Peptidyl-prolyl cis/trans isomerase NIMA-interacting 1 associates with insulin receptor substrate-1 and enhances insulin actions and adipogenesis

Upregulation of Pin1 contributes to alleviation of cognitive dysfunction in diabetic mice

OBJECTIVE

This study aimed to explore the molecular mechanism underlying the role of Pin1 in cognitive dysfunction in diabetic mice.

METHODS

Using a streptozotocin-induced diabetic mouse model, an adeno-associated virus carrying the Pin1 gene was used to upregulate Pin1 expression in the hippocampus of diabetic mice. Animal behavior tests and molecular biology techniques were further used to explore the role of Pin1 in cognitive dysfunction in diabetic mice.

RESULTS

Our study demonstrated that upregulation of Pin1 expression increased the phosphorylation of AKT and insulin receptor substrate 1 downstream signaling molecules of the IR-IGF1R pathway, increased the phosphorylation of GSK-3β, and concomitantly decreased the phosphorylation of Tau in the hippocampus of diabetic mice, thereby improving the ultrastructural pathology of the hippocampus and further alleviating diabetes-related cognitive impairment.

CONCLUSION

Pin1 can improve cognitive dysfunction in diabetic mice.

Hepatic Pin1 Expression, Particularly in Nuclei, Is Increased in NASH Patients in Accordance with Evidence of the Role of Pin1 in Lipid Accumulation Shown in Hepatoma Cell Lines

Our previous studies using rodent models have suggested an essential role for Pin1 in the pathogenesis of non-alcoholic steatohepatitis (NASH). In addition, interestingly, serum Pin1 elevation has been reported in NASH patients. However, no studies have as yet examined the Pin1 expression level in human NASH livers. To clarify this issue, we investigated the expression level and subcellular distribution of Pin1 in liver specimens obtained using needle-biopsy samples from patients with NASH and healthy liver donors. Immunostaining using anti-Pin1 antibody revealed the Pin1 expression level to be significantly higher, particularly in nuclei, in the livers of NASH patients than those of healthy donors. In the samples from patients with NASH, the amount of nuclear Pin1 was revealed to be negatively related to serum alanine aminotransferase (ALT), while tendencies to be associated with other serum parameters such as aspartate aminotransferase (AST) and platelet number were noted but did not reach statistical significance. Such unclear results and the lack of a significant relationship might well be attributable to our small number of NASH liver samples (n = 8). Moreover, in vitro, it was shown that addition of free fatty acids to medium induced lipid accumulation in human hepatoma HepG2 and Huh7 cells, accompanied with marked increases in nuclear Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1), in accordance with the aforementioned observations in human NASH livers. In contrast, suppression of Pin1 gene expression using siRNAs attenuated the free fatty acid-induced lipid accumulation in Huh7 cells. Taken together, these observations strongly suggest that increased expression of Pin1, particularly in hepatic nuclei, contributes to the pathogenesis of NASH with lipid accumulation.

The metabolic crosstalk between PIN1 and the tumour microenvironment

Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1) is a member of a family of peptidyl-prolyl isomerases that specifically recognizes and binds phosphoproteins, catalyzing the rapid cis-trans isomerization of phosphorylated serine/threonine-proline motifs, which leads to changes in the structures and activities of the targeted proteins. Through this complex mechanism, PIN1 regulates many hallmarks of cancer including cell autonomous metabolism and the crosstalk with the cellular microenvironment. Many studies showed that PIN1 is largely overexpressed in cancer turning on a set of oncogenes and abrogating the function of tumor suppressor genes. Among these targets, recent evidence demonstrated that PIN1 is involved in lipid and glucose metabolism and accordingly, in the Warburg effect, a characteristic of tumor cells. As an orchestra master, PIN1 finely tunes the signaling pathways allowing cancer cells to adapt and take advantage from a poorly organized tumor microenvironment. In this review, we highlight the trilogy among PIN1, the tumor microenvironment and the metabolic program rewiring.

The role of peptidyl-prolyl isomerase Pin1 in neuronal signaling in epilepsy

Epilepsy is a common symptom of many neurological disorders and can lead to neuronal damage that plays a major role in seizure-related disability. The peptidyl-prolyl isomerase Pin1 has wide-ranging influences on the occurrence and development of neurological diseases. It has also been suggested that Pin1 acts on epileptic inhibition, and the molecular mechanism has recently been reported. In this review, we primarily focus on research concerning the mechanisms and functions of Pin1 in neurons. In addition, we highlight the significance and potential applications of Pin1 in neuronal diseases, especially epilepsy. We also discuss the molecular mechanisms by which Pin1 controls synapses, ion channels and neuronal signaling pathways to modulate epileptic susceptibility. Since neurotransmitters and some neuronal signaling pathways, such as Notch1 and PI3K/Akt, are vital to the nervous system, the role of Pin1 in epilepsy is discussed in the context of the CaMKII-AMPA receptor axis, PSD-95-NMDA receptor axis, NL2/gephyrin-GABA receptor signaling, and Notch1 and PI3K/Akt pathways. The effect of Pin1 on the progression of epilepsy in animal models is discussed as well. This information will lead to a better understanding of Pin1 signaling pathways in epilepsy and may facilitate development of new therapeutic strategies.

MicroRNA-140-5p inhibitor attenuates memory impairment induced by amyloid-ß oligomer in vivo possibly through Pin1 regulation

AIMS

The peptidyl-prolyl cis/trans isomerase, Pin1, has a protective role in age-related neurodegeneration by targeting different phosphorylation sites of tau and the key proteins required to produce Amyloid-β, which are the well-known molecular signatures of Alzheimer's disease (AD) neuropathology. The direct interaction of miR-140-5p with Pin1 mRNA and its inhibitory role in protein translation has been identified. The main purpose of this study was to investigate the role of miRNA-140-5p inhibition in promoting Pin1 expression and the therapeutic potential of the AntimiR-140-5p in the Aß oligomer (AßO)-induced AD rat model.

METHODS

Spatial learning and memory were assessed in the Morris water maze. RT-PCR, western blot, and histological assays were performed on hippocampal samples at various time points after treatments. miRNA-140-5p inhibition enhanced Pin1 and ADAM10 mRNA expressions but has little effect on Pin1 protein level.

RESULTS

The miRNA-140-5p inhibitor markedly ameliorated spatial learning and memory deficits induced by AßO, and concomitantly suppressed the mRNA expression of inflammatory mediators TNFα and IL-1β, and phosphorylation of tau at three key sites (thr231, ser396, and ser404) as well as increased phosphorylated Ser473-Akt.

CONCLUSION

According to our results, Antimir-140-mediated improvement of AβO-induced neuronal injury and memory impairment in rats may provide an appropriate rationale for evaluating miR-140-5p inhibitors as a promising agent for the treatment of AD.

Circulating levels of PIN1 and glucose metabolism in young people with obesity

PURPOSE

Impaired activity of the peptidylprolyl cis/trans isomerase NIMA-interacting 1 (PIN1) isomerase might contribute to link disturbed glucose metabolism and risk of glucose related neurotoxicity, neurodegeneration and cognitive decline. The isomerase modulates also pathways of peripheral insulin sensitivity and secretion. We aimed at investigating the levels of circulating PIN1 in adolescents with obesity and any association with their glucose metabolism.

