65 Phagocytotic Activity of Mesenchymal Stem Cells Is an Important Mechanism in Repairing the Damaged Mesangium.

Objectives: Mesangial damage represents a crucial event in the pathogenesis and progression of many renal diseases. Using mesenchymal stem cells (MSCs) to repair the damaged mesangium has been shown to be a very promising therapeutic approach. However, the precise roles MSCs play in the repair process are still unclear. In the present study, we investigated the phagocytotic function of MSCs using fluorescent latex beads during the mesangium repair process. Methods: Mesangial cells (MCs) were cultured as a single layer in 48 glass-bottom well plates. Confluent MCs were made quiescent for 48 hours. Then they were incubated with glomerulopathic light chains (GLCs; 10 ug/mL), which were purified from the urine of patients with renal biopsy-proven light chain-related amyloidosis (n = 3) and light chain deposition disease (n = 3) for four days to establish an in vitro mesangial injury model. Subsequently, green fluorescent protein-labeled MSCs together with the florescent-labeled latex beads were added to assess the phagocytotic activity of MSCs. The entire process was monitored by fluorescence microscopy, and sequential photos were taken with the 6D Life Cell Imaging System (Carl Zeiss Microscopy, Thornwood, NY). Samples were collected 10 days after the introduction of the MSCs (day 14), and processed for light and transmission electron microscopy (TEM). Results: Within 24 hours, MSCs migrated to the damaged mesangial areas and transformed into a macrophage phenotype (CD68+, CD29−). During the repair process, florescent-labeled latex beads were engulfed by the transformed MSCs observed by fluorescence microscopy and further confirmed by TEM, indicating active phagocytotic function of MSCs. Conclusion: MSCs undergo both morphological and functional transformations as they proceed to repair the damaged mesangium. In contrast to previously believed paracrine fashion as the primary mode of MSCs repair, we provided strong evidence that phagocytotic activity of MSCs is an important mechanism involved in mesangial repairing. [ABSTRACT FROM AUTHOR]