Cellular uptake and subsequent intracellular trafficking of R8-liposomes introduced at low temperature

Intracellular trafficking is a determining factor in the transgene expression efficiency of gene vectors. In the present study, the mechanism of the cellular uptake of octaarginine (R8)-modified liposomes, when introduced at 37 °C and 4 °C, was investigated in living cells. Compared with 37 °C, the uptake of R8-liposomes was only slightly reduced at 4 °C. Dual imaging of liposomes and plasma membranes revealed that R8-liposomes were internalized by vesicular transport, and partially escaped to the cytosol at the perinuclear region at 37 °C. When introduced at 4 °C, intracellular liposomes were observed within a specific region close to the plasma membrane, and internalization of the plasma membrane was completely inhibited. Therefore, at 4 °C, R8-liposomes appear to enter cells via unique pathway, which is separate and distinct from energy-dependent vesicular transport. The subsequent nuclear delivery of encapsulated pDNA, when introduced at 4 °C, was less prominent compared with those introduced at 37 °C. Collectively, these findings demonstrate that a vesicular transport-independent pathway is responsible for the cellular uptake of liposomes. In addition, the uptake route is closely related to the subsequent nuclear delivery process; the operation of an endogenous vesicular sorting system is advantageous for the nuclear delivery of pDNA.