Loss of FKBP5 impedes adipocyte differentiation under both normoxia and hypoxic stress

FK506 binding protein 51: Its role in the adipose organ and beyond

There is a great body of evidence that the adipose organ plays a central role in the control not only of energy balance, but importantly, in the maintenance of metabolic homeostasis. Interest in the study of different aspects of its physiology grew in the last decades due to the pandemic of obesity and the consequences of metabolic syndrome. It was not until recently that the first evidence for the role of the high molecular weight immunophilin FK506 binding protein (FKBP) 51 in the process of adipocyte differentiation have been described. Since then, many new facets have been discovered of this stress-responsive FKBP51 as a central node for precise coordination of many cell functions, as shown for nuclear steroid receptors, autophagy, signaling pathways as Akt, p38 MAPK, and GSK3, as well as for insulin signaling and the control of glucose homeostasis. Thus, the aim of this review is to integrate and discuss the recent advances in the understanding of the many roles of FKBP51 in the adipose organ.

Genomic structural variation contributes to evolved changes in gene expression in high-altitude Tibetan sheep

Tibetan sheep were introduced to the Qinghai Tibet plateau roughly 3,000 B.P., making this species a good model for investigating genetic mechanisms of high-altitude adaptation over a relatively short timescale. Here, we characterize genomic structural variants (SVs) that distinguish Tibetan sheep from closely related, low-altitude Hu sheep, and we examine associated changes in tissue-specific gene expression. We document differentiation between the two sheep breeds in frequencies of SVs associated with genes involved in cardiac function and circulation. In Tibetan sheep, we identified high-frequency SVs in a total of 462 genes, including EPAS1, PAPSS2, and PTPRD. Single-cell RNA-Seq data and luciferase reporter assays revealed that the SVs had cis-acting effects on the expression levels of these three genes in specific tissues and cell types. In Tibetan sheep, we identified a high-frequency chromosomal inversion that exhibited modified chromatin architectures relative to the noninverted allele that predominates in Hu sheep. The inversion harbors several genes with altered expression patterns related to heart protection, brown adipocyte proliferation, angiogenesis, and DNA repair. These findings indicate that SVs represent an important source of genetic variation in gene expression and may have contributed to high-altitude adaptation in Tibetan sheep.

Expression Analysis of circRNAs in Human Adipogenesis

PURPOSE

Adipogenesis is one of the major pathways for generating obesity or overweight that can cause a range of metabolic disorders. Circular RNAs (circRNAs), a specific type of RNAs, have a significant influence on metabolic disorders. This study aims to find differentially expressed circRNAs (DECs) during human subcutaneous adipose tissue (SATs) adipogenesis.

PATIENTS AND METHODS

The human adipose tissue-derived stromal cells (hADSCs) were isolated from human SATs (n = 3), and then induced into adipocytes. Total RNAs were extracted from hADSCs and adipocytes, and he DECs were detected using circRNA microarray. The GO and KEGG pathways of DECs were analyzed by bioinformatic methods, and partial DECs were further validated by quantitative polymerase chain reaction (qPCR).

RESULTS

Our study detected a total of 1987 DECs, among which, 1134 were found upregulated and 853 were downregulated. GO analysis showed that the upregulated DECs have catalytic activity in intracellular organelle and cytoplasms, whereas downregulated DECs are enriched in organelle lumen, and are involved in positive regulation of developmental process. In addition, pathway results demonstrated that upregulated DECs are involved in platinum drug resistance and cellular senescence, and downregulated DECs are enriched in proteoglycans in cancer and focal adhesion pathway. Two circRNAs, namely has_circ_0001600 and has_circ_0001947 were validated to be significantly upregulated in adipocytes compared to hADSCs.

CONCLUSION

Our study explored DECs between hADSCs derived from SATs and adipocytes, and report that two circRNAs named has_circ_0001600 and has_circ_0001947 might be important factors involved in human adipogenesis, however, the molecular mechanism should be further explored.

Knocking out Fkbp51 decreases CCl4-induced liver injury through enhancement of mitochondrial function and Parkin activity

BACKGROUND AND AIMS

Previously, we found that FK506 binding protein 51 (Fkbp51) knockout (KO) mice resist high fat diet-induced fatty liver and alcohol-induced liver injury. The aim of this research is to identify the mechanism of Fkbp51 in liver injury.

