Pancreatic stellate cells: a starring role in normal and diseased pancreas

Inflammation in acute and chronic pancreatitis

PURPOSE OF REVIEW

This report reviews recent animal model and human studies associated with inflammatory responses in acute and chronic pancreatitis.

RECENT FINDINGS

Animal model and limited human acute and chronic pancreatitis studies unravel the dynamic nature of the inflammatory processes and the ability of the immune cells to sense danger and environmental signals. In acute pancreatitis, such molecules include pathogen-associated molecular pattern recognition receptors such as toll-like receptors, and the more recently appreciated damage-associated molecular pattern molecules or 'alarmin' high mobility group box 1 and IL-33. In chronic pancreatitis, a recent understanding of a critical role for macrophage-pancreatic stellate cell interaction offers a potential targetable pathway that can alter fibrogenesis. Microbiome research in pancreatitis is a new field gaining interest but will require further investigation.

SUMMARY

Immune cell contribution to the pathogenesis of acute and chronic pancreatitis is gaining more appreciation and further understanding in immune signaling presents potential therapeutic targets that can alter disease progression.

Pancreatic stellate cell: physiologic role, role in fibrosis and cancer

PURPOSE OF REVIEW

Ever since the first descriptions of methods to isolate pancreatic stellate cells (PSCs) from rodent and human pancreas 17 years ago, rapid advances have been made in our understanding of the biology of these cells and their functions in health and disease. This review updates recent literature in the field, which indicates an increasingly complex role for the cells in normal pancreas, pancreatitis and pancreatic cancer.

RECENT FINDINGS

Work reported over the past 12 months includes improved methods of PSC immortalization, a role for PSCs in islet fibrosis, novel factors causing PSC activation as well as those inducing quiescence, and translational research aimed at inhibiting the facilitatory effects of PSCs on disease progression in chronic pancreatitis as well as pancreatic cancer.

SUMMARY

Improved understanding of the role of PSCs in pancreatic pathophysiology has prompted a focus on translational studies aimed at developing novel approaches to modulate PSC function in a bid to improve clinical outcomes of two major fibrotic diseases of the pancreas: chronic pancreatitis and pancreatic cancer.

Anti-fibrotic effects of phenolic compounds on pancreatic stellate cells

BACKGROUND

Pancreatic fibrosis is a prominent histopathological characteristic of chronic pancreatitis and plausibly a dynamic process of transition to the development of pancreatic ductal adenocarcinoma. Conversely, the activation of pancreatic stellate cells (PSCs) has been recently suggested as the key initiating step in pancreatic fibrosis. As natural polyphenols had been largely applied in complementary therapies in the past decade, in this study, we aimed to investigate which groups of phenolic compounds exert promising inhibitory actions on fibrogenesis as there are few effective strategies for the treatment of pancreatic fibrosis to date.

METHODS

We examined the anti-fibrotic effects of a variety of herbal constituents using a cellular platform, the LTC-14 cells, which retained essential characteristics and morphologies of primary PSCs, by means of various biochemical assays including cell viability test, real-time polymerase chain reaction and Western blotting analysis.

RESULTS

Among a number of commonly used herbal constituents, we found that the application of rhein, emodin, curcumin and resveratrol significantly suppressed the mRNA and protein levels of several fibrotic mediators namely alpha-smooth muscle actin, type I collagen and fibronectin in LTC-14 cells against transforming growth factor-beta stimulation. Though the values of cytotoxicity varied, the mechanism of the anti-fibrotic action of these four phenolic compounds was principally associated with a decrease in the activation of the nuclear factor-kappaB signaling pathway.

CONCLUSIONS

Our findings suggest that the mentioned phenolic compounds may serve as anti-fibrotic agents in PSC-relating disorders and pathologies, particularly pancreatic fibrosis.

Acute pancreatitis

Acute pancreatitis, an inflammatory disorder of the pancreas, is the leading cause of admission to hospital for gastrointestinal disorders in the USA and many other countries. Gallstones and alcohol misuse are long-established risk factors, but several new causes have emerged that, together with new aspects of pathophysiology, improve understanding of the disorder. As incidence (and admission rates) of acute pancreatitis increase, so does the demand for effective management. We review how to manage patients with acute pancreatitis, paying attention to diagnosis, differential diagnosis, complications, prognostic factors, treatment, and prevention of second attacks, and the possible transition from acute to chronic pancreatitis.

Pancreatic cancer: The microenvironment needs attention too!

The abundant stromal/desmoplastic reaction, a characteristic feature of a majority of pancreatic adenocarcinomas (PDAC), has only recently been receiving some attention regarding its possible role in the pathobiology of pancreatic cancer. It is now well established that the cells predominantly responsible for producing the collagenous stroma are pancreatic stellate cells (PSCs). In addition to extracellular matrix proteins, the stroma also exhibits cellular elements including, immune cells, endothelial cells and neural cells. Evidence is accumulating to indicate the presence of significant interactions between PSCs and cancer cells as well as between PSCs and other cell types in the stroma. The majority of research reports to date, using in vitro and in vivo approaches, suggest that these interactions facilitate local growth as well as distant metastasis of pancreatic cancer, although a recent study using animals depleted of myofibroblasts has raised some questions regarding the central role of myofibroblasts in cancer progression. Nonetheless, novel therapeutic strategies have been assessed, mainly in the pre-clinical setting, in a bid to interrupt stromal-tumour interactions and inhibit disease progression. The next important challenge is for the translation of such pre-clinical strategies to the clinical situation so as to improve the outcome of patients with pancreatic cancer.

