Dioleoylphosphatidylglycerol Inhibits Heat Shock Protein B4 (HSPB4)-Induced Inflammatory Pathways In Vitro

Abstract

Our previous work shows that dioleoylphosphatidylglycerol (DOPG) accelerates corneal epithelial healing in vitro and in vivo by unknown mechanisms. Prior data demonstrate that DOPG inhibits toll-like receptor (TLR) activation and inflammation induced by microbial components (pathogen-associated molecular patterns, PAMPs) and by endogenous molecules upregulated in psoriatic skin, which act as danger-associated molecular patterns (DAMPs) to activate TLRs and promote inflammation. In the injured cornea, sterile inflammation can result from the release of the DAMP molecule, heat shock protein B4 (HSPB4), to contribute to delayed wound healing. Here, we show in vitro that DOPG inhibits TLR2 activation induced in response to HSPB4, as well as DAMPs that are elevated in diabetes, a disease that also slows corneal wound healing. Further, we show that the co-receptor, cluster of differentiation-14 (CD14), is necessary for PAMP/DAMP-induced activation of TLR2, as well as of TLR4. Finally, we simulated the high-glucose environment of diabetes to show that elevated glucose levels enhance TLR4 activation by a DAMP known to be upregulated in diabetes. Together, our results demonstrate the anti-inflammatory actions of DOPG and support further investigation into its development as a possible therapy for corneal injury, especially in diabetic patients at high risk of vision-threatening complications.

Phosphatidylglycerol to Treat Chronic Skin Wounds in Diabetes

“…Less well known is the fact that TLR2 also requires CD14 [ 90 , 91 , 92 ]. Indeed, we recently showed that a CD14-blocking antibody inhibited the activation of both TLR4 and TLR2 in response to PAMPs and DAMPs [ 93 ]. Kuronama et al [ 12 ] found that both CD14 and MD-2 can bind PG, and they have suggested that this binding interferes with the ability of these accessory proteins to bind microbial components such as LPS, thus inhibiting their capacity to promote TLR activation [ 94 ].…”

“…HMGB1 is reportedly a DAMP [ 131 ], functioning to activate pattern recognition receptors such as TLR4. In a recent study, we showed that HMGB1 activated TLR4, as monitored using a reporter cell line; importantly, DOPG inhibited TLR4 activation induced by HMGB1 [ 93 ]. In addition, several TLRs, including TLR2 and TLR4, are up-regulated in diabetic wounds, and TLR2- and TLR4-deficient knockout mice show accelerated wound healing [ 46 ].…”

“…In addition, several TLRs, including TLR2 and TLR4, are up-regulated in diabetic wounds, and TLR2- and TLR4-deficient knockout mice show accelerated wound healing [ 46 ]. The antimicrobial peptide S100A9 is increased in chronic wounds [ 46 ], and we have shown that S100A9 activates both TLR2 and TLR4; this S100A9-induced activation is inhibited by DOPG [ 15 , 93 ]. Thus, as noted above, the pro-proliferative, pro-differentiative, and anti-inflammatory actions of DOPG should be beneficial in promoting the healing of chronic skin wounds.…”