Cereblon expression in human peripheral blood mononuclear cells in response to in vitro stimulation with M. leprae

Background
The host immune responses associated with the clinical phenotypes of Mycobacterium leprae infection are not fully understood. The inflammatory complications of leprosy, leprosy reactions, particularly erythema nodosum leprosum (ENL), present therapeutic challenges. Thalidomide is an effective drug for ENL but is not widely available due to teratogenicity. Thalidomide binds cereblon (CRBN), a substrate receptor for the E3 ligase complex, promoting ubiquitination. Thus, we investigated the CRBN expression in human peripheral blood mononuclear cells (PBMCs) in response to in vitro stimulation with M. leprae with/without CRBN blockade peptide.

Methods
Blood samples were obtained from apparently BCG-vaccinated and BCGunvaccinated healthy volunteers. PBMC was isolated and stimulated with irradiated M. leprae with or without CRBN blockade peptide. CRBN, NF-kB, and PARK2 proteins were determined by ELISA, and their gene expression by qPCR.

Results
Stimulation with M. leprae significantly increased CRBN gene expression and protein production. Incubation of PBMCs with M. leprae with CRBN blockade significantly increased NF-kB expression. In a subgroup analysis, CRBN and NFkB gene expression following stimulation with M. leprae (p ≤ 0.05) was significantly higher in PBMCs from Mycobacterium bovis bacillus Calmette–Guérin (BCG)-vaccinated individuals compared to those from unvaccinated participants. PARK2 gene expression and parkin protein were significantly decreased in PBMCs stimulated with M. leprae compared to unstimulated PBMCs (p ≤ 0.05). In a subgroup analysis, PARK2 gene expression and parkin protein were decreased in the PBMCs from BCGunvaccinated individuals following incubation with M. leprae compared to those from BCG-vaccinated individuals. Stimulation of the PBMCs with M. leprae with CRBN blockade increased PARK2 gene expression and parkin protein production (p ≤ 0.05).

Conclusion
The findings are evidence that CRBN may have a role in modulating PARK2 and NF-kB gene expression in response to M. leprae infection. This needs further investigation in individuals with leprosy. The differential gene expression of CRBN and PARK2 in BCG-vaccinated and BCG-unvaccinated individuals could be further explored to understand the mechanism of BCG protection against leprosy.