METHODS

We enrolled 145 adolescents (age 12-17.8 years); 67 lean controls (46.2%) and 78 (53.8%) with overweight or obesity (males n = 62, 46%). We estimated glucose and insulin in fasting condition and after a standard oral glucose tolerance test; fasting serum levels of PIN1, amyloid β-protein 42 (Aβ42), presenilin 1 (PSEN1), glucagon-like peptide 1 (GLP1) and Non Esterified Fatty Acids (NEFA). We calculated the homeostasis model assessment of insulin resistance (HOMA-IR), the β cell function (HOMA-β) and the Adipo-IR.

RESULTS

There was no difference in PIN1 serum levels between normal weight individuals and patients with obesity. However, there was an inverse correlation between serum fasting PIN1 and glucose (r - 0.183 and p = 0.027). We confirmed levels of Aβ42 and PSEN1 were higher in teens with obesity than in lean controls and their correlation with the body mass index (Aβ42: r = 0.302, p = 0.0001, PSEN1 r = 0.231, p = 0.005) and the HOMA-IR (Aβ42: r = 0.219, p = 0.009, r = 0.170, p < 0.042).

CONCLUSIONS

There was no significant rise of circulating PIN1 levels in young individuals with obesity. Increased levels reported in the literature in adult patients are likely to occur late in the natural history of the disease with the onset of an overt impairment of glucose homeostasis.

The kingdom of the prolyl-isomerase Pin1: The structural and functional convergence and divergence of Pin1

More than 20 years since its discovery, our understanding of Pin1 function in various diseases continues to improve. Pin1 plays a crucial role in pathogenesis and has been implicated in metabolic disorders, cardiovascular diseases, inflammatory diseases, viral infection, cancer and neurodegenerative diseases such as Alzheimer’s, Parkinson’s and Huntington’s disease. In particular, the role of Pin1 in neurodegenerative diseases and cancer has been extensively studied. Our understanding of Pin1 in cancer also led to the development of cancer therapeutic drugs targeting Pin1, with some currently in clinical trial phases. However, identifying a Pin1-specific drug with good cancer therapeutic effect remains elusive, thus leading to the continued efforts in Pin1 research. The importance of Pin1 is highlighted by the presence of Pin1 orthologs across various species: from vertebrates to invertebrates and Kingdom Animalia to Plantae. Among these Pin1 orthologs, their sequence and structural similarity demonstrate the presence of conservation. Moreover, their similar functionality between species further highlights the conservancy of Pin1. As researchers continue to unlock the mysteries of Pin1 in various diseases, using different Pin1 models might shed light on how to better target Pin1 for disease therapeutics. This review aims to highlight the various Pin1 orthologs in numerous species and their divergent functional roles. We will examine their sequence and structural similarities and discuss their functional similarities and uniqueness to demonstrate the interconnectivity of Pin1 orthologs in multiple diseases.

Prolyl isomerase Pin1 interacts with adipose triglyceride lipase and negatively controls both its expression and lipolysis

BACKGROUND

Lipolysis is essential for the supply of nutrients during fasting, the control of body weight, and remodeling of white adipose tissues and thermogenesis. In the obese state, lipolysis activity and the expression of adipose triglyceride lipase (ATGL), a rate-limiting enzyme, is suppressed. However, the mechanism underlying the regulation of ATGL remains largely unknown. We previously reported that a high-fat diet obviously increases protein levels of the prolyl isomerase, Pin1, in epididymal white adipose tissue (epiWAT) of mice and that Pin1 KO mice are resistant to developing obesity.

RESULTS

The present study found that deletion of the Pin1 gene in epiWAT upregulated lipolysis and increased ATGL protein expression by ~2-fold. In addition, it was demonstrated that Pin1 directly associated with ATGL and enhanced its degradation through the ubiquitin proteasome system. Indeed, Pin1 overexpression decreased ATGL expression levels, whereas Pin1 knockdown by siRNA treatment upregulated ATGL protein levels without altering mRNA levels. Moreover, under a high fat diet (HFD)-fed condition, adipocyte-specific Pin1 KO (adipoPin1 KO) mice had 2-fold increase lipolytic activity and upregulated β-oxidation-related gene expressions. These mice also gained less body weight, and had better glucose metabolism according to the results of glucose and insulin tolerance tests.

CONCLUSION

Taken together, these results showed that Pin1 directly interacted with and degraded ATGL via a ubiquitin-proteasome system, consequently causing the downregulation of lipolysis. Therefore, Pin1 could be considered a target for the treatment of dyslipidemia and related disorders.

Roles of peptidyl-prolyl isomerase Pin1 in disease pathogenesis

Pin1 belongs to the peptidyl-prolyl cis-trans isomerases (PPIases) superfamily and catalyzes the cis-trans conversion of proline in target substrates to modulate diverse cellular functions including cell cycle progression, cell motility, and apoptosis. Dysregulation of Pin1 has wide-ranging influences on the fate of cells; therefore, it is closely related to the occurrence and development of various diseases. This review summarizes the current knowledge of Pin1 in disease pathogenesis.

Development of Pin1 Inhibitors and their Potential as Therapeutic Agents

The prolyl isomerase Pin1 is a unique enzyme, which isomerizes the cis-trans conformation between pSer/pThr and proline and thereby regulates the function, stability and/or subcellular distribution of its target proteins. Such regulations by Pin1 are involved in numerous physiological functions as well as the pathogenic mechanisms underlying various diseases. Notably, Pin1 deficiency or inactivation is a potential cause of Alzheimer's disease, since Pin1 induces the degradation of Tau. In contrast, Pin1 overexpression is highly correlated with the degree of malignancy of cancers, as Pin1 controls a number of oncogenes and tumor suppressors. Accordingly, Pin1 inhibitors as anti-cancer drugs have been developed. Interestingly, recent intensive studies have demonstrated Pin1 to be responsible for the onset or development of nonalcoholic steatosis, obesity, atherosclerosis, lung fibrosis, heart failure and so on, all of which have been experimentally induced in Pin1 deficient mice. In this review, we discuss the possible applications of Pin1 inhibitors to a variety of diseases including malignant tumors and also introduce the recent advances in Pin1 inhibitor research, which have been reported.

Xanthan gum protects temporomandibular chondrocytes from IL‑1β through Pin1/NF‑κB signaling pathway

Temporomandibular disorder (TMD) is a complicated and multi-factorial disease related to inflammation and cartilage destruction. Intra-articular injection of xanthan gum (XG) has been demonstrated to protect the joint cartilage and reduce osteoarthritis progression. However, the role and mechanism of XG in TMD is still unclear. In the present study, chondrocytes were isolated from rats and identified by immunofluorescence. Cells were stimulated by XG or interleukin (IL)-1β. Cell viability was analyzed by MTT assay. Tumor necrosis factor α (TNF-α) and IL-6 levels were determined by ELISA. The expression of monocyte chemoattractive protein-1 (MCP-1), inducible nitric oxide synthase (iNOS), collagens, matrix metalloproteinases (MMPs), peptidyl-prolyl isomerase 1 (Pin1) and phosphorylated nuclear factor κB (NF-κB) p65 (p-p65) was analyzed by quantitative PCR or western blotting. MMP activity was assessed by gelatin zymography. Compared with the control, XG treatment partially reversed the IL-1β-reduced cell viability. In addition, IL-1β stimulation increased inflammatory cytokine expression, including TNF-α, IL-6 secretion, MCP-1 and iNOS expression, whereas XG treatment reduced the expression of these inflammatory cytokines compared with that of the IL-1β-stimulated cells. Additionally, XG increased the expression of collagen, but reduced MMP expression and activity as compared with that in the IL-1β group. In addition, XG treatment prevented the IL-1β-increased Pin1 and p-p65 expression. These data suggested that XG reduced the expression of inflammatory cytokines and may maintain the balance between collagens and MMPs partially through the Pin1/NF-κB signaling pathway in IL-1β-stimulated temporomandibular chondrocytes. Therefore, XG may be useful in the treatment of TMD.

