Techniques for RNA extraction from cells cultured in starPEG-heparin hydrogels

Abstract

Three-dimensional (3D) cell culture models that provide a biologically relevant microenvironment are imperative to investigate cell-cell and cell-matrix interactions in vitro. Semi-synthetic star-shaped poly(ethylene glycol) (starPEG)-heparin hydrogels are widely used for 3D cell culture due to their highly tuneable biochemical and biomechanical properties. Changes in gene expression levels are commonly used as a measure of cellular responses. However, the isolation of high-quality RNA presents a challenge as contamination of the RNA with hydrogel residue, such as polymer or glycosaminoglycan fragments, can impact template quality and quantity, limiting effective gene expression analyses. Here, we compare two protocols for the extraction of high-quality RNA from starPEG-heparin hydrogels and assess three subsequent purification techniques. Removal of hydrogel residue by centrifugation was found to be essential for obtaining high-quality RNA in both isolation methods. However, purification of the RNA did not result in further improvements in RNA quality. Furthermore, we show the suitability of the extracted RNA for cDNA synthesis of three endogenous control genes confirmed via quantitative polymerase chain reaction (qPCR). The methods and techniques shown can be tailored for other hydrogel models based on natural or semi-synthetic materials to provide robust templates for all gene expression analyses.

Keywords: RNA extraction; heparin; hydrogels; three-dimensional cell culture.

Figure 1.

Three-dimensional culture of cells in starPEG–heparin hydrogels. (a) Representative maximum intensity projection of a z-stack confocal image depicting the cells in a 3D microenvironment. Blue, DAPI; green, CD31; red, F-actin. Scale bar, 250 µm. (b) Photograph of a starPEG–heparin hydrogel. Scale bar, 5 mm. (c) (i) Hydrogel residue (arrowhead) on an RNA isolation column after centrifugation of the cell lysate. (ii) Observation of a pellet (arrowhead) following centrifugation of the cell lysate.

Figure 2.

UV–Vis spectrophotometry of RNA extracted with the Zymo kit. (a) Without an additional centrifugation step. (b) Following an additional centrifugation step prior to loading the cell lysate onto the RNA isolation column.

Figure 3.

UV–Vis spectrophotometry of RNA isolated with the Zymo kit. (a) No further purification. (b) Purified with PCR inhibitor removal column. (c) Purified using heparinase digestion. (d) Purified using heparinase digestion followed by PCR inhibitor removal column.

Figure 4.

Graphs and gel images obtained from the Bioanalyser. (a) Zymo kit, not purified. (b) Zymo kit, purified with PCR inhibitor removal column. (c) Zymo kit, heparinase digestion. (d) Zymo kit, heparinase digestion followed by PCR inhibitor removal column. (e) Norgen kit, not purified. (f) Norgen kit, purified with PCR inhibitor removal column. (g) Norgen kit, heparinase digestion. (h) Norgen kit, heparinase digestion followed PCR inhibitor removal column.