Immunophilin Ligands Research Articles

Systematic investigation and comparison of US FDA-approved immunosuppressive drugs FK506, cyclosporine and rapamycin for neuromuscular regeneration following chronic nerve compression injury.

Aim: To compare therapeutic benefits of different immunophilin ligands for treating nerve injuries. Materials & methods: Cyclosporine, FK506 and rapamycin, were evaluated first in vitro on a serum-free culture of embryonic dorsal root gangliafollowed by a new in vivo model of chronic nerve compression. Results: Outcomes of the in vitro study have shown a potent effect of cyclosporine and FK506, on dorsal root ganglia axonal outgrowth, comparable to the effect of nerve growth factor. Rapamycin exhibited only amoderate effect. The in vivo study revealed the beneficial effects of cyclosporine, FK506 and rapamycin for neuromuscular regeneration. Cyclosporine showed the better maintenance of the tissues and function. Conclusion: Cyclosporine, FK506 and rapamycin drugs showed potential for treating peripheral nerve chronic compression injuries.

The Neurotrophic Effects and Mechanism of Action for FK1706 in Neurorrhaphy Rat Models and SH-SY5Y Cells.

FK1706 is a novel non-immunosuppressive immunophilin ligand with neurotrophic activity and exerts its neurotrophic effect through NGF. The present study aimed to elaborate on the neurotrophic activity and the mechanism of action of FK1706 in end-to-side neurorrhaphy rats and SH-SY5Y cells. In the regenerating nerves of neurorrhaphy rats, FK1706 increased the thickness of myelin sheath and the level of nerve regeneration-related proteins. The mechanism of action of FK1706 on neurite regrowth was elucidated in vitro by incubating SH-SY5Y cells in different conditions (Control, NGF, FK1706, NGF + FK1706, NGF + FK1706 + geldanamycin). Under the conditions where NGF was used, the phosphorylation level of major proteins (Raf-1 and ERK) in the Ras/Raf/MAPK/ERK signaling pathway related to SH-SY5Y cell proliferation was significantly enhanced following the application of FK1706. The number of viable cells, cell viability and neurite length of SH-SY5Y cells was maximal when NGF and FK1706 were used simultaneously. The binding level of HSP90 and Raf-1 in FK1706 group was the highest. These results indicated that FK1706 could significantly promote nerve regeneration after neurorrhaphy. The putative mechanism of action stated that FK1706 could promote the binding of HSP90 and Raf-1, make Raf-1 continue to be activated, thereby affecting key proteins in the Ras/Raf/MAPK/ERK signaling pathway related to the neurotrophic effects of NGF to promote the proliferation and neurite regrowth of nerve cells.

Topical RT1640 treatment effectively reverses gray hair and stem cell loss in a mouse model of radiation-induced canities.

Gray hair is a visible sign of tissue degeneration during aging. Graying is attributed to dysfunction of melanocyte stem cells (McSCs) that results in depletion of their melanin-producing progeny. This non-lethal phenotype makes the hair follicle and its pigment system an attractive model for investigating mechanisms that contribute to tissue aging and therapeutic strategies to combat this process. One potential combination therapeutic is RT1640, which is comprised of two drugs that are known to stimulate hair growth (cyclosporine A [CsA] and minoxidil), along with RT175, a non-immunosuppressive immunophilin ligand that is implicated in tissue regeneration. Using the ionizing radiation-induced acute mouse model of hair graying, we demonstrate that RT1640, over CsA alone, promotes regeneration of the hair pigment system during and following treatment. In non-irradiated mice, RT1640 is also physiologically active and successfully speeds hair growth and expands the McSC pool. It appears that this effect relies on the combined activities of the three drugs within RT1640 to simultaneously activate hair growth and McSCs as RT175 alone was insufficient to induce hair cycling in vivo, yet sufficient to drive the upregulation of the melanogenic program in vitro. This study sets the stage for further investigation into RT1640 and its components in McSC biology and, ultimately, melanocyte hypopigmentary disorders associated with disease and aging.