Mini Review: Opposing Pathologies in Cancer and Alzheimer's Disease: Does the PI3K/Akt Pathway Provide Clues?

This minireview is a brief overview examining the roles of insulin-like growth factors (IGFs) and the PI3K/Akt pathway in two apparently unconnected diseases: Alzheimer's dementia and cancer. For both, increased age is a major risk factor, and, in accord with the global rise in average life expectancy, their prevalence is also increasing. Cancer, however, involves excessive cell proliferation and metastasis, whereas Alzheimer's disease (AD) involves cell death and tissue destruction. The apparent "inverse" nature of these disease states is examined here, but also some important commonalities in terms of the PI3K/Akt pathway, glucose utilization and cell deregulation/death. The focus here is on four key molecules associated with this pathway; notably, the insulin receptor substrate 1 (IRS-1), cellular tumor antigen p53 (p53), peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1) and low-density lipoprotein receptor-related protein-1 (LRP1), all previously identified as potential therapeutic targets for both diseases. The insulin-resistant state, commonly reported in AD brain, results in neuronal glucose deprivation, due to a dampening down of the PI3K/Akt pathway, including overactivity of the mammalian target of rapamycin 1 (mTORC1) complex, hyperphosphorylation of p53 and neuronal death. This contrasts with cancer, where there is overstimulation of the PI3K/Akt pathway and the suppression of mTORC1 and p53, enabling abundant energy and unrestrained cell proliferation. Although these disease states appear to be diametrically opposed, the same key molecules are controlling pathology and, with differential targeting of therapeutics, may yet provide a beneficial outcome for both.

Pin1 Plays Essential Roles in NASH Development by Modulating Multiple Target Proteins

Pin1 is one of the three known prolyl-isomerase types and its hepatic expression level is markedly enhanced in the obese state. Pin1 plays critical roles in favoring the exacerbation of both lipid accumulation and fibrotic change accompanying inflammation. Indeed, Pin1-deficient mice are highly resistant to non-alcoholic steatohepatitis (NASH) development by either a high-fat diet or methionine-choline-deficient diet feeding. The processes of NASH development can basically be separated into lipid accumulation and subsequent fibrotic change with inflammation. In this review, we outline the molecular mechanisms by which increased Pin1 promotes both of these phases of NASH. The target proteins of Pin1 involved in lipid accumulation include insulin receptor substrate 1 (IRS-1), AMP-activated protein kinase (AMPK) and acetyl CoA carboxylase 1 (ACC1), while the p60 of the NF-kB complex and transforming growth factor β (TGF-β) pathway appear to be involved in the fibrotic process accelerated by Pin1. Interestingly, Pin1 deficiency does not cause abnormalities in liver size, appearance or function. Therefore, we consider the inhibition of increased Pin1 to be a promising approach to treating NASH and preventing hepatic fibrosis.

Prolyl isomerase Pin1 in metabolic reprogramming of cancer cells

Pin1 is one member of a group consisting of three prolyl isomerases. Pin1 interacts with the motif containing phospho-Ser/Thr-Pro of substrates and enhances cis-trans isomerization of peptide bonds, thereby controlling the functions of these substrates. Importantly, the Pin1 expression level is highly upregulated in most cancer cells and correlates with malignant properties, and thereby with poor outcomes. In addition, Pin1 was revealed to promote the functions of multiple oncogenes and to abrogate tumor suppressors. Accordingly, Pin1 is well recognized as a master regulator of malignant processes. Recent studies have shown that Pin1 also binds to a variety of metabolic regulators, such as AMP-activated protein kinase, acetyl CoA carboxylase and pyruvate kinase2, indicating Pin1 to have major impacts on lipid and glucose metabolism in cancer cells. In this review, we focus on the roles of Pin1 in metabolic reprogramming, such as "Warburg effects", of cancer cells. Our aim is to introduce these important roles of Pin1, as well as to present evidence supporting the possibility of Pin1 inhibition as a novel anti-cancer strategy.

Identification of Prolyl isomerase Pin1 as a novel positive regulator of YAP/TAZ in breast cancer cells

The Hippo signalling pathway plays very important roles in tumorigenesis, metastasis, organ size control, and drug resistance. Although, it has been shown that the two major components of Hippo pathway, YAP and TAZ, play very crucial role in tumorigenesis and drug resistance, the exact molecular mechanisms are still unknown. Recently, we have shown that the prolyl isomerase Pin1 regulates the activity of Hippo pathway through interaction with Hippo component LATS kinase. Thus we asked if Pin1 is also able to interact with other Hippo pathway components. Therefore, in order to investigate whether Pin1 can interacts with other components of the Hippo pathway, we performed GST-pull down and co-immunoprecipitation (Co-IP) assays and have identified two Hippo components YAP and TAZ oncoproteins as novel binding partner of Pin1. We found that Pin1 interacts with YAP/TAZ in a phosphorylation-independent manner and WW domain of Pin1 is necessary for this interaction. Moreover, by using real time qRT-PCR, Cycloheximide chase, luciferase reporter, cell viability and soft agar assays, we have shown that Pin1 increases the tumorigenic and drug-resistant activity of YAP/TAZ through stabilization of YAP/TAZ at protein levels. Together, we have identified Pin1 as a novel positive regulator of YAP/TAZ in tumorigenesis and drug resistance of breast cancer cells. These findings will provide a significant contribution for targeting the Pin1-YAP/TAZ signaling for the successful treatment of tumorigenesis and drug resistance of breast and other cancers in the future.

Oncogenic Hijacking of the PIN1 Signaling Network

Cellular choices are determined by developmental and environmental stimuli through integrated signal transduction pathways. These critically depend on attainment of proper activation levels that in turn rely on post-translational modifications (PTMs) of single pathway members. Among these PTMs, post-phosphorylation prolyl-isomerization mediated by PIN1 represents a unique mechanism of spatial, temporal and quantitative control of signal transduction. Indeed PIN1 was shown to be crucial for determining activation levels of several pathways and biological outcomes downstream to a plethora of stimuli. Of note, studies performed in different model organisms and humans have shown that hormonal, nutrient, and oncogenic stimuli simultaneously affect both PIN1 activity and the pathways that depend on PIN1-mediated prolyl-isomerization, suggesting the existence of evolutionarily conserved molecular circuitries centered on this isomerase. This review focuses on molecular mechanisms and cellular processes like proliferation, metabolism, and stem cell fate, that are regulated by PIN1 in physiological conditions, discussing how these are subverted in and hijacked by cancer cells. Current status and open questions regarding the use of PIN1 as biomarker and target for cancer therapy as well as clinical development of PIN1 inhibitors are also addressed.

Possible involvement of normalized Pin1 expression level and AMPK activation in the molecular mechanisms underlying renal protective effects of SGLT2 inhibitors in mice

BACKGROUND

Recently, clinical studies have shown the protective effects of sodium glucose co-transporter2 (SGLT2) inhibitors against progression of diabetic nephropathy, but the underlying molecular mechanisms remain unclear.

METHODS

Diabetic mice were prepared by injecting nicotinamide and streptozotocin, followed by high-sucrose diet feeding (NA/STZ/Suc mice). The SGLT2 inhibitor canagliflozin was administered as a 0.03% (w/w) mixture in the diet for 4 weeks. Then, various parameters and effects of canagliflozin on diabetic nephropathy were investigated.

