Role of Proprotein Convertase Subtilisin/Kexin Type 9 in the Pathogenesis of Graves’ Orbitopathy in Orbital Fibroblasts

Abstract

BackgroundThe proprotein convertase subtilisin/kexin type 9 (PCSK9) has been implicated in the pathogenesis of inflammatory diseases. We sought to investigate the role of PCSK9 in the pathogenesis of Graves’ orbitopathy (GO) and whether it may be a legitimate target for treatment.MethodsThe PCSK9 was compared between GO (n=11) and normal subjects (n=7) in orbital tissue explants using quantitative real-time PCR, and in cultured interleukin-1β (IL-1β)-treated fibroblasts using western blot. Western blot was used to identify the effects of PCSK9 inhibition on IL-1β-induced pro-inflammatory cytokines production and signaling molecules expression as well as levels of adipogenic markers and oxidative stress-related proteins. Adipogenic differentiation was identified using Oil Red O staining. The plasma PCSK9 concentrations were compared between patients with GO (n=44) and healthy subjects (n=26) by ELISA.ResultsThe PCSK9 transcript level was higher in GO tissues. The depletion of PCSK9 blunted IL-1β-induced expression of intercellular adhesion molecule 1 (ICAM-1), IL-6, IL-8, and cyclooxygenase-2 (COX-2) in GO and non-GO fibroblasts. The levels of activated nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and phosphorylated forms of Akt and p38 were diminished when PCSK9 was suppressed in GO fibroblasts. Decreases in lipid droplets and attenuated levels of peroxisome proliferator-activated receptor gamma (PPARγ), CCAAT/enhancer-binding protein β (C/EBPβ), and leptin as well as hypoxia-inducible factor 1α (HIF-1α), manganese superoxide dismutase (MnSOD), thioredoxin (Trx), and heme oxygenase-1 (HO-1) were noted when PCSK9 was suppressed during adipocyte differentiation. The plasma PCSK9 level was significantly higher in GO patients and correlated with level of thyrotropin binding inhibitory immunoglobulin (TBII) and the clinical activity score (CAS).ConclusionsPCSK9 plays a significant role in GO. The PCSK9 inhibition attenuated the pro-inflammatory cytokines production, oxidative stress, and fibroblast differentiation into adipocytes. PCSK9 may serve as a therapeutic target and biomarker for GO.

Association of fibroblast growth factor 10 with the fibrotic and inflammatory pathogenesis of Graves’ orbitopathy

“…In this study, although basal levels of FGF10 differed between GO and non-GO orbital tissues and primary cells, the inhibitory effect of FGF10 on fibrosis did not differ between GO and non-GO cells. According to previous studies [ 20 , 33 – 35 ], GO and non-GO cells under primary culture conditions often show similar patterns of response to stimulation and inhibition of specific targets that may not reflect actual clinical events. Nonetheless, it is notable that our study found a significant difference in FGF10 expression levels between GO and non-GO tissues and OFs.…”

Insight into the Evolving Role of PCSK9

“…However, elevated levels of PCSK9 have been found in patients with Graves’ orbitopathy and its concentration has positively correlated with autoantibodies against TSH receptor and clinical activity score. In vitro studies showed that PCSK9 inhibition significantly reduced pro-inflammatory cytokines production, oxidative stress markers and adipocytes formation in Graves’ orbitopathy [ 139 ]. Those observations suggest that PCSK9 level might be considered as a potential marker in the course of Graves’ orbitopathy.…”

Thyroid eye disease

“…[ 102 ] Orbital adipose tissue from TED patients had higher PCSK9 transcript levels than controls and knock-down of PCSK9 blocked proinflammatory cytokine production and adipogenesis in Graves’ OFs, suggesting PCSK9 as a potential promising therapeutic target. [ 103 ]…”