Nuclear immunophilin FKBP39 from Drosophila melanogaster drives spontaneous liquid-liquid phase separation

The FKBP39 from Drosophila melanogaster is a multifunctional regulatory immunophilin. It contains two globular domains linked by a highly charged disordered region. The N-terminal domain shows homology to the nucleoplasmin core domain, and the C-terminal domain is characteristic for the family of the FKBP immunophilin ligand binding domain. The specific partially disordered structure of the protein inspired us to investigate whether FKBP39 can drive spontaneous liquid-liquid phase separation (LLPS). Preliminary analyses using CatGranule and Pi-Pi contact predictors suggested a propensity for LLPS. Microscopy observations revealed that FKBP39 can self-concentrate to form liquid condensates. We also found that FKBP39 can lead to LLPS in the presence of RNA and peptides containing Arg-rich linear motifs derived from selected nuclear and nucleolar proteins. These heterotypic interactions have a stronger propensity for driving LLPS when compared to the interactions mediated by self-associating FKBP39 molecules. To investigate whether FKBP39 can drive LLPS in the cellular environment, we analysed it in fusion with YFP in COS-7 cells. The specific distribution and diffusion kinetics of FKBP39 examined by FRAP experiments provided evidence that immunophilin is an important driver of phase separation. The ability of FKBP39 to go into heterotypic interaction may be fundamental for ribosome subunits assembly.

Cyclophilin A inhibition as potential treatment of human aortic valve calcification

Aortic valve stenosis (AS) is a pathological condition that affects about 3% of the population, representing the most common valve disease. The main clinical feature of AS is represented by the impaired leaflet motility, due to calcification, which leads to the left ventricular outflow tract obstruction during systole. The formation and accumulation of calcium nodules are driven by valve interstitial cells (VICs). Unfortunately, to date, the in vitro and in vivo studies were not sufficient to fully recapitulate all the pathological pathways involved in AS development, as well as to define a specific and effective pharmacological treatment for AS patients.Cyclophilin A (CyPA), the most important immunophilin and endogenous ligand of cyclosporine A (CsA), is strongly involved in several detrimental cardiovascular processes, such as calcification. To date, there are no data on the CyPA role in VIC-mediated calcification process of AS. Here, we aimed to identify the role of CyPA in AS by studying VIC calcification, in vitro.In this study, we found that (i) CyPA is up-regulated in stenotic valves of AS patients, (ii) pro-calcifying medium promotes CyPA secretion by VICs, (iii) in vitro treatment of VICs with exogenous CyPA strongly stimulates calcium deposition, and (iv) exogenous CyPA inhibition mediated by CsA analogue MM284 abolished in vitro calcium potential. Thus, CyPA represents a biological target that may act as a novel candidate in the detrimental AS development and its inhibition may provide a novel pharmacological approach for AS treatment.

Bifunctional Small-Molecule Ligands of K-Ras Induce Its Association with Immunophilin Proteins.

Here we report the design, synthesis, and characterization of bifunctional chemical ligands that induce the association of Ras with ubiquitously expressed immunophilin proteins such as FKBP12 and cyclophilin A. We show this approach is applicable to two distinct Ras ligand scaffolds, and that both the identity of the immunophilin ligand and the linker chemistry affect compound efficacy in biochemical and cellular contexts. These ligands bind to Ras in an immunophilin-dependent fashion and mediate the formation of tripartite complexes of Ras, immunophilin, and the ligand. The recruitment of cyclophilin A to GTP-bound Ras blocks its interaction with B-Raf in biochemical assays. Our study demonstrates the feasibility of ligand-induced association of Ras with intracellular proteins and suggests it as a promising therapeutic strategy for Ras-driven cancers.

Bifunctional Small‐Molecule Ligands of K‐Ras Induce Its Association with Immunophilin Proteins

AbstractHere we report the design, synthesis, and characterization of bifunctional chemical ligands that induce the association of Ras with ubiquitously expressed immunophilin proteins such as FKBP12 and cyclophilin A. We show this approach is applicable to two distinct Ras ligand scaffolds, and that both the identity of the immunophilin ligand and the linker chemistry affect compound efficacy in biochemical and cellular contexts. These ligands bind to Ras in an immunophilin‐dependent fashion and mediate the formation of tripartite complexes of Ras, immunophilin, and the ligand. The recruitment of cyclophilin A to GTP‐bound Ras blocks its interaction with B‐Raf in biochemical assays. Our study demonstrates the feasibility of ligand‐induced association of Ras with intracellular proteins and suggests it as a promising therapeutic strategy for Ras‐driven cancers.

Effect of Different Doses and Times of FK506 on Different Areas of the Hippocampus in the Rat Model of Transient Global Cerebral Ischemia-Reperfusion.