METHODS

Carbon tetrachloride (CCl4)-induced liver injury was compared between Fkbp51 KO and wild type (WT) mice. Step-wise and in-depth analyses were applied, including liver histology, biochemistry, RNA-Seq, mitochondrial respiration, electron microscopy, and molecular assessments. The selective FKBP51 inhibitor (SAFit2) was tested as a potential treatment to ameliorate liver injury.

RESULTS

Fkbp51 knockout mice exhibited protection against liver injury, as evidenced by liver histology, reduced fibrosis-associated markers and lower serum liver enzyme levels. RNA-seq identified differentially expressed genes and involved pathways, such as fibrogenesis, inflammation, mitochondria, and oxidative metabolism pathways and predicted the interaction of FKBP51, Parkin, and HSP90. Cellular studies supported co-localization of Parkin and FKBP51 in the mitochondrial network, and Parkin was shown to be expressed higher in the liver of KO mice at baseline and after liver injury relative to WT. Further functional analysis identified that KO mice exhibited increased ATP production and enhanced mitochondrial respiration. KO mice have increased mitochondrial size, increased autophagy/mitophagy and mitochondrial-derived vesicles (MDV), and reduced reactive oxygen species (ROS) production, which supports enhancement of mitochondrial quality control (MQC). Application of SAFit2, an FKBP51 inhibitor, reduced the effects of CCl4-induced liver injury and was associated with increased Parkin, pAKT, and ATP production.

CONCLUSIONS

Downregulation of FKBP51 represents a promising therapeutic target for liver disease treatment.

FK-binding protein 5: Possible relevance to the pathogenesis of metabolic dysfunction and alcohol-associated liver disease

The FK506-binding protein (FKBP5) plays significant roles in mediating stress responses by interacting with glucocorticoids, participating in adipogenesis, and influencing various cellular pathways throughout the body. In this review, we described the potential role of FKBP5 in the pathogenesis of two common chronic liver diseases, metabolic dysfunction-associated steatotic liver disease (MASLD), and alcohol-associated liver disease (ALD). We provided an overview of the FK-binding protein family and elucidated their roles in cellular stress responses, metabolic diseases, and adipogenesis. We explored how FKBP5 may mechanistically influence the pathogenesis of MASLD and ALD and provided insights for further investigation into the role of FKBP5 in these two diseases.

The Effect of Theaflavins on the Gut Microbiome and Metabolites in Diabetic Mice

With the development of diabetes, the gut microbiome falls into a state of dysbiosis, further affecting its progression. Theaflavins (TFs), a type of tea polyphenol derivative, show anti-diabetic properties, but their effect on the gut microbiome in diabetic mice is unclear. It is unknown whether the improvement of TFs on hyperglycemia and hyperlipidemia in diabetic mice is related to gut microbiota. Therefore, in this study, different concentrations of TFs were intragastrically administered to mice with diabetes induced by a high-fat-diet to investigate their effects on blood glucose, blood lipid, and the gut microbiome in diabetic mice, and the plausible mechanism underlying improvement in diabetes was explored from the perspective of the gut microbiome. The results showed that the TFs intervention significantly improved the hyperglycemia and hyperlipidemia of diabetic mice and affected the structure of the gut microbiome by promoting the growth of bacteria positively related to diabetes and inhibiting those negatively related to diabetes. The changes in short-chain fatty acids in mice with diabetes and functional prediction analysis suggested that TFs may affect carbohydrate metabolism and lipid metabolism by regulating the gut microbiome. These findings emphasize the ability of TFs to shape the diversity and structure of the gut microbiome in mice with diabetes induced by a high-fat diet combined with streptozotocin and have practical implications for the development of functional foods with TFs.

Potential inhibitors for FKBP51: an in silico study using virtual screening, molecular docking and molecular dynamics simulation

Over the years, FK506-binding proteins have been targeted for different pharmaceutical interests. The FK506-binding protein, encoded by the FKBP5 gene, is responsible for stress and metabolic-related disorders, including cancer. In addition, the FKBD-I domain of the protein is a potential target for endocrine-related physiological diseases. In the present study, a set of natural compounds from the ZINC database was screened against FKBP51 protein using in silico strategy, namely pharmacophore modeling, molecular docking, and molecular dynamic simulation. A protein-ligand-based pharmacophore model workflow was employed to identify small molecules. The resultant compounds were then assessed for their toxicity using ADMET prediction. Based on ADMET prediction, 4768 compounds were selected for molecular docking to elucidate their binding mode. Based on the binding energy, 857 compounds were selected, and their Similarity Tanimoto coefficient was calculated, followed by clustering according to Jarvis-Patrick clustering methods (Jarp). The clustered singletons resulted in 14 hit compounds. The top 05 hit compounds and 05 known compounds were then subjected to 100 ns MD simulation to check the stability of complexes. The study revealed that the selected complexes are stable throughout the 100 ns simulation; for FKBD-I (4TW6), crystal structure compared with FKBP-51 (1KT0) crystal structure. Finally, the binding free energies of the hit complexes were calculated using molecular mechanics energies combined with Poisson-Boltzmann. The data reveal that all the complexes show negative BFEs, indicating a good affinity of the hit compounds to the protein. The top five compounds are, therefore, potential inhibitors for FKBP51. Communicated by Ramaswamy H. Sarma.

