An improved method for processing chondroprogenitor pellets following chondrogenic differentiation for histology and immunohistochemical staining using agarose

Purpose

In-vitro models of cartilage regeneration based on pellet cultures have been widely used to evaluate chondrogenic potential of the cell of interest and predict probable in-vivo behavior. However, pellet processing is a major challenge during handling (due to small size and possible damage to structural contour following sectioning and staining). The present study aimed to utilize human articular cartilage derived chondroprogenitors to assess if agarose-encapsulation of pellets prior to paraffin processing enable easier handling without affecting tissue morphology, glycosaminoglycan staining and immunohistochemical analysis of Collagen type II protein.

Methods

Passage 3 chondroprogenitors (n = 3) were evaluated for MSC markers using flow cytometry and subjected to chondrogenic differentiation as pellets cultures. Post-differentiation, the pellets were subjected to either: a) paraffin embedding, b) agarose encapsulation followed by paraffin embedding or c) agarose encapsulation followed by cryosectioning. All sections were subjected to histological staining for glycosaminoglycan uptake: Alcian blue, Safranin O (Bern score) and Toluidine blue with immunohistochemical processing for collagen type II protein deposition.

Results

With respect to staining and structural integrity, comparable uptake was seen in both paraffin sections and agarose embedded sections while the latter exhibited notably uniform pellets with distinct marginal demarcation. Although plain paraffin and agarose encapsulated sections demonstrated equivalent staining as represented by comparable Bern scores, glycosaminoglycan uptake, and Collagen type II deposition, cryosections exhibited significantly poor staining properties.

Conclusion

Agarose encapsulation of differentiated pellets prior to routine paraffin embedding, eases handling difficulties whilst maintaining structural integrity with optimal staining outcomes.