encodes a histone methyltransferase whose de novo mutations are identified in schizophrenia (SCZ) patients and confer a large increase in disease risk. Here, we generate Setd1a mutant mice ...carrying the frameshift mutation that closely mimics a loss-of-function variant of SCZ. Our Setd1a (+/−) mice display various behavioral abnormalities relevant to features of SCZ, impaired excitatory synaptic transmission in layer 2/3 (L2/3) pyramidal neurons of the medial prefrontal cortex (mPFC), and altered expression of diverse genes related to neurodevelopmental disorders and synaptic functions in the mPFC. RNAi-mediated Setd1a knockdown (KD) specifically in L2/3 pyramidal neurons of the mPFC only recapitulates impaired sociality among multiple behavioral abnormalities of Setd1a (+/−) mice. Optogenetics-assisted selective stimulation of presynaptic neurons combined with Setd1a KD reveals that Setd1a at postsynaptic site is essential for excitatory synaptic transmission. Our findings suggest that reduced SETD1A may attenuate excitatory synaptic function and contribute to the pathophysiology of SCZ.
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•Setd1a (+/−) mice mimicking a frameshift mutation of a SCZ patient are generated•Setd1a (+/−) mice display various abnormal behaviors relevant to features of SCZ•Postsynaptic SETD1A is crucial for excitatory synaptic function and structure•Setd1a in layer 2/3 pyramidal neurons of mPFC is involved in mouse social behavior
Nagahama et al. demonstrate that mimicking a de novo mutation of the schizophrenia-risk gene SETD1A in mice induces various abnormal behaviors relevant to schizophrenia. Setd1a in postsynaptic neurons positively regulates excitatory synaptic transmission and structure in the medial prefrontal cortex through histone modification and regulating the expression of diverse synaptic genes.
There is increasing evidence for a crucial role of aberrant mineralocorticoid receptor (MR) activation in heart failure, with clinical studies showing beneficial effects of MR blockade. However, the ...mechanisms of MR activation in heart failure remain unclear. In this study, we observed that the small GTPase Rac1 contributes to myocardial MR activation, whereas Rac1-MR pathway activation leads to cardiac dysfunction. Mouse hearts subjected to chronic pressure overload induced by transverse aortic constriction showed Rac1 activation and increased nuclear accumulation of MR and expression of MR target genes, suggesting MR activation. Pharmacological inhibition of Rac1 and heterozygous deletion of Rac1 in cardiomyocytes suppressed Rac1-induced MR signaling and reduced NADPH oxidase 4 gene induction and reactive oxygen species overproduction, which attenuated transverse aortic constriction-induced cardiac hypertrophy and dysfunction. Consistently, treatment with the selective MR antagonist eplerenone blocked transverse aortic constriction-induced MR signaling and NADPH oxidase 4 gene upregulation, which improved cardiac hypertrophy and dysfunction. These findings suggest that Rac1-MR pathway activation in the myocardium is involved in development of heart failure induced by pressure load via recruitment of the responsible isoform of NADPH oxidase. Thus, the cardiac Rac1-MR-NADPH oxidase 4 pathway may be a therapeutic target for treatment of the pressure-overloaded heart.
Genetically modified nonhuman primates (NHP) are useful models for biomedical research. Gene editing technologies have enabled production of target-gene knock-out (KO) NHP models. ...Target-gene-KO/knock-in (KI) efficiency of CRISPR/Cas9 has not been extensively investigated in marmosets. In this study, optimum conditions for target gene modification efficacies of CRISPR/mRNA and CRISPR/nuclease in marmoset embryos were examined. CRISPR/nuclease was more effective than CRISPR/mRNA in avoiding mosaic genetic alteration. Furthermore, optimal conditions to generate KI marmoset embryos were investigated using CRISPR/Cas9 and 2 different lengths (36 nt and 100 nt) each of a sense or anti-sense single-strand oligonucleotide (ssODN). KIs were observed when CRISPR/nuclease and 36 nt sense or anti-sense ssODNs were injected into embryos. All embryos exhibited mosaic mutations with KI and KO, or imprecise KI, of c-kit. Although further improvement of KI strategies is required, these results indicated that CRISPR/Cas9 may be utilized to produce KO/KI marmosets via gene editing.
