Immunophilin FKBP52 Research Articles

Decrease of the Immunophilin FKBP52 Accumulation in Human Brains of Alzheimer's Disease and FTDP-17

Human neurodegenerative diseases characterized by abnormal intraneuronal inclusions of the tau protein, or "tauopathies", include Alzheimer's disease (AD), Pick's disease, progressive supranuclear palsy, corticobasal degeneration as well as fronto-temporal dementia and Parkinsonism linked to chromosome 17 (FTDP-17). Several abnormalities of tau may contribute to the pathological processes, yet the mechanisms involved in tau cellular toxicity remain unclear. Previously, we demonstrated an interaction between various isoforms of tau and the immunophilin FKBP52 (FK506-Binding Protein), suggesting a direct involvement of FKBP52 in tau function. Here we analyze the expression of FKBP52 in human brains of patients with different tauopathies, including AD. Immunohistofluorescence studies carried out on cerebral cortex in different tauopathies reveal that FKBP52 is not sequestered by filamentous tau inclusions while FKBP52 is colocalized with tau in the control case brains. We found that FKBP52 expression level is abnormally low in frontal cortex of AD and FTDP-17 brains, as compared to controls, despite no alteration in the FKBP52 mRNA expression level. The possible involvement of FKBP52 in pathological tau expression/function is discussed.

Galectin-1 Markedly Reduces the Incidence of Resorptions in Mice Missing Immunophilin FKBP52

Progesterone (P(4)) signaling is critical for pregnancy. We previously showed that immunopilin FK506 binding protein (FKBP)52 serves as a cochaperone to optimize progesterone receptor (PR) function in the uterus, and its deficiency leads to P(4) resistance in a pregnancy stage-specific and genetic background-dependent manner in mice. In particular, sc placement of SILASTIC implants carrying P(4) rescued implantation failure in CD1 Fkbp52(-/-) mice, but the resorption rate was substantially high at midgestation due to reduced P(4) responsiveness. Because downstream targets of P(4)-FKBP52-PR signaling in the uterus to support pregnancy are not clearly understood, we performed proteomic analysis using Fkbp52(-/-), PR-deficient (Pgr(-/-)), and wild-type (WT) uteri. We found that the expression of galectin-1 (Gal1), an evolutionarily conserved glycan-binding protein, was significantly down-regulated in both Fkbp52(-/-) and Pgr(-/-) uteri compared with WT uteri. During early gestation, Lgals1, which encodes Gal1, was distinctly expressed in stromal and decidual cells. Lgals1 expression was much lower in d 4 Fkbp52(-/-) uteri compared with WT uteri, and this reduction was reversed by P(4) supplementation. More interestingly, concomitant supplementation of recombinant Gal1 significantly suppressed the high resorption rate and leukocyte infiltration at implantation sites in CD1 Fkbp52(-/-) females carrying P(4) SILASTIC implants. These findings suggest that uterine Gal1 is an important downstream target of P(4)-FKBP52-PR signaling in the uterus to support P(4) responsiveness during pregnancy.

Cytoplasmic travels of the ecdysteroid receptor in target cells: pathways for both genomic and non-genomic actions.

Signal transduction of the insect steroid hormones, ecdysteroids, is mediated by the ecdysteroid receptor, EcR. In various cells of the insect Rhodnius prolixus, EcR is present in both the nucleus and the cytoplasm, where it undergoes daily cycling in abundance and cellular location at particular developmental times of the last larval instar that are specific to different cell types. EcR favors a cytoplasmic location in the day and a nuclear location in the night. This study is the first to examine the potential mechanisms of intracellular transport of EcR and reveals close similarities with some of its mammalian counterparts. In double and triple labels using several antibodies, immunohistochemistry, and confocal laser scanning microscopy, we observed co-localization of EcR with the microtubules (MTs). Treatments with either the MT-stabilizing agent taxol or with colchicine, which depolymerizes MTs, resulted in considerable reduction in nuclear EcR with a concomitant increase in cytoplasmic EcR suggesting that MT disruption inhibits receptor accumulation in the nucleus. EcR also co-localizes with the chaperone Hsp90, the immunophilin FKBP52, and the light chain 1 of the motor protein dynein. All these factors also co-localize with MTs. We propose that in Rhodnius, EcR exerts its genomic effects by forming a complex with Hsp90 and FKBP52, which uses dynein on MTs as a mechanism for daily nucleocytoplasmic shuttling. The complex is transported intact to the nucleus and dissociates within it. We propose that EcR utilizes the cytoskeletal tracks for movement in a manner closely similar to that used by the glucocorticoid receptor. We also observed co-localization of EcR with mitochondria which suggests that EcR, like its mammalian counterparts, may be involved in the coordination of non-genomic responses of ecdysteroids in mitochondria.

