Abnormal lymphatic phenotype in a CRISPR mouse model of the human lymphedema-causing Connexin47 R260C point mutation.

Connexin proteins form gap junctions controlling exchange of ions and small molecules between cells and play an important role in movement of lymph within lymphatic vessels. Connexin47 (CX47) is highly expressed in lymphatic endothelial cells and CX47 missense mutations, i.e., R260C, cosegregate with primary lymphedema in humans. However, studies utilizing CX47 knockout mice have failed to demonstrate any lymphatic anomalies. To unravel the lymphatic consequences of expressing a mutant CX47 protein, we used CRISPR technology to create a mouse carrying a Cx47 missense mutation (Cx47R259C) equivalent to the human CX47R260C missense mutation associated with human primary lymphedema. Intradermal Evans Blue dye injection identified a 2-fold increase in regional lymph nodes in homozygous Cx47R259C mice compared to wildtype, particularly in the jugular region (4.8 ± 0.4 and 2.0 ± 0.0, respectively, p<0.01). Associated lymphatic channels were increased in Cx47R259C mice and mesenteric lymph reflux occurred in homozygous Cx47R259C mice but not in wildtype. Contractility of superficial cervical lymphatics, assessed by pressure myography, was reduced in homozygous Cx47R259C mice compared to wildtype. In conclusion, our data are the first to demonstrate a role for the Cx47 protein in lymphatic anatomy and function. This phenotype is similar to that found with other valve deficient mouse mutants, e.g., in Foxc2. Of significance, this study is the first to use CRISPR technology to develop a pre-clinical model of primary lymphedema and demonstrates the importance of distinguishing between lack of and presence of mutant protein when developing clinically relevant animal models for translation of pre-clinical findings.

Lymphatic communication: connexin junction, what's your function?

This article reviews recent findings on expression and function of connexin proteins--the structural subunits of gap junction intercellular channels in the lymphatic vasculature--both during development and in the mature lymphatic vessel. Highlighted in particular are recent mouse connexin knockout studies which show that connexins are crucial for normal lymphatic development. We discuss, in general terms, both channel-dependent as well as channel-independent functions of connexins and raise some of the many unanswered questions about the mechanism(s) of action and physiological roles of connexins in the lymphatic vasculature.