Reducing brain Aβ burden ameliorates high-fat diet-induced fatty liver disease in APP/PS1 mice

High-fat diet (HFD)-induced fatty liver disease is a deteriorating risk factor for Alzheimer's disease (AD). Mitigating fatty liver disease has been shown to attenuate AD-like pathology in animal models. However, it remains unclear whether enhancing Aβ clearance through immunotherapy would in turn attenuate HFD-induced fatty liver or whether its efficacy would be compromised by long-term exposure to HFD. Here, the therapeutic potentials of an anti-Aβ antibody, NP106, was investigated in APP/PS1 mice by HFD feeding for 44 weeks. The data demonstrate that NP106 treatment effectively reduced Aβ burden and pro-inflammatory cytokines in HFD-fed APP/PS1 mice and ameliorated HFD-aggravated cognitive impairments during the final 18 weeks of the study. The rejuvenating characteristics of microglia were evident in APP/PS1 mice with NP106 treatment, namely enhanced microglial Aβ phagocytosis and attenuated microglial lipid accumulation, which may explain the benefits of NP106. Surprisingly, NP106 also reduced HFD-induced hyperglycemia, fatty liver, liver fibrosis, and hepatic lipids, concomitant with modifications in the expressions of genes involved in hepatic lipogenesis and fatty acid oxidation. The data further reveal that brain Aβ burden and behavioral deficits were positively correlated with the severity of fatty liver disease and fasting serum glucose levels. In conclusion, our study shows for the first time that anti-Aβ immunotherapy using NP106, which alleviates AD-like disorders in APP/PS1 mice, ameliorates fatty liver disease. Minimizing AD-related pathology and symptoms may reduce the vicious interplay between central AD and peripheral fatty liver disease, thereby highlighting the importance of developing AD therapies from a systemic disease perspective.

Reduced mitochondria membrane potential and lysosomal acidification are associated with decreased oligomeric Aβ degradation induced by hyperglycemia: A study of mixed glia cultures

Diabetes is a risk factor for Alzheimer’s disease (AD), a chronic neurodegenerative disease. We and others have shown prediabetes, including hyperglycemia and obesity induced by high fat and high sucrose diets, is associated with exacerbated amyloid beta (Aβ) accumulation and cognitive impairment in AD transgenic mice. However, whether hyperglycemia reduce glial clearance of oligomeric amyloid-β (oAβ), the most neurotoxic Aβ aggregate, remains unclear. Mixed glial cultures simulating the coexistence of astrocytes and microglia in the neural microenvironment were established to investigate glial clearance of oAβ under normoglycemia and chronic hyperglycemia. Ramified microglia and low IL-1β release were observed in mixed glia cultures. In contrast, amoeboid-like microglia and higher IL-1β release were observed in primary microglia cultures. APPswe/PS1dE9 transgenic mice are a commonly used AD mouse model. Microglia close to senile plaques in APPswe/PS1dE9 transgenic mice exposed to normoglycemia or chronic hyperglycemia exhibited an amoeboid-like morphology; other microglia were ramified. Therefore, mixed glia cultures reproduce the in vivo ramified microglial morphology. To investigate the impact of sustained high-glucose conditions on glial oAβ clearance, mixed glia were cultured in media containing 5.5 mM glucose (normal glucose, NG) or 25 mM glucose (high glucose, HG) for 16 days. Compared to NG, HG reduced the steady-state level of oAβ puncta internalized by microglia and astrocytes and decreased oAβ degradation kinetics. Furthermore, the lysosomal acidification and lysosomal hydrolysis activity of microglia and astrocytes were lower in HG with and without oAβ treatment than NG. Moreover, HG reduced mitochondrial membrane potential and ATP levels in mixed glia, which can lead to reduced lysosomal function. Overall, continuous high glucose reduces microglial and astrocytic ATP production and lysosome activity which may lead to decreased glial oAβ degradation. Our study reveals diabetes-induced hyperglycemia hinders glial oAβ clearance and contributes to oAβ accumulation in AD pathogenesis.

EK100 and Antrodin C Improve Brain Amyloid Pathology in APP/PS1 Transgenic Mice by Promoting Microglial and Perivascular Clearance Pathways

Alzheimer’s disease (AD) is characterized by the deposition of β-amyloid peptide (Aβ). There are currently no drugs that can successfully treat this disease. This study first explored the anti-inflammatory activity of seven components isolated from Antrodia cinnamonmea in BV2 cells and selected EK100 and antrodin C for in vivo research. APPswe/PS1dE9 mice were treated with EK100 and antrodin C for one month to evaluate the effect of these reagents on AD-like pathology by nesting behavior, immunohistochemistry, and immunoblotting. Ergosterol and ibuprofen were used as control. EK100 and antrodin C improved the nesting behavior of mice, reduced the number and burden of amyloid plaques, reduced the activation of glial cells, and promoted the perivascular deposition of Aβ in the brain of mice. EK100 and antrodin C are significantly different in activating astrocytes, regulating microglia morphology, and promoting plaque-associated microglia to express oxidative enzymes. In contrast, the effects of ibuprofen and ergosterol are relatively small. In addition, EK100 significantly improved hippocampal neurogenesis in APPswe/PS1dE9 mice. Our data indicate that EK100 and antrodin C reduce the pathology of AD by reducing amyloid deposits and promoting nesting behavior in APPswe/PS1dE9 mice through microglia and perivascular clearance, indicating that EK100 and antrodin C have the potential to be used in AD treatment.

The Effects of Aβ1-42 Binding to the SARS-CoV-2 Spike Protein S1 Subunit and Angiotensin-Converting Enzyme 2

Increasing evidence suggests that elderly people with dementia are vulnerable to the development of severe coronavirus disease 2019 (COVID-19). In Alzheimer's disease (AD), the major form of dementia, β-amyloid (Aβ) levels in the blood are increased; however, the impact of elevated Aβ levels on the progression of COVID-19 remains largely unknown. Here, our findings demonstrate that Aβ1-42, but not Aβ1-40, bound to various viral proteins with a preferentially high affinity for the spike protein S1 subunit (S1) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the viral receptor, angiotensin-converting enzyme 2 (ACE2). These bindings were mainly through the C-terminal residues of Aβ1-42. Furthermore, Aβ1-42 strengthened the binding of the S1 of SARS-CoV-2 to ACE2 and increased the viral entry and production of IL-6 in a SARS-CoV-2 pseudovirus infection model. Intriguingly, data from a surrogate mouse model with intravenous inoculation of Aβ1-42 show that the clearance of Aβ1-42 in the blood was dampened in the presence of the extracellular domain of the spike protein trimers of SARS-CoV-2, whose effects can be prevented by a novel anti-Aβ antibody. In conclusion, these findings suggest that the binding of Aβ1-42 to the S1 of SARS-CoV-2 and ACE2 may have a negative impact on the course and severity of SARS-CoV-2 infection. Further investigations are warranted to elucidate the underlying mechanisms and examine whether reducing the level of Aβ1-42 in the blood is beneficial to the fight against COVID-19 and AD.

