Abstract
Introduction and Objective
Low back pain (LBP) is a disorder strongly associated with intervertebral disc degeneration (IDD) with an important impact on the quality of life of affected people. To date, LBP treatment is based on conservative methods with the aim to reduce back pain without restoring the degenerative environment of the disc. The main cause of IDD is the drastic reduction of the proteoglycan content within the nucleus pulposus (NP), eventually leading to the loss of disc water content, micro-architecture, biochemical and mechanical properties. A promising approach for disc regeneration is represented by the transplantation of mesenchymal stromal cells (MSCs). The exact mechanism remains unknown. Growing evidence suggests that MSCs can influence cells and modulate cells’ behaviour by secreting a set of bioactive factors. MSCs secretome is composed of several molecules such as soluble protein, lipids, nucleic acids and extracellular vesicles (EVs) involved in inflammation, immunomodulation, cell survival and intercellular communication. The aim of this study was to evaluate the in vitro effects of MSCs secretome on human NP cells (hNPCs) in a 3D culture model with and without inflammatory stimulus.
Materials and Methods
MSCs secretome was collected from bone marrow-MSCs (BM-MSCs) and adipose tissue-MSCs (ASCs) after centrifugation and obtained by culturing cells without fetal bovine serum (FBS) for 48 hours. hNPCs were isolated from surgical specimens through digestion with type II collagenase, culture expanded in vitro, encapsulated in alginate beads (three-dimensional culture system) and treated with growth medium (controls), BM-MSCs or ASCs secretome with or without interleukin-1 beta (IL-1b). After 7 days, total RNA was extracted and reverse-transcribed. Gene expression levels of catabolic and anabolic genes were analyzed through real time-polymerase chain reaction (qPCR). Cell proliferation and glycosaminoglycan (GAG) production was assessed by flow cytometry and 1,9-dimethylmethylene blue (DMMB), respectively. hNPCs in alginate beads were stained with Live/Dead assay and detected using confocal immunofluorescence microscopy. Data were analyzed using Graphpad prism 8 and expressed as mean ± S.D. One-way ANOVA analysis was used to compare differences among the groups under exam.
Results
Our results reported an increase of hNPCs proliferation after treatment with both MSCs-secretomes. In detail, cell proliferation levels increased at 7 days after ASC-secretome (p ≤ 0,05) and BM-secretome (p ≥ 0,05) treatment compared to control. Live/dead staining showed that cell death was reduced by BM-secretome (p ≤ 0,05); in combined treatment of BM-secretome with IL1b 10ng/mL (p ≤ 0,05) at 7 days compared to control. There is not a significant difference between treated and untreated hNPCs’ GAG synthesis. In addition, gene expression levels resulted to be modulated by MSCs-secretomes under study compared to controls.
Conclusions
Although the cell-therapy may be considered an attractive and safe option, MSCs require long and expensive processes. In conclusion, our experimental conditions supported as BM-MSCs and ASCs secretomes could represent cell-free alternative approaches in IDD, overcoming translational limits of cell therapy to the clinical practice.