Background Stroke is a major worldwide problem that is leading to a high mortality rate in humans. Ischemia, as the most common type of stroke, is characterized by tissue damage that can occur due to insufficient blood flow to the brain even for a brief duration, leading to the release of inflammatory factors, cytokines, and free radicals. In this study, we investigated the effective dose and injection time of FK506 as an immunophilin ligand for providing a suitable effect on cells of CA2, CA3, and dentate gyrus of the hippocampus. Methods In this in vivo study, a total of 48 male Wistar rats were divided into nine groups. The ischemia model was induced by the ligation of bilateral common carotid arteries. The doses of FK506 (3, 6, and 10 mg/kg) were administered intravenously (IV) at the beginning of reperfusion, followed by repeated injections (10 mg/kg) at 6, 24, 48, and 72 hours after ischemia, respectively. Brains were removed and prepared for Nissl staining and the TdT-mediated dUTP Nick End Labeling method. Results Data showed that global ischemia did not decrease the number of viable pyramidal cells in CA2 and CA3 regions, but significant differences were observed in the number of viable granular cells and apoptotic bodies in the dentate gyrus between the control and ischemia groups. Repeated doses of 6 mg/kg of FK506 at an interval of 48 hours were deemed to be the suitable dose and best time of injection. Conclusions It seems that FK506 can ameliorate the extent of apoptosis and may be a good candidate for the treatment of ischemia-induced brain damage.

Pharmacological induction of hypoxia-inducible transcription factor ARNT attenuates chronic kidney failure.

Progression of chronic kidney disease associated with progressive fibrosis and impaired tubular epithelial regeneration is still an unmet biomedical challenge because, once chronic lesions have manifested, no effective therapies are available as of yet for clinical use. Prompted by various studies across multiple organs demonstrating that preconditioning regimens to induce endogenous regenerative mechanisms protect various organs from later incurring acute injuries, we here aimed to gain insights into the molecular mechanisms underlying successful protection and to explore whether such pathways could be utilized to inhibit progression of chronic organ injury. We identified a protective mechanism controlled by the transcription factor ARNT that effectively inhibits progression of chronic kidney injury by transcriptional induction of ALK3, the principal mediator of antifibrotic and proregenerative bone morphogenetic protein-signaling (BMP-signaling) responses. We further report that ARNT expression itself is controlled by the FKBP12/YY1 transcriptional repressor complex and that disruption of such FKBP12/YY1 complexes by picomolar FK506 at subimmunosuppressive doses increases ARNT expression, subsequently leading to homodimeric ARNT-induced ALK3 transcription. Direct targeting of FKBP12/YY1 with in vivo morpholino approaches or small molecule inhibitors, including GPI-1046, was equally effective for inducing ARNT expression, with subsequent activation of ALK3-dependent canonical BMP-signaling responses and attenuated chronic organ failure in models of chronic kidney disease, and also cardiac and liver injuries. In summary, we report an organ-protective mechanism that can be pharmacologically modulated by immunophilin ligands FK506 and GPI-1046 or therapeutically targeted by in vivo morpholino approaches.

The effects of FK1706 on nerve regeneration and bladder function recovery following an end-to-side neurorrhaphy in rats.

BackgroundImmunophilin ligands are neuroregenerative agents binding to FK506 binding proteins, by which stimulate recovery of neurons in a variety of injury nerves. FK1706 is a novel immunophilin ligand which has neuroprotective and neuroregenerative effects but without immunosuppressive activity. At present, most reports about FK1706 in ameliorating nerve injury and functional recovery are limited to cavernous nerve injury and erectile function recovery. This study aimed to demonstrate the effects of FK1706 on nerve regeneration and bladder function recovery following an end-to-side neurorrhaphy in rat models.MethodThe numbers of regenerated myelinated axons of the pelvic parasympathetic nerve (PPN) in the three groups’ rats (FK1706 + ETS, ETS and control groups) were evaluated. Their intravesical pressure (IVP), S100β and growth associated protein 43 (GAP43) expressions were also compared.ResultsIn FK1706 + ETS group, 90% the rats showed that the frequency of FG labeled neurons was larger than the 3.5 cutoff value, 100% the rats showed that the frequency of FG-FB double-labeled neurons was larger than the 5.5 cutoff value. The average maximum of IVP in FK1706 + ETS group reached 76.3% of the value in control group. Their average number of myelinated axons of regenerated PPN reached 80% of the amount in control group. The nerve regeneration-associated markers data indicated that the expression level of S100β and GAP43 in FK1706 + ETS group was approximately 2-fold higher than that of ETS group (P < 0.05).ConclusionsAfter end-to-side neurorrhaphy, FK1706 effectively enhanced the nerve regeneration and bladder function recovery.

