Leucine‐rich repeat kinase 2‐sensitive Na + /Ca 2+ exchanger activity in dendritic cells

ABSTRACT Gene variants of the leucine‐rich repeat kinase 2 (LRRK2) are associated with susceptibility to Parkinson's disease (PD). Besides brain and periphery, LRRK2 is expressed in various immune cells including dendritic cells (DCs), antigen‐presenting cells linking innate and adaptive immunity. However, the function of LRRK2 in the immune system is still incompletely understood. Here, Ca 2+ ‐signaling was analyzed in DCs isolated from gene‐targeted mice lacking lrrk2 ( Lrrk2 ‐/‐ ) and their wild‐type littermates (Lrrk2). According to Western blotting, Lrrk2 was expressed in Lrrk2 +/+ DCs but not in Lrrk2 ‐/‐ DCs. Cytosolic Ca 2+ levels ([Ca 2+ ] i ) were determined utilizing Fura‐2 fluorescence and whole cell currents to decipher electrogenic transport. The increase of [Ca 2+ ] i following inhibition of sarcoendoplasmatic Ca 2+ ‐ATPase with thapsigargin (1 μM) in the absence of extracellular Ca 2+ (Ca 2+ ‐release) and the increase of [Ca 2+ ] i following subsequent readdition of extracellular Ca 2+ (SOCE) were both significantly larger in Lrrk2 ‐/‐ than in Lrrk2 +/+ DCs. The augmented increase of [Ca 2+ ] i could have been due to impaired Ca 2+ extrusion by K + ‐independent (NCX) and/or K + ‐dependent (NCKX) Na + /Ca 2+ ‐exchanger activity, which was thus determined from the increase of [Ca 2+ ] i , (Δ[Ca 2+ ] i ), and current following abrupt replacement of Na + containing (130 mM) and Ca 2+ free (0 mM) extracellular perfusate by Na + free (0 mM) and Ca 2+ containing (2 mM) extracellular perfusate. As a result, both slope and peak of Δ [Ca 2+ ] i as well as Na + /Ca 2+ exchanger‐induced current were significantly lower in Lrrk2 ‐/‐ than in Lrrk2 +/+ DCs. A 6 or 24 hour treatment with the LRRK2 inhibitor GSK2578215A (1 μM) significantly decreased NCX1 and NCKX1 transcript levels, significantly blunted Na + /Ca 2+ ‐exchanger activity, and significantly augmented the increase of [Ca 2+ ] i following Ca 2+ ‐release and SOCE. In conclusion, the present observations disclose a completely novel functional significance of LRRK2, i.e. , the up‐regulation of Na + /Ca 2+ exchanger transcription and activity leading to attenuation of Ca 2+ ‐signals in DCs.—Yan, J., Almilaji, A., Schmid, E., Elvira, B., Shimshek, D. R., van der Putten, H., Wagner, C. A., Shumilina, E., Lang, F. Leucine‐rich repeat kinase 2‐sensitive Na + /Ca2 + exchanger activity in dendritic cells. FASEB J. 29, 1701‐1710 (2015). www.fasebj.org