Characteristic changes of cerebellar proteins associated with cerebellar hypoplasia in jaundiced Gunn rats and the prevention of these by phototherapy

Multilevel proteomics reveals host perturbations by SARS-CoV-2 and SARS-CoV

The emergence and global spread of SARS-CoV-2 has resulted in the urgent need for an in-depth understanding of molecular functions of viral proteins and their interactions with the host proteome. Several individual omics studies have extended our knowledge of COVID-19 pathophysiology^1-10. Integration of such datasets to obtain a holistic view of virus-host interactions and to define the pathogenic properties of SARS-CoV-2 is limited by the heterogeneity of the experimental systems. Here we report a concurrent multi-omics study of SARS-CoV-2 and SARS-CoV. Using state-of-the-art proteomics, we profiled the interactomes of both viruses, as well as their influence on the transcriptome, proteome, ubiquitinome and phosphoproteome of a lung-derived human cell line. Projecting these data onto the global network of cellular interactions revealed crosstalk between the perturbations taking place upon infection with SARS-CoV-2 and SARS-CoV at different levels and enabled identification of distinct and common molecular mechanisms of these closely related coronaviruses. The TGF-β pathway, known for its involvement in tissue fibrosis, was specifically dysregulated by SARS-CoV-2 ORF8 and autophagy was specifically dysregulated by SARS-CoV-2 ORF3. The extensive dataset (available at https://covinet.innatelab.org ) highlights many hotspots that could be targeted by existing drugs and may be used to guide rational design of virus- and host-directed therapies, which we exemplify by identifying inhibitors of kinases and matrix metalloproteases with potent antiviral effects against SARS-CoV-2.

Biology of Bilirubin Photoisomers

Phototherapy is the main treatment for neonatal hyperbilirubinemia. In acute treatment of extreme hyperbilirubinemia, intensive phototherapy may have a role in 'detoxifying' the bilirubin molecule to more polar photoisomers, which should be less prone to crossing the blood-brain barrier, providing a 'brain-sparing' effect. This article reviews the biology of bilirubin isomers. Although there is evidence supporting the lower toxicity of bilirubin photoisomers, there are studies showing the opposite. There are methodologic weaknesses in most studies and better-designed experiments are needed. In an infant acutely threatened by bilirubin-induced brain damage, intensified phototherapy should be used expediently and aggressively.

Impairment of enzymatic antioxidant defenses is associated with bilirubin-induced neuronal cell death in the cerebellum of Ugt1 KO mice

Severe hyperbilirubinemia is toxic during central nervous system development. Prolonged and uncontrolled high levels of unconjugated bilirubin lead to bilirubin-induced encephalopathy and eventually death by kernicterus. Despite extensive studies, the molecular and cellular mechanisms of bilirubin toxicity are still poorly defined. To fill this gap, we investigated the molecular processes underlying neuronal injury in a mouse model of severe neonatal jaundice, which develops hyperbilirubinemia as a consequence of a null mutation in the Ugt1 gene. These mutant mice show cerebellar abnormalities and hypoplasia, neuronal cell death and die shortly after birth because of bilirubin neurotoxicity. To identify protein changes associated with bilirubin-induced cell death, we performed proteomic analysis of cerebella from Ugt1 mutant and wild-type mice. Proteomic data pointed-out to oxidoreductase activities or antioxidant processes as important intracellular mechanisms altered during bilirubin-induced neurotoxicity. In particular, they revealed that down-representation of DJ-1, superoxide dismutase, peroxiredoxins 2 and 6 was associated with hyperbilirubinemia in the cerebellum of mutant mice. Interestingly, the reduction in protein levels seems to result from post-translational mechanisms because we did not detect significant quantitative differences in the corresponding mRNAs. We also observed an increase in neuro-specific enolase 2 both in the cerebellum and in the serum of mutant mice, supporting its potential use as a biomarker of bilirubin-induced neurological damage. In conclusion, our data show that different protective mechanisms fail to contrast oxidative burst in bilirubin-affected brain regions, ultimately leading to neurodegeneration.