Neuroprotective and Nerve Regenerative Approaches for Treatment of Erectile Dysfunction after Cavernous Nerve Injury.

Erectile dysfunction (ED) is a significant cause of reduced quality of life in men and their partners. Cavernous nerve injury (CNI) during pelvic surgery results in ED in greater than 50% of patients, regardless of additional patient factors. ED related to CNI is difficult to treat and typically poorly responsive to first- and second-line therapeutic options. Recently, a significant amount of research has been devoted to exploring neuroprotective and neuroregenerative approaches to salvage erectile function in patients with CNI. In addition, therapeutic options such as neuregulins, immunophilin ligands, gene therapy, stem cell therapy and novel surgical strategies, have shown benefit in pre-clinical, and limited clinical studies. In the era of personalized medicine, these new therapeutic technologies will be the future of ED treatment and are described in this review.

A β-Turn Motif in the Steroid Hormone Receptor's Ligand-Binding Domains Interacts with the Peptidyl-prolyl Isomerase (PPIase) Catalytic Site of the Immunophilin FKBP52.

The immunophilin FKBP52 interacts with nuclear steroid hormone receptors. Studying the crystal structure of human estrogen receptor α (hERα) and using nuclear magnetic resonance, we show here that the short V(364)PGF(367) sequence, which is located within its ligand-binding domain and adopts a type II β-turn conformation in the protein, binds the peptidyl-prolyl isomerase (PPIase or rotamase) FK1 domain of FKBP52. Interestingly, this turn motif displays strong similarities with the FKBP52 FK1 domain-binding moiety of macrolide immunomodulators such as rapamycin and GPI-1046, an immunophilin ligand with neuroprotective characteristics. An increase in the hydrophobicity of the residue preceding the proline and cyclization of the VPGF peptide strengthen its recognition by the FK1 domain of FKBP52. Replacement of the Pro residue with a dimethylproline also enhances this interaction. Our study not only contributes to a better understanding of how the interaction between the FK1 domain of FKBP52 and steroid hormone receptors most likely works but also opens new avenues for the synthesis of FKBP52 FK1 peptide ligands appropriate for the control of hormone-dependent physiological mechanisms or of the functioning of the Tau protein. Indeed, it has been shown that FKBP52 is involved in the intraneuronal dynamics of the Tau protein.

Repair of Neurological Function in Response to FK506 Through CaN/NFATc1 Pathway Following Traumatic Brain Injury in Rats

Tacrolimus (FK506), an immunophilin ligand, has been widely shown to be neuroprotective in a posttraumatic period. The nuclear factor of activated T cells (NFATc1) pathway plays an important role in regenerating neurological function following traumatic brain injury (TBI), but the precise mechanism underlying FK506-induced repair of neurological functions remains unclear. In the present study, a total of 210 SD rats were enrolled and randomly divided into sham group, TBI group and FK506 group. The rats in the TBI and FK506 groups were inflicted with moderate TBI left lateral fluid percussion impact. A modified neurological severity score (mNSS) system was used to evaluate the severity of effects on nerve function. mNSS levels were significantly lower in the FK506 group than in the TBI group. The zaccumulation of cerebral water content was lower, cerebral Aquaporin 4 (AQP4) mRNA level was lower, the number of growth-associated protein-43 (GAP-43)-positive cells was higher, and the distribution of vesicles containing excitatory neurotransmitters was altered in the injured cortex in the FK506 group. Moreover, the cortical mRNA and serum protein expression levels of interleukin-2 (IL-2) and interferon-γ (IFN-γ) were decreased in FK506 group, especially at 6h and at 1day after TBI. At days 1-28 after TBI, the expression of cleaved-caspase 3, which indicates apoptosis, was lower in the FK506 group than in the TBI group. Mechanistically, FK506 significantly down-regulated the mRNA and protein levels of calcium-regulated phosphatase (calcineurin, CaN) and inhibited the activation of NFATc1. These results demonstrate that FK506 relieved inflammatory responses by regulating the NFATc1 signaling pathway and promoting the synaptic reconstruction of neurons and glial cells by regulating cell apoptosis, thereby facilitated improvements in neurological function.

