Biomedical subjects

L S Haug

Publications and source records attributed to L S Haug.

6 recordsLinked to original sources

PubMed2000

Reduced [3H]IP3 binding but unchanged IP3 receptor levels in the rat hippocampus CA1 region following transient global ischemia and tolerance induction.

Changes in inositol (1,4,5)-trisphosphate (IP3) binding properties and the protein level of the IP3 receptor have been reported in different pathological conditions in the brain, e.g. cerebral ischemia, Alzheimer's disease, and Huntingtons disease. We used the 4-vessel occlusion model in rat brain to investigate the effect of transient ischemia insults on the IP3 receptor mRNA level, the IP3 receptor protein level and [3H]IP3 binding. Recirculation periods were limited (1-72 h) to avoid the development of delayed neuronal death. We found that the IP3 receptor mRNA levels were decreased after damage-inducing ischemia (9 min) in the hippocampus CA1 and CA3 regions. The mRNA levels were unaltered after tolerance-inducing ischemia (3 min). However, [3H]IP3 binding was significantly reduced after both damage- and tolerance-inducing ischemia in the hippocampus CA1 region. Furthermore, all investigated brain areas showed a decreased [3H]IP3 binding when tolerance-inducing ischemia was followed by a second ischemic insult (3 + 8.5 min ischemia). The IP3 receptor protein levels remained constant in all investigated brain areas. These results indicate that a reduced [3H]IP3 binding capability in the particularly vulnerable areas occurs as an early consequence of cerebral ischemia, before IP3 receptor protein levels are reduced in these areas. Structural or conformational changes altering IP3 binding may be of necessity on the pathway leading to down-regulation of IP3 receptor protein levels, as observed by others.

Adaptation, Physiological↗

PubMed2000

Degradation of the type I inositol 1,4,5-trisphosphate receptor by caspase-3 in SH-SY5Y neuroblastoma cells undergoing apoptosis.

The type I inositol 1,4,5-trisphosphate (IP(3)) receptor is selectively down-regulated in several neurodegenerative diseases, including Alzheimer's disease, Huntington's chorea, and ischemia, all conditions in which apoptotic neuronal loss occurs. In the present study, we used a neuronal cell line, human neuroblastoma SH-SY5Y cells, to investigate whether the levels of IP(3) receptor are changed during apoptosis in these cells. Following induction of apoptosis by staurosporine, the immunoreactivity of the type I IP(3) receptor in microsome preparations from SH-SY5Y cells was reduced within 2 h, with a further reduction during subsequent hours. Immunoblot analyses, using antibodies to poly(ADP-ribose) polymerase and spectrin breakdown products, revealed proteolysis of these caspase-3 substrates within 3 h, confirming that IP(3) receptor cleavage is an early consequence of apoptosis. In vitro incubation of SH-SY5Y microsomes or immunopurified IP(3) receptor from rat cerebellum with recombinant caspase-3 led to generation of immunoreactive breakdown products similar to those observed in intact cells, suggesting that the type I IP(3) receptor is a potential substrate for caspase-3. Preincubation of the neuroblastoma cells with the caspase-3 inhibitor Z-Asp-Glu-Val-Asp-fluoromethyl ketone prevented IP(3) receptor degradation. These results show that the type I IP(3) receptor is a substrate for caspase-3 in neuronal cells and indicate that apoptotic down-regulation of IP(3) receptor levels may contribute to the pathology of neurodegenerative conditions.

Amino Acid Motifs↗

PubMed1999

Phosphorylation of the inositol 1,4,5-trisphosphate receptor by cyclic nucleotide-dependent kinases in vitro and in rat cerebellar slices in situ.

We have examined cyclic nucleotide-regulated phosphorylation of the neuronal type I inositol 1,4,5-trisphosphate (IP3) receptor immunopurified from rat cerebellar membranes in vitro and in rat cerebellar slices in situ. The isolated IP3 receptor protein was phosphorylated by both cAMP- and cGMP-dependent protein kinases on two distinct sites as determined by thermolytic phosphopeptide mapping, phosphopeptide 1, representing Ser-1589, and phosphopeptide 2, representing Ser-1756 in the rat protein (Ferris, C. D., Cameron, A. M., Bredt, D. S., Huganir, R. L., and Snyder, S. H. (1991) Biochem. Biophys. Res. Commun. 175, 192-198). Phosphopeptide maps show that cAMP-dependent protein kinase (PKA) labeled both sites with the same time course and same stoichiometry, whereas cGMP-dependent protein kinase (PKG) phosphorylated Ser-1756 with a higher velocity and a higher stoichiometry than Ser-1589. Synthetic decapeptides corresponding to the two phosphorylation sites (peptide 1, AARRDSVLAA (Ser-1589), and peptide 2, SGRRESLTSF (Ser-1756)) were used to determine kinetic constants for the phosphorylation by PKG and PKA, and the catalytic efficiencies were in agreement with the results obtained by in vitro phosphorylation of the intact protein. In cerebellar slices prelabeled with [32P]orthophosphate, activation of endogenous kinases by incubation in the presence of cAMP/cGMP analogues and specific inhibitors of PKG and PKA induced in both cases a 3-fold increase in phosphorylation of the IP3 receptor. Thermolytic phosphopeptide mapping of in situ labeled IP3 receptor by PKA showed labeling on the same sites (Ser-1589 and Ser-1756) as in vitro. In contrast to the findings in vitro, PKG preferentially phosphorylated Ser-1589 in situ. Because both PKG and the IP3 receptor are specifically enriched in cerebellar Purkinje cells, PKG may be an important IP3 receptor regulator in vivo.

