Background and Aims

Background: We and others have reported the patrolling behaviour of CX3CR1⁺ myeloid cells in blood vessels, which has consequences to pathological vascular remodelling. However the influence of the patrolling CX3CR1⁺ myeloid cells on regulating vascular smooth muscle contraction in atherosclerotic enviournment is not known.

Aim: We tested the hypothesis that patrolling CX3CR1⁺ myeloid cells due to their close association with vascular lumen, play a role in regulating vascular tone.

Methods

Single cell contractions (under normal and atherosclerotic conditions) coupled with imaging, arterial ring contractions in tissuebaths and fluorescence activated cell sorting techniques were used to study the vascular smooth muscle contractions and its calcium dynamics (Fluo-4 loaded cells) following stimulation with vasoconstrictors (Phenylephrine and Angiotensin II) in absence or presence of freshly isolated CX3CR1⁺ myeloid cells from bone marrow.

Results

Myeloid cells significantly enhanced the Angiotension II (Ang II) induced contraction by 81.62 ± 12.45 % and intracellular calcium levels by 30.19 ± 9.18 %. This effect on intracellular calcium levels was not blocked by 10 uM nifidipine in presence of myeloid cells. A continuous calcium oscillations was observed, which was insensitive to nifidipine (10 uM) and Thapsigargin (0.1 uM) but was sensitive to U73122 (10 uM) and SKF96365 (10 uM), indicating the involvement of TRPC channels. Upon co-culturing of VSMC with CX3CR1⁺ myeloid cells a 4 fold increase in factors regulating TRPC channels in VSMC was quantified using high mass accuracy mass spectrometry.

Conclusions

A novel mechanism of vascular tone regulation by myeloid cells relevent to understanding atherosclerotic pathology is reported here.