Neuroprotective effects of the immunomodulatory drug FK506 in a model of HIV1-gp120 neurotoxicity.

BackgroundHIV-associated neurocognitive disorders (HAND) continue to be a common morbidity associated with chronic HIV infection. It has been shown that HIV proteins (e.g., gp120) released from infected microglial/macrophage cells can cause neuronal damage by triggering inflammation and oxidative stress, activating aberrant kinase pathways, and by disrupting mitochondrial function and biogenesis. Previous studies have shown that FK506, an immunophilin ligand that modulates inflammation and mitochondrial function and inhibits calcineurin, is capable of rescuing the neurodegenerative pathology in models of Parkinson’s disease, Alzheimer’s disease, and Huntington’s disease. In this context, the main objective of this study was to evaluate if FK506 could rescue the neuronal degeneration and mitochondrial alterations in a transgenic (tg) animal model of HIV1-gp120 neurotoxicity.MethodsGFAP-gp120 tg mice were treated with FK506 and analyzed for neuropathology, behavior, mitochondrial markers, and calcium flux by two-photon microscopy.ResultsWe found that FK506 reduced the neuronal cell loss and neuro-inflammation in the gp120 tg mice. Moreover, while vehicle-treated gp120 tg mice displayed damaged mitochondria and increased neuro-inflammatory markers, FK506 rescued the morphological mitochondrial alterations and neuro-inflammation while increasing levels of optic atrophy 1 and mitofusin 1. By two-photon microscopy, calcium levels were not affected in the gp120 tg mice and no effects of FK506 were detected. However, at a functional level, FK506 ameliorated the gp120 tg mice hyperactivity in the open field.ConclusionsTogether, these results suggest that FK506 might be potentially neuroprotective in patients with HAND by mitigating inflammation and mitochondrial alterations.

II. Dissociation free energies in drug-receptor systems via nonequilibrium alchemical simulations: application to the FK506-related immunophilin ligands.

The recently proposed fast switching double annihilation (FS-DAM) [Cardelli et al., J. Chem. Theory Comput., 2015, 11, 423] is aimed at computing the absolute standard dissociation free energies for the chemical equilibrium RL ⇌ R + L occurring in solution through molecular dynamics (MD) simulations at the atomistic level. The technique is based on the production of fast nonequilibrium annihilation trajectories of one of the species (the ligand) in the solvated RL complex and in the bulk solvent. As detailed in the companion theoretical paper, the free energies of these two nonequilibrium annihilation processes are recovered by using an unbiased unidirectional estimate derived from the Crooks theorem exploiting the inherent Gaussian nature of the annihilation work. The FS-DAM technique was successfully applied to the evaluation of the dissociation free energy of the complexes of Zn(ii) cations with an inhibitor of the Tumor Necrosis Factor α converting enzyme. Here we apply the technique to a real drug-receptor system, by satisfactorily reproducing the experimental dissociation free energies of FK506-related bulky ligands towards the native FKBP12 enzyme and by predicting the dissociation constants for the same ligands towards the mutant I56D. The effect of such mutations on the binding affinity of FK506-related ligands is relevant for assessing the thermodynamic forces regulating molecular recognition in FKBP12 inhibition.

Immunophilins: Structures, Mechanisms and Ligands.

Immunophilins consist of a family of highly conserved proteins which possess binding abilities to immunosuppressive drugs. Cyclophilins (Cyps) and FK506-binding proteins (FKBP) are family proteins collectively referred as immunophilins. Most Cyps and FKBP family members catalyse peptidyl-prolyl cis/trans isomerase (PPIase) mediated reactions and form binary complexes with their ligands cyclosporine A and FK506. Immunophilins are also involved in key biochemical processes including protein folding, receptor signalling, protein trafficking, and transcription and exhibit versatile biological functions, when complexed with their ligands. Therapeutic implications of immunophilins and effects of their ligands in neurodegenerative disorders, cancer, and infectious diseases have been accumulating in recent years. This review focuses on molecular characteristics of the canonical and non-canonical immunophilin family members from human and Plasmodium falciparum and P. vivax, recent progress on immunophilin inhibitor development, and future perspectives of structure-based design of non-immunosuppressive immunophilin ligands with potential pharmacological activities against infectious diseases.

Immunophilin ligands in peripheral nerve regeneration.