A high-sucrose diet aggravates Alzheimer's disease pathology, attenuates hypothalamic leptin signaling, and impairs food-anticipatory activity in APPswe/PS1dE9 mice

High-fat and high-sugar diets contribute to the prevalence of type 2 diabetes and Alzheimer's disease (AD). Although the impact of high-fat diets on AD pathogenesis has been established, the effect of high-sucrose diets (HSDs) on AD pathogenesis remains unclear. This study sought to determine the impact of HSDs on AD-related pathologies. Male APPswe/PS1dE9 (APP/PS1) transgenic and wild-type mice were provided with HSD and their cognitive and hypothalamus-related noncognitive parameters, including feeding behaviors and glycemic regulation, were compared. HSD-fed APP/PS1 mice showed increased neuroinflammation, as well as increased cortical and serum levels of amyloid-β. HSD-fed APP/PS1 mice showed aggravated obesity, hyperinsulinemia, insulin resistance, and leptin resistance, but there was no induction of hyperphagia or hyperleptinemia. Leptin-induced phosphorylation of signal transducer and activator of transcription 3 in the dorsomedial and ventromedial hypothalamus was reduced in HSD-fed APP/PS1 mice, which might be associated with attenuated food-anticipatory activity, glycemic dysregulation, and AD-related noncognitive symptoms. Our study demonstrates that HSD aggravates metabolic stresses, increases AD-related pathologies, and attenuates hypothalamic leptin signaling in APP/PS1 mice.

Xuefu Zhuyu decoction ameliorates obesity, hepatic steatosis, neuroinflammation, amyloid deposition and cognition impairment in metabolically stressed APPswe/PS1dE9 mice

ETHNOPHARMACOLOGICAL RELEVANCE

Metabolic syndrome and vascular dysfunction was suggested to be the risk factors for Alzheimer's disease (AD). Xuefu Zhuyu decoction (XZD) is a traditional Chinese medicine used to treat metabolic syndrome and cardiac-cerebral vascular disease. The effects of XZD on ameliorating metabolic syndrome, amyloid-related pathologies and cognitive impairment in an animal model of AD with metabolic stress was investigated.

MATERIALS AND METHOD

The animal model of AD with metabolic stress was created by administrating high-fat diet and a low-dose injection of streptozotocin prior to the appearance of senile plaques in APP/PS1 transgenic mice. The diabesity-associated metabolic changes and AD-related pathological alterations were examined.

RESULTS

We found that XZD reduced body weight, insulin and leptin level, HOMA-IR, hepatic triglyceride, serum Aβ42 in the metabolic stressed AD animal. XZD also ameliorated oral glucose tolerant, Aβ deposition, astrocyte and microglia activation in the vicinity of plaques, and nesting behavior in the metabolic stressed AD animal.

CONCLUSION

The results of this study suggest that XZD is able to reduce the peripheral metabolic stress-mediated vascular hypoperfusion, neuroinflammation and AD-related pathology in APP/PS1 mice.

Identifying N-linked glycan moiety and motifs in the cysteine-rich domain critical for N-glycosylation and intracellular trafficking of SR-AI and MARCO

BACKGROUND

The accumulation of soluble oligomeric amyloid-β peptide (oAβ) proceeding the formation of senile plaques contributes to synaptic and memory deficits in Alzheimer's disease. Our previous studies have indentified scavenger receptor A (SR-A), especially SR-A type I (SR-AI), as prominent scavenger receptors on mediating oAβ clearance by microglia while glycan moiety and scavenger receptor cysteine-rich (SRCR) domain may play the critical role. Macrophage receptor with collagenous structure (MARCO), another member of class A superfamily with a highly conserved SRCR domain, may also play the similar role on oAβ internalization. However, the role of N-glycosylation and SRCR domain of SR-AI and MARCO on oAβ internalization remains unclear.

RESULT

We found that oAβ internalization was diminished in the cells expressing SR-AI harboring mutations of dual N-glycosylation sites (i.e. N120Q-N143Q and N143Q-N184Q) while they were normally surface targeted. Normal oAβ internalization was observed in 10 SR-AI-SRCR and 4 MARCO-SRCR surface targeted mutants. Alternatively, the SRCR mutants at β-sheet and α-helix and on disulfide bone formation obstructed receptor's N-glycosylation and surface targeting.

CONCLUSION

Our study reveals that N-glycan moiety is more critical than SRCR domain for SR-A-mediated oAβ internalization.

Lithospermic acid attenuates 1-methyl-4-phenylpyridine-induced neurotoxicity by blocking neuronal apoptotic and neuroinflammatory pathways

Background

Parkinson’s disease is the second most common neurodegenerative disorders after Alzheimer’s disease. The main cause of the disease is the massive degeneration of dopaminergic neurons in the substantia nigra. Neuronal apoptosis and neuroinflammation are thought to be the key contributors to the neuronal degeneration.

Results

Both CATH.a cells and ICR mice were treated with 1-methyl-4-phenylpyridin (MPP⁺) to induce neurotoxicity in vitro and in vivo. Western blotting and immunohistochemistry were also used to analyse neurotoxicity, neuroinflammation and aberrant neurogenesis in vivo. The experiment in CATH.a cells showed that the treatment of MPP⁺ impaired intake of cell membrane and activated caspase system, suggesting that the neurotoxic mechanisms of MPP⁺ might include both necrosis and apoptosis. Pretreatment of lithospermic acid might prevent these toxicities. Lithospermic acid possesses specific inhibitory effect on caspase 3. In mitochondria, MPP⁺ caused mitochondrial depolarization and induced endoplasmic reticulum stress via increasing expression of chaperone protein, GRP-78. All the effects mentioned above were reduced by lithospermic acid. In animal model, the immunohistochemistry of mice brain sections revealed that MPP⁺ decreased the amount of dopaminergic neurons, enhanced microglia activation, promoted astrogliosis in both substantia nigra and hippocampus, and MPP⁺ provoked the aberrant neurogenesis in hippocampus. Lithospermic acid significantly attenuates all of these effects induced by MPP⁺.

Conclusions

Lithospermic acid is a potential candidate drug for the novel therapeutic intervention on Parkinson’s disease.

Effects of maternal immune activation on adult neurogenesis in the subventricular zone-olfactory bulb pathway and olfactory discrimination

Maternal infection and maternal immune activation (MIA) during pregnancy increase risks for psychiatric disorders such as schizophrenia and autism. Many deficits related to psychiatric disorders are observed in adult offspring of MIA animal models, including behavioral abnormalities, morphological defects in various brain regions, and dysregulation of neurotransmitter systems. It has previously been shown that MIA impairs adult neurogenesis in the dentate gyrus of the hippocampus. In this study, we examined whether MIA affects adult neurogenesis in the subventricular zone (SVZ)-olfactory bulb (OB) pathway. Polyinosinic-polycytidylic acid (PolyI:C), a synthetic analog of double-stranded RNA mimicking viral infection, was injected into pregnant mice on gestation day 9.5 to activate immune systems. In the SVZ-OB pathway of adult offspring, different cell types of the neural stem cell lineage responded differently to MIA. Neural stem cells and neuroblasts were decreased. Cell proliferation of transit-amplifying cells was impaired. Consequently, newborn neurons were reduced in the OB. Olfactory deficiency has been suggested as a biomarker for schizophrenia. Here we found that olfactory discrimination was compromised in adult MIA offspring. Taken together, these findings show that MIA leads to defective adult neurogenesis in the SVZ-OB pathway, and the impairment of adult neurogenesis may lead to deficits in olfactory functions.

