Duration of Reduction in Enduring Stress-Induced Hyperalgesia Via FKBP51 Inhibition Depends on Timing of Administration Relative to Traumatic Stress Exposure

Discovery of a Potent Proteolysis Targeting Chimera Enables Targeting the Scaffolding Functions of FK506-Binding Protein 51 (FKBP51)

The FK506-binding protein 51 (FKBP51) is a promising target in a variety of disorders including depression, chronic pain, and obesity. Previous FKBP51-targeting strategies were restricted to occupation of the FK506-binding site, which does not affect core functions of FKBP51. Here, we report the discovery of the first FKBP51 proteolysis targeting chimera (PROTAC) that enables degradation of FKBP51 abolishing its scaffolding function. Initial synthesis of 220 FKBP-focused PROTACs yielded a plethora of active PROTACs for FKBP12, six for FKBP51, and none for FKBP52. Structural analysis of a binary FKBP12:PROTAC complex revealed the molecular basis for negative cooperativity. Linker-based optimization of first generation FKBP51 PROTACs led to the PROTAC SelDeg51 with improved cellular activity, selectivity, and high cooperativity. The structure of the ternary FKBP51:SelDeg51:VCB complex revealed how SelDeg51 establishes cooperativity by dimerizing FKBP51 and the von Hippel-Lindau protein (VHL) in a glue-like fashion. SelDeg51 efficiently depletes FKBP51 and reactivates glucocorticoid receptor (GR)-signalling, highlighting the enhanced efficacy of full protein degradation compared to classical FKBP51 binding.

A DNA methylation signature in the stress driver gene Fkbp5 indicates a neuropathic component in chronic pain

BACKGROUND

Epigenetic changes can bring insight into gene regulatory mechanisms associated with disease pathogenicity, including chronicity and increased vulnerability. To date, we are yet to identify genes sensitive to epigenetic regulation that contribute to the maintenance of chronic pain and with an epigenetic landscape indicative of the susceptibility to persistent pain. Such genes would provide a novel opportunity for better pain management, as their epigenetic profile could be targeted for the treatment of chronic pain or used as an indication of vulnerability for prevention strategies. Here, we investigated the epigenetic profile of the gene Fkbp5 for this potential, using targeted bisulphite sequencing in rodent pre-clinical models of chronic and latent hypersensitive states.

RESULTS

The Fkbp5 promoter DNA methylation (DNAm) signature in the CNS was significantly different between models of persistent pain, and there was a significant correlation between CNS and peripheral blood Fkbp5 DNAm, indicating that further exploration of Fkbp5 promoter DNAm as an indicator of chronic pain pathogenic origin is warranted. We also found that maternal separation, which promotes the persistency of inflammatory pain in adulthood, was accompanied by long-lasting reduction in Fkbp5 DNAm, suggesting that Fkbp5 DNAm profile may indicate the increased vulnerability to chronic pain in individuals exposed to trauma in early life.

CONCLUSIONS

Overall, our data demonstrate that the Fkbp5 promoter DNAm landscape brings novel insight into the differing pathogenic origins of chronic pain, may be able to stratify patients and predict the susceptibility to chronic pain.

Corticosterone mediates FKBP51 signaling and inflammation response in the trigeminal ganglion in chronic stress-induced corneal hyperalgesia mice

Stress-induced hyperalgesia is a health-threatening condition that lacks effective therapeutic intervention, impairing the quality of life. Interestingly, a high prevalence of corneal pain symptoms was also found in patients experienced severe stressors. Excessive secretion corticosterone in rodents has been shown to contribute to the development of visceral and mechanical hyperalgesia under stressful conditions. The co-chaperone protein FK506-binding protein 5 (FKBP5) was reported to modulate steroid sensitivity and inhibition of FKBP51 possessed anxiolytic and anti-hyperalgesic in the stressed-mice model. However, whether corticosterone and FKBP5 play a role in chronic stress-induced corneal hyperalgesia remains unknown. The aim of this study was to evaluate the corneal sensitivity after exposure to chronic restraint stress (CRS) and investigate the potential role of corticosterone and FKBP5 mediated proinflammatory cytokines release in trigeminal ganglion (TG) in corneal hyperalgesia under chronic stressful situations. Firstly, mice displayed increased corneal sensitivity without changes in tear production and corneal injury after CRS for 4 hours/day for 14 days. Meanwhile, corticosterone deficiency via adrenalectomy could prevent CRS-induced corneal hyperalgesia, whereas chronic corticosterone feeding increased the corneal sensitivity accompanied by increasing proinflammatory cytokines levels of phospho-NF-κB (p-NF-κB), tumor necrosis factor (TNF)-α and interleukin (IL)-1β in the TG on d14. Notably, we found that FKBP51 was significantly upregulated in the TG in the stressed-mice. Intraperitoneal injection of FKBP51 inhibitor significantly alleviated CRS-induced corneal hyperalgesia, and reversed calcitonin gene related peptide (CGRP) increase and proinflammatory cytokines production in the TG. Moreover, FKBP51 inhibitor could also exert its anti-hyperalgesic effect on corneal pain through intra-TG injection. Our study proves that CRS can induce corneal hyperalgesia in mice and uncovers the role of corticosterone and FKBP51 in modulating corneal sensitivity, providing a novel treatment strategy for stress-induced corneal hyperalgesia. AVAILABILITY OF DATA AND MATERIALS: All data and additional file are available upon request from the corresponding author.

Analysis of the Selective Antagonist SAFit2 as a Chemical Probe for the FK506-Binding Protein 51

The FK506-binding protein 51 (FKBP51) has emerged as an important regulator of the mammalian stress response and is involved in persistent pain states and metabolic pathways. The FK506 analog SAFit2 (short for selective antagonist of FKBP51 by induced fit) was the first potent and selective FKBP51 ligand with an acceptable pharmacokinetic profile. At present, SAFit2 represents the gold standard for FKBP51 pharmacology and has been extensively used in numerous biological studies. Here we review the current knowledge on SAFit2 as well as guidelines for its use.