Hyaluronic acid-laminin hydrogels increase neural stem cell transplant retention and migratory response to SDF-1α

Abstract

The chemokine SDF-1α plays a critical role in mediating stem cell response to injury and disease and has specifically been shown to mobilize neural progenitor/stem cells (NPSCs) towards sites of neural injury. Current neural transplant paradigms within the brain suffer from low rates of retention and engraftment after injury. Therefore, increasing transplant sensitivity to injury-induced SDF-1α represents a method for increasing neural transplant efficacy. Previously, we have reported on a hyaluronic acid-laminin based hydrogel (HA-Lm gel) that increases NPSC expression of SDF-1α receptor, CXCR4, and subsequently, NPSC chemotactic migration towards a source of SDF-1α in vitro. The study presented here investigates the capacity of the HA-Lm gel to promote NPSC response to exogenous SDF-1α in vivo. We observed the HA-Lm gel to significantly increase NPSC transplant retention and migration in response to SDF-1α in a manner critically dependent on signaling via the SDF-1α-CXCR4 axis. This work lays the foundation for development of a more effective cell therapy for neural injury, but also has broader implications in the fields of tissue engineering and regenerative medicine given the essential roles of SDF-1α across injury and disease states.

Keywords: Biomaterials; CXCL12; Chemotaxis; Neural progenitor cells; Regenerative medicine; Tissue engineering.

Figure 1

Schematic illustrating the effect of the HA-Lm gel on NPSCs. After 48 hours of culture on the HA-Lm gel, NSPCs (shown as blue cells) upregulate CXCR4 (shown as green cell surface receptor) (A). This correlates with increased NPSC chemotactic migration towards an SDF-1α source (shown in orange and labeled) that is dependent on both HA and laminin components of the gel (B)[30].

Figure 2

Experimental overview and schematic illustrating NPSC retention and migration. SDF-1α was injected 0.5 mm lateral of the NPSC injection site and NPSC retention was calculated based on image sections including both needle tracks (i), where NPSC migration was calculated based on image sections excluding NPSCs that remained within the needle track (ii).

Figure 3

NPSC retention and migration at days 1 and 3. Representative images demonstrate increased NPSC retention (overview) and migration (inset) in the HA-Lm gel at days 1 (B) and 3 (D) compared to bolus NPSC injections (A, C, respectively). NPSC retention was quantified as shown in the schematic (Ei). Average NPSC retention was significantly increased at 1 and 3 days when transplanted in the HA-Lm gel compared to bolus (Eii). Overview scale bar is 150 μm, inset scale bar is 100 μm. *p<0.05 compared to bolus of same time point.

Figure 4

SDF-1α gradient quantification. SDF-1α stained sections demonstrate the injection sites of bolus SDF-1α and NPSCs in bolus (A) and HA-Lm (B) transplant groups at 3 days after injection. SDF-1α gradients, reported as average pixel intensity of SDF-1α channel, were maintained out to 3 days after injection and were not significantly different between bolus and HA-Lm NPSC groups (p≥0.2889, C).

Figure 5

Quantitative analysis of NSPC migration at days 1 and 3. The count of NPSCs migrating away from the injection site towards the exogenous SDF-1α was significantly increased in the HA-Lm gel compared to bolus injection at both 1 and 3 days (A). When normalized to NPSC retention, the HA-Lm gel increased sustained NPSC migration compared to bolus conditions (B,C). NPSCs transplanted bolus exhibited reduced numbers of migrating NPSCs at day 3 compared to day 1, while NPSC migration at day 3 was increased over that at day 1 when transplanted in the HA-Lm gel (not significantly different, B). Sustained NPSC migration at day 3 to a distance of 0.23 – 0.345 mm away from NPSC injection site was significantly increased when transplanted in the HA-Lm gel compared to bolus (C). *p<0.05 compared to bolus injection group of same time point.

Figure 6

Pre-incubation with AMD3100 significantly reduced NPSC migration, but not NPSC retention at 3 days. Representative images illustrate high NPSC retention (A) and reduction in NPSC migration at day 3 (B). Average NPSC retention in the HA-Lm gel is not significantly different with the addition of AMD3100 pre-incubation at 3 days (p=0.6377, B). However, NPSC migration is significantly reduced when pre-incubated with AMD3100 compared to NPSCs transplanted within the HA-Lm gel without AMD3100 pre-incubation(D). *p<0.05 compared to all other groups. Overview scale bar is 250 μm, inset scale bar is 100 μm.