Amyloid β peptide-mediated neurotoxicity is attenuated by the proliferating microglia more potently than by the quiescent phenotype

Background

The specific role of microglia on Aβ-mediated neurotoxicity is difficult to assign in vivo due to their complicated environment in the brain. Therefore, most of the current microglia-related studies employed the isolated microglia. However, the previous in vitro studies have suggested either beneficial or destructive function in microglia. Therefore, to investigate the phenotypes of the isolated microglia which exert activity of neuroprotective or destructive is required.

Results

The present study investigates the phenotypes of isolated microglia on protecting neuron against Aβ-mediated neurotoxicity. Primary microglia were isolated from the mixed glia culture, and were further cultured to distinct phenotypes, designated as proliferating amoeboid microglia (PAM) and differentiated process-bearing microglia (DPM). Their inflammatory phenotypes, response to amyloid β (Aβ), and the beneficial or destructive effects on neurons were investigated. DPM may induce both direct neurotoxicity without exogenous stimulation and indirect neurotoxicity after Aβ activation. On the other hand, PAM attenuates Aβ-mediated neurotoxicity through Aβ phagocytosis and/or Aβ degradation.

Conclusions

Our results suggest that the proliferating microglia, but not the differentiated microglia, protect neurons against Aβ-mediated neurotoxicity. This discovery may be helpful on the therapeutic investigation of Alzheimer’s disease.

Cudrania cochinchinensis attenuates amyloid β protein-mediated microglial activation and promotes glia-related clearance of amyloid β protein

Background

Microglial inflammation may significantly contribute to the pathology of Alzheimer’s disease. To examine the potential of Cudrania cochinchinensis to ameliorate amyloid β protein (Aβ)-induced microglia activation, BV-2 microglial cell line, and the ramified microglia in the primary glial mixed cultured were employed.

Results

Lipopolysaccharide (LPS), Interferon-γ (IFN-γ), fibrillary Aβ (fAβ), or oligomeric Aβ (oAβ) were used to activate microglia. LPS and IFN-γ, but not Aβs, activated BV-2 cells to produce nitric oxide through an increase in inducible nitric oxide synthase (iNOS) expression without significant effects on cell viability of microglia. fAβ, but not oAβ, enhanced the IFN-γ-stimulated nitric oxide production and iNOS expression.

The ethanol/water extracts of Cudrania cochinchinensis (CC-EW) and the purified isolated components (i.e. CCA to CCF) effectively reduced the nitric oxide production and iNOS expression stimulated by IFN-γ combined with fAβ. On the other hand, oAβ effectively activated the ramified microglia in mixed glial culture by observing the morphological alteration of the microglia from ramified to amoeboid. CC-EW and CCB effectively prohibit the Aβ-mediated morphological change of microglia. Furthermore, CC-EW and CCB effectively decreased Aβ deposition and remained Aβ in the conditioned medium suggesting the effect of CC-EW and CCB on promoting Aβ clearance. Results are expressed as mean ± S.D. and were analyzed by ANOVA with post-hoc multiple comparisons with a Bonferroni test.

Conclusions

The components of Cudrania cochinchinensis including CC-EW and CCB are potential for novel therapeutic intervention for Alzheimer’s disease.

Cysteine-rich domain of scavenger receptor AI modulates the efficacy of surface targeting and mediates oligomeric Aβ internalization

Background

Insufficient clearance of soluble oligomeric amyloid-β peptide (oAβ) in the central nervous system leads to the synaptic and memory deficits in Alzheimer's disease (AD). Previously we have identified scavenger receptor class A (SR-A) of microglia mediates oligomeric amyloid-β peptide (oAβ) internalization by siRNA approach. SR-A is a member of cysteine-rich domain (SRCR) superfamily which contains proteins actively modulating the innate immunity and host defense, however the functions of the SRCR domain remain unclear. Whether the SRCR domain of SR-AI modulates the receptor surface targeting and ligand internalization was investigated by expressing truncated SR-A variants in COS-7 cells. Surface targeting of SR-A variants was examined by live immunostaining and surface biotinylation assays. Transfected COS-7 cells were incubated with fluorescent oAβ and acetylated LDL (AcLDL) to assess their ligand-internalization capabilities.

Result

Genetic ablation of SR-A attenuated the internalization of oAβ and AcLDL by microglia. Half of oAβ-containing endocytic vesicles was SR-A positive in both microglia and macrophages. Clathrin and dynamin in SR-AI-mediated oAβ internalization were involved. The SRCR domain of SR-AI is encoded by exons 10 and 11. SR-A variants with truncated exon 11 were intracellularly retained, whereas SR-A variants with further truncations into exon 10 were surface-targeted. The fusion of exon 11 to the surface-targeted SR-A variant lacking the SRCR domain resulted in the intracellular retention and the co-immunoprecipitation of Bip chaperon of the endoplasmic reticulum. Surface-targeted variants were N-glycosylated, whereas intracellularly-retained variants retained in high-mannose states. In addition to the collagenous domain, the SRCR domain is a functional binding domain for oAβ and AcLDL. Our data suggest that inefficient folding of SR-AI variants with truncated SRCR domain was recognized by the endoplasmic reticulum associated degradation which leads to the immature N- glycosylation and intracellular retention.

Conclusion

The novel functions of the SRCR domain on regulating the efficacy of receptor trafficking and ligand binding may lead to possible approaches on modulating the innate immunity in Alzheimer’s disease and atherosclerosis.

The Effects of Co-Treatment of 9-cis-Retinoic Acid and 15-Deoxy-Δ (12,14)-prostaglandin J2 on Microglial Activation

Microglial activation plays an important role in the regulation of neuronal function and contributes to the development of neurodegeneration in Alzheimer’s disease (AD). Activation of nuclear peroxisome proliferator-activated receptor gamma (PPARγ) by an endogenous agonist, 15-deoxy-Δ(12,14)-prostaglandin J2 (15d-PGJ2), has been shown to be beneficial in many diseases with aberrant immune responses. Here, we report that co-treatment with 15d-PGJ2 and its synergistic partner, 9-cis-retinoic acid (RA), may modulate, but not abolish, microglial immune response activated by β-amyloid (Aβ) and interferon gamma (IFNγ). The co-treatment of RA and 15d-PGJ2 inhibited Aβ/IFNγ-activated immune response in primary microglia, as evidenced by suppressed expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2); and the effect was not affected by treatment with a PPARγ antagonist, GW9662. Data suggest that PPARγ activation may not contribute to the anti-inflammatory properties of the co-treatment. The co-treatment promoted microglial Aβ clearance in cultures; and the effect can be prevented by blocking PPARγ activation using GW9662. The effects of the co-treatment on Aβ clearance may be PPARγ-dependent. Intriguingly, secretion of microglial pro-nerve growth factor (pro-NGF) was inhibited by Aβ/IFNγ treatment in a dose-dependent manner, suggesting that secretion of microglial pro-NGF may not contribute to the Aβ/IFNγ-activated microglial immune response. Taken together, the co-treatment may be beneficial for AD therapy; however, our data suggest that multiple mechanisms may underlie the beneficial effects of the co-treatment and are not limited to PPARγ activation only.