NUCLEAR RECEPTORS

NUCLEAR RECEPTORS

The 90-kDa Heat-shock Protein (Hsp90)-binding Immunophilin FKBP51 Is a Mitochondrial Protein That Translocates to the Nucleus to Protect Cells against Oxidative Stress

Confocal microscopy images revealed that the tetratricopeptide repeat motif (TPR) domain immunophilin FKBP51 shows colocalization with the specific mitochondrial marker MitoTracker. Signal specificity was tested with different antibodies and by FKBP51 knockdown. This unexpected subcellular localization of FKBP51 was confirmed by colocalization studies with other mitochondrial proteins, biochemical fractionation, and electron microscopy imaging. Interestingly, FKBP51 forms complexes in mitochondria with the glucocorticoid receptor and the Hsp90/Hsp70-based chaperone heterocomplex. Although Hsp90 inhibitors favor FKBP51 translocation from mitochondria to the nucleus in a reversible manner, TPR domain-deficient mutants of FKBP51 are constitutively nuclear and fully excluded from mitochondria, suggesting that a functional TPR domain is required for its mitochondrial localization. FKBP51 overexpression protects cells against oxidative stress, whereas FKBP51 knockdown makes them more sensitive to injury. In summary, this is the first demonstration that FKBP51 is a major mitochondrial factor that undergoes nuclear-mitochondrial shuttling, an observation that may be related to antiapoptotic mechanisms triggered during the stress response.

FKBP51 and the NF-κB regulatory pathway in cancer

Constitutive activation of NF-κB occurs in a significant percentage of human cancers. Genetic abnormalities of tumors often enhance normal NF-κB signaling. Chronic inflammation is also associated with constitutive NF-κB activation and increases the risk of cancer. Aberrant NF-κB activation favors cellular transformation, sustains cancer survival, and contributes to tumor invasion. Strategies to inhibit NF-κB represent a promising therapeutic option against cancer. In the last decade, several studies point to the large immunophilin FKBP51 as an important element for the control of NF-κB activation in human neoplasia. This article is an overview of the causes of aberrant NF-κB regulation in cancer and highlights recent papers that implicate FKBP51 in such deregulation.

Hyperactivity of the hypothalamus–pituitary–adrenal axis in lipopolysaccharide-induced neurodevelopmental model of schizophrenia in rats: Effects of antipsychotic drugs

Recent data indicate that a significant number of schizophrenic patients are hypercortisolemic and that glucocorticoids are involved in the pathogenesis of schizophrenia. The aim of the present study was to evaluate whether behavioural schizophrenia-like changes in the lipopolysaccharide (LPS)-induced neurodevelopmental model of this brain disorder are associated with alterations in the level of plasma corticosterone, the concentration of glucocorticoid receptors and the amount of the immunophilin FKBP51, the glucocorticoid receptor co-chaperone, in the hippocampus and frontal cortex. We found that the adult offspring of prenatally LPS-treated rats showed a deficit in prepulse inhibition (PPI), an enhancement of amphetamine-induced locomotor activity, an elevated plasma level of corticosterone and a decrease in both the glucocorticoid receptor level in the hippocampus and the FKBP51 concentration in the frontal cortex. Most of these changes were reversed by the atypical antipsychotic drug clozapine, whereas chlorpromazine had no effect on PPI but attenuated the amphetamine-induced hyperactivity and normalised the hippocampal level of glucocorticoid receptors. The changes in the level of plasma corticosterone and cortical FKBP51 were attenuated by chlorpromazine in female offspring only. This study supports the hypothesis of hypothalamic–pituitary–adrenal (HPA) axis hyperactivity in schizophrenia and suggests that this hyperactivity results from a decrease in the hippocampal glucocorticoid receptor level and a decrease in FKBP51 in the frontal cortex.