RESULTS

Canagliflozin administration to NA/STZ/Suc mice normalized hyperglycemia as well as elevated renal mRNA of collagen 1a1, 1a2, CTGF, TNFα and MCP-1. Microscopic observation revealed reduced fibrotic deposition in the kidneys of canagliflozin-treated NA/STZ/Suc mice. Interestingly, the protein level of Pin1, reportedly involved in the inflammation and fibrosis affecting several tissues, was markedly increased in the NA/STZ/Suc mouse kidney, but this was normalized with canagliflozin treatment. The cells showing increased Pin1 expression in the kidney were mainly mesangial cells, along with podocytes, based on immunohistochemical analysis. Furthermore, it was revealed that canagliflozin induced AMP-activated kinase (AMPK) activation concentration-dependently in CRL1927 mesangial as well as THP-1 macrophage cell lines. AMPK activation was speculated to suppress mesangial cell proliferation and exert anti-inflammatory effects in hematopoietic cells.

CONCLUSION

Therefore, we can reasonably suggest that normalized Pin1 expression and AMPK activation contribute to the molecular mechanisms underlying SGLT2 inhibitor-induced suppression of diabetic nephropathy, possibly at least in part by reducing inflammation and fibrotic change.

Adipocyte biology: It is time to upgrade to a new model

Globally, the obesity pandemic is profoundly affecting quality of life and economic productivity, but efforts to address this, especially on a pharmacological level, have generally proven unsuccessful to date, serving as a stark demonstration that our understanding of adipocyte biology and pathophysiology is incomplete. To deliver better insight into adipocyte function and obesity, we need improved adipocyte models with a high degree of fidelity in representing the in vivo state and with a diverse range of experimental applications. Adipocyte cell lines, especially 3T3-L1 cells, have been used extensively over many years, but these are limited in terms of relevance and versatility. In this review, I propose that primary adipose-derived stromal/stem cells (ASCs) present a superior model with which to study adipocyte biology ex vivo. In particular, ASCs afford us the opportunity to study adipocytes from different, functionally distinct, adipose depots and to investigate, by means of in vivo/ex vivo studies, the effects of many different physiological and pathophysiological factors, such as age, body weight, hormonal status, diet and nutraceuticals, as well as disease and pharmacological treatments, on the biology of adipocytes and their precursors. This study will give an overview of the characteristics of ASCs and published studies utilizing ASCs, to highlight the areas where our knowledge is lacking. More comprehensive studies in primary ASCs will contribute to an improved understanding of adipose tissue, in healthy and dysfunctional states, which will enhance our efforts to more successfully manage and treat obesity.

Mitochondrial dysfunction in metabolism and ageing: shared mechanisms and outcomes?

Mitochondria are key in the metabolism of aerobic organisms and in ageing progression and age-related diseases. Mitochondria are essential for obtaining ATP from glucose and fatty acids but also in many other essential functions in cells including aminoacids metabolism, pyridine synthesis, phospholipid modifications and calcium regulation. On the other hand, the activity of mitochondria is also the principal source of reactive oxygen species in cells. Ageing and chronic age-related diseases are associated with the deregulation of cell metabolism and dysfunction of mitochondria. Cell metabolism is controlled by three major nutritional sensors: mTOR, AMPK and Sirtuins. These factors control mitochondrial biogenesis and dynamics by regulating fusion, fission and turnover through mito- and autophagy. A complex interaction between the activity of these nutritional sensors, mitochondrial biogenesis rate and dynamics exists and affect ageing, age-related diseases including metabolic disease. Further, mitochondria maintain a constant communication with nucleus modulating gene expression and modifying epigenetics. In this review we highlight the importance of mitochondria in ageing and the repercussion in the progression of age-related diseases and metabolic disease.

Pin1 Modulation in Physiological Status and Neurodegeneration. Any Contribution to the Pathogenesis of Type 3 Diabetes?

Prolyl isomerases (Peptidylprolyl isomerase, PPIases) are enzymes that catalyze the isomerization between the cis/trans Pro conformations. Three subclasses belong to the class: FKBP (FK506 binding protein family), Cyclophilin and Parvulin family (Pin1 and Par14). Among Prolyl isomerases, Pin1 presents as distinctive feature, the ability of binding to the motif pSer/pThr-Pro that is phosphorylated by kinases. Modulation of Pin1 is implicated in cellular processes such as mitosis, differentiation and metabolism: The enzyme is dysregulated in many diverse pathological conditions, i.e., cancer progression, neurodegenerative (i.e., Alzheimer’s diseases, AD) and metabolic disorders (i.e., type 2 diabetes, T2D). Indeed, Pin1 KO mice develop a complex phenotype of premature aging, cognitive impairment in elderly mice and neuronal degeneration resembling that of the AD in humans. In addition, since the molecule modulates glucose homeostasis in the brain and peripherally, Pin1 KO mice are resistant to diet-induced obesity, insulin resistance, peripheral glucose intolerance and diabetic vascular dysfunction. In this review, we revise first critically the role of Pin1 in neuronal development and differentiation and then focus on the in vivo studies that demonstrate its pivotal role in neurodegenerative processes and glucose homeostasis. We discuss evidence that enables us to speculate about the role of Pin1 as molecular link in the pathogenesis of type 3 diabetes i.e., the clinical association of dementia/AD and T2D.

Protective Effect of Sex Hormone-Binding Globulin against Metabolic Syndrome: In Vitro Evidence Showing Anti-Inflammatory and Lipolytic Effects on Adipocytes and Macrophages

Sex hormone-binding globulin (SHBG) is a serum protein released mainly by the liver, and a low serum level correlates with a risk for metabolic syndrome including diabetes, obesity, and cardiovascular events. However, the underlying molecular mechanism(s) linking SHBG and metabolic syndrome remains unknown. In this study, using adipocytes and macrophages, we focused on the in vitro effects of SHBG on inflammation as well as lipid metabolism. Incubation with 20 nM SHBG markedly suppressed lipopolysaccharide- (LPS-) induced inflammatory cytokines, such as MCP-1, TNFα, and IL-6 in adipocytes and macrophages, along with phosphorylations of JNK and ERK. Anti-inflammatory effects were also observed in 3T3-L1 adipocytes cocultured with LPS-stimulated macrophages. In addition, SHBG treatment for 18 hrs or longer significantly induced the lipid degradation of differentiated 3T3-L1 cells, with alterations in its corresponding gene and protein levels. Notably, these effects of SHBG were not altered by coaddition of large amounts of testosterone or estradiol. In conclusion, SHBG suppresses inflammation and lipid accumulation in macrophages and adipocytes, which might be among the mechanisms underlying the protective effect of SHBG, that is, its actions which reduce the incidence of metabolic syndrome.

Food polyphenols targeting peptidyl prolyl cis/trans isomerase Pin1

We searched for inhibitors against prolyl isomerase Pin1 in order to develop functional foods to prevent and cure various Pin1 related diseases such as cancer, diabetes, cardiovascular disease, Alzheimers's disease, and so on. We created a polyphenol library consisting of ingredients in healthy foods and beverages, since polyphenols like epigallocatechin gallate (EGCG) in green tea and 974B in brown algae had been identified as its Pin1 inhibitors. Several polyphenols such as EGCG derivatives, caffeic acid derivatives and tannic acid inhibited Pin1 activity. These results provide a first step in development of the functional foods and beverage targeting Pin1 and its related diseases.

