Villi are small, finger-like projections of the small intestine that facilitate the absorption of dietary molecules, including lipids, from the intestinal lumen. Lacteals, lymphatic microvessels that extend into the center of each villus, are involved in shuttling accumulated subepithelial lipids into the lymphatic system. Although it is clear that lacteals play a vital role in dietary lipid transport, the precise physiological mechanics of the in vivo transport process are not known. Kibaek Choe, Jeon Yeob Jang, Intae Park and colleagues at the Korea Advanced Institute of Science and Technology (KAIST) and the Pusan National University School of Medicine utilized an intravital imaging approach to gain a better understanding of lacteal function. Using a video-rate imaging system, the authors were able to visualize the movement of fluorescently tagged lipids in individual villi of the mouse small intestine. Lacteals were observed to drain higher molecular weight lipids and other large molecules that were not efficiently taken up by capillaries in the villi. In addition, the high-frame rate of this system allowed the authors to determine that lacteals undergo cycles of rapid contraction and relaxation, which help move lipids into the lymphatic system. This rhythmic cycling was mediated by smooth muscles surrounding the lacteal and through neural inputs from the autonomic nervous system. Together, the data demonstrate the power of studying physiological systems in vivo with high-powered imaging systems. Moreover, these tools should lead to a more complete view of lipid and therapeutic drug uptake from the intestinal lumen. The accompanying movies show real-time imaging of murine intestinal lacteals on a custom-built video-rate laser scanning confocal microscope. Video 1 shows that the contractile movement of intestinal lacteals (green;Prox-GFP) drains dietary lipids (red). Video 2 shows smooth muscles (red; actin-dsRed) surrounding a contracting lacteal (green; Prox-GFP).
Lacteals are lymphatic vessels located at the center of each intestinal villus and provide essential transport routes for lipids and other lipophilic molecules. However, it is unclear how absorbed molecules are transported through the lacteal. Here, we used reporter mice that express GFP under the control of the lymphatic-specific promoter
Kibaek Choe, Jeon Yeob Jang, Intae Park, Yeseul Kim, Soyeon Ahn, Dae-Young Park, Young-Kwon Hong, Kari Alitalo, Gou Young Koh, Pilhan Kim