Dose- and time-dependent glucocorticoid receptor signaling in podocytes

Glucocorticoids (GC) are the primary therapy for idiopathic nephrotic syndrome (NS). Recent evidence has identified glomerular podocytes as a potential site of GC action in this disease. The objectives of this study were to determine the presence of key components of the glucocorticoid receptor (GR) complex and the functionality of this signaling pathway in podocytes and to explore potential opportunities for manipulation of GC responsiveness. Here, we show that cultured murine podocytes express key components of the GR complex, including the GR, heat shock protein 90, and the immunophilins FKBP51 and FKBP52. The functionality of GR-mediated signaling was verified by measuring several GC (dexamethasone)-induced responses, including 1) increases in mRNA and protein levels of selected GC-regulated genes (FKBP51, phenol sulfotransferase 1, αB-crystallin); 2) downregulation of the GR protein; 3) increased phosphorylation of the GR; and 4) translocation of the GR into the nuclear fraction. Dexamethasone-induced phosphorylation and downregulation of GR protein were also demonstrated in isolated rat glomeruli. Podocyte gene expression in response to dexamethasone was regulated at both the transcriptional and posttranscriptional levels, the latter also including protein degradation. Short-term, high-dose GC treatment resulted in similar changes in gene expression and GR phosphorylation to that of long-term, low-dose GC treatment, thus providing a molecular rationale for the known efficacy of pulse GC therapy in NS. Induction of FKBP51 and downregulation of the GR represent negative feedback mechanisms that can potentially be exploited to improve clinical GC efficacy. Collectively, these findings demonstrate the presence of key molecular components of the GR signaling pathway and its functionality in podocytes and identify novel opportunities for improving clinical GC efficacy in the treatment of NS.

Inhibition of Drp1-dependent mitochondrial fragmentation and apoptosis by a polypeptide antagonist of calcineurin.

During apoptosis, mitochondria lose their membrane potential and undergo fragmentation around the time of release of cytochrome c. Apoptotic fission is at least in part sustained by the translocation of dynamin-related protein 1 (Drp1), normally located in the cytosol, to mitochondria. This process depends on dephosphorylation of Drp1 by the phosphatase calcineurin. Here, we report the identification of a novel inhibitor of this process. A polypeptide (PPD1) from the immunophilin FKBP52 inhibits calcineurin activation triggered by mitochondrial dysfunction. PPD1 blocks Drp1 translocation to mitochondria and fragmentation of the organelle. PPD1 delays apoptosis by intrinsic stimuli by preventing fragmentation and release of cytochrome c. Cells expressing PPD1 display enhanced clonogenic ability after exposure to staurosporine. A genetic analysis revealed that the activity of PPD1 is independent of the BH3-only protein BAD, another target of calcineurin during apoptosis, and is not additive to inhibition of Drp1. Thus, PPD1 is a novel inhibitor of apoptosis that elucidates the function of calcineurin-dependent mitochondrial fragmentation in the amplification of cell death.

The hsp90-FKBP52 Complex Links the Mineralocorticoid Receptor to Motor Proteins and Persists Bound to the Receptor in Early Nuclear Events

In this study, we demonstrate that the subcellular localization of the mineralocorticoid receptor (MR) is regulated by tetratricopeptide domain (TPR) proteins. The high-molecular-weight immunophilin (IMM) FKBP52 links the MR-hsp90 complex to dynein/dynactin motors favoring the cytoplasmic transport of MR to the nucleus. Replacement of this hsp90-binding IMM by FKBP51 or the TPR peptide favored the cytoplasmic localization of MR. The complete movement machinery, including dynein and tubulin, could be recovered from paclitaxel/GTP-stabilized cytosol and was fully reassembled on stripped MR immune pellets. The whole MR-hsp90-based heterocomplex was transiently recovered in the soluble fraction of the nucleus after 10 min of incubation with aldosterone. Moreover, cross-linked MR-hsp90 heterocomplexes accumulated in the nucleus in a hormone-dependent manner, demonstrating that the heterocomplex can pass undissociated through the nuclear pore. On the other hand, a peptide that comprises the DNA-binding domain of MR impaired the nuclear export of MR, suggesting the involvement of this domain in the process. This study represents the first report describing the entire molecular system that commands MR nucleocytoplasmic trafficking and proposes that the MR-hsp90-TPR protein heterocomplex is dissociated in the nucleus rather than in the cytoplasm.

