Particle tracking analysis for the intracellular trafficking of nanoparticles modified with African swine fever virus protein p54-derived peptide

Abstract

Previous studies showed that the cytoplasmic transport of nanoparticles to the nucleus is driven by a vesicular sorting system. Artificial approaches for targeting a microtubule-associating motor complex is also a challenge. We describe herein the development of a liposomal nanoparticle, the surface of which is modified with stearylated octa-arginine (STR-R8), and a dynein light chain (LC8)-associated peptide derived from an African swine fever virus protein p54 (p54(149-161)) with polyethyleneglycol (PEG) as a spacer (p54(149-161)-PEG/R8-liposomal nanoparticles (LNPs)). The p54(149-161)-PEG/R8-LNPs preferentially gain access to the nucleus, resulting in a one- to two-order of magnitude higher transfection activity in comparison with p54(149-161)-free nanoparticles (PEG/R8-LNPs). Further studies of particle tracking in HeLa cells stably expressing green fluorescent protein (GFP)-tagged tubulin (GFP/Tub-HeLa) indicate that p54(149-161) stimulated the transport of nanoparticles along fibrous tubulin structures. Moreover, a part of the p54(149-161)-PEG/R8-LNPs appeared to undergo quasi-straight transport without sharing the tracks corresponding to PKH67, the plasma membrane of which had been prestained with a marker just before transfection, while corresponding movement was never observed in the case of PEG/R8-LNPs. These findings suggest that a portion of the p54(149-161)-modified nanoparticles can use microtubule-dependent transport without the need for an assist by a vesicular sorting system.

Figure 1

Design of nanoparticles. pDNA was condensed with protamine, and thereafter encapsulated in the lipid envelope. A cysteine-introduced and C-terminally amidated peptides was conjugated to the Mal-PEG-DSPE via a Michael addition reaction to prepare the peptide-conjugated PEG lipid (peptide-PEG-DSPE). The surface of the nanoparticles was modified with octa-arginine (R8) and PEG by incorporating the stearylated-R8 (STR-R8) and synthesized peptide-PEG-DSPEs. PEG, polyethylene glycol.

Figure 2

Transfection activity and intracellular copy numbers of pDNA delivered with LNPs. (a) PEG/R8-LNPs and peptide-conjugated PEG/R8- LNPs were transfected to HeLa cells for 24 hours. Each bar represents the mean gene expression of the reporter gene (luciferase) ± SD. Indicated molar percentage (to the total lipid amount) of peptide-PEG-DSPE or PEG-DSPE was incorporated into the lipid envelope. Asterisks represent a significant difference, as determined by the Mann–Whitney U-test (*P < 0.05). (b) PEG/R8-LNPs and p54_149-161-PEG/R8-LNPs (2 µg pDNA) at 37 ^oC for 6 hours. After purification of the cellular DNA, intracellular copy numbers were quantified by Real-time PCR. Data are represented as the mean ± SD (N = 3). Asterisks represent a significant difference determined by one-way ANOVA, followed by Student's t-test. (c) The cells were incubated with PEG/R8- LNPs or p54_149-161-PEG/R8-LNPs in serum-free medium in the presence or absence of 10 µmol/l nocodazole for 3 hours, followed by incubation in Dulbecco's modified Eagle medium containing 10% serum and 100 µmol/l _D-luciferin. The time shown in the x-axis started from the addition of LNP solutions and the measurement started from 4 hours. The insert represents the relative gene expressions of LNPs from 4 to 12 hours in the absence of nocodazole, normalized by those at 12 hours. Statistical analyses were performed by one-way ANOVA followed by Bonferroni's multiple comparison test (**P < 0.01 against PEG/R8-LNPs, and ^##P < 0.01 against nocodazole-treated condition) or one-way ANOVA followed by Student's t-test (inset; *P < 0.05 and **P < 0.01 against PEG/R8-LNPs). LNP, liposomal nanoparticles; PEG, polyethylene glycol.

Figure 3

Imaging of PEG/R8-LNPs and p54_149-161-PEG/R8-LNPs for the analysis of intracellular trafficking. (a) PEG/R8-LNPs and (b) p54_149-161- PEG/R8-LNPs encapsulating rhodamine-labeled pDNA were transfected to GFP/Tub-HeLa cells for 1, 2, and 3 hours (represented in left, middle, and right panels, respectively). GFP, green fluorescent protein; PEG, polyethylene glycol.

Figure 4

A series of time lapse images for PEG/R8-LNPs and p54_149-161- PEG/R8-LNPs. Typical particle tracks of (a) PEG/R8-LNPs and (b) p54_149-161-PEG/R8-LNPs obtained for 10-second frame intervals are represented. The original videos are represented in Supplementary Video S1 and S2 online. In the far right column, overlay images are represented to show the trajectories. PEG, polyethylene glycol.

Figure 5

Dual imaging of vesicular transport and LNPs. (a and b) Typical images for the directional transport of PEG/R8-LNPs (a) and p54_149-161-PEG/R8-LNPs (b) encapsulating rhodamine-labeled pDNA. Rhodamine-pDNA was represented as red. The transport vesicles stained with PKH67 are represented as green. In the rightmost column, overlay images were represented to show the trajectories. (c) The average velocities (v) obtained by the curve fitting of MSD-Δt curves for quasi-straight trajectories of PEG/R8-LNPs (n = 12) and p54_149-161-PEG/R8-LNPs (n = 12) was plotted. Black bars represent the mean values. PEG, polyethylene glycol.

Figure 6

A series of time lapse images for PEG/R8-LNPs and p54_149-161- PEG/R8-LNPs free from the vesicular transport. (a) PEG/R8-LNPs and (b) p54_149-161-PEG/R8-LNPs encapsulating rhodamine-pDNA was transfected to the HeLa cells prestained by PKH67. Typical examples of the particles free from co-localization with endosomal compartment are shown. In the rightmost column, overlay images were represented to show the trajectories. (c) The average velocity (v) obtained by the curve fitting of MSD-Δt curves for quasi-straight trajectories of p54_149-161-PEG/R8- LNPs (n = 14) was plotted. Black bar represent the mean values. Quasi-straight trajectory was not observed in PEG/R8-LNPs. N.D., not detected; PEG, polyethylene glycol.