Relation of adipose tissue and skeletal muscle FKBP5 expression with insulin sensitivity and the regulation of FKBP5 by insulin and free fatty acids

PURPOSE

Recent studies suggest that FK506 binding protein 51 (FKBP51), a negative regulator of glucocorticoid response, encoded by FKBP5, may influence insulin action. The aim of the present study was to assess the relationship between subcutaneous adipose tissue (AT) and skeletal muscle FKBP5 expression in relation to insulin sensitivity in healthy individuals and to study its regulation by insulin and circulating free fatty acid (FFA) elevation.

METHODS

The study group comprised 96 male subjects, 49 normal-weight and 47 overweight/obese. Hyperinsulinemic clamp, subcutaneous AT and skeletal muscle biopsies were performed. In a subgroup of 20 subjects, two 6 h clamps were performed, with and without Intralipid/heparin infusion, and tissue biopsies were obtained before and after each clamp.

RESULTS

AT FKBP5 expression was lower in overweight/obese individuals in comparison with normal-weight individuals (p = 0.004). Muscle FKBP5 expression did not differ between the groups, however, it was inversely related to insulin sensitivity (r = -0.32, p = 0.002). FKBP5 expression decreased in AT (p = 0.003) and increased in muscle (p < 0.0001) after insulin infusion. Intralipid/heparin diminished insulin-induced increase in muscle FKBP5.

CONCLUSION

Our data show that lower AT FKBP5 expression is related to obesity, whereas muscle FKBP5 expression is associated with insulin resistance. AT and muscle FKBP5 expression is differentially regulated by insulin.

Carotenoid transporter CD36 expression depends on hypoxia-inducible factor-1α in mouse soleus muscles

Dietary β-carotene induces muscle hypertrophy and prevents muscle atrophy in red slow-twitch soleus muscles, but not in white fast-twitch extensor digitorum longus (EDL) muscles and gastrocnemius muscles. However, it remains unclear why these beneficial effects of β-carotene are elicited in soleus muscles. To address this issue, we focused on carotenoid transporters in skeletal muscles. In mice, Cd36 mRNA levels were higher in red muscle than in white muscle. The siRNA-mediated knockdown of CD36 decreased β-carotene uptake in C2C12 myotubes. In soleus muscles, CD36 knockdown inhibited β-carotene-induced increase in muscle mass. Intravenous injection of the hypoxia marker pimonidazole produced more pimonidazole-bound proteins in soleus muscles than in EDL muscles, and the hypoxia-inducible factor-1 (HIF-1) α protein level was higher in soleus muscles than in EDL muscles. In C2C12 myotubes, hypoxia increased the expression of CD36 and HIF-1α at the protein and mRNA levels, and HIF-1α knockdown reduced hypoxia-induced increase in Cd36 mRNA level. In soleus muscles, HIF-1α knockdown reduced Cd36 mRNA level. These results indicate that CD36 is predominantly involved in β-carotene-induced increase in soleus muscle mass of mice. Furthermore, we demonstrate that CD36 expression depends on HIF-1α in the soleus muscles of mice, even under normal physiological conditions.

Identification of Circular RNA Expression Profiles in White Adipocytes and Their Roles in Adipogenesis