Immunophilins are a family of receptors for immunosuppressive drugs like cyclo-sporin A, FK506, rapamycin and their non-immunosuppressive analogues, which are collectively referred to as immunophilin ligands. The present study aimed to review neuroprotective and neuroregenerative actions of immunophilin ligands on peripheral nerve injuries. The special emphasis was given to well-known immunosuppressive drug FK506. Its historical background, administration routes, dosages, neuroregenerative, neuroprotective actions, therapeutic time window in administration, action mechanism and side effects of FK506 were reviewed.

Immunophilin-protein interactions in Plasmodium falciparum.

Immunophilins comprise two protein families, cyclophilins (CYPs) and FK506-binding proteins (FKBPs), and are the major receptors for the immunosuppressive drugs cyclosporin A (CsA) and FK506 (tacrolimus), respectively. Most eukaryotic species have at least one immunophilin and some of them have been associated with pathogenesis of infectious or parasitic diseases or the action of antiparasitic drugs. The human malarial parasite Plasmodium falciparum has 13 immunophilin or immunophilin-like genes but the functions of their products are unknown. We set out to identify the parasite proteins that interact with the major CYPs, PfCYP19A and PfCYP19B, and the FKBP, PfFKBP35, using a combination of co-immunoprecipitation and yeast two-hybrid screening. We identified a cohort of putative interacting partners and further investigation of some of these revealed potentially novel roles in parasite biology. We demonstrated that (i) P. falciparum CYPs interacted with the heat shock protein 70, (ii) treatment of parasites with CYP ligands disrupted transport of the rhoptry-associated protein 1, and (iii) PfFKBP35 interacted with parasite histones in a way that might modulate gene expression. These findings begin to elucidate the functions of immunophilins in malaria. Furthermore, the known antimalarial effects of CsA, FK506 and non-immunosuppressive derivatives of these immunophilin ligands could be mediated through these partner proteins.

2015 update of erectile dysfunction management following radical prostatectomy: from basic research to clinical management.

Radical prostatectomy (RP) is the most commonly employed curative intervention for the treatment of prostate cancer. However, due to the proximity of the cavernous nerves (CN) to the prostate, RP results in transient and/often permanent erectile dysfunction (ED). While the prevention of traction injuries during the RP is critical for the preservation of erectile function, several preclinical studies have demonstrated the beneficial effects of neuroprotective (or neuroregenerative) agents in mitigating neuronal injuries sustained during RP. The maintenance or restoration of erectile function after injury may be enhanced in the postoperative period by the stimulation of neurogenesis to protect and restore injured nerves from further deterioration. The present review aims to evaluate and summarize research of these treatment strategies as published in the National Library of Medicine (Pubmed) from 2000 to 2015. The keywords used for the search were ED, RP, CN injury, immunophilin ligands, neurotrophins and phosphodiesterase (PDE)5 inhibitors, and animal models. Current guidelines for treatment targeting CN recovery recommend the use of immunophilin ligands, neurotrophins, brain-derived neurotrophic factor, glial cell-line derived neurotrophic factor, sonic hedgehog (Shh), Rho-kinase, PDE5 inhibitors, erythropoietin (EPO), hyperbaric oxygen, gene, stem cells, and triiodothyronine (T3) therapy. Additionally, this review identifies remaining gaps in general knowledge and recent updates recognizing the need for further preclinical and clinical trials.

FK506 reduces neuroinflammation and dopaminergic neurodegeneration in an α-synuclein-based rat model for Parkinson's disease

Alpha-synuclein (α-synuclein) is considered a key player in Parkinson's disease (PD), but the exact relationship between α-synuclein aggregation and dopaminergic neurodegeneration remains unresolved. There is increasing evidence that neuroinflammatory processes are closely linked to dopaminergic cell death, but whether the inflammatory process is causally involved in PD or rather reflects secondary consequences of nigrostriatal pathway injury is still under debate. We evaluated the therapeutic effect of the immunophilin ligand FK506 in a rAAV2/7 α-synuclein overexpression rat model. Treatment with FK506 significantly increased the survival of dopaminergic neurons in a dose-dependent manner. No reduction in α-synuclein aggregation was apparent in this time window, but FK506 significantly lowered the infiltration of both T helper and cytotoxic T cells and the number and subtype of microglia and macrophages. These data suggest that the anti-inflammatory properties of FK506 decrease neurodegeneration in this α-synuclein-based PD model, pointing to a causal role of neuroinflammation in the pathogenesis of PD.