High glucose causes vascular dysfunction through Akt/eNOS pathway: reciprocal modulation by juglone and resveratrol

Transient elevations in blood glucose level may lead to changes in vascular function. Herein, we investigated the effects of high-glucose or high-fructose challenge, as well as potential influence of juglone or resveratrol on vascular reactivity, Akt/eNOS, and insulin signaling effectors in rat aorta. Aortic segments of rats were incubated with high glucose (30 mmol/L) or high fructose (2 mmol/L) in the absence and presence of juglone (5 μmol/L) or resveratrol (10 μmol/L). Acute high-glucose incubation markedly decreased acetylcholine-induced relaxation, which is further inhibited by juglone, but ameliorated by resveratrol. Incubation with high glucose caused significant reduction in pAkt/total Akt and peNOS/total eNOS ratios, as well as in the expression of some genes involved in insulin signaling. Juglone produced a further impairment, whereas resveratrol resulted in an improvement on the expression profiles of these proteins and genes. Acute exposure of aortic segments to high glucose causes a reduction in acetylcholine-induced relaxation in association with suppression of Akt/eNOS pathway, as well as several genes in insulin signaling pathway. Juglone and resveratrol have opposite actions on vascular relaxation and the above signaling targets. These findings could be relevant for the treatment of hyperglycemia-induced vascular complications.

Structure and function of the human parvulins Pin1 and Par14/17

Parvulins belong to the family of peptidyl-prolyl cis/trans isomerases (PPIases) assisting in protein folding and in regulating the function of a broad variety of proteins in all branches of life. The human representatives Pin1 and Par14/17 are directly involved in processes influencing cellular maintenance and cell fate decisions such as cell-cycle progression, metabolic pathways and ribosome biogenesis. This review on human parvulins summarizes the current knowledge of these enzymes and intends to oppose the well-studied Pin1 to its less well-examined homolog human Par14/17 with respect to structure, catalytic and cellular function.

Peptidyl-prolyl isomerase Pin1 deficiency attenuates angiotensin II-induced abdominal aortic aneurysm formation in ApoE-/- mice

Peptidyl-prolyl isomerase Pin1 has been reported to be associated with endothelial dysfunction. However, the role of smooth muscle Pin1 in the vascular system remains unclear. Here, we examined the potential function of Pin1 in smooth muscle cells (SMCs) and its contribution to abdominal aortic aneurysm (AAA) pathogenesis. The level of Pin1 expression was found to be elevated in human AAA tissues and mainly localized to SMCs. We constructed smooth muscle-specific Pin1 knockout mice to explore the role of this protein in AAA formation and to elucidate the underlying mechanisms. AAA formation and elastin degradation were hindered by Pin1 depletion in the angiotensin II-induced mouse model. Pin1 depletion reversed the angiotensin II-induced pro-inflammatory and synthetic SMC phenotype switching via the nuclear factor (NF)-κB p65/Klf4 axis. Moreover, Pin1 depletion inhibited the angiotensin II-induced matrix metalloprotease activities. Mechanically, Pin1 deficiency destabilized NF-κB p65 by promoting its polyubiquitylation. Further, we found STAT1/3 bound to the Pin1 promoter, revealing that activation of STAT1/3 was responsible for the increased expression of Pin1 under angiotensin II stimulation. Thus, these results suggest that Pin1 regulates pro-inflammatory and synthetic SMC phenotype switching and could be a novel therapeutic target to limit AAA pathogenesis.

The prolyl isomerase Pin1 increases β-cell proliferation and enhances insulin secretion

The prolyl isomerase Pin1 binds to the phosphorylated Ser/Thr-Pro motif of target proteins and enhances their cis-trans conversion. This report is the first to show that Pin1 expression in pancreatic β cells is markedly elevated by high-fat diet feeding and in ob/ob mice. To elucidate the role of Pin1 in pancreatic β cells, we generated β-cell-specific Pin1 KO (βPin1 KO) mice. These mutant mice showed exacerbation of glucose intolerance but had normal insulin sensitivity. We identified two independent factors underlying impaired insulin secretion in the βPin1 KO mice. Pin1 enhanced pancreatic β-cell proliferation, as indicated by a reduced β-cell mass in βPin1 KO mice compared with control mice. Moreover, a diet high in fat and sucrose failed to increase pancreatic β-cell growth in the βPin1 KO mice, an observation to which up-regulation of the cell cycle protein cyclin D appeared to contribute. The other role of Pin1 was to activate the insulin-secretory step: Pin1 KO β cells showed impairments in glucose- and KCl-induced elevation of the intracellular Ca²⁺ concentration and insulin secretion. We also identified salt-inducible kinase 2 (SIK2) as a Pin1-binding protein that affected the regulation of Ca²⁺ influx and found Pin1 to enhance SIK2 kinase activity, resulting in a decrease in p35 protein, a negative regulator of Ca²⁺ influx. Taken together, our observations demonstrate critical roles of Pin1 in pancreatic β cells and that Pin1 both promotes β-cell proliferation and activates insulin secretion.

Epicatechin downregulates adipose tissue CCL19 expression and thereby ameliorates diet-induced obesity and insulin resistance

BACKGROUND AND AIMS

Epicatechin (EC) intake has been suggested to be beneficial for the prevention of cardiovascular disorders, and it is well known that adipose tissue inflammation is one of the major risk factors for coronary heart diseases. The purpose of the present study was to determine the in vitro and in vivo effects of EC on adipose tissue inflammation and obesity.

METHODS AND RESULTS

DNA microarray analysis was performed to evaluate the effects of EC on gene expression in adipocytes co-cultured with bacterial endotoxin-stimulated macrophages. To determine the in vivo effects of the catechin, C57BL/6 mice were fed either a high-fat diet (HFD) or HFD combined with EC, and metabolic changes were observed EC suppressed the expression of many inflammatory genes in the adipocytes co-cultured with endotoxin-stimulated macrophages. Specifically, EC markedly suppressed chemokine (CC motif) ligand 19 (CCL19) expression. The target cell of EC appeared to macrophages. The in vivo study indicated that mice fed the EC-supplemented HFD were protected from diet-induced obesity and insulin resistance. Accordingly, the expression levels of genes associated with inflammation in adipose tissue and in the liver were downregulated in this group of mice.

CONCLUSIONS

EC exerts beneficial effects for the prevention of adipose tissue inflammation and insulin resistance. Since we previously reported that mice deficient in the CCL19 receptor were protected from diet-induced obesity and insulin resistance, it can be concluded that the beneficial effects of EC could be mediated, at least in part, by marked suppression of CCL19 expression.

Role of PIN1 on in vivo periodontal tissue and in vitro cells

BACKGROUND

Although expression of peptidyl-prolyl cis/trans isomerase NIMA-interacting 1 (PIN1) was reported in bone tissue, the precise role of PIN1 in periodontal tissue and cells remain unclear.

MATERIAL & METHODS

To elucidate the roles of PIN1 in periodontal tissue, its expression in periodontal tissue and cells, and effects on in vitro 4 osteoblast differentiation and the underlying signaling mechanisms were evaluated.

RESULTS

PIN1 was expressed in mouse periodontal tissues including periodontal ligament cells (PDLCs), cementoblasts and osteoblasts at the developing root formation stage (postnatal, PN14) and functional stage of tooth (PN28). Treatment of PIN1 inhibitor juglone, and gene silencing by RNA interference promoted osteoblast differentiation in PDLCs and cementoblasts, whereas the overexpression of PIN1 inhibited. Moreover, osteogenic medium-induced activation of AMPK, mTOR, Akt, ERK, p38 and NF-jB pathways were enhanced by PIN1 siRNA, but attenuated by PIN1 overexpression. Runx2 expressions were induced by PIN1 siRNA, but downregulated by PIN1 overexpression.