Control of Alzheimer's Amyloid Beta Toxicity by the High Molecular Weight Immunophilin FKBP52 and Copper Homeostasis in Drosophila

FK506 binding proteins (FKBPs), also called immunophilins, are prolyl-isomerases (PPIases) that participate in a wide variety of cellular functions including hormone signaling and protein folding. Recent studies indicate that proteins that contain PPIase activity can also alter the processing of Alzheimer's Amyloid Precursor Protein (APP). Originally identified in hematopoietic cells, FKBP52 is much more abundantly expressed in neurons, including the hippocampus, frontal cortex, and basal ganglia. Given the fact that the high molecular weight immunophilin FKBP52 is highly expressed in CNS regions susceptible to Alzheimer's, we investigated its role in Aβ toxicity. Towards this goal, we generated Aβ transgenic Drosophila that harbor gain of function or loss of function mutations of FKBP52. FKBP52 overexpression reduced the toxicity of Aβ and increased lifespan in Aβ flies, whereas loss of function of FKBP52 exacerbated these Aβ phenotypes. Interestingly, the Aβ pathology was enhanced by mutations in the copper transporters Atox1, which interacts with FKBP52, and Ctr1A and was suppressed in FKBP52 mutant flies raised on a copper chelator diet. Using mammalian cultures, we show that FKBP52 (−/−) cells have increased intracellular copper and higher levels of Aβ. This effect is reversed by reconstitution of FKBP52. Finally, we also found that FKBP52 formed stable complexes with APP through its FK506 interacting domain. Taken together, these studies identify a novel role for FKBP52 in modulating toxicity of Aβ peptides.

Peptidyl-Prolyl Isomerase FKBP52 Controls Chemotropic Guidance of Neuronal Growth Cones via Regulation of TRPC1 Channel Opening

Immunophilins, including FK506-binding proteins (FKBPs), are protein chaperones with peptidyl-prolyl isomerase (PPIase) activity. Initially identified as pharmacological receptors for immunosuppressants to regulate immune responses via isomerase-independent mechanisms, FKBPs are most highly expressed in the nervous system, where their physiological function as isomerases remains unknown. We demonstrate that FKBP12 and FKBP52 catalyze cis/trans isomerization of regions of TRPC1 implicated in controlling channel opening. FKBP52 mediates stimulus-dependent TRPC1 gating through isomerization, which is required for chemotropic turning of neuronal growth cones to netrin-1 and myelin-associated glycoprotein and for netrin-1/DCC-dependent midline axon guidance of commissural interneurons in the developing spinal cord. By contrast, FKBP12 mediates spontaneous opening of TRPC1 through isomerization and is not required for growth cone responses to netrin-1. Our study demonstrates a novel physiological function of proline isomerases in chemotropic nerve guidance through TRPC1 gating and may have significant implication in clinical applications of immunophilin-related therapeutic drugs.

Modulation of glucocorticoid receptor nuclear translocation in neurons by immunophilins FKBP51 and FKBP52: Implications for major depressive disorder

Mood disorders associated with dysfunction of the hypothalamic–pituitary–adrenal (HPA) axis are common psychiatric conditions. The glucocorticoid receptor (GR) is a steroid-activated nuclear receptor that, upon binding to cortisol, translocates to the nucleus where it targets genes related to neuronal metabolism and plasticity. In patients suffering from major depressive disorder (MDD), hypercortisolemia is a common finding. In the current study we investigated the molecular events associated with the FK506 binding proteins (FKBP) -52 and -51 response to cortisol exposure in neuronal cell cultures and their effect on GR translocation. We noted that FK506 altered nuclear localization of the GR and inhibited expression of GR-responsive genes. Furthermore, siRNA knockdown of FKBP4 gene, coding for the immunophilin FKBP52, inhibited cortisol-activated GR nuclear translocation, while knockdown of FKBP5, coding for immunophilin FKBP51, was associated with increased baseline GR nuclear localization. We propose that immunophilins are modulators of the cortisol–HPA axis response to stress and related chronic brain disorders.