Obesity and its related metabolic diseases have become great public health threats worldwide. Although accumulated evidence suggests that circRNA is a new type of non-coding RNAs regulating various physiological and pathological processes, little attention has been paid to the expression profiles and functions of circRNAs in white adipose tissue. In this study, 3,771 circRNAs were detected in three stages of white adipogenesis (preadipocyte, differentiating preadipocyte, and mature adipocyte) by RNA-seq. Experimental validation suggested that the RNA-seq results are highly reliable. We found that nearly 10% of genes which expressed linear RNAs in adipocytes could also generate circRNAs. In addition, 40% of them produced multiple circRNA isoforms. We performed correlation analysis and found that a great deal of circRNAs (nearly 50%) and their parental genes were highly correlated in expression levels. A total of 41 differential expression circRNAs (DECs) were detected during adipogenesis and an extremely high ratio of them (80%) were correlated with their parental genes, indicating these circRNAs may potentially play roles in regulating the expression of their parental genes. KEGG enrichment and GO annotation of the parental genes suggesting that the DECs may participate in several adipogenesis-related pathways. Following rigorous selection, we found that many up-regulated circRNAs contain multiple miRNAs binding sites, such as miR17, miR-30c, and miR-130, indicating they may potentially facilitate their regulatory functions by acting as miRNA sponges. These results suggest that plenty of circRNAs are expressed in white adipogenesis and the DECs may serve as new candidates for future adipogenesis regulation.

The deficiency of FKBP-5 inhibited hepatocellular progression by increasing the infiltration of distinct immune cells and inhibiting obesity-associated gut microbial metabolite

Background

Gut microbiota has a number of essential roles in nutrition metabolism and immune homeostasis, and is closely related to hepatocellular progression. In recent years, studies have also shown that FK506 binding protein 5 (FKBP-5) plays a crucial role in immune regulation. However, it is not yet clear whether FKBP-5 promotes the development of hepatocellular carcinoma (HCC) by affecting immune function and gut microbiota.

Methods

FKBP-5 expression was verified by immunochemistry and western blot and reverse transcription polymerase chain reaction (RT-qPCR) assays. After treatment in WT and FKBP-5^-/- mice, the histological characteristic of mice liver tissue was assessed by H&E staining, and hepatic leukocytes and hepatic NKT cells were identified by flow cytometer. Meanwhile, primary bile acids (BAs), secondary BAs, serum total cholesterol, and the weight of abdomen adipose tissues were examined, and the gut microbiota was evaluated by 16S ribosomal ribonucleic acid (rRNA) sequencing.

Results

We discovered that FKBP-5 was highly expressed in HCC tissues. Meanwhile, FKBP-5 deletion inhibited tumor progression by increasing CD⁸⁺ T, CD⁴⁺ T, NKT and CD⁴⁺NKT cells in mice after diethylnitrosamine (DEN) injection. Besides, we proved that FKBP-5 deletion generated rapid and significant reductions in the intestinal BAs, the weight of abdomen adipose tissues and the serum total cholesterol. FKBP-5 deletion also led to a change in the composition of gut microbiota, suggesting that BAs are the main dietary factor regulating gut microbiota, which could be affected by FKBP-5 deletion. Further, we uncovered that anti-CD4 and anti-CD8 treatments facilitated hepatocellular progression by modulating gut microbiota composition in FKBP-5^-/- mice.

Conclusions

Therefore, we demonstrated that FKBP-5 deletion inhibited hepatocellular progression by modulating immune response and gut microbiome-mediated BAs metabolism.

The glucocorticoid receptor-FKBP51 complex contributes to fear conditioning and posttraumatic stress disorder

Posttraumatic stress disorder (PTSD) can develop after exposure to severe psychological trauma, leaving patients with disabling anxiety, nightmares, and flashbacks. Current treatments are only partially effective, and development of better treatments is hampered by limited knowledge of molecular mechanisms underlying PTSD. We have discovered that the glucocorticoid receptor (GR) and FK506 binding protein 51 (FKBP51) form a protein complex that is elevated in PTSD patients compared with unaffected control subjects, subjects exposed to trauma without PTSD, and patients with major depressive disorder (MDD). The GR-FKBP51 complex is also elevated in fear-conditioned mice, an aversive learning paradigm that models some aspects of PTSD. Both PTSD patients and fear-conditioned mice had decreased GR phosphorylation, decreased nuclear GR, and lower expression of 14-3-3ε, a gene regulated by GR. We created a peptide that disrupts GR-FKBP51 binding and reverses behavioral and molecular changes induced by fear conditioning. This peptide reduces freezing time and increases GR phosphorylation, GR-FKBP52 binding, GR nuclear translocation, and 14-3-3ε expression in fear-conditioned mice. These experiments demonstrate a molecular mechanism contributing to PTSD and suggest that the GR-FKBP51 complex may be a diagnostic biomarker and a potential therapeutic target for preventing or treating PTSD.

