CCR7-CCL19/CCL21 Axis is Essential for Effective Arteriogenesis in a Murine Model of Hindlimb Ischemia

In order to identify factors that stimulate arteriogenesis after ischemia, we followed gene expression profiles in two extreme models for collateral artery formation over 28 days after hindlimb ischemia, namely "good-responding" C57BL/6 mice and "poor-responding" BALB/c mice.

Although BALB/c mice show very poor blood flow recovery after ischemia, most known proarteriogenic genes were upregulated more excessively and for a longer period than in C57BL/6 mice. In clear contrast, chemokine genes Ccl19, Ccl21a, and Ccl21c and the chemokine receptor CCR7 were upregulated in C57BL/6 mice 1 day after hindlimb ischemia, but not in BALB/C mice. CCL19 and CCL21 regulate migration and homing of T lymphocytes via CCR7. When subjecting CCR7^-/-/LDLR^-/- mice to hindlimb ischemia, we observed a 20% reduction in blood flow recovery compared with that in LDLR^-/- mice. Equal numbers of α-smooth muscle actin-positive collateral arteries were found in the adductor muscles of both mouse strains, but collateral diameters were smaller in the CCR7^-/-/LDLR^-/-. Fluorescence-activated cell sorter analyses showed that numbers of CCR7⁺ T lymphocytes (both CD4⁺ and CD8⁺) were decreased in the spleen and increased in the blood at day 1 after hindlimb ischemia in LDLR^-/- mice. At day 1 after hindlimb ischemia, however, numbers of activated CD4⁺ T lymphocytes were decreased in the draining lymph nodes of LDLR^-/- mice compared with CCR7^-/-/LDLR^-/- mice.

These data show that CCR7-CCL19/CCL21 axis facilitates retention CD4⁺ T lymphocytes at the site of collateral artery remodeling, which is essential for effective arteriogenesis.