Long-range activation of FKBP51 transcription by the androgen receptor via distal intronic enhancers

Androgen receptor (AR) is a ligand-controlled transcription factor frequently deregulated in prostate carcinomas. Since there is scarce information on the action of AR on the chromatin level, we have elucidated the molecular mechanisms underlying the androgen-dependent regulation of immunophilin FKBP51 in prostate cancer cells. In comparison to the canonical AR target PSA, FKBP51 is more rapidly and strongly induced by androgen, with the regulation occurring merely at the transcriptional level. FKBP51 locus harbors 13 in silico-predicted androgen response elements (AREs), with most of them located downstream from transcription start site (TSS) and capable of binding AR in vitro. Chromatin immunoprecipitation assays in VCaP and LNCaP prostate cancer cells indicate that activation of the locus by the AR relies on four major intronic sites, with the compound ARE-containing sites ≥90 kb downstream from the TSS playing critical roles. Binding of agonist-loaded AR onto these sites in vivo was accompanied with significant recruitment of RNA polymerase II and BRM-containing chromatin remodeling complexes to the FKBP51 locus, which resulted in changes in the histone density of the locus. Our results indicate that very distal AREs act as genuine and robust enhancers, highlighting the importance of long-range regulation of transcription by the AR.

XAP2 inhibits glucocorticoid receptor activity in mammalian cells

XAP2 is member of a protein family sharing the TPR protein interaction motif. It displays close homology to the immunophilins FKBP51 and FKBP52 that act via the Hsp90 folding machinery to regulate the glucocorticoid receptor (GR). We show that XAP2 inhibits GR by reducing its responsiveness to hormone in transcriptional activation. The effect of XAP2 on GR requires its interaction with Hsp90 through the TPR motif. The PPIase-like region turned out to be enzymatically inactive. Thus, PPIase activity is not essential for the action of XAP2 on GR, similarly to FKBP51 and FKBP52.

Differential expression of immunophilins FKBP51 and FKBP52 in the frontal cortex of HIV-infected patients with major depressive disorder.

Patients infected with human immunodeficiency virus (HIV) have a higher risk of developing major depressive disorder (MDD) than the general population. Immunophilins FKBP51 and FKBP52 are expressed in cortical neurons and regulate the function of the glucocorticoid receptor (GR). Previous reports have shown that genetic variants in the FKBP5 gene encoding FKBP51 are linked to psychiatric disorders. We sought to determine whether immunophilins are upregulated in HIV infection. To determine whether FKBP52 and FKBP51 are associated with MDD and/or HIV, we compared protein and gene expression in autopsy tissues from the frontal cortical gray matter. The study cases were divided into five groups: control, MDD, MDD with psychosis, HIV(+), and HIV(+) with MDD. Gene expression and protein levels were determined by real-time PCR and Western blot analysis of fresh frozen tissues. Genotyping of previously published alleles of the FKBP5 gene was also performed. We found correlation of upregulation of both immunophilins in the HIV-infected groups. In the HIV(+) population with MDD, FKBP4 expression is significantly higher while FKBP5 is more variable. After analyzing the FKBP5 gene for single nucleotide polymorphisms, we found that rs3800373 CC genotype is more frequent in the MDD and MDD/Psychosis groups. We hypothesized that the levels of FKBP51, as modulator of the nuclear translocation of GR, would be lower in MDD. Instead, an increase in FKBP51 at both the transcript (FKBP5) and protein level correlated with MDD. Increased FKBP4 expression of correlated to HIV(+)MDD but not to HIV without MDD.

Deficiency of Immunophilin FKBP52 Promotes Endometriosis

Endometriosis is a common gynecological disease that affects approximately 10% of women of childbearing age. It is characterized by endometrial growth outside the uterus and often results in inflamed lesions, pain, and reduced fertility. Although heightened estrogenic activity and/or reduced progesterone responsiveness are considered to be involved in the etiology of endometriosis, neither the extent of their participation nor the underlying mechanisms are clearly understood. Heterogeneous uterine cell types differentially respond to estrogen and progesterone (P(4)). P(4), primarily acting via its nuclear receptor (PR), activates gene transcription and impacts many reproductive processes. Deletion of Fkbp52, an immunophilin cochaperone for PR, results in uterine-specific P(4) resistance in mice, creating an opportunity to study the unique aspects of P(4) signaling in endometriosis. Here we explored the roles of FKBP52 in this disease using Fkbp52(-/-) mice. We found that the loss of FKBP52 encourages the growth of endometriotic lesions with increased inflammation, cell proliferation, and angiogenesis. We also found remarkable down-regulation of FKBP52 in cases of human endometriosis. Our results provide the first evidence corroborated by genetic studies in mice for a potential role of an immunophilin cochaperone in the etiology of human endometriosis. This investigation is highly relevant for clinical application, particularly because P(4) resistance is favorably indicated in endometriosis and other gynecological diseases.