CONCLUSION

In summary, this study is the first to demonstrate that PIN1 is expressed in developing periodontal tissue, and in vitro PDLCs and cementoblasts. PIN1 inhibition stimulates osteoblast differentiation, and thus may play an important role in periodontal regeneration.

Effect of miglitol on the suppression of nonalcoholic steatohepatitis development and improvement of the gut environment in a rodent model

BACKGROUND

The gut environment has been considered to play a role in the development of nonalcoholic steatohepatitis (NASH). α-glucosidase inhibitors (α-GIs) delay carbohydrate absorption and may change the gut environment. We considered that the protective effect of α-GIs against NASH development is related to changes in the gut environment and thus investigated the effects of miglitol, an α-GI, on NASH development and the gut environment.

METHODS

Mice were divided into three groups and fed a normal chow diet (NCD), a high-fat high-sucrose diet (HFHSD), or HFHSD plus 0.04% miglitol (HFHSD plus M) for 12 weeks.

RESULTS

Insulin resistance developed more in the HFHSD group than in the NCD group, whereas it was suppressed in the HFHSD plus M group. NASH was evaluated histologically, biochemically, and on the basis of messenger RNA expression levels. Miglitol treatment suppressed HFHSD-induced NASH development with the suppression of hepatic Toll-like receptor 4 expression, increased glucagon-like peptide 1 (GLP-1) concentration, and reduced lipopolysaccharide concentration in portal plasma. Regarding the gut environment, the intestinal transit time was shortened and colon inflammation was suppressed in the HFHSD plus M group compared with the HFHSD group. Regarding the gut microbiota, the abundances of Erysipelotrichaceae and Coriobacteriaceae were increased in the HFHSD group compared with the NCD group, whereas the increase was suppressed in the HFHSD plus M group.

CONCLUSIONS

We demonstrated that miglitol has a protective effect against HFHSD-induced NASH development. The increased GLP-1 secretion and the suppression of endotoxemia, associated with the changes in the gut environment, including the gut microbiota, could contribute to the underlying mechanisms.

Brown Algae Polyphenol, a Prolyl Isomerase Pin1 Inhibitor, Prevents Obesity by Inhibiting the Differentiation of Stem Cells into Adipocytes

BACKGROUND

While screening for an inhibitor of the peptidyl prolyl cis/trans isomerase, Pin1, we came across a brown algae polyphenol that blocks the differentiation of fibroblasts into adipocytes. However, its effectiveness on the accumulation of fat in the body has never been studied.

METHODOLOGY/PRINCIPAL FINDINGS

Oral administration of brown algae polyphenol to mice fed with a high fat diet, suppressed the increase in fat volume to a level observed in mice fed with a normal diet. We speculate that Pin1 might be required for the differentiation of stem cell to adipocytes. We established wild type (WT) and Pin1-/- (Pin1-KO) adipose-derived mesenchymal stem cell (ASC) lines and found that WT ASCs differentiate to adipocytes but Pin1-KO ASCs do not.

CONCLUSION AND SIGNIFICANCE

Oral administration of brown algae polyphenol, a Pin1 inhibitor, reduced fat buildup in mice. We showed that Pin1 is required for the differentiation of stem cells into adipocytes. We propose that oral intake of brown algae polyphenol is useful for the treatment of obesity.

Pin1 enhances adipocyte differentiation by positively regulating the transcriptional activity of PPARγ

Pin1 is a peptidylprolyl cis/trans isomerase and it has a unique enzymatic activity of catalyzing isomerization of the peptide bond between phospho-serine/threonine and proline. Through the conformational change of its substrates, Pin1 regulates diverse biological processes including adipogenesis. In mouse embryonic fibroblasts and 3T3-L1 preadipocytes, overexpression of Pin1 enhances adipocyte differentiation whereas inhibition of Pin1 activity suppresses it. However, the precise functions of Pin1 during adipogenesis are not clear. In the present study, we investigated the potential targets of Pin1 during adipogenesis. We found that Pin1 interacts directly with and regulates the transcriptional activity of PPARγ, a key regulator of adipogenesis. In addition, ERK activity and Ser273 of PPARγ, a potential ERK phosphorylation target site, are important for the regulation of PPARγ function by Pin1 in 3T3-L1 cells. Taken together our results suggest a novel regulatory mechanism of Pin1 during adipogenesis, in which Pin1 enhances adipocyte differentiation by regulating the function of PPARγ.

Physiological and Pathogenic Roles of Prolyl Isomerase Pin1 in Metabolic Regulations via Multiple Signal Transduction Pathway Modulations

Prolyl isomerases are divided into three groups, the FKBP family, Cyclophilin and the Parvulin family (Pin1 and Par14). Among these isomerases, Pin1 is a unique prolyl isomerase binding to the motif including pSer/pThr-Pro that is phosphorylated by kinases. Once bound, Pin1 modulates the enzymatic activity, protein stability or subcellular localization of target proteins by changing the cis- and trans-formations of proline. Several studies have examined the roles of Pin1 in the pathogenesis of cancers and Alzheimer's disease. On the other hand, recent studies have newly demonstrated Pin1 to be involved in regulating glucose and lipid metabolism. Interestingly, while Pin1 expression is markedly increased by high-fat diet feeding, Pin1 KO mice are resistant to diet-induced obesity, non-alcoholic steatohepatitis and diabetic vascular dysfunction. These phenomena result from the binding of Pin1 to several key factors regulating metabolic functions, which include insulin receptor substrate-1, AMPK, Crtc2 and NF-κB p65. In this review, we focus on recent advances in elucidating the physiological roles of Pin1 as well as the pathogenesis of disorders involving this isomerase, from the viewpoint of the relationships between signal transductions and metabolic functions.

PPIA is a novel adipogenic factor implicated in obesity

OBJECTIVE

To assess the role of peptidyl-prolyl cis/trans isomerase a (PPIA) in adipogenesis and obesity.

METHODS

Fat mass and adipocyte sizes of PPIA-/- and wild-type mice were compared. The role of PPIA in adipocyte differentiation of 3T3L1 and MEFs cells was analyzed by gene silencing and overexpression. The roles of PPIA in obesity were observed on a high-fat diet obesity model and a gestational diabetes obesity model.

RESULTS

PPIA-/- mice had significantly less fat than PPIA+/+ mice. The adipocyte size of PPIA-/- mice was significantly smaller than wild type. Silencing PPIA in 3T3L1 cells significantly impaired its adipocyte differentiation ability. Similarly, MEFs from PPIA-/- mice differentiated less than wild type, while their differentiation ability was restored by PPIA overexpression. PPIA-silenced 3T3L1 cells had significantly lower expression of PPARG, C/EBPA, and C/EBPB at late stage of adipocyte differentiation, which was the same in PPIA-/- MEFs. When fed a high-fat diet, PPIA-/- mice gained significantly less weight than wild type, accompanied by reduced PPARG, C/EBPA, and C/EBPB expression. PPIA expression was significantly higher in adipose tissue of gestational diabetes rat offspring, which had higher inguinal fat/body weight ratios than normal rat offspring.

CONCLUSIONS

PPIA was a novel adipogenic factor important in obesity.