Taurine protects against bilirubin-induced hyperexcitation in rat anteroventral cochlear nucleus neurons

No effective medication for hyperbilirubinemia yet exists. Taurine is believed to exert a neuroprotective action. The aim of the present study was to determine whether taurine protected neurons of the rat anteroventral cochlear nucleus (AVCN) against bilirubin-induced neuronal hyperexcitation. AVCN neurons were isolated from 13 to 15-day-old Sprague-Dawley rats. The effects of bilirubin on the spontaneous excitatory postsynaptic currents (sEPSCs) and action potential currents were compared with those exerted by bilirubin and taurine together. Bilirubin dramatically increased the frequencies of sEPSCs and action potential currents, but not sEPSC amplitude. Taurine suppressed the enhanced frequency of action potentials induced by bilirubin, in a dose-dependent manner. In addition, taurine decreased the amplitude of voltage-dependent calcium channel currents that were enhanced upon addition of bilirubin. We explored the mechanism of the protective effects exerted by taurine using GABAA and glycine receptor antagonists, bicuculline and strychnine, respectively. Addition of bicuculline and strychnine eliminated the protective effects of taurine. Neither bilirubin nor taurine affected the sensitivity of the glutamate receptor. Our findings thus indicate that taurine protected AVCN neurons against bilirubin-induced neuronal hyperexcitation by activating the GABAA and glycine receptors and inhibiting calcium flow through voltage-gated channels. Thus, taurine may be effective in treatment of neonatal hyperbilirubinemia.

A transcriptome analysis identifies molecular effectors of unconjugated bilirubin in human neuroblastoma SH-SY5Y cells

BACKGROUND

The deposition of unconjugated bilirubin (UCB) in selected regions of the brain results in irreversible neuronal damage, or Bilirubin Encephalopathy (BE). Although UCB impairs a large number of cellular functions in other tissues, the basic mechanisms of neurotoxicity have not yet been fully clarified. While cells can accumulate UCB by passive diffusion, cell protection may involve multiple mechanisms including the extrusion of the pigment as well as pro-survival homeostatic responses that are still unknown.

RESULTS

Transcriptome changes induced by UCB exposure in SH-SY5Y neuroblastoma cell line were examined by high density oligonucleotide microarrays. Two-hundred and thirty genes were induced after 24 hours. A Gene Ontology (GO) analysis showed that at least 50 genes were directly involved in the endoplasmic reticulum (ER) stress response. Validation of selected ER stress genes is shown by quantitative RT-PCR. Analysis of XBP1 splicing and DDIT3/CHOP subcellular localization is presented.

CONCLUSION

These results show for the first time that UCB exposure induces ER stress response as major intracellular homeostasis in surviving neuroblastoma cells in vitro.

Hyperbilirubinemia-related behavioral and neuropathological changes in rats: a possible schizophrenia animal model

BACKGROUND

Patients with schizophrenia show a significantly higher frequency of hyperbilirubinemia than patients suffering from other psychiatric disorders and the general healthy population. We examined the hyperbilirubinemia on behavioral and neuropathological changes in rats as a possible animal model of schizophrenia.

METHODS

Gunn rats with severe hyperbilirubinemia (j/j), Gunn rats without severe hyperbilirubinemia (+/j), and Wistar rats were examined by open-field, social interaction, and prepulse inhibition tests. TUNEL, AgNOR and Ki-67 were also assayed on paraffin-embedded brain sections of these rats.

RESULTS

Compared to Wistar rats, both Gunn j/j and +/j rats showed hyperlocomotion, high sniffing scores, and low defecation scores. They showed significantly more aggressive behaviors and impaired prepulse inhibition. The numbers of Ki-67-labeled cells and AgNOR were lower and the number of TUNEL-positive cells was higher than that of Wistar rats.

CONCLUSIONS

These results might support the neurodevelopmental hypothesis of schizophrenia. Both Gunn j/j and +/j rats may be a useful animal model and provide clues to the role of hyperbilirubinemia in schizophrenia.

Inositol 1,4,5 trisphosphate (IP3) receptor

The intensive molecular and biochemical study of IP(3)R has made great progress in elucidating the following unique properties of IP(3)R: 1) IP(3) dependent Ca(2+) release is quantal in nature; 2) IP(3)R allosterically and dynamically changes its form; 3) IP(3)R is functional even though it is fragmented by proteases into several pieces; 4) IP(3)R forms a functional association with a variety of molecules inside the cell, and with the channels on the plasma membrane; 5) the extremely high IP(3) binding affinity (500 approximately 1000 times higher than the original IP(3)R) sequence in the IP(3) binding region is covered with a suppressor sequence at the N-terminal. In parallel with these biochemical studies, studies on the role of IP(3)R during development have greatly advanced. Since IP(3)R was identified as a developmentally regulated phospho-glycoprotein, the Ca(2+) channel P400, it has diverse but essential functions in development and normal cell function.

Bilirubin-induced apoptosis in cultured rat neural cells is aggravated by chenodeoxycholic acid but prevented by ursodeoxycholic acid

BACKGROUND/AIMS

Unconjugated bilirubin (UCB) can be neurotoxic in jaundiced neonates and in patients with Crigler-Najjar syndrome. UCB toxicity may culminate in cell death, however, the occurrence of apoptosis has never been investigated. Ursodeoxycholic acid (UDCA) is a strong modulator of the apoptotic threshold in both hepatic and nonhepatic cells. The aims of this study were to determine whether apoptosis plays a role in neural cell death induced by UCB, and to investigate the ability of UDCA to prevent cell death.