Enlargement of Abeta aggregates through chemokine-dependent microglial clustering

The number of microglia surrounding senile plaques is correlated with the size of plaques in Alzheimer's disease (AD). It is unclear whether more microglia are passively recruited toward larger senile plaques or, conversely, microglia recruited to senile plaques directly contribute to the growth of plaques. In this study, BV-2 microglia were used to delineate the role of microglia in the growth of plaques using time-lapse recording. Aggregated beta amyloid peptide (Abeta)-induced BV-2 microglia to form clusters. The recruitment of BV-2 microglia bearing membrane-adhered Abeta enlarged preexisting Abeta aggregates. The receptors involved in the microglial uptake of Abeta, including integrin, formyl peptide like receptor 1, and scavenger receptors, also mediated the microglial clustering. Neutralization antibodies against chemokines significantly attenuated Abeta-induced microglial clustering and the enlargement of Abeta aggregates. Our results reveal a novel role of microglia in directly increasing the size of Abeta aggregates and suggest the targeting of Abeta-mediated microglial chemotactic migration in developing therapeutic interventions for AD.

Multiple regulatory elements mediating neuronal-specific expression of zebrafish sodium channel gene, scn8aa

Zebrafish scn8aa sodium channels mediate the majority of sodium conductance, which is essential for the embryonic locomotor activities. Here, we investigated the transcriptional regulation of scn8aa in developing zebrafish embryos by constructing a GFP reporter driven by a 15-kb fragment of scn8aa gene designed as scn8aa:GFP. GFP expression patterns of scn8aa:GFP temporally and spatially recapitulated the expression of endogenous scn8aa mRNA during zebrafish embryonic development, with one exception in the inner nuclear layer of the retina. Three novel elements, along with an evolutionarily conserved element shared with mouse SCN8A, modulated neuronal-specific expression of scn8aa. The deletion of each positive element reduced the expression levels in neurons without inducing ectopic GFP expression in non-neuronal cells. Our results demonstrate that these four regulatory elements function cooperatively to enhance scn8aa expression in the zebrafish nervous system.

Inactivation of zebrafish mrf4 leads to myofibril misalignment and motor axon growth disorganization

Mrf4 is a basic helix-loop-helix (bHLH) transcription factor associated with myogenesis. Two mrf4 transcripts, mrf4_tv1 and mrf4_tv2, were identified in zebrafish generated by alternative splicing. To study their biological functions, we separately injected the Mrf4-morpholinos, including MO1 (mrf4_tv1:mrf4_tv2 knockdown), MO2+MO3 (mrf4_tv1:mrf4_tv2 knockdown), MO3 (mrf4_tv1 knockdown), and MO4 (mrf4_tv2 knockdown), into zebrafish embryos to observe mrf4 gene knockdown phenotypes. No phenotypic abnormalities were observed following injection with 0.5 ng of MO1 but those injected with 4.5, 9, or 13.5 ng displayed curved-body phenotypes, such as indistinct somite boundaries, and a lack of uniformly sized cell blocks. Similar results were also observed in the (MO2+MO3)-, MO3-, and MO4-injected groups. To further investigate the molecular mechanisms that lead to curved-body phenotypes, we stained embryos with alpha-bungrotoxin and specific monoclonal antibodies F59, Znp1, and Zn5 to detect morphological changes in acetyl-choline receptor (AChR) clusters, muscle fibers, common path of the primary neurons, and secondary neurons axonal projections, respectively. Our results show that the muscle fibers of mrf4_(tv1:tv2)-morphant aligned disorderly and lost their integrity and attachment, while the defects became milder in either mrf4_tv1-morphant or mrf4_tv2-morphant. On the other hand, reduced axonal projections and AChR clusters were found in both mrf4_tv2-morphant and mrf4_(tv1:tv2)-morphant but distributed normally in the mrf4_tv1-morphant. We conclude that Mrf4_tv2 is involved in alignment of muscle fibers, and Mrf4_tv1 might have cooperative function with Mrf4_tv2 in muscle fiber alignment, without affecting the muscle-nerve connection.

Movement disorder and neuromuscular change in zebrafish embryos after exposure to caffeine

Though caffeine is broadly distributed in many plants and foods, little is known about the teratogenic effects of caffeine during early embryonic development. Here, we used zebrafish as a model to test toxicity and teratogenicity since they have transparent eggs, making the organogenesis of zebrafish embryos easier to observe. When the exposure doses of caffeine were less than 150 ppm (17.5, 35, 50, 100 and 150 ppm), the zebrafish embryos exhibited no significant differences in survival rates after comparison with vehicle-control (0 ppm) group. As the exposure dosages increased, the survival rates decreased. No embryos survived after treatment with 300 ppm caffeine or higher dosages. The most evident change in embryos treated with caffeine was a shorter body length (vehicle-control: 3.26+/-0.01 mm, n=49; vs 150 ppm of caffeine: 2.67+/-0.03 mm, n=50). In addition, caffeine-treated embryos exhibited significantly reduced tactile sensitivity frequencies of touch-induced movement (vehicle-control: 9.93+/-0.77 vs 17.5-150 ppm caffeine: 5.37+/-0.52-0.10+/-0.06). Subtle changes are easily observed by staining with specific monoclonal antibodies F59, Znp1 and Zn5 to detect morphological changes in muscle fibers, primary motor axons and secondary motor axon projections, respectively. Our data show that the treatment of caffeine leads to misalignment of muscle fibers and motor neuron defects, especially secondary motor neuron axonal growth defects.

cAMP/PKA regulates osteogenesis, adipogenesis and ratio of RANKL/OPG mRNA expression in mesenchymal stem cells by suppressing leptin

Background

Mesenchymal stem cells (MSCs) are a pluripotent cell type that can differentiate into adipocytes, osteoblasts and other cells. The reciprocal relationship between adipogenesis and osteogenesis was previously demonstrated; however, the mechanisms remain largely unknown.

Methods and Findings

We report that activation of PKA by 3-isobutyl-1 methyl xanthine (IBMX) and forskolin enhances adipogenesis, the gene expression of PPARγ2 and LPL, and downregulates the gene expression of Runx2 and osteopontin, markers of osteogenesis. PKA activation also decreases the ratio of Receptor Activator of the NF-κB Ligand to Osteoprotegerin (RANKL/OPG) gene expression – the key factors of osteoclastogenesis. All these effects are mediated by the cAMP/PKA/CREB pathway by suppressing leptin, and may contribute to PKA stimulators-induced in vivo bone loss in developing zebrafish.

Conclusions

Using MSCs, the center of a newly proposed bone metabolic unit, we identified cAMP/PKA signaling, one of the many signaling pathways that regulate bone homeostasis via controlling cyto-differentiation of MSCs and altering RANKL/OPG gene expression.

