Novel immunosuppressive effect of FK506 by upregulation of PD-L1 via FKBP51 in heart transplantation

FKBP51 protects hair cells of utricles from gentamicin-induced toxicity in vitro: possible relation to the activities of NF-κB signaling pathway

FK506-binding protein 51 (FKBP51) belongs to the immunophilin family, which is related to regulation of cell growth and apoptosis. The present study was designed to explore the expression of FKBP51 in murine utricle hair cells (HCs) and the possible mechanisms underpinning the actions of FKBP51 relevant to gentamicin-mediated toxicity, with special attention given to nuclear factor-kappa B (NF-κB) activities in vitro. Here, we found, for the first time, that FKBP51 was widely expressed in both cytoplasm and cytomembrane. Moreover, the expression of FKBP51 in cultured HCs of utricle was downregulated after exposure to 1 mM gentamicin for 24 h. Then, the fkbp51 knockout mice were utilized to further investigate the role of FKBP51 in HCs in response to gentamicin. And the absence of FKBP51 led to severe HCs loss, accumulated ROS levels, and increased apoptotic factors, which could be alleviated by 2 mM N-acetyl-l-cysteine (NAC) to certain degree. In addition, mechanistic studies with 10 mM BAY 11-7082 showed that FKBP51 protected HCs against gentamicin-induced damage, at least in part, via blocking the NF-κB pathway activation. Taken together, our new findings suggest that FKBP51 might serve as a new target for the prevention of HCs of utricle from aminoglycoside-induced vestibular toxicity.

FKBP5 as a key regulator of metabolic processes in birds: Insights from chicken pectoral muscle

FK506-binding protein 5 (FKBP5) is a negative regulator of the glucocorticoid response and may play an important role in regulating metabolic homeostasis in birds. However, limited information is available regarding its role in avian species. This study aimed to clarify the spatiotemporal characteristics of chicken FKBP5 and investigate the effects of exogenous stimuli on its expression. Real-time quantitative PCR (RT-qPCR) was utilized to analyze the spatiotemporal expression patterns of FKBP5 in chickens. Additionally, the impact of exogenous stimuli, including fasting, energy restriction, and insulin/pyruvate/glucose injections, on FKBP5 expression in the pectoral muscle was investigated. The results showed that FKBP5 is broadly expressed in various bird tissues, with dominant expression in insulin-sensitive tissues. The FKBP5 levels in birds are dramatically modulated during development in insulin-sensitive tissues, with the highest expression observed in striated muscle and liver at embryonic day 19 (E19) (P < 0.01). The basal level of FKBP5 in the pectoral muscle of broilers is higher than that in Silky chickens. Insulin administration leads to a rapid drop in blood glucose levels in both breeds, with a slower recovery in AA broilers (P < 0.01). However, FKBP5 expression in the pectoral muscle initially shows a slight drop, followed by a sharp increase over time after insulin administration (P < 0.01). Additionally, breed heterogeneity in FKBP5 expression was observed in the pectoral muscle upon insulin stimulation, with broilers showing stronger insulin sensitivity compared to Silky chickens. A 24-hour fasting period downregulated blood glucose levels (P < 0.01) and FKBP5 expression in the pectoral muscle of AA broilers (P < 0.01). A 30% energy restriction over three weeks slightly reduced blood glucose levels (P = 0.075) and significantly decreased FKBP5 levels in the pectoralis muscle of broilers. In addition, pyruvate increased blood glucose and pectoralis FKBP5 transcription levels at 60 min (P < 0.01), whereas glucose increased blood glucose levels but had no effect on FKBP5 expression. Overall analysis showed a negative correlation between FKBP5 expression in the pectoral muscle and blood glucose levels (ρ = -0.405, P < 0.001). In conclusion, FKBP5 is a key player in the metabolic regulation of birds, with its expression being highly dynamic and tissue-specific. Insulin regulates FKBP5 expression in pectoral muscles in a time-dependent manner, while pyruvate increases FKBP5 levels and fasting/energy restriction reduces FKBP5 mRNA expression in the pectoral muscles.

