Chronic LiCl pretreatment suppresses thrombin-stimulated intracellular calcium mobilization through TRPC3 in astroglioma cells

OBJECTIVES

Transient receptor potential canonical type 3 (TRPC3) channels are activated in B lymphoblast cell lines from patients with bipolar disorder (BD), and its expression is reduced by chronic lithium treatment, implicating TRPC3 in the intracellular calcium (Ca²⁺ ) dyshomeostasis of BD. Thrombin, via a protease-activated receptor, moderates Ca²⁺ signaling and TRPC3 in astrocytes, and also cell proliferation. We examined whether lithium pretreatment attenuates thrombin-stimulated TRPC3 expression and function in astrocytes, and levels of the calcium-binding peptide, S100B, which is expressed mainly in these cells.

METHODS

Human astroglioma, U-87MG, cells were pretreated with 1 mmol L^-1 LiCl for 1 day (acute), 3 days (subacute), and 7 days (chronic). To examine the role of TRPC3, genetically stable knockdown TRPC3 cells (TRPC3^Low cells) were constructed using U-87MG cells. Thrombin (2.0 U/mL)-stimulated Ca²⁺ mobilization was measured by ratiometric fluorimetry. Changes in TRPC3 and S100B expression levels were determined by quantitative reverse transcription-polymerase chain reaction and immunoblotting, respectively. Cell proliferation was also measured using the WST-8 assay.

RESULTS

In this cell model, thrombin-stimulated Ca²⁺ mobilization, and both TRPC3 and S100B expression were suppressed by chronic LiCl pretreatment and the knockdown of TRPC3. Additionally, cell proliferation was attenuated in TRPC3^Low cells, compared with the negative control vector-transfected cell.

CONCLUSIONS

The reduced Ca²⁺ mobilization and S100B expression levels following chronic LiCl pretreatment and in TRPC3^Low cells support the notion that TRPC3 modulates S100B expression and is the target of the LiCl effect. Downregulation of TRPC3 may be an important mechanism by which lithium ameliorates pathophysiological intracellular Ca²⁺ disturbances as observed in BD, accounting, in part, for its mood-stabilizing effects.