Treatment with sodium benzoate leads to malformation of zebrafish larvae

Sodium benzoate (SB) is a commonly used food preservative and anti-microbial agent in many foods from soup to cereals. However, little is known about the SB-induced toxicity and teratogenicity during early embryonic development. Here, we used zebrafish as a model to test the toxicity and teratogenicity because of their transparent eggs; therefore, the organogenesis of zebrafish embryos is easy to observe. After low dosages of SB (1-1000 ppm) treatment, the zebrafish embryos exhibited a 100% survival rate. As the exposure dosages increased, the survival rates decreased. No embryos survived after treatment with 2000 ppm SB. The 50% lethal dose (LD(50)) of zebrafish is found to be in the range of 1400-1500 ppm. Gut abnormalities, malformation of pronephros, defective hatching gland and edema in pericardial sac were observed after treatment with SB. Compared to untreated littermates (vehicle-treated control), SB-treated embryos exhibited significantly reduced tactile sensitivity frequencies of touch-induced movement (vehicle-treated control: 27.60+/-1.98 v.s. 1000 ppm SB: 7.89+/-5.28; N=30). Subtle changes are easily observed by staining with specific monoclonal antibodies F59, Znp1 and alpha6F to detect morphology changes in muscle fibers, motor axons and pronephros, respectively. Our data showed that the treatment of SB led to misalignment of muscle fibers, motor neuron innervations, excess acetyl-choline receptor cluster and defective pronephric tubes. On the basis of these observations, we suggest that sodium benzoate is able to induce neurotoxicity and nephrotoxicity of zebrafish larvae.

Knockdown of zebrafish Nav1.6 sodium channel impairs embryonic locomotor activities

Although multiple subtypes of sodium channels are expressed in most neurons, the specific contributions of the individual sodium channels remain to be studied. The role of zebrafish Na(v)1.6 sodium channels in the embryonic locomotor movements has been investigated by the antisense morpholino (MO) knockdown. MO1 and MO2 are targeted at the regions surrounding the translation start site of zebrafish Na(v)1.6 mRNA. MO3 is targeted at the RNA splicing donor site of exon 2. The correctly spliced Na(v)1.6 mRNA of MO3 morphants is 6% relative to that of the wild-type embryos. Na(v)1.6-targeted MO1, MO2 and MO3 attenuate the spontaneous contraction, tactile sensitivity, and swimming in comparison with a scrambled morpholino and mutated MO3 morpholino. No significant defect is observed in the development of slow muscles, the axonal projection of primary motoneurons, and neuromuscular junctions. The movement impairments caused by MO1, MO2, and MO3 suggest that the function of Na(v)1.6 sodium channels is essential on the normal early embryonic locomotor activities.

Structural and biochemical characterization of inhibitor-1α

Inhibitor-1alpha is one of the isoforms of human protein phosphatase inhibitor-1. It is a product of alternative splicing of inhibitor-1 gene and lacks 51 internal amino acids from residue 84 to 134 of inhibitor-1. Here we have characterized the structural and biochemical properties of inhibitor-1alpha. Structural analysis of recombinant inhibitor-1alpha by NMR spectroscopy revealed that inhibitor-1alpha adopts a predominantly random coil conformation. Excluding the region from residue 84 to 134 of inhibitor-1, the structural features of inhibitor-1 and inhibitor-1alpha are almost the same as each other. The IC(50) value of inhibitor-1alpha in inhibition of Protein phosphatase-1 (PP1) is comparable to that of inhibitor-1, indicating that inhibitor-1alpha is a potent inhibitor of PP1 when Thr-35 is phosphorylated by PKA. For phosphorylation by PKA and dephosphorylation by protein phosphatase-1, -2A, and -2B, the measured kinetic parameters of inhibitor-1alpha are very close to those of inhibitor-1. Taken together, these results suggest that inhibitor-1alpha preserves the structure of inhibitor-1, the PP1 inhibitory activity and the functional specificities toward phosphorylation by PKA and dephosphorylation by protein phosphatase-1, -2A, and -2B.

Structural variation in human apolipoprotein E3 and E4: secondary structure, tertiary structure, and size distribution

Human apolipoprotein E (apoE) is a 299-amino-acid protein with a molecular weight of 34 kDa. The difference between the apoE3 and apoE4 isoforms is a single residue substitution involving a Cys-Arg replacement at residue 112. ApoE4 is positively associated with atherosclerosis and late-onset and sporadic Alzheimer's disease (AD). ApoE4 and its C-terminal truncated fragments have been found in the senile plaques and neurofibrillary tangles in the brain of AD patients. However, detail structural information regarding isoform and domain interaction remains poorly understood. We prepared full-length, N-, and C-terminal truncated apoE3 and apoE4 proteins and studied their structural variation. Sedimentation velocity and continuous size distribution analysis using analytical ultracentrifugation revealed apoE3(72-299) as consisting of a major species with a sedimentation coefficient of 5.9. ApoE4(72-299) showed a wider and more complicated species distribution. Both apoE3 and E4 N-terminal domain (1-191) existed with monomers as the major component together with some tetramer. The oligomerization and aggregation of apoE protein increased when the C-terminal domain (192-271) was incorporated. The structural influence of the C-terminal domain on apoE is to assist self-association with no significant isoform preference. Circular dichroism and fluorescence studies demonstrated that apoE4(72-299) possessed a more alpha-helical structure with more hydrophobic residue exposure. The structural variation of the N-terminal truncated apoE3 and apoE4 protein provides useful information that helps to explain the greater aggregation of the apoE4 isoform and thus has implication for the involvement of apoE4 in AD.

Increased expression of manganese-superoxide dismutase in fibroblasts of patients with CPEO syndrome

Alterations in the expression of free radical scavenging enzymes and production of reactive oxygen species (ROS) in tissue cells may contribute to the pathogenesis of mitochondrial diseases such as chronic progressive external ophthalmoplegia (CPEO) syndrome. Since the mitochondria with impaired respiratory function in affected tissues generate more ROS via electron leakage, we examined the expression levels of free radical scavenging enzymes in primary culture of muscle fibroblasts of eight patients with CPEO syndrome. The results showed that the enzyme activity and protein levels of Mn-SOD of the fibroblasts from CPEO patients were significantly increased but those of Cu,Zn-SOD, catalase and glutathione peroxidase (GPx) were not increased compared with controls. A similar pattern was observed in the mRNA levels of Mn-SOD and GPx in muscle fibroblasts of all CPEO patients. The activity ratios of Mn-SOD/catalase and Mn-SOD/GPx in muscle fibroblasts of the CPEO patients were increased 1.7-3.4 and 1.8- to 5.3-fold, respectively, compared to those of the controls. Moreover, by using flow cytometry we found that the production of O2(*-) and H2O2 in the fibroblasts was about 2 times higher than those of controls. The 8-OHdG/dG ratios in total DNA of muscle biopsies from three CPEO patients were much higher than those of age-matched controls as determined by high performance liquid chromatography (HPLC). In the light of these findings, we suggest that the increase in expression of Mn-SOD, ROS production and oxidative damage in affected tissues may play an important role in the pathogenesis and progression of the CPEO syndrome.

