Rapamycin Ameliorates Age-Dependent Obesity Associated with Increased mTOR Signaling in Hypothalamic POMC Neurons

The prevalence of obesity in older people is the leading cause of metabolic syndromes. Central neurons serving as homeostatic sensors for body-weight control include hypothalamic neurons that express pro-opiomelanocortin (POMC) or neuropeptide-Y (NPY) and agouti-related protein (AgRP). Here, we report an age-dependent increase of mammalian target of rapamycin (mTOR) signaling in POMC neurons that elevates the ATP-sensitive potassium (K(ATP)) channel activity cell-autonomously to silence POMC neurons. Systemic or intracerebral administration of the mTOR inhibitor rapamycin causes weight loss in old mice. Intracerebral rapamycin infusion into old mice enhances the excitability and neurite projection of POMC neurons, thereby causing?a reduction of food intake and body weight. Conversely, young mice lacking the mTOR-negative regulator TSC1 in POMC neurons, but not those lacking TSC1 in NPY/AgRP neurons, were obese. Our study reveals that an increase in mTOR signaling in hypothalamic POMC neurons contributes to age-dependent obesity. VIDEO ABSTRACT:     

Polyglutamine-expanded ataxin-7 decreases nuclear translocation of NF-kappaB p65 and impairs NF-kappaB activity by inhibiting proteasome activity of cerebellar neurons

Our recent study indicated that polyglutamine-expanded ataxin-7-Q75 induced apoptotic death of cultured cerebellar neurons by downregulating Bcl-x(L) expression and activating mitochondrial apoptotic cascade. Mutant polyglutamine-expanded proteins are believed to impair the proteolytic function of ubiquitin-proteasome system by sequestering components of proteasomes. Proteasome degradation of IkappaBalpha permits nuclear translocation of NF-kappaB and is required for continuous NF-kappaB activity, which supports the survival of cultured cerebellar neurons by inducing Bcl-x(L) expression. Thus, we tested the hypothesis that mutant ataxin-7-Q75 causes proteasome dysfunction and impairs NF-kappaB activity, leading to reduced Bcl-x(L) expression, caspase activation and cerebellar neuronal death. EMSA assays indicate that DNA-binding activity of NF-kappaB was significantly decreased in cerebellar neurons expressing ataxin-7-Q75. Similar to mutant ataxin-7-Q75, NF-kappaB inhibitor APEQ induced cerebellar neuronal death by decreasing Bcl-x(L) expression and activating caspase-9. Mutant ataxin-7-Q75 inhibited the proteolytic activity of proteasomes in cerebellar neurons. Proteasome inhibitor MG132 also caused cerebellar neuronal death by decreasing Bcl-x(L) expression and activating caspase-9. Both ataxin-7-Q75 and MG132 caused the cytosolic accumulation of IkappaBalpha in cerebellar neurons. Mutant ataxin-7-Q75 or MG132 increased the cytosolic level of NF-kappaB p65 and decreased the nuclear NF-kappaB p65 level. Our study provides the evidence that polyglutamine-expanded ataxin-7-Q75 decreases nuclear translocation of NF-kappaB p65 and impairs NF-kappaB activity by inhibiting proteasome activity of cerebellar neurons.     

Bidirectional regulation of dendritic voltage-gated potassium channels by the fragile X mental retardation protein

How transmitter receptors modulate neuronal signaling by regulating voltage-gated ion channel expression remains an open question. Here we report dendritic localization of mRNA of Kv4.2 voltage-gated potassium channel, which regulates synaptic plasticity, and its local translational regulation by fragile X mental retardation protein (FMRP) linked to fragile X syndrome (FXS), the most common heritable mental retardation. FMRP suppression of Kv4.2 is revealed by elevation of Kv4.2 in neurons from fmr1 knockout (KO) mice and in neurons expressing Kv4.2-3'UTR that binds FMRP. Moreover, treating hippocampal slices from fmr1 KO mice with Kv4 channel blocker restores long-term potentiation induced by moderate stimuli. Surprisingly, recovery of Kv4.2 after N-methyl-D-aspartate receptor (NMDAR)-induced degradation also requires FMRP, likely due to NMDAR-induced FMRP dephosphorylation, which turns off FMRP suppression of Kv4.2. Our study of FMRP regulation of Kv4.2 deepens our knowledge of NMDAR signaling and reveals a FMRP target of potential relevance to FXS.     

