Increased contractile activity and dilation of popliteal lymphatic vessels in the TNF-α-overexpressing TNF^ΔARE/+ arthritic mouse

Aims: TNF-α acute treatment has been found to disrupt lymphatic drainage in the setting of arthritis through the NF-kB-iNOS- signaling pathway. We examined whether popliteal lymphatic vessels (pLVs) contractile activity was altered in 12- and 24- week-old females of an arthritic mouse model overexpressing TNF-α (TNF^ΔARE/+).

Main methods: pLVs were prepared for intravital imaging to measure lymph flow speed, and ex vivo functional responses to a stepwise increase in transmural pressure in the absence or presence of the non-selective NOS inhibitor (L-NNA) or the selective iNOS inhibitor (1400W) were compared between TNF^ΔARE/+ and WT mice. Total eNOS (t-eNOS) and eNOS phosphorylated at ser1177 (p-eNOS) were evaluated by western blotting.

Key findings: In vivo imaging revealed a significantly increase in lymph flow speed in TNF^ΔARE/+ mice in comparison to WT at both ages. Pressure myography showed an increase in contraction frequency, diameters and fractional pump flow at both ages, whereas amplitude and ejection fraction were significantly decreased in older TNF^ΔARE/+ mice. Additionally, contraction frequency was increased in the presence of 1400W, and systolic diameter was abolished with L-NNA in TNF^ΔARE/+ mice compared to WT. Significant increases in p-eNOS expression and neutrophil recruitment (MPO activity) were observed in TNF^ΔARE/+ mice compared to WT.

Significance: Our data reveal functional changes in pLVs, especially in advanced stage of arthritis. These alterations may be related to eNOS and iNOS response, which can affect drainage of the inflammatory content from the joints.