METHODS

Cultured rat astrocytes were incubated with UCB (17 and 86 microM) plus albumin (5.7 and 28.7 microM) for 4-22 h. In addition, astrocytes and neurones were treated with either UCB, 50 microM UDCA, or their combination for 4 h. Cultures were scored for nonviable cells by trypan blue dye exclusion. Apoptosis was assessed by Hoechst staining and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labelling assay.

RESULTS

UCB induced a concentration- and time-dependent decrease in astrocyte viability. Apoptosis was 4- and 7-fold increased after 4 h exposure to 17 and 86 microM UCB, respectively (P < 0.01). UDCA reduced apoptosis to <7%, which represents a appoximately 60% protection (P < 0.01). Cholic acid was not protective, and chenodeoxyholic acid aggravated UCB toxicity (P < 0.05). Finally, neurones showed a 1.5-fold greater sensitivity than astrocytes to UCB, while UDCA was still protective.

CONCLUSIONS

UCB is toxic to both astrocytes and neurones, causing cell death through an apoptotic process. Moreover, UDCA inhibits UCB-induced apoptosis in neural cells and this could not be mimicked by other bile acids.

Bilirubin induces apoptosis via activation of NMDA receptors in developing rat brain neurons

Increased amounts of bilirubin, the end product of heme degradation, are known to be detrimental to the central nervous system, especially in preterm newborns. In an attempt to delineate the cellular mechanisms by which unconjugated bilirubin exerts its toxic effects on neuronal cells in the developing brain, bilirubin (0.25-5 microM) was added to the extracellular medium of 6-day-old primary cultured neurons from the embryonic rat forebrain, and cell alterations were studied over the ensuing 96 h. Bilirubin decreased cell viability dose dependently with an ED(50) around 1 microM. At the dose of 0.5 microM, it triggered delayed cell death that affected 24% of the neurons. Nuclear incorporation of the fluorescent dye DAPI (4,6-diamidino-2-phenylindole) depicted the presence of apoptosis (16%). Apoptosis features were confirmed by DNA fragmentation reflected by a progressive loss of [(3)H]thymidine and sequential changes in macromolecular synthesis, as shown by the time course of [(3)H]leucine incorporation, as well as by the beneficial effects of cycloheximide and caspase inhibitors. In parallel, treatments with glutamate receptor antagonists showed that MK-801, but not NBQX, protected neurons against bilirubin neurotoxicity, suggesting a role for NMDA receptors in bilirubin effects. Coupled with previous work about glutamate toxicity in the same culture model, these data support the hypothesis that low levels of free bilirubin may promote programmed neuronal death corresponding to an apoptotic process which involves caspase activation and requires the participation of NMDA receptors, along with bilirubin-induced inhibition of protein kinase C activity.

Comparative study of glial marker proteins in the hypoplastic cerebellum of jaundiced Gunn rats

The behavior of marker proteins of glial cells [alpha-enolase, beta-S100 protein, and glial fibrillary acidic protein (GFAP)] was investigated quantitatively by using enzyme immunoassay systems during the development of cerebellar hypoplasia in jaundiced Gunn rats. A neuronal marker protein, gamma-enolase, was also measured as a reference. At postnatal day 8 corresponding to the early stage of cerebellar damage, the amount of beta-S100 on a protein basis was significantly higher in jaundiced homozygotes (jj) than in control nonjaundiced heterozygotes (j+), whereas no differences in alpha- and gamma-enolases and GFAP were observed between the two groups of rats. At days 15 and 30, which correspond, respectively, to the advanced and late stages of cerebellar damage, the three glial proteins, especially GFAP, were higher and the neuronal protein was lower in the jj rat cerebellum than in the control. These results are consistent with the reported histological observations that neuronal cells are vulnerable and damaged by bilirubin, whereas glial cells seem to be less sensitive. On the other hand, the amounts of beta-S100 and alpha-enolase per cerebellum were significantly lower in jj rats at days 15 and 30, as in the case of gamma-enolase, whereas that of GFAP remained at the same level as the control at day 15 and showed a slight but significant decrease at day 30. The possibility is suggested that beta-S100 and GFAP may be available as biochemical indicators of glial cells, especially in the early and advanced stages of cerebellar damage, respectively, but that alpha-enolase is less available.