Distinct mechanisms account for beta-amyloid toxicity in PC12 and differentiated PC12 neuronal cells

Whether reactive oxygen species (ROS) mediate beta-amyloid (A beta) neurotoxicity remains controversial. Naive PC12 cells (PC12) and nerve growth factor-differentiated PC12 cells (dPC12) were used to study the role of ROS in cell death induced by A beta(25-35). The viability of PC12 and dPC12 cells decreased by 30-40% after a 48-hour exposure to 20 microM A beta(25-35). Microscopic examination showed that A beta(25-35) induced necrosis in PC12 cells and apoptosis in dPC12 cells. Vitamin E (100 microM) and other antioxidants protected PC12 cells, but not dPC12 cells, against the cytotoxic effect of A beta(25-35). Since H(2)O(2) has been proposed to be involved in A beta toxicity, the effects of H(2)O(2) on PC12 and dPC12 cells were studied. Differentiated PC12 cells appeared to be significantly more resistant to H(2)O(2) than naive PC12 cells. These data suggest that ROS may mediate A beta(25-35) toxicity in PC12 cells but not in dPC12 cells. Because the intracellular levels of ROS were elevated during the differentiation of PC12 cells, the baseline levels of ROS in these two model cell types may determine the intracellular mediators for A beta(25-35) toxicity. Therefore, the protective effects of antioxidants against A beta may depend upon the redox state of the cells.

Identification of the alternative splice products encoded by the human protein phosphatase inhibitor-1 gene

We have isolated three major cDNA fragments of protein phosphatase inhibitor-1 from human brain and liver by RT-PCR. The 536 bp fragment encoded the wild-type of inhibitor-1 while two other fragments were alternative splice products of the inhibitor-1 gene, which was confirmed by partial genomic DNA sequencing. The 380 bp fragment encoded an in-frame 51-residue-deleted inhibitor-1, named inhibitor-1alpha, and the deletion occurred from residue 84 to 134 of inhibitor-1. The 316 bp fragment termed inhibitor-1beta was derived from an internal deletion of 536 bp fragment. This deletion resulted in an out of frame shift, allowing the 316 bp fragment that encoded the partial sequence of inhibitor-1. Based on the reported mRNA sequence of inhibitor-1 and evidence from our RT-PCR, we suggested that inhibitor-1beta consisted of 132 amino acids of which the N-terminal 61 amino acid sequences were identical to inhibitor-1 while the sequence after residue-61 was markedly different.

Primary structure and developmental expression of zebrafish sodium channel Na(v)1.6 during neurogenesis

A zebrafish sodium channel cDNA encoding a 1949-amino acid polypeptide, Na(v)1.6, was isolated. Two transcripts were detected in zebrafish adult brain but not in cardiac or skeletal muscle. The RNase protection analysis confirmed the neural specificity of zebrafish Na(v)1.6 24 hours postfertilization (hpf) Na(v)1.6 was expressed in the trigeminal ganglion, anterior and posterior lateral line ganglia, rhombomeres, and Rohon-Beard neurons. This preferential localization suggests that Na(v)1.6 plays an important role in tactile sensitivity. The abundance of zebrafish Na(v) 1.6 mRNA in the central and peripheral nervous systems increased markedly between 48 and 72 hpf, during the maturation of the nervous system.

Expression of zebrafish Hoxa1a in neuronal cells of the midbrain and anterior hindbrain

The expression pattern of zebrafish hoxa1a mRNA during embryonic development was studied. Herein, we show that hoxa1a mRNA is expressed in the ventral region of both the midbrain and anterior hindbrain during the developmental period from the pharyngula to the protruding-mouth stages via whole-mount in situ hybridization. Furthermore, double-labeling with anti-zHu antibody confirms that the zebrafish hoxa1a gene is expressed in neuronal cells. The observed temporal and spatial distributions of zebrafish hoxa1a mRNA differ greatly from the expression patterns of zebrafish hoxb1a and hoxb1b paralagous genes. In addition, in embryos injected with mouse ihh mRNA, hoxa1a-expressing cells increase in number with a dorsalized expression pattern in the midbrain.

Age-associated changes of superoxide dismutase and catalase activities in the rat brain

Oxygen free radicals have been proposed to be involved in the process of aging. Superoxide dismutase (SOD) and catalase are important for antioxidative defense. In this study, profiles of SOD, catalase, and their mRNA levels were investigated in the frontal, parietal, temporal and occipital lobes, subcortex and cerebellum of male Wistar rats at ages 1-21 months. The total SOD and Mn SOD activities increased with age and exhibited higher levels at 6 and 12 months but decreased thereafter. Activity of catalase showed a similar trend and notably peaked at 12 months. The mRNA levels of Cu/Zn SOD, Mn SOD, and catalase remained constant in all areas tested (frontal, parietal, temporal and occipital lobes, and subcortex) except the cerebellum. Post-transcriptional regulation was involved in modulating the enzymes' activities during aging. Furthermore, the rate of mitochondrial generation of the superoxide anion (O(2)(-).) increased gradually with aging. Taken together, the results suggest that the increase of oxidative potential and the loss of proper antioxidant defense in the rats appear to be highly involved in the aging process of the brain.

ATP-stimulated c-fos and zif268 mRNA expression is inhibited by chemical hypoxia in a rat brain-derived type 2 astrocyte cell line, RBA-2

The stimulus-transcriptional coupling during ischemia/hypoxia was examined for ATP-stimulated expression of immediate early genes (IEGs; c-fos, zif268, c-myc and nur77) in a rat brain-derived type 2 astrocyte cell line, RBA-2. Incubation of cells with 1 mM of extracellular ATP stimulated time-dependent expression of c-fos and zif268. ATP induced the largest increases in zif268 mRNA and a lesser one in c-fos mRNA. ATP also induced a slight increase in nur77 mRNA but was ineffective in inducing c-myc expression in these cells. Brief exposure of cells to potassium cyanide to simulate chemical hypoxia induced 9-fold and 7-fold transient increases in c-fos and zif268 expression, respectively, but did not affect c-myc or nur77 expression. When cyanide and ATP were added together, the expression of c-fos and zif268 expression was inhibited, and the effect was mimicked by simulating chemical hypoxia with sodium azide. To elucidate the mechanism involved, the effect of cyanide on ATP-stimulated increases in intracellular Ca(2+) concentrations, [Ca(2+)](i), and phospholipase D (PLD) activities were measured. Cyanide induced an increase in [Ca(2&plus);](i) and further enhanced the ATP-stimulated increases in [Ca(2+)](i) and PLD activities. Nevertheless, metabolic inhibitor, iodoacetate, blocked the ATP-induced c-fos and partially inhibited zif268 expression, and deprivation of cells with glucose also inhibited the ATP-induced c-fos expression. Taken together, these results demonstrate that both extracellular ATP and chemical hypoxia induce c-fos and zif268 expression in RBA-2 type 2 astrocytes. The chemical hypoxia inhibited ATP-stimulated c-fos and zif268 expression is not due to alterations in Ca(2+) and PLD signaling, and is at least partially related to metabolic disturbance in these cells.

