PKR Promotes Oxidative Stress and Apoptosis of Human Articular Chondrocytes by Causing Mitochondrial Dysfunction through p38 MAPK Activation—PKR Activation Causes Apoptosis in Human Chondrocytes

Abstract

Osteoarthritis (OA) is one of the most common types of arthritis in the elderly people. It has been known that chondrocyte apoptosis occurs in OA cartilage; however, the detailed molecular mechanism remains unclear. In the current study, we aimed to elucidate the role of double-stranded RNA-dependent protein kinase R (PKR) in the TNF-α-caused apoptosis in chondrocytes. Human articular chondrocytes were digested from cartilages of OA subjects who accepted arthroplastic knee surgery. Our results showed that phosphorylation of p38 MAPK was increased after TNF-α stimulation or PKR activation using poly (I:C), and TNF-α-induced p38 MAPK upregulation was inhibited by PKR inhibition, suggesting phosphor-p38 MAPK was regulated by PKR. Moreover, we found that PKR participated in the p53-dependent destruction of AKT following activation of p38 MAPK. The inhibition of AKT led to the reduced expression of PGC-1α, which resulted in mitochondrial dysfunction and increased oxidative stress. We showed that the reduction of oxidative stress using antioxidant Mito TEMPO lowered the TNF-α-induced caspase-3 activation and TUNEL-positive apoptotic cells. The diminished apoptotic response was also observed after repression of PKR/p38 MAPK/p53/AKT/PGC-1α signaling. Taken together, we demonstrated that the aberrant mitochondrial biogenesis and increased oxidative stress in chondrocytes after TNF-α stimulation were mediated by PKR, which may contribute to the chondrocyte apoptosis and cartilage degeneration in OA.

Chondrocyte Aging: The Molecular Determinants and Therapeutic Opportunities

“…ROS directly damage proteins, activate p38 MAPKinduced apoptosis and NF-κB-induced cartilage breakdown via upregulation of ADAMTS-5 and MMP13, suggesting the importance of oxidative damage and the IL-1 pathway in initiating the age-related changes that lead to the development of OA. In support of this mechanism, a recent study has revealed the involvement of double-stranded RNA-dependent protein kinase R (PKR) in regulating p38 MAPK and p53-dependent destruction of Akt, resulted in aberrant mitochondrial biogenesis and increased oxidative stress in chondrocytes (Ma et al, 2019). Predictions by computational modeling, show the inhibitory effect of blocking the IL-1 pathway on MMP13 production and inhibition of ALK1-mediated MMP-13 synthesis in the amelioration of cartilage degeneration of aged cartilage.…”

Targeting the integrated stress response in ophthalmology

“…Pharmacological activation of ISR signaling can be achieved by activating eIF2α kinases. Halofuginone, 124 histidinol, 116 asparaginase, 125 and arginine deiminase 126 are known to be GCN2 activators; BTdCPU activates HRI 127 ; BEPP and poly (I:C) are PKR activators 128,129 ; and CCT020312 130,131 is a selective PERK activator. These potential drugs were mostly studied for cancer treatment, and the application in ophthalmology fields is just emerging.…”

“…Poly (I:C), polyinosinic:poycytidylic acid, has similar structure to the doublestranded RNA which leads to PKR activation. 129 In vivo, topical and systemic administrated Poly (I:C) has been known for decades to induce tear interferon against HSV in rabbit and human eyes. 136,137…”

Medicinal plants used against various inflammatory biomarkers for the management of rheumatoid arthritis

“…[ 51,52 ] The p38/MAPK activation contributes to the inflammation apoptosis by increasing the BAX and releasing cytochrome c activating caspase‐3 causing apoptosis of chondrocytes associating the cartilage matrix degradation leading to pain and deformity of joint in arthritis. [ 53 ] The activated p38/MAPK causes the activation of transcriptional factors like TRAF1 and ATF2 contributing to the inflammation by elevating the expression of pro‐inflammatory mediators (TNF‐alpha, IL‐1 and IL‐6) promoting the oxidative stress mediating apoptosis. [ 53,54 ] Therefore, the inhibition of the p38/MAPK reduces the cytokine production further decreasing the inflammation and preventing the damaging of cartilages and joints.…”

“…[ 53 ] The activated p38/MAPK causes the activation of transcriptional factors like TRAF1 and ATF2 contributing to the inflammation by elevating the expression of pro‐inflammatory mediators (TNF‐alpha, IL‐1 and IL‐6) promoting the oxidative stress mediating apoptosis. [ 53,54 ] Therefore, the inhibition of the p38/MAPK reduces the cytokine production further decreasing the inflammation and preventing the damaging of cartilages and joints. [ 55 ] The herbal vegetative plants raspberry, blueberries , Punica granatum Linn and Gardenia jasminoides Ellis possessing active constituents like polyphenols and flavonoids (epicatechin‐3‐gallate, quercetin, hesperetin, myricetin, genistein, kaempferol, etc.)…”