Nephrin Contributes to Insulin Secretion and Affects Mammalian Target of Rapamycin Signaling Independently of Insulin Receptor

Nephrin belongs to a family of highly conserved proteins with a well characterized function as modulators of cell adhesion and guidance, and nephrin may have a role in metabolic pathways linked to podocyte and pancreatic β-cell survival. However, this role is incompletely characterized. In this study, we developed floxed nephrin mice for pancreatic β-cell-specific deletion of nephrin, which had no effect on islet size and glycemia. Nephrin deficiency, however, resulted in glucose intolerance in vivo and impaired glucose-stimulated insulin release ex vivo Glucose intolerance was also observed in eight patients with nephrin mutations compared with three patients with other genetic forms of nephrotic syndrome or nine healthy controls.In vitro experiments were conducted to investigate if nephrin affects autocrine signaling through insulin receptor A (IRA) and B (IRB), which are both expressed in human podocytes and pancreatic islets. Coimmunoprecipitation of nephrin and IRB but not IRA was observed and required IR phosphorylation. Nephrin per se was sufficient to induce phosphorylation of p70S6K in an phosphatidylinositol 3-kinase-dependent but IR/Src-independent manner, which was not augmented by exogenous insulin. These results suggest a role for nephrin as an independent modulator of podocyte and pancreatic β-cell nutrient sensing in the fasting state and the potential of nephrin as a drug target in diabetes.

Peptidyl-prolyl isomerases: functionality and potential therapeutic targets in cardiovascular disease

Peptidyl-prolyl cis/trans isomerases (PPIases) are a conserved group of enzymes that catalyse the conversion between cis and trans conformations of proline imidic peptide bonds. These enzymes play critical roles in regulatory mechanisms of cellular function and pathophysiology of disease. There are three different classes of PPIases and increasing interest in the development of specific PPIase inhibitors. Cyclosporine A, FK506, rapamycin and juglone are known PPIase inhibitors. Herein, we review recent advances in elucidating the role and regulation of the PPIase family in vascular disease. We focus on peptidyl-prolyl cis/trans isomerase NIMA-interacting 1 (Pin1), an important member of the PPIase family that plays a role in cell cycle progression, gene expression, cell signalling and cell proliferation. In addition, Pin1 may be involved in atherosclerosis. The unique role of Pin1 as a molecular switch that impacts on multiple downstream pathways necessitates the evaluation of a highly specific Pin1 inhibitor to aid in potential therapeutic drug discovery.

Prolyl isomerase Pin1 negatively regulates AMP-activated protein kinase (AMPK) by associating with the CBS domain in the γ subunit

AMP-activated protein kinase (AMPK) plays a critical role in metabolic regulation. In this study, first, it was revealed that Pin1 associates with any isoform of γ, but not with either the α or the β subunit, of AMPK. The association between Pin1 and the AMPK γ1 subunit is mediated by the WW domain of Pin1 and the Thr(211)-Pro-containing motif located in the CBS domain of the γ1 subunit. Importantly, overexpression of Pin1 suppressed AMPK phosphorylation in response to either 2-deoxyglucose or biguanide stimulation, whereas Pin1 knockdown by siRNAs or treatment with Pin1 inhibitors enhanced it. The experiments using recombinant Pin1, AMPK, LKB1, and PP2C proteins revealed that the protective effect of AMP against PP2C-induced AMPKα subunit dephosphorylation was markedly suppressed by the addition of Pin1. In good agreement with the in vitro data, the level of AMPK phosphorylation as well as the expressions of mitochondria-related genes, such as PGC-1α, which are known to be positively regulated by AMPK, were markedly higher with reduced triglyceride accumulation in the muscles of Pin1 KO mice as compared with controls. These findings suggest that Pin1 plays an important role in the pathogenic mechanisms underlying impaired glucose and lipid metabolism, functioning as a negative regulator of AMPK.

Protection from diet-induced obesity and insulin resistance in mice lacking CCL19-CCR7 signaling

OBJECTIVE

Several chemokines play important roles in recruiting the monocyte/macrophage lineage into adipose tissues. We previously found CCL19 was highly expressed in adipocytes cocultured with macrophages stimulated by endotoxin. This study aimed to evaluate the role of CCL19-CCR7 axis on obesity and insulin resistance.

METHODS

Serum CCL19 concentration was examined in obese model mice challenged by endotoxin. CCL19 receptor-null, Ccr7(-/-), mice and wild-type mice fed a high-fat diet or normal diet were used to investigate the role of CCL19 signals on obesity-associated inflammation.

RESULTS

CCL19 protein was elevated in the sera of obese model mice challenged by endotoxin. Ccr7(-/-) mice were protected from diet-induced obesity and insulin resistance. The adipose tissue and liver expression of inflammatory genes of Ccr7(-/-) mice was much lower than in diet-induced obese mice. Ccr7(-/-) mice were protected from fatty liver and dyslipidemia and exhibited increased thermogenesis on high-fat feeding. CCL19 attracts activated dendritic cells (DC). The expression of the DC markers, CD11b and 11c, was not observed in the adipose tissues of Ccr7(-/-) mice fed a high-fat diet, which might be closely associated with the protection of these mice from obesity.

CONCLUSIONS

The CCL19-CCR7 pathway associates with the development of high-fat-induced obesity and insulin resistance.

Pin1 Inhibitor Juglone Exerts Anti-Oncogenic Effects on LNCaP and DU145 Cells despite the Patterns of Gene Regulation by Pin1 Differing between These Cell Lines

Background

Prostate cancer initially develops in an androgen-dependent manner but, during its progression, transitions to being androgen-independent in the advanced stage. Pin1, one of the peptidyl-prolyl cis/trans isomerases, is reportedly overexpressed in prostate cancers and is considered to contribute to accelerated cell growth, which may be one of the major factors contributing to their androgen-independent growth. Thus, we investigated how Pin1 modulates the gene expressions in both androgen-dependent and androgen-independent prostate cancer cell lines using microarray analysis. In addition, the effects of Juglone, a commercially available Pin1 inhibitor were also examined.

Methods

Two prostate cancer cell-lines, LNCaP (androgen-dependent) and DU145 (androgen-independent), were treated with Pin1 siRNA and its effects on gene expressions were analyzed by microarray. Individual gene regulations induced by Pin1 siRNA or the Pin1 inhibitor Juglone were examined using RT-PCR. In addition, the effects of Juglone on the growth of LNCaP and DU145 transplanted into mice were investigated.

Results

Microarray analysis revealed that transcriptional factors regulated by Pin1 differed markedly between LNCaP and DU145 cells, the only exception being that Nrf was regulated in the same way by Pin1 siRNA in both cell lines. Despite this marked difference in gene regulations, Pin1 siRNA and Juglone exert a strong inhibitory effect on both the LNCaP and the DU145 cell line, suppressing in vitro cell proliferation as well as tumor enlargement when transplanted into mice.

Conclusions

Despite Pin1-regulated gene expressions differing between these two prostate cancer cell-lines, LNCaP (androgen-dependent) and DU145 (androgen-independent), Pin1 inhibition suppresses proliferation of both cell-lines. These findings suggest the potential effectiveness of Pin1 inhibitors as therapeutic agents for prostate cancers, regardless of their androgen sensitivity.