Life cycles,phenology and genetic structure of endangered Megacrania tsudai Shiraki (Phasmatodea: Phasmatidae): Male individuals from a geographic parthenogenesis species

Megacrania tsudai, a peripherally distributed member of Megacrania, requires conservation in Taiwan; it has limited distribution in Taiwan and its eastern offshore islands. It feeds on screw pines (Pandanus odoratissimus) in nature and has demonstrated a specific defensive mechanism involving actinidine secretion from the prothoracic gland. However, details of its distribution area, life cycle and developmental phenology remain largely unknown. In this study, a field survey and review of published works revealed M. tsudai distribution in coastal zones and along river shores near estuaries. At room temperature, the egg period was 128 days. The development of the first to sixth instars required 17, 26, 27, 26, 34 and 43 days, respectively, on average; and a generation cycle required approximately 204 days. The phenology of the mesonotal granules was recorded. Moreover, genetic analysis of the mitochondrial cytochrome oxidase I (COI), 16S ribosomal DNA (16S rDNA) and the nuclear ribosomal spacer indicated the occurrence of genetic drift. Therefore, the rearing procedures proposed in this study for the primary and last instars of M. tsudai can facilitate its conservation. Megacrania tsudai was previously recorded as parthenogenetic; however, two male individuals were fostered unexpectedly. The male body length was 91 mm, which is shorter than the female length (120 mm). During mating, the male climbs onto the female's back and protrudes its genitalia downward. Geographical parthenogenesis is likely the reproductive strategy among peripheral M. tsudai; however, the rarely found M. tsudai male could be an intermediate link of reproductive strategy in the transition from tychoparthenogenesis to parthenogenesis.     

Opposing functions for retromer and Rab11 in extracellular vesicle traffic at presynaptic terminals

Neuronal extracellular vesicles (EVs) play important roles in intercellular communication and pathogenic protein propagation in neurological disease. However, it remains unclear how cargoes are selectively packaged into neuronal EVs. Here, we show that loss of the endosomal retromer complex leads to accumulation of EV cargoes including amyloid precursor protein (APP), synaptotagmin-4 (Syt4), and neuroglian (Nrg) at Drosophila motor neuron presynaptic terminals, resulting in increased release of these cargoes in EVs. By systematically exploring known retromer-dependent trafficking mechanisms, we show that EV regulation is separable from several previously identified roles of neuronal retromer. Conversely, mutations in rab11 and rab4, regulators of endosome-plasma membrane recycling, cause reduced EV cargo levels, and rab11 suppresses cargo accumulation in retromer mutants. Thus, EV traffic reflects a balance between Rab4/Rab11 recycling and retromer-dependent removal from EV precursor compartments. Our data shed light on previous studies implicating Rab11 and retromer in competing pathways in Alzheimer’s disease, and suggest that misregulated EV traffic may be an underlying defect.     

异源PDGF-A链表达对CHO细胞生长和转化的作用

用DNA磷酸钙盐沉淀方法把含人PDGF(血小板衍生生长因子)A链cDNA的表达质粒pSV_2neo-A转染CHO细胞(中国仓鼠卵巢细胞),然后经G 418(400-800 μg/ml)筛选分离20个转染细胞株。选出其中At_1和Aot7细胞株所进行的实验结果表明,这些细胞的形态和生长行为均发生明显的变化,PDGF-A链mRNA的表达水平比CHO细胞明显增高,胞质有强阳性的PDGF荧光反应,显示有PDGF样蛋白的合成。这些细胞不但生长速率加快,有高密度持续生长的特性,而且能在软琼脂培基上形成大集落和在裸鼠体内接种形成纤维肉瘤,提示外源PDGF-A链基因的表达有使CHO细胞生长失控和发生细胞恶性转化的作用。