Autoradiographic characterization of [3H]inositol (1,4,5) trisphosphate and [3H]inositol (1,3,4,5) tetrakisphosphate binding sites in human brain

Altered calcium signaling following traumatic brain injury

Cell death and dysfunction after traumatic brain injury (TBI) is caused by a primary phase, related to direct mechanical disruption of the brain, and a secondary phase which consists of delayed events initiated at the time of the physical insult. Arguably, the calcium ion contributes greatly to the delayed cell damage and death after TBI. A large, sustained influx of calcium into cells can initiate cell death signaling cascades, through activation of several degradative enzymes, such as proteases and endonucleases. However, a sustained level of intracellular free calcium is not necessarily lethal, but the specific route of calcium entry may couple calcium directly to cell death pathways. Other sources of calcium, such as intracellular calcium stores, can also contribute to cell damage. In addition, calcium-mediated signal transduction pathways in neurons may be perturbed following injury. These latter types of alterations may contribute to abnormal physiology in neurons that do not necessarily die after a traumatic episode. This review provides an overview of experimental evidence that has led to our current understanding of the role of calcium signaling in death and dysfunction following TBI.

Expression of the brain-specific membrane adapter protein p42IP4/centaurin alpha, a Ins(1,3,4,5)P4/PtdIns(3,4,5)P3 binding protein, in developing rat brain

Inositolphosphates and phosphatidylinositides are important second messengers. Previously p42(IP4), a protein with high affinity for both Ins(1,3,4,5)P(4) and PtdIns(3,4,5)P(3) has been characterized in our laboratory. In the present study mRNA levels of p42(IP4) were quantified during development (ages: 7, 14, 21 days and adult) by means of ribonuclease protection assay in various rat brain regions (cerebellum, cortex, striatum, thalamus, hypothalamus, olfactory bulb, hippocampus and tectum (superior and inferior colliculus)). A high level of p42(IP4) mRNA was detected in the cortex (ca. 1 pg specific RNA per microg of total RNA) which stayed highly independent of the age of the animals. In hippocampus and in the thalamus, p42(IP4) mRNA levels were comparable to those in the cortex in the first and second week postnatally, but decreased to lower levels in the adult brain. In striatum, the mRNA increased, albeit less intensely than in hippocampus and thalamus, until day 21 postnatally, and then decreased in the adult rat brain. Cerebellar p42(IP4) mRNA showed a slow increase within the first 3 weeks postnatally, and remained rather high in the adult brain. The protein expression of p42(IP4), tested within the same samples by Western blot staining, was consistent with mRNA values. For comparison, glutamic acid decarboxylase (isoforms GAD65/GAD67), an enzyme, for which some regional brain specific distribution is already known, was also examined. The mRNA levels of GAD and its developmental regulation clearly differed from that of p42(IP4). In summary, p42(IP4) expressed in several neuronal cell types, did not seem to be restricted to specific developmental stages, but the high absolute expression levels at all developmental stages indicated that p42(IP4) is a protein fundamental for neuronal functioning.

Loss of inositol 1,4,5-trisphosphate receptor sites and decreased PKC levels correlate with staging of Alzheimer's disease neurofibrillary pathology

Inositol 1,4,5-trisphosphate (IP3), inositol 1,3,4,5-tetrakisphosphate (IP4) and protein kinase C (PKC) play important roles in the phosphoinositide hydrolysis signal transducing pathway. Several studies have shown severe deficits in both IP3 receptor levels and PKC levels and activity in Alzheimer's disease brain, although the relationship of these changes to disease pathology is poorly understood. In the present study, we determined the autoradiographic localization of [3H]IP3 and [3H]IP4 binding to their calcium mobilizing receptor sites and [3H]phorbol 12,13-dibutyrate ([3H]PDBu) binding to PKC in sections of entorhinal cortex/hippocampal formation and cerebellum from 24 cases that had been staged for Alzheimer's disease-related neurofibrillary changes and amyloid deposition according to Braak and Braak [Acta Neuropathol. Berl., 82 (1991) 239-259]. Results indicated that [3H]IP3 binding showed a trend towards a decline with staging for neurofibrillary changes in the entorhinal region (0.05 < P < 0.10, ANOVA) and subiculum (0.05 < P < 0.10). In the former region, [3H]IP3 binding showed a significant decline with staging for amyloid deposition (P < 0.05). [3H]IP3 binding in the CA1 region showed statistically significant declines with respect to both neurofibrillary changes and amyloid staging (P < 0.05). [3H]IP3 binding levels in the other hippocampal subregions were too low to quantify accurately. The binding of [3H]IP4 showed no significant changes with either neurofibrillary changes or amyloid staging in any of the regions investigated. In contrast, [3H]PDBu binding showed significant declines with neurofibrillary staging in the entorhinal region (P < 0.01), subiculum (P < 0.001), CA1 (P < 0.001), CA2 (P < 0.001), CA3 (P < 0.001) and CA4 (P < 0.0001) regions and the dentate gyrus (P < 0.0001). Of these regions, only the subiculum showed a significant decline of [3H]PDBu binding with amyloid staging. There were no significant neurofibrillary or amyloid stage-related changes in either [3H]IP3, [3H]IP4 or [3H]PDBu binding in the molecular layer of the cerebellum. These findings suggest that reduced IP3 receptor and PKC levels in the entorhinal cortex/hippocampal formation reflect and may be important for the progression of Alzheimer's disease neurofibrillary pathology. The data also suggests that hippocampal IP3 receptor loss is related to the extent of amyloid deposition.