Surfactant Secretion in LRRK2 Knock-Out Rats: Changes in Lamellar Body Morphology and Rate of Exocytosis

Pika Miklavc,Kristin E Thompson,Konstantin Ehinger,Manfred Frick,Derya R Shimshek,Nina Hobi,Elisa Greggio

doi:10.1371/journal.pone.0084926

Pika Miklavc, Kristin E Thompson + Show 5 more

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https://doi.org/10.1371/journal.pone.0084926

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Abstract

Leucine-rich repeat kinase 2 (LRRK2) is known to play a role in the pathogenesis of various diseases including Parkinson disease, morbus Crohn, leprosy and cancer. LRRK2 is suggested to be involved in a number of cell biological processes such as vesicular trafficking, transcription, autophagy and lysosomal pathways. Recent histological studies of lungs of LRRK2 knock-out (LRRK2 -/-) mice revealed significantly enlarged lamellar bodies (LBs) in alveolar type II (ATII) epithelial cells. LBs are large, lysosome-related storage organelles for pulmonary surfactant, which is released into the alveolar lumen upon LB exocytosis. In this study we used high-resolution, subcellular live-cell imaging assays to investigate whether similar morphological changes can be observed in primary ATII cells from LRRK2 -/- rats and whether such changes result in altered LB exocytosis. Similarly to the report in mice, ATII cells from LRRK2 -/- rats contained significantly enlarged LBs resulting in a >50% increase in LB volume. Stimulation of ATII cells with ATP elicited LB exocytosis in a significantly increased proportion of cells from LRRK2 -/- animals. LRRK2 -/- cells also displayed increased intracellular Ca2+ release upon ATP treatment and significant triggering of LB exocytosis. These findings are in line with the strong Ca2+-dependence of LB fusion activity and suggest that LRRK2 -/- affects exocytic response in ATII cells via modulating intracellular Ca2+ signaling. Post-fusion regulation of surfactant secretion was unaltered. Actin coating of fused vesicles and subsequent vesicle compression to promote surfactant expulsion were comparable in cells from LRRK2 -/- and wt animals. Surprisingly, surfactant (phospholipid) release from LRRK2 -/- cells was reduced following stimulation of LB exocytosis possibly due to impaired LB maturation and surfactant loading of LBs. In summary our results suggest that LRRK2 -/- affects LB size, modulates intracellular Ca2+ signaling and promotes LB exocytosis upon stimulation of ATII cells with ATP.

Highlights

Leucine-rich repeat kinase 2 (LRRK2) is a,280 kDa protein with two enzymatic domains (Ras of complex GTPase domain and kinase domain) and several protein-protein interaction domains such as an amino terminal leucine-rich repeat domain and a carboxy terminal WD40 domain [1,2]
Surfactant secretion assay Based on our finding that knock-out of LRRK2 results in a significantly enhanced lamellar bodies (LBs) fusion response in alveolar type II (ATII) cells when stimulated with 100 mM ATP, we examined whether this results in increased surfactant secretion
One study found that genetic ablation of LRRK2 results in an increased number and size of secondary lysosomes in kidney proximal tubules cells and LBs in ATII cells in the lung [29]

Summary

Introduction

LRRK2 is a ,280 kDa protein with two enzymatic domains (Ras of complex GTPase domain and kinase domain) and several protein-protein interaction domains such as an amino terminal leucine-rich repeat domain and a carboxy terminal WD40 domain [1,2]. Mutations in LRRK2 are associated with the familial form of Parkinson disease [3,4,5,6,7] but were linked to inflammatory bowel disease [8], leprosy [9], and cancer [10]. LRRK2 is expressed in the cells of the immune system and was suggested to be involved in monocyte maturation [12,13]. It is involved in regulation of microglial inflammatory responses which may be associated with late-onset Parkinson disease [14,15]

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