Oxidative stress is insignificant in N1S1-transplanted hepatoma despite markedly declined activities of the antioxidant enzymes

It has been proposed that persistent oxidative stress accounts for the increased levels of DNA damage in cancer tissues. We have examined the profile of anti-oxidant enzymes in a transplanted hepatic tumor model by injecting N1S1 rat hepatoma cells into the liver of Sprague-Dawley rats. The transplanted N1S1 tumors displayed characteristics resembling human hepatocellular carcinoma. The immunoreactivities of catalase (CAT), manganese-superoxide dismutase (Mn SOD), copper/zinc-SOD (Cu/Zn SOD), and glutathione peroxidase (GPx) were found to decrease significantly. The enzyme activity in tumors decreased 26.2-, 4.2-, 4.5-, and 5.4-fold for CAT, Mn SOD, Cu/Zn SOD, and GPx, respectively, relative to those in normal liver tissue from the same animals. In contrast, the mRNA levels of CAT and GPx in tumors decreased only 5- and 2-fold, respectively, and the mRNA levels of Cu/Zn SOD and Mn SOD showed either no change or an increase as compared to those of normal liver tissue. The contents of 8-hydroxy-2'-deoxyguanosine (8-OH-dG) and thiobarbituric acid-reactive substances (TBARS) were comparable to those of normal controls. Furthermore, mitochondrial production of superoxide in tumors was 4 times lower than that in normal tissues. In conclusion, the data indicate that the reduced activities of anti-oxidant enzymes in the N1S1 tumor did not cause significant oxidative stress.

Characterization of the inhibition of protein phosphatase-1 by DARPP-32 and inhibitor-2

Phospho-DARPP-32 (where DARPP-32 is dopamine- and cAMP-regulated phosphoprotein, Mr 32,000), its homolog, phospho-inhibitor-1, and inhibitor-2 are potent inhibitors (IC50 approximately 1 nM) of the catalytic subunit of protein phosphatase-1 (PP1). Our previous studies have indicated that a region encompassing residues 6-11 (RKKIQF) and phospho-Thr-34, of phospho-DARPP-32, interacts with PP1. However, little is known about specific regions of inhibitor-2 that interact with PP1. We have now characterized in detail the interaction of phospho-DARPP-32 and inhibitor-2 with PP1. Mutagenesis studies indicate that within DARPP-32 Phe-11 and Ile-9 play critical roles, with Lys-7 playing a lesser role in inhibition of PP1. Pro-33 and Pro-35 are also important, as is the number of amino acids between residues 7 and 11 and phospho-Thr-34. For inhibitor-2, deletion of amino acids 1-8 (I2-(9-204)) or 100-204 (I2-(1-99)) had little effect on the ability of the mutant proteins to inhibit PP1. Further deletion of residues 9-13 (I2-(14-204)) resulted in a large decrease in inhibitory potency (IC50 approximately 800 nM), whereas further COOH-terminal deletion (I2-(1-84)) caused a moderate decrease in inhibitory potency (IC50 approximately 10 nM). Within residues 9-13 (PIKGI), mutagenesis indicated that Ile-10, Lys-11, and Ile-13 play critical roles. The peptide I2-(6-20) antagonized the inhibition of PP-1 by inhibitor-2 but had no effect on inhibition by phospho-DARPP-32. In contrast, the peptide D32-(6-38) antagonized the inhibition of PP1 by phospho-DARPP-32, inhibitor-2, and I2-(1-120) but not I2-(85-204). These results indicate that distinct amino acid motifs contained within the NH2 termini of phospho-DARPP-32 (KKIQF, where italics indicate important residues) and inhibitor-2 (IKGI) are critical for inhibition of PP1. Moreover, residues 14-84 of inhibitor-2 and residues 6-38 of phospho-DARPP-32 share elements that are important for interaction with PP1.

Heatstroke induces c-fos expression in the rat hypothalamus

We induced heat stress in urethane-anesthetized rats (the animals were exposed to an ambient temperature at 42 degrees C), and monitored their colon temperature, mean arterial pressure and local cerebral blood flow. Rats 0, 20, 40 or 80 min after heat stress were sacrificed for determination of c-fos mRNA and protein expression in the paraventricular nucleus (PVN), supraoptic nucleus (SON) and preoptic nucleus (PON). The heatstroke, which appears as profound decreases in both mean arterial pressure and local cerebral blood flow and increases in colon temperature, is produced 80 min after heat stress. We show the c-fos mRNA and protein is strongly induced in all these nuclei of rat hypothalamus after the onset of heatstroke. We conclude that c-fos expression in the hypothalamus during rat heatstroke is associated with hyperthermia, arterial hypotension and cerebral ischemia.

Heat shock protein expression protects against death following exposure to heatstroke in rats

Rats 0, 16, or 48 h after heat shock (42 degrees C core temperature for 15 min) or chemical stress (5 mg/kg sodium arsenite, i.p.) were exposed to a high ambient temperature (43 degrees C) to induce heatstroke onset. The moment in which the mean arterial pressure and cerebral blood flow began to decrease from their peak values was taken as the onset of heatstroke. Prior heat shock or chemical stress conferred significant protection against heatstroke-induced arterial hypotension, cerebral ischemia, cerebral neuronal damage and death, and correlated with expression of HSP72 in brain, heart, liver and kidney at 16 h. However, at 48 h, when HSP72 expression returned to basal values, the above responses that occurred after the onset of heatstroke of two groups (0 h group VS 48 h group) were indistinguishable. The data suggest that HSP72 presence increases survival in rat heatstroke by attenuating arterial hypotension, cerebral ischemia and neuronal damage.

The E protein CTF4 and acetylcholine receptor expression in development and denervation supersensitivity

Motor activity blocks the extrasynaptic expression of many genes in skeletal muscle, including those encoding ion channels, receptors, and adhesion molecules. Denervation reinduces transcription throughout the multinucleated myofiber, restoring the developmental pattern of expression, especially of the genes coding for the acetylcholine receptor. A screen for trans-acting factors binding to the enhancer region of the alpha-subunit gene of the acetylcholine receptor identified CTF4, a ubiquitously expressed and alternatively spliced chicken homologue of the human E protein transcription factor HTF4/HEB. Expression of the CTF4 locus closely parallels that of myogenin and acetylcholine receptor during development and maturation of skeletal muscle, but transcription is not similarly regulated by neuronal cues. Alternative splicing within the region encoding the transactivation domain generates two CTF4 isoforms with different tissue distributions, but similar binding affinities for the acetylcholine receptor alpha-subunit enhancer and similar transcriptional potential when complexed to myogenin. Direct injection of a myogenin, but not a MyoD, antisense expression vector into denervated skeletal muscle caused a significant decrease in the transcriptional activation of a depolarization-sensitive reporter gene. Similarly, injection of a CTF4, but less so of an E12, antisense expression vector impaired the denervation response, further implicating the involvement of a myogenin/CTF4 heterodimer in the expression of AChR genes in vivo.

Changes in extracellular serotonin in rat hypothalamus affect thermoregulatory function

Experiments were carried out to determine the effects of altering the serotonin (5-HT) levels in the hypothalamus on thermoregulatory function in unanesthetized restrained rats. Local perfusion of the hypothalamus with dialysis solution containing 5-hydroxytryptophan (a 5-HT precursor), fluoxetine (a 5-HT reuptake inhibitor), or high potassium significantly increased both colonic temperature (Tco) and the extracellular concentrations of 5-HT in the hypothalamus. Reciprocally, both extracellular concentration of 5-HT in the hypothalamus and Tco were decreased with a dialysis solution containing tetrodotoxin (which blocks the voltage-dependent sodium channel), zero calcium concentration, or systemic administration of 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT,5-HT1A agonist). Intrahypothalamic administration of 8-OH-DPAT and (2,5-dimethoxy-4-iodophenyl)-2-aminopropane (a 5-HT2 agonist) produced hypothermic and hyperthermic effects, respectively. The results indicate that elevating the 5-HT levels in the hypothalamus activates postsynaptic 5-HT2 receptors and results in hyperthermic effects, whereas stimulation of presynaptic 5-HT1A receptors in the hypothalamus reduces the endogenous 5-HT release and results in hypothermic effects.