Mammalian target of rapamycin (mTOR) has been implicated in human neurological diseases such as tuberous sclerosis complex (TSC), neurodegeneration, and autism. However, little is known about when ...and how mTOR is involved in the pathogenesis of these diseases, due to a lack of animal models that directly increase mTOR activity. Here, we generated transgenic mice expressing a gain-of-function mutant of mTOR in the forebrain in a temporally controlled manner. Selective activation of mTORC1 in embryonic stages induced cortical atrophy caused by prominent apoptosis of neuronal progenitors, associated with upregulation of HIF-1α. In striking contrast, activation of the mTORC1 pathway in adulthood resulted in cortical hypertrophy with fatal epileptic seizures, recapitulating human TSC. Activated mTORC1 in the adult cortex also promoted rapid accumulation of cytoplasmic inclusions and activation of microglial cells, indicative of progressive neurodegeneration. Our findings demonstrate that mTORC1 plays different roles in developmental and adult stages and contributes to human neurological diseases.
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•mTORC1 activation leads atrophy in embryonic cortex but hypertrophy in adulthood•Embryonic activation of mTORC1 causes HIF-1-associated apoptosis of progenitors•Activation of mTORC1 in postmitotic neurons impairs cortical neuronal migration•mTORC1 activation recapitulates tuberous sclerosis and neurodegeneration
Mammalian target of rapamycin (mTOR) is a central hub of cellular energy metabolism. Although mTOR has been implicated in many human neurological diseases, little is known about when and how mTOR is involved in the pathogenesis of these diseases. In this study, Kassai et al. show that mTORC1 plays surprisingly different roles during developmental and adult stages in the cerebral cortex. Abnormal activation of mTORC1 causes microcephaly in the embryonic stage and induces tuberous sclerosis and neurodegeneration in adulthood.
Rac signaling affects numerous downstream targets in vitro; however, few studies have established in vivo levels. We generated mice with a single knockout (KO) of Rac1 ...(Keratin5(K5)-Cre;Rac1flox/flox, Rac1-KO) and double KO of Rac1 and Rac3 (K5-Cre;Rac1flox/flox;Rac3−/−, Rac1/Rac3-DKO) in keratinocytes. The hairless phenotype in Rac1-KO mice was markedly exacerbated in Rac1/Rac3-DKO mice. Strikingly, Rac1-KO mice exhibited thinner dermal white adipose tissue, which was considerably further reduced in Rac1/Rac3-DKO mice. DNA microarray using primary keratinocytes from Rac1/Rac3-DKO mice exhibited decreased mRNA levels of Bmp2, Bmp5, Fgf20, Fgf21, Fgfbp1, and Pdgfα. Combinational treatment with bone morphogenetic protein (BMP) 2 and fibroblast growth factor (FGF) 21 in culture medium, but not individual purified recombinant proteins, could differentiate 3T3-L1 fibroblasts into adipocytes, as could culture media from primary keratinocytes. Conversely, addition of anti-BMP2 or anti-FGF21 antibodies into the culture medium inhibited fibroblast differentiation. In addition, BMP2 and FGF21 treatment promoted adipocyte differentiation only of rat primary white adipocyte precursors but not rat primary brown adipocyte precursors. Furthermore, BMP2 and FGF21 treatment enhanced adipogenesis of normal human dermal fibroblasts. Notably, brown adipogenesis promoted by FGF21 was inhibited by BMP2. Thus, we propose a complex paracrine pathway from keratinocytes to intradermal pre-adipocytes, which functions as a Rac-dependent modulator of both white and brown adipogenesis.