FK506-Binding Protein 51 Regulates Nuclear Transport of the Glucocorticoid Receptor β and Glucocorticoid Responsiveness

A spliced variant of the human glucocorticoid receptor GRbeta has been implicated in glucocorticoid responsiveness in glaucoma. Over-expression of the FK506-binding immunophilin FKBP51 also causes a generalized state of glucocorticoid resistance. In the present study, the roles of FKBP51 in the nuclear transport of GRbeta and glucocorticoid responsiveness were investigated. Human trabecular meshwork cells (GTM3 and TM5) and HeLa cells were treated with dexamethasone (DEX) and FK506 and transfected with GRbeta and FKBP51 expression vectors. Coimmunoprecipitation and Western blot analyses were performed to study interactions of FKBP51 and FKBP52 with GRalpha, GRbeta, Hsp90, or dynein. The cells were transfected with a GRE-luciferase reporter to evaluate the effects of DEX and FK506 and the overexpression of GRbeta and FKBP51 on glucocorticoid-mediated gene expression. FKBP51 was involved in constitutive nuclear transport of both GRalpha and -beta in the absence of ligands. FKBP52 appeared to be solely responsible for the nuclear transport of ligand-activated GRalpha. DEX stimulated the translocation of GRalpha but not GRbeta. Overexpression of either GRbeta or FKBP51 stimulated GRbeta translocation and reduced DEX-induced luciferase in HeLa cells. FK506 did not alter DEX-induced translocation of GRalpha. However, FK506 increased the association of FKBP51 with GRbeta and stimulated DEX-induced translocation of GRbeta in normal TM cells, but not in glaucoma TM cells. Increased nuclear GRbeta significantly inhibited glucocorticoid responsiveness in TM cells. Nuclear transport of GRbeta represents a novel mechanism through which FKBP51 alters GC sensitivity. GRbeta and FKBP51 may be responsible for increased responsiveness in steroid-induced ocular hypertensive individuals as well as in patients with glaucoma.

Binding of rapamycin analogs to calcium channels and FKBP52 contributes to their neuroprotective activities

Rapamycin is an immunosuppressive immunophilin ligand reported as having neurotrophic activity. We show that modification of rapamycin at the mammalian target of rapamycin (mTOR) binding region yields immunophilin ligands, WYE-592 and ILS-920, with potent neurotrophic activities in cortical neuronal cultures, efficacy in a rodent model for ischemic stroke, and significantly reduced immunosuppressive activity. Surprisingly, both compounds showed higher binding selectivity for FKBP52 versus FKBP12, in contrast to previously reported immunophilin ligands. Affinity purification revealed two key binding proteins, the immunophilin FKBP52 and the beta1-subunit of L-type voltage-dependent Ca(2+) channels (CACNB1). Electrophysiological analysis indicated that both compounds can inhibit L-type Ca(2+) channels in rat hippocampal neurons and F-11 dorsal root ganglia (DRG)/neuroblastoma cells. We propose that these immunophilin ligands can protect neurons from Ca(2+)-induced cell death by modulating Ca(2+) channels and promote neurite outgrowth via FKBP52 binding.

FKBP52 deficiency–conferred uterine progesterone resistance is genetic background and pregnancy stage specific

Immunophilin FKBP52 serves as a cochaperone to govern normal progesterone (P(4)) receptor (PR) function. Using Fkbp52(-/-) mice, we show intriguing aspects of uterine P(4)/PR signaling during pregnancy. Implantation failure is the major phenotype found in these null females, which is conserved on both C57BL6/129 and CD1 backgrounds. However, P(4) supplementation rescued implantation and subsequent decidualization in CD1, but not C57BL6/129, null females. Surprisingly, experimentally induced decidualization in the absence of blastocysts failed in Fkbp52(-/-) mice on either background even with P(4) supplementation, suggesting that embryonic signals complement uterine signaling for this event. Another interesting finding was that while P(4) at higher than normal pregnancy levels conferred PR signaling sufficient for implantation in CD1 null females, these levels were inefficient in maintaining pregnancy to full term. However, elevating P(4) levels further restored PR signaling to a level optimal for successful term pregnancy with normal litter size. Collectively, the results show that the indispensability of FKBP52 in uterine P(4)/PR signaling is a function of genetic disparity and is pregnancy stage specific. Since there is evidence for a correlation between P(4) supplementation and reduced risks of P(4)-resistant recurrent miscarriages and remission of endometriosis, these findings have clinical implications for genetically diverse populations of women.