We have recently reported that chronic lithium profoundly alters the intracellular concentration of the rat. This reduction in a Myristoylated Alanine Rich C Kinase Substrate (MARCKS) protein appears to parallel the time course of action of lithium in the clinical treatment of bipolar disorder. Accumulating evidence from our laboratory and others implicates PKC in the long term action of lithium in the brain as well as the regulation of some of its major phosphoprotein substrates, including MARCKS. In order to move this research to the next phase of examining our hypotheses regarding the mechanism of action of lithium in regulating this PKC substrate, we must initiate the development of a physiologically relevant cell system, amenable to sophisticated experimental approaches and devoid of the limitations of in vivo models. In this Small Grant proposal we will establish a new cell model system using immortalized hippocampal cells in culture, and take advantage of current cellular heterogeneity to initiate a subcloning strategy to isolate and stabilize phenotypic properties as a valuable resource for our future studies. For example, while we have identified MARCKS expression in an early passage of these cells, we anticipate the development of subclones with differential levels of expression of this phosphoprotein. Inasmuch as lithium's action in brain appears to depend upon limited access to inositol, we will develop analogous conditions for lithium exposure in our cell system. We will replicate our in vivo findings in these hippocampal cells and examine transcriptional, translational and posttranslational mechanisms by which lithium alters the regulation and expression of MARCKS in the hippocampus. These studies will provide the necessary foundation to pursue more major funding in the future to examine the possibility that the action of lithium on MARCKS is shared by other known major PKC substrates unique to brain. In addition, we will then be in an excellent position to test our hypothesis that alterations in MARCKS and/or the other phosphoproteins may play a critical role in the action of chronic lithium on the regulation of muscarinic receptors coupled to phospholipase C in key regions of the brain.
| Lenox, R H; McNamara, R K; Papke, R L et al. (1998) Neurobiology of lithium: an update. J Clin Psychiatry 59 Suppl 6:37-47 |
| McNamara, R K; Lenox, R H (1998) Distribution of the protein kinase C substrates MARCKS and MRP in the postnatal developing rat brain. J Comp Neurol 397:337-56 |
| McNamara, R K; Lenox, R H (1997) Comparative distribution of myristoylated alanine-rich C kinase substrate (MARCKS) and F1/GAP-43 gene expression in the adult rat brain. J Comp Neurol 379:48-71 |
| Watson, D G; Lenox, R H (1996) Chronic lithium-induced down-regulation of MARCKS in immortalized hippocampal cells: potentiation by muscarinic receptor activation. J Neurochem 67:767-77 |
| Lenox, R H; McNamara, R K; Watterson, J M et al. (1996) Myristoylated alanine-rich C kinase substrate (MARCKS): a molecular target for the therapeutic action of mood stabilizers in the brain? J Clin Psychiatry 57 Suppl 13:23-31;discussion 32-3 |