Up-regulation of beta-actin, cyclophilin and GAPDH in N1S1 rat hepatoma

Beta-actin, cyclophilin and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) are all constantly expressed proteins that regulate cellular structures and endogenous cytoarchitectural functions. In this study, we used an in vivo N1S1 rat hepatoma model to examine changes in the expression levels of these housekeeping genes in normal and tumor liver samples. The beta-actin, cyclophilin and GAPDH genes were all up-regulated in tumor groups as compared to the controls. Our results suggest that up-regulation of beta-actin, cyclophilin and GAPDH genes may be essential for oncogenesis in hepatoma.

Silencing the type II sodium channel gene: a model for neural-specific gene regulation

Neural-specific expression of a sodium channel mini-gene has been shown to be mediated by a 28 bp silencer element, RE1, located in the 5' flanking region of the gene. This element is active exclusively in cell lines that do not express the endogenous brain type II sodium channel gene, including fibroblast, skeletal muscle, and certain neuronal cell lines. All of these non-type II expressing cells contain RE1-binding complexes. On the basis of mutational analysis and in vivo "repressor trap" experiments, we propose that cell-specific RE1-binding proteins are responsible, at least in part, for restricting expression of the type II sodium channel gene to specific neurons in the vertebrate nervous system.

Analysis of binding and activating functions of the chick muscle acetylcholine receptor gamma-subunit upstream sequence

1. The skeletal muscle acetylcholine receptor comprises several subunits whose coordinated expression during myogenesis is probably controlled by cis elements in the individual subunit genes. We have previously analyzed promoter regions of the alpha and delta genes (Wang et al., 1988, 1990); to gain further insight into receptor regulation, we have now studied the promoter of the chick muscle gamma-subunit gene. 2. This analysis was faciliated by the close upstream proximity of the coding region of the delta-subunit gene and the consequent brevity (740 bp) of the untranslated linker connecting the two genes (Nef et al., 1984). Nuclease protection and primer extension analysis revealed that transcription of the gamma-subunit gene starts at position 56 upstream of the translational initiation site. 3. Nested deletions of the promoter region were employed to identify functionally important elements. A 360-bp sequence (-324 to +36) was found to activate transcription, in a position- and orientation-independent manner, during myotube formation. This sequence comprises 5 M-CAT (Nikovits et al., 1986) similarities and contains, at positions -52/-47 and -33/-28, two CANNTG (Lassar et al., 1989) motifs. 4. Binding experiments were performed by means of gel retardation, gel shift competition, and footprint analysis. The CANNTG motifs were found to bind MyoD and myogenin fusion proteins and to interact with proteins in nuclear extracts from cultured myotubes. 5. Point mutations in the CANNTG motifs revealed that these elements are crucial for full promoter activity in myotubes and essential in fibroblasts cotransfected with a myogenin expression vector. 6. We conclude that the activity of the gamma-subunit gene is determined largely by E boxes, which in vivo are likely to be activated by MyoD family proteins; in addition, other transactivators such as the M-CAT binding protein presumably play a role. Both CANNTG elements and M-CAT motifs are also present in the alpha- and delta-subunit enhancer and may therefore account for the coordinate expression of the three subunits during muscle differentiation.

Protein synthesis is required for the denervation-triggered activation of acetylcholine receptor genes

The effect of cycloheximide (CHX) on denervation-induced acetylcholine receptor (AChR) expression was investigated in chickens one day after nerve section, using probe excess solution hybridization to quantitate AChR alpha-subunit gene transcript levels and run-on analysis to measure subunit gene activity. The increase in alpha-subunit transcripts that normally follows denervation was prevented when drug treatment was commenced 2 h before or after denervation but was not blocked when CHX administration was begun 6 h after the operation. Drug-induced reduction of transcript levels results from decreased activity of genes coding for the alpha-, delta-, and gamma-subunits; in contrast, the transcription rates of several non-receptor genes are not affected by CHX. The results suggest that the de novo synthesis of a transcriptional activator is required as a mediating event in the signalling pathway linking the plasma membrane and AChR gene expression.

Expression of the acetylcholine receptor delta-subunit gene in differentiating chick muscle cells is activated by an element that contains two 16 bp copies of a segment of the alpha-subunit enhancer

The acetylcholine receptor is a multimeric membrane protein whose expression is activated during muscle differentiation and upon denervation of adult muscle. To gain insight into the coordinate expression of receptor subunits during myogenesis we have analyzed the chick muscle receptor delta-subunit gene upstream region. The delta-subunit gene lacks canonical promoter elements (CCAAT and TATA boxes). Nuclease protection and primer extension analysis revealed that transcription starts at six major and several minor sites between -110 and -30 upstream of the translational initiation site; two sites, at positions -77 and -66, give rise to approximately 50% of all transcripts. Using nested deletions of the proximal 960 bp of the 5' flanking region of this gene we have identified a 62 bp sequence (-207 to -146) that activates transcription in a position independent manner. This enhancer-like element is activated during myotube formation; it contains two distinct functional moieties, each resembling the same 16 bp portion of the stage and tissue specific alpha-subunit gene enhancer which we have characterized previously [Wang et al. (1988) Neuron, 1, 527-534]. This common element, which also comprises several previously proposed skeletal muscle specific motifs [Buskin, J. N. and Hauschka, S. D. (1989) Mol. Cell Biol., 9, 2627-2640; Mar, J. H. and Ordahl, C. P. (1988) Proc. Natl. Acad. Sci. USA, 85, 6404-6408], may account for the coordinate expression of the two subunits. The cell specificity of the delta-subunit gene 5' flanking region is partly due to the enhancer, partly to an inhibitory element upstream of -207.

Skeletal muscle denervation activates acetylcholine receptor genes

Transcriptional activity of acetylcholine receptor subunit genes was investigated in innervated and denervated chick skeletal muscle. The sciatic nerve of 3-d-old White Leghorn chicks was sectioned unilaterally; after various intervals, nuclei were isolated from operated and sham-operated animals, and run-on assays performed. Nuclei were incubated with 32P-UTP, and total RNA was extracted and hybridized onto filters containing an excess of subunit-specific DNA. Specific transcripts were detected by autoradiography and quantitated densitometrically. A sharp increase in transcriptional activity was observed to begin approximately 1/2 d after the operation and peak 1 d later when transcriptional rates reached approximately seven-, six-, and fivefold control levels for the alpha-, delta-, and gamma-subunit genes, respectively. The specificity of the effect was ascertained by normalization to total RNA synthesis and by the demonstration that several nonreceptor genes respond differently to denervation. These results suggest that a denervation signal reaches the genome to induce receptor expression. In addition, since the increase in mRNA levels significantly exceeds what can be accounted for by increased gene activity, posttranscriptional effects are suggested.