Murine in vitro cellular models to better understand adipogenesis and its potential applications

Adipogenesis has been extensively studied using in vitro models of cellular differentiation, enabling long-term regulation of fat cell metabolism in human adipose tissue (AT) material. Many studies promote the idea that manipulation of this process could potentially reduce the prevalence of obesity and its related diseases. It has now become essential to understand the molecular basis of fat cell development to tackle this pandemic disease, by identifying therapeutic targets and new biomarkers. This review explores murine cell models and their applications for study of the adipogenic differentiation process in vitro. We focus on the benefits and limitations of different cell line models to aid in interpreting data and selecting a good cell line model for successful understanding of adipose biology.

Proof-of-concept for CRISPR/Cas9 gene editing in human preadipocytes: Deletion of FKBP5 and PPARG and effects on adipocyte differentiation and metabolism

CRISPR/Cas9 has revolutionized the genome-editing field. So far, successful application in human adipose tissue has not been convincingly shown. We present a method for gene knockout using electroporation in preadipocytes from human adipose tissue that achieved at least 90% efficiency without any need for selection of edited cells or clonal isolation. We knocked out the FKBP5 and PPARG genes in preadipocytes and studied the resulting phenotypes. PPARG knockout prevented differentiation into adipocytes. Conversely, deletion of FKBP51, the protein coded by the FKBP5 gene, did not affect adipogenesis. Instead, it markedly modulated glucocorticoid effects on adipocyte glucose metabolism and, furthermore, we show some evidence of altered transcriptional activity of glucocorticoid receptors. This has potential implications for the development of insulin resistance and type 2 diabetes. The reported method is simple, easy to adapt, and enables the use of human primary preadipocytes instead of animal adipose cell models to assess the role of key genes and their products in adipose tissue development, metabolism and pathobiology.

Role of Parkin-mediated mitophagy in glucocorticoid-induced cardiomyocyte maturation

Glucocorticoids can promote cardiomyocyte maturation. However, the mechanism underlying glucocorticoid-mediated cardiomyocyte maturation is still unclear. Mitophagy plays a key role in cardiomyocyte maturation. Based on current knowledge, our study evaluated the effects of the glucocorticoid dexamethasone (100 nM) on the maturation of mouse embryonic stem cell-derived cardiomyocytes and the role of mitophagy in this maturation. The results showed that dexamethasone can promote embryonic stem cell-derived cardiomyocyte maturation, inhibit cardiomyocyte proliferation, and promote myocardial fiber arrangement. However, dexamethasone did not affect mitochondrial morphology in cardiomyocytes. Glucocorticoid receptor inhibitors (RU486, 1 nM) can inhibit dexamethasone-mediated cardiomyocyte maturation. Additionally, dexamethasone can promote mitophagy in embryonic stem cell-derived cardiomyocytes and induce LC3 and lysosomal aggregation in mitochondria. The inhibition of mitophagy can inhibit the cardiomyocyte maturation effect of dexamethasone. Furthermore, our research found that dexamethasone may mediate the occurrence of mitophagy in cardiomyocytes through Parkin. The siRNA-mediated inhibition of Parkin expression can inhibit mitochondrial autophagy caused by dexamethasone, thus inhibiting cardiomyocyte maturation. Overall, our study found that dexamethasone can promote embryonic stem cell-derived cardiomyocyte maturation through Parkin-mediated mitophagy.

Evidence of increased hypoxia signaling in fetal liver from maternal nutrient restriction in mice

BACKGROUND

Intrauterine growth restriction (IUGR) is a pregnancy condition where fetal growth is reduced, and offspring from IUGR pregnancies are at increased risk for type II diabetes as adults. The liver is susceptible to fetal undernutrition experienced by IUGR infants and animal models of growth restriction. This study aimed to examine hepatic expression changes in a maternal nutrient restriction (MNR) mouse model of IUGR to understand fetal adaptations that influence adult metabolism.

METHODS

Liver samples of male offspring from MNR (70% of ad libitum starting at E6.5) or control pregnancies were obtained at E18.5 and differential expression was assessed by RNAseq and western blots.

RESULTS

Forty-nine differentially expressed (FDR < 0.1) transcripts were enriched in hypoxia-inducible pathways including Fkbp5 (1.6-fold change), Ccng2 (1.5-fold change), Pfkfb3 (1.5-fold change), Kdm3a (1.2-fold change), Btg2 (1.6-fold change), Vhl (1.3-fold change), and Hif-3a (1.3-fold change) (FDR < 0.1). Fkbp5, Pfkfb3, Kdm3a, and Hif-3a were confirmed by qPCR, but only HIF-2a (2.2-fold change, p = 0.002) and HIF-3a (1.3 p = 0.03) protein were significantly increased.

