Introduction:
Mutations in GJC2, which encodes connexin47 (Cx47), are associated with lymphedema. Moreover, Cx47 mRNA was recently found in human lymphatic endothelial cells (LECs).
Hypothesis:
Lymphatic endothelial Cx47 has a role in lymphatic physiology and pathology.
Methods:
Confocal microscopy and qPCRs were used to assess expression of Cx47. Lymphatic drainage was studied by subcutaneous Evans Blue injections in the footpad of 12 week-old ApoE
-/-
or Cx47
eGFP/eGFP
ApoE
-/-
mice. Atherosclerosis was studied in 15 months-old ApoE
-/-
or Cx47
eGFP/eGFP
ApoE
-/-
mice.
Results:
Cx47 was expressed in lymphangions of mesenteric collecting vessels in Cx47
eGFP/eGFP
Prox1-mOrange2 mice as assessed by microscopy and its expression was confirmed by qPCR on mesentery, gut and skin mRNA of ApoE
-/-
but not Cx47
eGFP/eGFP
ApoE
-/-
mice. Interestingly, lymphatic drainage was enhanced in Cx47-deficient mice (n=10/11, p<0.05). To address whether Cx47 affects chronic immuno-inflammatory pathology atherosclerotic plaque formation was studied in 15-month old male ApoE
-/-
and Cx47
eGFP/eGFP
ApoE
-/-
mice on regular chow. These studies showed that Cx47-deficiency does not affect the size or composition (e.g. lipid, collagen or macrophage content) of aortic plaques in the aortic root. However, plaque development in the thoracic-abdominal aorta of 15 months-old mice tended to be larger in Cx47
eGFP/eGFP
ApoE
-/-
mice (21±5 vs 30±4 % lipid area, n=10, p=0.08). Unexpectedly, total cholesterol (TC) and LDL, but not HDL, triglycerides or free fatty acids, were increased in serum of Cx47
eGFP/eGFP
ApoE
-/-
mice as compared to ApoE
-/-
serum (TC: 472±24 vs 647±18 mg/dL, n=10, p<0.01; and LDL: 272±20 vs 443±17 mg/dL, n=10, p<0.001, respectively). Increased lymphatic drainage from plaques in Cx47
eGFP/eGFP
ApoE
-/-
mice may, partially, compensate for increased serum TC and LDL thereby preventing exuberant atherosclerotic plaque formation despite increased serum lipid levels.
Conclusions:
In conclusion, Cx47 is expressed in LECs of the lymphangion and seems implicated in multiple aspects of lymphatic (patho)physiology.