Amino Acid Sequence↗

PubMed1998

Intracerebroventricular administration of quinolinic acid induces a selective decrease of inositol(1,4,5)-trisphosphate receptor in rat brain.

[3H]inositol(1,4,5)-trisphosphate (IP3) binding studies have shown decreased [3H]IP3 binding to brain tissue in several neurodegenerative diseases, including Alzheimer's and Huntington's diseases. In addition, previous results obtained from brains of Alzheimer patients indicated a reduction of IP3-receptor protein correlated to neuronal loss. The neurotoxic effect of the glutamate receptor agonist quinolinic acid (QUIN) was therefore examined with respect to the level of IP3-receptor immunoreactivity in rat brain. Neuronal lesions were estimated with antibodies to marker proteins for striatal medium-sized spiny neurons (dopamine- and cyclic AMP-regulated phosphoprotein, Mr 32,000; DARPP-32), synaptic vesicles (synaptophysin), mitochondria (phosphate-activated glutaminase; PAG) and glial cells (glial fibrillary acidic protein; GFAP). Injection of QUIN into rat neostriatum induced a massive loss of striatal medium-sized spiny neurons, and led to a comparable loss of IP3-receptor and PAG immunoreactivity, suggesting a neuronal localisation of both these proteins. In an effort to induce less pronounced excitotoxic damage, intracerebroventricular infusion of QUIN was performed. Following this lesion, the neostriatum showed a negligible loss of DARPP-32 immunoreactivity (-11+/-5%), but contained only 43+/-3% of IP3-receptor immunoreactivity levels compared to controls. In the hippocampus, cerebellum and entorhinal cortex, the IP3-receptor loss was less pronounced. The decrease in the level of IP3-receptor immunoreactivity appears to be selective with respect to the other proteins studied, and the IP3-receptor thus shows extreme sensitivity to QUIN neurotoxicity in the neostriatum.

Animals↗

PubMed1996

Decreased inositol (1,4,5)-trisphosphate receptor levels in Alzheimer's disease cerebral cortex: selectivity of changes and possible correlation to pathological severity.

We used immunoblotting and radioligand binding techniques to compare levels of the calcium-mobilizing receptor for the phosphoinositide hydrolysis-derived intracellular second messenger inositol (1,4,5)-trisphosphate (IP3) in post mortem samples from the temporal, frontal and parietal cortices of eight Alzheimer's disease (AD) and eight matched control cases. Immunoblotting with an antibody directed against the C-terminal end of the rat type I IP3-receptor showed that IP3-receptor protein levels were significantly reduced in the temporal (to 59 +/- 6% of controls, P = 0.0002) and frontal (to 62 +/- 10% of controls, P = 0.04), but not in the parietal cortices (to 63 +/- 13% of controls, P = 0.1) of the AD cases, compared to controls. The number of [3H]IP3 radioligand binding sites was significantly decreased in the temporal cortex, but not frontal and parietal cortices, of the AD brains. The decreased levels of both immunoreactive IP3-receptor protein and [3H]IP3 binding in the temporal cortex correlated with a semi-quantitative score for the severity of AD neuropathology. No significant changes were seen in the levels of glial fibrillary acidic protein, synaptophysin or phosphate-activated glutaminase, as markers for astrocytes, neuronal vesicles and mitochondria, respectively. It is concluded that in affected AD brain regions, the IP3-receptor may represent a sensitive target for proteolysis, possibly mediated by activation of the Ca(2+)-activated neutral protease calpain. These degenerative changes may in part be responsible for the disruption of Ca2+ homeostasis in AD-sensitive neurons.

Aged↗

PubMed1993

Calcium-induced degradation of the inositol (1,4,5)-trisphosphate receptor/Ca(2+)-channel.

Ca(2+)-induced degradation of the neuronal inositol (1,4,5)-trisphosphate receptor, a protein which regulates Ca(2+)-release from intracellular stores, has been examined. The IP3-receptor, immunopurified from rat cerebellum, appeared to be an excellent substrate for purified Ca(2+)-activated neutral protease (calpain). Incubation of membranes or immunopurified IP3-receptor with Ca2+ and cerebellar cytosol also resulted in degradation of the receptor. Two main fragments with approximate molecular masses of 130 and 95 kDa were generated, both of which appeared to derive from the carboxyterminal Ca(2+)-channel-containing part of the protein. These data suggest that activation of the IP3-receptor, by causing increases in intracellular [Ca2+], might result in degradation of the N-terminal, IP3-binding part of the receptor.

Animals↗