CONCLUSION

Although a moderate impact, these data support evidence of fetal adaptation to reduced nutrients by increased hypoxia signaling in the liver.

FKBP5 expression in human adipose tissue: potential role in glucose and lipid metabolism, adipogenesis and type 2 diabetes

PURPOSE

Here, we explore the involvement of FKBP51 in glucocorticoid-induced insulin resistance (IR) in human subcutaneous adipose tissue (SAT), including its potential role in type 2 diabetes (T2D). Moreover, we assess the metabolic effects of reducing the activity of FKBP51 using the specific inhibitor SAFit1.

METHODS

Human SAT was obtained by needle biopsies of the lower abdominal region. FKBP5 gene expression was assessed in fresh SAT explants from a cohort of 20 T2D subjects group-wise matched by gender, age and BMI to 20 non-diabetic subjects. In addition, human SAT was obtained from non-diabetic volunteers (20F/9M). SAT was incubated for 24 h with or without the synthetic glucocorticoid dexamethasone and SAFit1. Incubated SAT was used to measure the glucose uptake rate in isolated adipocytes.

RESULTS

FKBP5 gene expression levels in SAT positively correlated with several indices of IR as well as glucose area under the curve during oral glucose tolerance test (r = 0.33, p < 0.05). FKBP5 gene expression levels tended to be higher in T2D subjects compared to non-diabetic subjects (p = 0.088). Moreover, FKBP5 gene expression levels were found to inversely correlate with lipolytic, lipogenic and adipogenic genes. SAFit1 partly prevented the inhibitory effects of dexamethasone on glucose uptake.

CONCLUSIONS

FKBP5 gene expression in human SAT tends to be increased in T2D subjects and is related to elevated glucose levels. Moreover, FKBP5 gene expression is inversely associated with the expression of lipolytic, lipogenic and adipogenic genes. SAFit1 can partly prevent glucose uptake impairment by glucocorticoids, suggesting that FKBP51 might be a key factor in glucocorticoid-induced IR.

Type 2 diabetes and cardiometabolic risk may be associated with increase in DNA methylation of FKBP5

Background

Subclinical hypercortisolism and hypothalamic-pituitary-adrenal (HPA) axis dysfunction are associated with type 2 diabetes (T2DM), cardiovascular disease, and metabolic dysfunction. Intronic methylation of FKBP5 has been implicated as a potential indicator of chronic cortisol exposure. Our overall objective in this study was to determine the association of chronic cortisol exposure, measured via percent methylation of FKBP5 at intron 2, with percent glycosylated hemoglobin (HbA1c), low-density lipoprotein cholesterol (LDL-cholesterol), waist circumference (WC), and body mass index (BMI), in a clinic-based sample of 43 individuals with T2DM.

Results

Greater percent methylation of the FKBP5 intron 2 at one CpG-dinucleotide region was significantly associated with higher HbA1c (β = 0.535, p = 0.003) and LDL cholesterol (β = 0.344, p = 0.037) and a second CpG-dinucleotide region was significantly associated with higher BMI and WC (β = 0.516, p = 0.001; β = 0.403, p = 0.006, respectively).

Conclusions

FKBP5 methylation may be a marker of higher metabolic risk in T2DM, possibly secondary to higher exposure to cortisol. Further work should aim to assess the longitudinal association of FKBP5 with cardiovascular disease and glycemic outcomes in T2DM as a first step in understanding potential preventive and treatment-related interventions targeting the HPA axis.

The FKBP51 Glucocorticoid Receptor Co-Chaperone: Regulation, Function, and Implications in Health and Disease

Among the chaperones and co-chaperones regulating the glucocorticoid receptor (GR), FK506 binding protein (FKBP) 51 is the most intensely investigated across different disciplines. This review provides an update on the role of the different co-chaperones of Hsp70 and Hsp90 in the regulation of GR function. The development leading to the focus on FKBP51 is outlined. Further, a survey of the vast literature on the mechanism and function of FKBP51 is provided. This includes its structure and biochemical function, its regulation on different levels—transcription, post-transcription, and post-translation—and its function in signaling pathways. The evidence portraying FKBP51 as a scaffolding protein organizing protein complexes rather than a chaperone contributing to the folding of individual proteins is collated. Finally, FKBP51’s involvement in physiology and disease is outlined, and the promising efforts in developing drugs targeting FKBP51 are discussed.