Osteoarthritis is a leading cause of disability in the elderly with heavy burden on individuals, families and society. Today, for most non-terminally symptomatic patients, turning to medication for pain relief, but not a cure, is the main method for osteoarthritis treatment, and for terminal joint osteoarthritis patients, the only effective cure is the total joint replacement [2, 4]. Therefore, due to the unclear mechanism induced treatment resistent and high burden of osteoarthritis, illuminate the relationship between the nervous system and osteoarthritis may provide us a new method to solve the puzzle that osteoarthritis brings us.
Evidence from animal to clinical models have demonstrated that osteoarthritis-like joint damage is not only limited to the destruction of cartilage chondrocytes, synovial tissues, subchondral bone, but also associated with the disorder of the peripheral and central nervous system [9, 10].
It’s well known that joint pain evoking is mainly correlated with the sensitization of peripheral nociceptive neurons and hyperexcitability of nociceptive neurons in central nervous system, which is closely associated with the synovial inflammation. Lei et al. [11] suggested that SDIM1, whose overexpression exhibited a role of improving survival of neuro-progenitor cells after injury, showed an significantly increased expression in synovial tissues of osteoarthritis patients with high pain. Bullock et al. [12] revealed CGRP release might play an important role in the peripheral sensitization during joint degeneration in osteoarthritis. Brutus et al. [13] summarized four known functional genetic variants (SCN9A, COMT, TRPV1 and P2X7) in pain candidate genes that influence pain experiences in patients with osteoarthritis.
In this paper, bioinformatics technology was used to identify the DEGs of osteoarthritis, and at last, HES1, JUN, and IER2 were identified as the key genes that may take vital roles in the regulation of nervous system as well as osteoarthritis.
HES1, also known as Hes family bHLH transcription factor 1, is a downstream effector of Notch signaling. Activated Notch signaling can induce the activation of HES1 and hence inducing the expression of MMP13, which has the potential to promote the degradation of chondrogenic ECM, and resulted in the degeneration of cartilage [14]. Ni et al. [15] revealed that OSM is up-regulated in the synovial tissue of knee osteoarthritis and OSM-treated MC3T3-E1 cells showed a down-regulated HES1 in a time-dependent manner. Sugita et al. [16] reported that Hes1 induced Adamts5 and Mmp13, which are catabolic enzymes that break down cartilage matrix. Additionally, Matsuzaki, et al. [17] identified that Hes1 expression in mature neurons in the adult mouse brain is required for normal behaviors. Harris, et al. [18] demonstrated that HES1 has the potential of promoting the quiescence and proliferation of adult neural stem cells.
JUN, one of the transcription factor for activator protein 1, can mediate catabolic transcription, cell apoptosis and cell death. Chen et al. [19] reported that JUN was down-regulated in osteoarthritis knee cartilage compared to normal knee cartilage. Cai, et al. [20] demonstrated that osteoarthritis synovial tissues exhibit a decreased expression of JUN. While, studies also showed that blocking the JUN could prevent the degradation and apoptosis of chondrocytes [21], and the inhibition of JUN transcriptional activity protects against osteoarthritis cartilage destruction [22]. Moreover, studies also showed that JUN could participate in the regulation of antioxidant responses in neurons [23] and may have the potential of regulating the peripheral myelin development [24] and neuronal polarization during brain development [25].
IER2, short for immediate early response 2, is a protein function as a potential transcriptional factor or transcriptional coactivator which seems to play a pivotal role in regulating tumor cells. Xu et al. [26] reported that IER2 promotes the migration and invasion of hepatocellular carcinoma cell adhesion and motility. Xu et al. [27] demonstrated that IER2 promotes the migration and invasion of hepatocellular carcinoma cells via regulating the activity of Rho GTPases. Moreover, Moriya et al. [28] reported that ier2 mRNA was distributed in the telencephalon, midbrain and the hypothalamus. Besides, previous study [20] also reported that IER2 was down-regulated in osteoarthritis knee cartilage compared to normal knee cartilage. While, there is no research about IER2 on the specific mechanism of osteoarthritis and nervous system by now.
In this study, we demonstrated that HES1, JUN, and IER2 may take vital parts in the regulation of nervous system and osteoarthritis, and the result was validated by using qRT-PCR finally. Meanwhile, we also found that there are still somewhat controversial between the previous studies. Considering of this, there must be still have some unknown mechanism between these three genes, osteoarthritis as well as nervous system. So, it’s necessary to undertake more research to confirm our speculation.