Cyclic nucleotides and the activity of glia maturation factor in the hypoplastic cerebellum of developing jaundiced Gunn rats

Developmental changes of cyclic nucleotides were studied in the hypoplastic cerebellum of jaundiced Gunn rats over the period of postnatal days 8 to 30. The mitogenic activity of glia maturation factor was also measured at day 15. In jaundiced homozygotes (jj), the amount of cyclic GMP on a protein basis was not significantly different from that in control heterozygotes (j+) at either day 8 or 15, but at day 30 it was reduced to about 19% of the control. On the other hand, a lowered nucleotide level on a wet weight basis in jj rats was already statistically significant at day 15. In contrast to cyclic GMP, the rates of increase of cyclic AMP on a wet weight basis were almost the same in the two groups of rats, but the nucleotide levels on a protein basis at days 15 and 30 were a little, but significantly, higher in jj rats than in j+ rats. The activity of glia maturation factor in jj rats was found to be 1.5-3 times as high as that in j+ rats. Possible implications of the present results are discussed.

Age-dependent and selective binding of beta-bungarotoxin to GABAergic neurons in the rat cerebellum

beta-Bungarotoxin (BuTx)-binding cells were immunocytochemically examined in the developing rat cerebellum. The tissue was incubated with BuTx and then immunostained with antiserum against its toxoid. On postnatal day 6, only Golgi cells were positive for immunoreaction. Immunoreactive Golgi cells were reduced in number on day 15 and disappeared on day 25. On day 15, Purkinje cells were strongly stained, while some basket and stellate cells stained weakly. On day 25 and in adult, basket and stellate cells were more immunoreactive than Purkinje cells. Thus, age-dependent and selective binding of BuTx was restricted to gamma-aminobutyric acid (GABA)ergic neurons.

Improved separation at low temperature of glycoproteins by Con A-Sepharose affinity chromatography in the presence of sodium dodecyl sulfate (SDS)

The Con A-Sepharose affinity chromatography of glycoproteins was even more effective at 4 degrees C than that at room temperature (26-28 degrees C) in the presence of sodium dodecyl sulfate (SDS). Application of this methodology to the separation of several glycoproteins from SDS-solubilized membrane proteins in rat cerebellum, including a glycoprotein characteristic of the Purkinje cells, was successful.

Studies on a cerebellar 50,000-dalton protein associated with cerebellar hypoplasia in jaundiced Gunn rats: its identity with glial fibrillary acidic protein as evidenced by the improved immunoblotting method

On the basis of our previous findings that a 50,000-dalton protein (GR-50) shows a marked increase in the hypoplastic cerebellum of jaundiced homozygous Gunn rats and its electrophoretic behavior is similar to that of glial fibrillary acidic protein (GFAP), we tried to identify GR-50 as GFAP by two-dimensional electrophoresis of rat cerebellar membrane proteins using an improved immunoblotting method. In this method a blot immunostained for a specific antigen was also visualized for other proteins, thereby enabling us to determine the location of the antigen on the blot more precisely. With the methodology it was found that GFAP antigen occupied exactly the same position as GR-50 on the blot, suggesting strongly the identity of both proteins. Immunohistochemical studies revealed that in the cerebellum of homozygotes compared with that of heterozygotes GFAP antigen was greatly increased and that it was especially rich in the homozygous rat cerebellar lobules with a high degree of hypoplasia. Further, it was shown that not only the fibers of the Bergmann glial cells but also their somata were intensely immunostained in the affected lobules. A 47,000-dalton protein (SG-47), which has been reported to be increased in staggerer mutant mice with cerebellar hypoplasia, also immunoreacted with the antiserum to GFAP.

Two proteins associated with cerebellar hypoplasia in jaundiced Gunn rats

Two cerebellar proteins with apparent molecular weights of 250,000 (GR-250) and 50,000 (GR-50) are closely associated with cerebellar hypoplasia in jaundiced homozygous Gunn rats. These proteins, found in Gunn rat cerebellum (4-60 days of age) and cerebrum as well as staggerer mouse cerebellum, were studied with electrophoretic techniques. After 8 days of life, GR-250 decreased and GR-50 increased in the homozygous Gunn rat cerebellum. The pI's of GR-250 and GR-50 were 4.7-5.8 and 4.6-4.9, respectively, and the former protein was shown to bind to Concanavalin A. A comparative study between cerebella of Gunn rats and staggerer mice revealed that GR-250 and P400, a protein generally thought to be characteristic of the Purkinje cells, were identical. Evidence was also obtained showing that GR-250 was present in the Gunn rat cerebrum. GR-50 was not detectable in the staggerer mouse cerebellum but instead, a protein (MW 47,000) was found to be increased in the mutant mouse cerebellum.