Rab11a Regulates Dense-Core Vesicles Supply to the Cellular Periphery and Facilitates Neurosecretion in Chromaffin Cells

Rab GTPases are key regulators of membrane trafficking. However, few Rabs have been identified to participate in the secretion processes of synaptic and secretory vesicles. In the present study, we sought to investigate the role of Rab11a, a protein classically involved in recycling pathways, in the regulation of dense-core vesicle (DCV) secretion in mouse chromaffin cells, a well-established neurosecretory model. By the use of confocal imaging, we found that Rab11a colocalized with DCV. Importantly, the expression of the dominant-negative mutant (S25N) or constitutive-active mutant (Q70L) forms of Rab11a increased the DCV cargo neuropeptide Y (NPY) at Golgi. Additionally, upon expression of S25N or Q70L, or the overexpression of Rab11a-WT form, we found that: (1) NPY decreased at the cell periphery; (2) the fluorescent timer mK-GO-NPY showed a decrease in newly formed DCV at the cell periphery; and (3) there was a decrease in the exocytic response, measured by patch-clamped membrane capacitance recording. Remarkably, the effects of Rab11a-S25N or Rab11a-Q70L expression were stronger than those observed upon Rab11a-WT overexpression, suggesting a dependency of DCV distribution and secretion on Rab11a GDP-to-GTP cycle. On the other hand, the effects of Rab11a-WT overexpression may be explained by an imbalance toward the GTP-bound form of Rab11a, which might sequester endogenous effectors and freeze the exocytic process at intermediate steps. Therefore, this study suggests that Rab11a facilitates the supply of DCV at the plasma membrane by positively modulating the generation and/or transport of new DCV, and, in this way, supporting the exocytic response.