The Novel Functions of High-Molecular-Mass Complexes Containing Insulin Receptor Substrates in Mediation and Modulation of Insulin-Like Activities: Emerging Concept of Diverse Functions by IRS-Associated Proteins

Insulin-like peptides, such as insulin-like growth factors (IGFs) and insulin, induce a variety of bioactivities, such as growth, differentiation, survival, increased anabolism, and decreased catabolism in many cell types and in vivo. In general, IGFs or insulin bind to IGF-I receptor (IGF-IR) or insulin receptor (IR), activating the receptor tyrosine kinase. Insulin receptor substrates (IRSs) are known to be major substrates of receptor kinases, mediating IGF/insulin signals to direct bioactivities. Recently, we discovered that IRSs form high-molecular-mass complexes (referred to here as IRSomes) even without IGF/insulin stimulation. These complexes contain proteins (referred to here as IRSAPs; IRS-associated proteins), which modulate tyrosine phosphorylation of IRSs by receptor kinases, control IRS stability, and determine intracellular localization of IRSs. In addition, in these complexes, we found not only proteins that are involved in RNA metabolism but also RNAs themselves. Thus, IRSAPs possibly contribute to modulation of IGF/insulin bioactivities. Since it is established that disorder of modulation of insulin-like activities causes various age-related diseases including cancer, we could propose that the IRSome is an important target for treatment of these diseases.

A high-throughput screen for inhibitors of the prolyl isomerase, Pin1, identifies a seaweed polyphenol that reduces adipose cell differentiation

The peptidyl prolyl cis/trans isomerase Pin1 enhances the uptake of triglycerides and the differentiation of fibroblasts into adipose cells in response to insulin stimulation. Pin1 downregulation could be a potential approach to prevent and treat obesity-related disorders. In order to identify an inhibitor of Pin1 that exhibited minimal cytotoxicity, we established a high-throughput screen for Pin1 inhibitors and used this method to identify an inhibitor from 1,056 crude fractions of two natural product libraries. The candidate, a phlorotannin called 974-B, was isolated from the seaweed, Ecklonia kurome. 974-B inhibited the differentiation of mouse embryonic fibroblasts and 3T3-L1 cells into adipose cells without inducing cytotoxicity. We discovered the Pin1 inhibitor, 974-B, from the seaweed, E. kurome, and showed that it blocks the differentiation of fibroblasts into adipose cells, suggesting that 974-B could be a lead drug candidate for obesity-related disorders.

The role of PIN1 on odontogenic and adipogenic differentiation in human dental pulp stem cells

Recently, the involvement of PIN1, a peptidyl-prolyl cis/trans isomerase, has been reported in age-related bone homeostasis and adipogenesis. However, the role of PIN1 during odontogenic and adipogenic differentiation remains to be fully understood, particularly regarding human dental pulp stem cells (HDPSCs). Thus, in the present study, we have investigated the role of PIN1 in odontogenic and adipogenic differentiation of HDPSCs and signaling pathways possibly involved. PIN1 mRNA and protein level were upregulated in a time-dependent manner during adipogenic differentiation, increasing until 1 day of odontogenic induction and then steadily declined during odontogenic differentiation. Treatment of a known PIN1 inhibitor, juglone, significantly increased odontogenic differentiation as confirmed by alkaline phosphatase (ALP) activity, calcium deposition, and mRNAs induction of odontogenic markers [ALP, osteopontin (OPN), osteocalcin (OCN), dentin sialophosphoprotein (DSPP), and dentin matrix protein 1 (DMP-1)]. On the contrary, adipogenic differentiation was dramatically reduced upon juglone treatment, with concomitant downregulation of lipid droplet accumulation and adipogenic marker genes [peroxisome proliferation-activated receptor gamma (PPARγ), lipoprotein lipase (LPL), and adipocyte fatty acid-binding protein (AP2)]. In contrast to PIN1 inhibition, the overexpression of PIN1 via adenoviral infection (Ad-PIN1) in HDPSCs inhibited odontogenic differentiation but increased adipogenic differentiation, in which stem cell property markers such as stage-specific embryonic antigen-4 (SSEA-4) and STRO-1 were upregulated during odontogenic differentiation but downregulated in adiopogenic differentiation. Consistently, juglone-mediated inhibition of PIN1 augmented the osteogenic medium (OM)-induced activation of bone morphogenetic protein (BMP), Wnt/β-catenin, extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and nuclear factor-kappa B (NF-κB) pathway, which response was reversed by Ad-PIN1. Moreover, juglone blocked the adipogenic induction medium-induced activation of PPARγ, C/EBPα, C/EBPβ, ERK, and NF-κB pathways, which was rescued by Ad-PIN1 infection. In summary, the present study shows for the first time that PIN1 acts as an important modulator of odontogenic and adipogenic differentiation of HDPSCs and may have clinical implications for regenerative dentistry.

Pin1 promotes GR transactivation by enhancing recruitment to target genes

The glucocorticoid receptor (GR) is a ligand activated transcription factor, serving to regulate both energy metabolism and immune functions. Factors that influence cellular sensitivity to glucocorticoids (GC) are therefore of great interest. The N-terminal of the GR contains numerous potential proline-directed phosphorylation sites, some of which can regulate GR transactivation. Unrestricted proline isomerisation can be inhibited by adjacent serine phosphorylation and requires a prolyl isomerise, Pin1. Pin1 therefore determines the functional outcome of proline-directed kinases acting on the GR, as cis/trans isomers are distinct pools with different interacting proteins. We show that Pin1 mediates GR transactivation, but not GR trans-repression. Two N-terminal GR serines, S203 and S211, are targets for Pin1 potentiation of GR transactivation, establishing a direct link between Pin1 and the GR. We also demonstrate GC-activated co-recruitment of GR and Pin1 to the GILZ gene promoter. The Pin1 effect required both its WW and catalytic domains, and GR recruitment to its GRE was Pin1-dependent. Therefore, Pin1 is a selective regulator of GR transactivation, acting through N-terminal phospho-serine residues to regulate GR recruitment to its target sites in the genome. As Pin1 is dysregulated in disease states, this interaction may contribute to altered GC action in inflammatory conditions.

Par14 protein associates with insulin receptor substrate 1 (IRS-1), thereby enhancing insulin-induced IRS-1 phosphorylation and metabolic actions

Pin1 and Par14 are parvulin-type peptidyl-prolyl cis/trans isomerases. Although numerous proteins have been identified as Pin1 substrates, the target proteins of Par14 remain largely unknown. Par14 expression levels are increased in the livers and embryonic fibroblasts of Pin1 KO mice, suggesting a compensatory relationship between the functions of Pin1 and Par14. In this study, the association of Par14 with insulin receptor substrate 1 (IRS-1) was demonstrated in HepG2 cells overexpressing both as well as endogenously in the mouse liver. The analysis using deletion-mutated Par14 and IRS-1 constructs revealed the N-terminal portion containing the basic domain of Par14 and the two relatively C-terminal portions of IRS-1 to be involved in these associations, in contrast to the WW domain of Pin1 and the SAIN domain of IRS-1. Par14 overexpression in HepG2 markedly enhanced insulin-induced IRS-1 phosphorylation and its downstream events, PI3K binding with IRS-1 and Akt phosphorylation. In contrast, treating HepG2 cells with Par14 siRNA suppressed these events. In addition, overexpression of Par14 in the insulin-resistant ob/ob mouse liver by adenoviral transfer significantly improved hyperglycemia with normalization of hepatic PEPCK and G6Pase mRNA levels, and gene suppression of Par14 using shRNA adenovirus significantly exacerbated the glucose intolerance in Pin1 KO mice. Therefore, although Pin1 and Par14 associate with different portions of IRS-1, the prolyl cis/trans isomerization in multiple sites of IRS-1 by these isomerases appears to be critical for efficient insulin receptor-induced IRS-1 phosphorylation. This process is likely to be one of the major mechanisms regulating insulin sensitivity and also constitutes a potential therapeutic target for novel insulin-sensitizing agents.