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Ror2 receptor tyrosine kinase plays crucial roles in developmental morphogenesis and tissue‐/organo‐genesis. In the developing brain, Ror2 is expressed in neural stem/progenitor cells (NPCs) and ...involved in the regulation of their stemness. However, it remains largely unknown about its role in the adult brain. In this study, we show that Ror2 is up‐regulated in reactive astrocytes in the neocortices within 3 days following stab‐wound injury. Intriguingly, Ror2‐expressing astrocytes were detected primarily at the area surrounding the injury site, where astrocytes express Nestin, a marker of NPCs, and proliferate in response to injury. Furthermore, we show by using astrocyte‐specific Ror2 knockout (KO) mice that a loss of Ror2 in astrocytes attenuates injury‐induced proliferation of reactive astrocytes. It was also found that basic fibroblast growth factor (bFGF) is strongly up‐regulated at 1 day post injury in the neocortices, and that stimulation of cultured quiescent astrocytes with bFGF restarts their cell cycle and induces expression of Ror2 during the G1 phase predominantly in proliferating cells. By using this culture method, we further show that the proportions of Ror2‐expressing astrocytes increase following treatment with the histone deacetylases inhibitors including valproic acid, and that bFGF stimulation increases the levels of Ror2 expression within the respective cells. Moreover, we show that bFGF‐induced cell cycle progression into S phase is inhibited or promoted in astrocytes from Ror2 KO mice or NPCs stably expressing Ror2‐GFP, respectively. Collectively, these findings indicate that Ror2 plays a critical role in regulating the cell cycle progression of reactive astrocytes following brain injury, GLIA 2016. GLIA 2017;65:182–197
Main Points
Ror2 is up‐regulated in reactive astrocytes in the neocortices following brain injury.
Loss of Ror2 attenuates injury‐induced proliferation of reactive astrocytes.
bFGF might contribute to induce expression of Ror2 in reactive astrocytes.
Autophagy is an intracellular degradation system, but its physiological functions in vertebrates are not yet fully understood. Here, we show that autophagy is required for inflation of air-filled ...organs: zebrafish swim bladder and mouse lung. In wild-type zebrafish swim bladder and mouse lung type II pulmonary epithelial cells, autophagosomes are formed and frequently fuse with lamellar bodies. The lamellar body is a lysosome-related organelle that stores a phospholipid-containing surfactant complex that lines the air-liquid interface and reduces surface tension. We find that autophagy is critical for maturation of the lamellar body. Accordingly, atg-deficient zebrafish fail to maintain their position in the water, and type-II-pneumocyte-specific Fip200-deficient mice show neonatal lethality with respiratory failure. Autophagy suppression does not affect synthesis of the surfactant phospholipid, suggesting that autophagy supplies lipids and membranes to lamellar bodies. These results demonstrate an evolutionarily conserved role of autophagy in lamellar body maturation.
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•Autophagy is required for larval survival and swim bladder inflation in zebrafish•Autophagy is required for maturation of surfactant-containing lamellar bodies•Autophagosomes fuse with lamellar bodies in the swim bladder and lung•FIP200 in the lung is essential for neonatal survival and respiration in mice
Physiological functions of macroautophagy remain not fully understood in vertebrates. Morishita et al. demonstrate that autophagy is required for inflation of air-filled organs: zebrafish swim bladder and mouse lung. In the swim bladder and type II pulmonary epithelial cells, autophagosomes fuse with lamellar bodies, which drives lamellar body maturation.
White adipocytes are unique in that they contain large unilocular lipid droplets that occupy most of the cytoplasm. To identify genes involved in the maintenance of mature adipocytes, we expressed ...dominant-negative PPARgamma in 3T3-L1 cells and performed a microarray screen. The fat-specific protein of 27 kDa (FSP27) was strongly downregulated in this context. FSP27 expression correlated with induction of differentiation in cultured preadipocytes, and the protein localized to lipid droplets in murine white adipocytes in vivo. Ablation of FSP27 in mice resulted in the formation of multilocular lipid droplets in these cells. Furthermore, FSP27-deficient mice were protected from diet-induced obesity and insulin resistance and displayed an increased metabolic rate due to increased mitochondrial biogenesis in white adipose tissue (WAT). Depletion of FSP27 by siRNA in murine cultured white adipocytes resulted in the formation of numerous small lipid droplets, increased lipolysis, and decreased triacylglycerol storage, while expression of FSP27 in COS cells promoted the formation of large lipid droplets. Our results suggest that FSP27 contributes to efficient energy storage in WAT by promoting the formation of unilocular lipid droplets, thereby restricting lipolysis. In addition, we found that the nature of lipid accumulation in WAT appears to be associated with maintenance of energy balance and insulin sensitivity.
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