Preparation and evaluation of novel oral tacrolimus nanocochleates for organ transplantation to reduce individual differences and improve drug safety

After organ transplantation, patients require treatment with immunosuppressive drugs to prevent immune rejection and transplantation failure. Tacrolimus (FK506) is a widely used immunosuppressant known for its potent immunosuppressive effect and narrow therapeutic range. Monitoring of FK506 blood concentrations is essential to avoid nephrotoxicity. In this study, a novel FK506 nanomedicine (FK506 cochleates) was developed using a microfluidic method to reduce variability among individuals and improve drug safety. The particle size of FK506 cochleates was (183.3 ± 1.4) nm, the zeta potential was -(39.28 ± 2.12) mV, and the encapsulation efficiency was more than 85 %. Particle size of FK506 cochleates could be maintained for up to 12 weeks in freeze-dried powder form. Small-angle X-ray scattering (SAXS) experiment confirmed the formation of cochleates by adding calcium solution. In vitro release studies demonstrated a sustained-release profile of FK506 from the cochleates carrier. Furthermore, the cochleates carrier could protect FK506 from the influence of stomach acid and slowly release the drug in the intestine. After oral administration, FK506 cochleates exhibited sustained-release properties in rats, accumulating in the spleen and lymph nodes - key anatomical sites for FK506's pharmacological action. Importantly, FK506 cochleates significantly prolonged the survival time in the rabbit heart transplantation model while maintaining good safety profiles. In conclusion, the FK506 cochleates showed promising potential for enhancing drug safety in therapeutic organ transplantation.

Programmed Death Ligand-1-Overexpressing Donor Exosomes Mediate Donor-Specific Immunosuppression by Delivering Co-Inhibitory Signals to Donor-Specific T Cells

Programmed death ligand-1 (PD-L1) and donor antigens are critical for donor immature dendritic cells (DCs) targeting donor-specific T cells to induce transplant tolerance. This study aims to clarify whether DC-derived exosomes (DEX) with donor antigens (H2b) and high levels of PD-L1 expression (DEXPDL1+ ) can help to suppress graft rejection. In this study, it is demonstrated that DEXPDL1+ presents donor antigens, as well as PD-L1 co-inhibitory signals, directly or semi-directly via DCs to H2b-reactive T cells. This dual signal presentation can prolong the survival of heart grafts from B6 (H2b) mice but not from C3H (H2k) mice by inhibiting T cell activation, inducing activated T cell apoptosis, and modulating the balance of T cell differentiation from inflammatory to regulatory. Additionally, even though DEXPDL1+ treatment cannot induce tolerance after short-term treatment, this study provides a new vehicle for presenting co-inhibitory signals to donor-specific T cells. This novel strategy may facilitate the realization of donor-specific tolerance via the further optimization of drug-loading combinations and therapeutic regimens to elevate their killing ability.

Role of FKBP5 and its genetic mutations in stress-induced psychiatric disorders: an opportunity for drug discovery

Stress-induced mental health disorders are affecting many people around the world. However, effective drug therapy for curing psychiatric diseases does not occur sufficiently. Many neurotransmitters, hormones, and mechanisms are essential in regulating the body's stress response. One of the most critical components of the stress response system is the hypothalamus-pituitary-adrenal (HPA) axis. The FKBP prolyl isomerase 51 (FKBP51) protein is one of the main negative regulators of the HPA axis. FKBP51 negatively regulates the cortisol effects (the end product of the HPA axis) by inhibiting the interaction between glucocorticoid receptors (GRs) and cortisol, causing reduced transcription of downstream cortisol molecules. By regulating cortisol effects, the FKBP51 protein can indirectly regulate the sensitivity of the HPA axis to stressors. Previous studies have indicated the influence of FKBP5 gene mutations and epigenetic changes in different psychiatric diseases and drug responses and recommended the FKBP51 protein as a drug target and a biomarker for psychological disorders. In this review, we attempted to discuss the effects of the FKBP5 gene, its mutations on different psychiatric diseases, and drugs affecting the FKBP5 gene.

The role of PD-1 signaling in health and immune-related diseases

Programmed cell death 1 receptor (PD-1) and its ligands constitute an inhibitory pathway to mediate the mechanism of immune tolerance and provide immune homeostasis. Significantly, the binding partners of PD-1 and its associated ligands are diverse, which facilitates immunosuppression in cooperation with other immune checkpoint proteins. Accumulating evidence has demonstrated the important immunosuppressive role of the PD-1 axis in the tumor microenvironment and in autoimmune diseases. In addition, PD-1 blockades have been approved to treat various cancers, including solid tumors and hematological malignancies. Here, we provide a comprehensive review of the PD-1 pathway, focusing on the structure and expression of PD-1, programmed cell death 1 ligand 1 (PD-L1), and programmed cell death 1 ligand 2 (PD-L2); the diverse biological functions of PD-1 signaling in health and immune-related diseases (including tumor immunity, autoimmunity, infectious immunity, transplantation immunity, allergy and immune privilege); and immune-related adverse events related to PD-1 and PD-L1 inhibitors.

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.