There is a continuous layer of cells around primary sensory neurons that are located in the dorsal root ganglia (DRG) and trigeminal ganglia. These cells are specialized cells called satellite glial cells (SGCs). According to Wang and team (2019), these cells are vital to control or regulate the transmission of signals within sensory ganglia as well as the microenvironment of the neurons. Research has also suggested that these cells can secrete and release chemical messengers such as ATP and cytokines. As they also express glutamine synthetase, their features are on the lines of that of astrocytes.
There are evident changes seen in SGCs biochemically and morphologically when there are injury and inflammation of peripheral nerves. Such damage and hence altered homeostasis cause an increased level of glial fibrillary acidic protein (GFAP) in SGCs becoming reactive.
Another article published by Menachem in Frontiers in Cellular Neuroscience in 2015 described that tyrosine hydroxylase was present in many SGCs in a colon inflammation model. This enzyme synthesizes norepinephrine associated with the sympathetic nervous system which in turn has been indicated in pain and injury. Studies in mice models revealed that inducing pain by the endotoxin lipopolysaccharide showed the same changes in SGCs seen in dorsal root ganglia. SGCs were also activated when inflammation of the colon was induced in rats. Thus, SGCs are implicated in pain: a key factor that hinders healthy life and activities!
Wang and team published an article in Neural regeneration research discussing SGC isolation from neonatal rat DRGs without digestion. DRGs were isolated from the spinal cavity of neonatal rats on 1:1 of DMEM/F12with penicillin/streptomycin on ice. These DRGs were cultured on SGC medium.
The cells obtained showed positive staining for SGC markers such as GS, GFAP, and S100β and were negative for SOX10 showing that the cells were SGCs and not Schwann cells. A point of interest was these cells also expressed nestin and P75NTR: markers for neural crest progenitors! Thus, SGCs possess features of neural stem cells.
Primary SGC cultures require study as these cells produce factors such as tumor necrosis factor-α involved in inflammation and pain. As there are several cells such as neurons, fibroblasts, Schwann cells along with SGCs in the DRG, a point that needs to be addressed is getting a pure SGC culture. While the addition of glutamine causes excess excitation in mature neurons thus, leading to their death-the culture still however contains glial cells. The Wang team used medium without serum-containing B27 that led to the lowered division of Schwann cells and fibroblasts thus, giving around 95% SGC purity.
DRGs from humans face challenges in terms of ethics hence several other models are used such as rats, cats, and chicken. The Wang article reported that in vitro culture of adult rats show lower cell survival and migration when compared to the neonatal rats they used. This becomes important given that the results are directly influenced by the age of animals used. A few additional points include:
- The activity of the cultured cells is more when the time of sampling the DRG is shorter.
- The tissue around the spinal cord should be removed with care and precision. Growth of DRG is facilitated while fibroblasts are suppressed when the surrounding surface envelope and neurofilaments are also removed from the DRG.
- in vitro is increased when the cells quickly attach to a growth matrix such as poly-D-lysine hydrobromide or poly-L-lysine.
HananiMenachem (2015) Role of satellite glial cells in gastrointestinal pain.Frontiers in Cellular Neuroscience(9): 412. URL=https://www.frontiersin.org/article/10.3389/fncel.2015.00412
Wang, X. B., Ma, W., Luo, T., Yang, J. W., Wang, X. P., Dai, Y. F., … Li, L. Y. (2019). A novel primary culture method for high-purity satellite glial cells derived from rat dorsal root ganglion. Neural regeneration research, 14(2), 339–345.doi:10.4103/1673-5374.244797