Chronic hyperglycemia induces trans-differentiation of human pancreatic stellate cells and enhances the malignant molecular communication with human pancreatic cancer cells

Background

Diabetes mellitus is linked to pancreatic cancer. We hypothesized a role for pancreatic stellate cells (PSC) in the hyperglycemia induced deterioration of pancreatic cancer and therefore studied two human cell lines (RLT-PSC, T3M4) in hyperglycemic environment.

Methodology/Principal Findings

The effect of chronic hyperglycemia (CHG) on PSCs was studied using mRNA expression array with real-time PCR validation and bioinformatic pathway analysis, and confirmatory protein studies. The stress fiber formation (IC: αSMA) indicated that PSCs tend to transdifferentiate to a myofibroblast-like state after exposure to CHG. The phosphorylation of p38 and ERK1/2 was increased with a consecutive upregulation of CDC25, SP1, cFOS and p21, and with downregulation of PPARγ after PSCs were exposed to chronic hyperglycemia. CXCL12 levels increased significantly in PSC supernatant after CHG exposure independently from TGF-β1 treatment (3.09-fold with a 2.73-fold without TGF-β1, p<0.05). The upregualtion of the SP1 transcription factor in PSCs after CHG exposure may be implicated in the increased CXCL12 and IGFBP2 production. In cancer cells, hyperglycemia induced an increased expression of CXCR4, a CXCL12 receptor that was also induced by PSC’s conditioned medium. The receptor-ligand interaction increased the phosphorylation of ERK1/2 and p38 resulting in activation of MAP kinase pathway, one of the most powerful stimuli for cell proliferation. Certainly, conditioned medium of PSC increased pancreatic cancer cell proliferation and this effect could be partially inhibited by a CXCR4 inhibitor. As the PSC conditioned medium (normal glucose concentration) increased the ERK1/2 and p38 phosphorylation, we concluded that PSCs produce other factor(s) that influence(s) pancreatic cancer behaviour.

Conclusions

Hyperglycemia induces increased CXCL12 production by the PSCs, and its receptor, CXCR4 on cancer cells. The ligand-receptor interaction activates MAP kinase signaling that causes increased cancer cell proliferation and migration.

Vitamin D receptor-mediated stromal reprogramming suppresses pancreatitis and enhances pancreatic cancer therapy

The poor clinical outcome in pancreatic ductal adenocarcinoma (PDA) is attributed to intrinsic chemoresistance and a growth-permissive tumor microenvironment. Conversion of quiescent to activated pancreatic stellate cells (PSCs) drives the severe stromal reaction that characterizes PDA. Here, we reveal that the vitamin D receptor (VDR) is expressed in stroma from human pancreatic tumors and that treatment with the VDR ligand calcipotriol markedly reduced markers of inflammation and fibrosis in pancreatitis and human tumor stroma. We show that VDR acts as a master transcriptional regulator of PSCs to reprise the quiescent state, resulting in induced stromal remodeling, increased intratumoral gemcitabine, reduced tumor volume, and a 57% increase in survival compared to chemotherapy alone. This work describes a molecular strategy through which transcriptional reprogramming of tumor stroma enables chemotherapeutic response and suggests vitamin D priming as an adjunct in PDA therapy. PAPERFLICK:

Cellular localization of β-carotene 15,15' oxygenase-1 (BCO1) and β-carotene 9',10' oxygenase-2 (BCO2) in rat liver and intestine

The intestine and liver are crucial organs for vitamin A uptake and storage. Liver accounts for 70% of total body retinoid stores. Vitamin A deficiency (VAD) is a major micronutrient deficiency around the world. The provitamin A carotenoid, β-carotene, is a significant source of vitamin A in the diet. β-Carotene 15,15' oxygenase-1 (BCO1) and β-carotene 9',10' oxygenase-2 (BCO2) are the two known carotenoid cleavage enzymes in humans. BCO1 and BCO2 are highly expressed in liver and intestine. Hepatocytes and hepatic stellate cells are two main cell types involved in the hepatic metabolism of retinoids. Stellate-like cells in the intestine also show ability to store vitamin A. Liver is also known to accumulate carotenoids, however, their uptake, retention and metabolism in specific liver and intestinal cell types is still unknown. Hence, we studied the cellular and subcellular expression and localization of BCO1 and BCO2 proteins in rat liver and intestine. We demonstrate that both BCO1 and BCO2 proteins are localized in hepatocytes and mucosal epithelium. We also show that BCO1 is also highly expressed in hepatic stellate cells (HSC) and portal endothelial cells in liver. At the subcellular level in liver, BCO1 is found in cytosol, while BCO2 is found in mitochondria. In intestine, immunohistochemistry showed strong BCO1 immunoreactivity in the duodenum, particularly in Brunner's glands. Both BCO1 and BCO2 showed diffuse presence along epithelia with strong immunoreactivity in endothelial cells and in certain epithelial cells which warrant further investigation as possible intestinal retinoid storage cells.

Anti-fibrotic effect of trans-resveratrol on pancreatic stellate cells

Trans-resveratrol, also known as 3,5,4'-trihydroxy-trans-stilbene, is a natural stilbenoid found at high concentration in skins of red grapes and berries. Over the recent years, it has been reported with a variety of beneficial effects such as antioxidant, anti-aging and anti-inflammatory bioactivities; thus often utilized as an active substance in human and veterinary therapeutics. In the current study, we aimed to delineate the mechanism of its anti-fibrotic action by means of various biochemical assays, such as immunofluorescent staining, real-time polymerase chain reaction and Western blotting analyses in a cellular model, the LTC-14 cells, which retain essential characteristics and morphological features of primary pancreatic stellate cells (PSCs). Our results demonstrated that the application of trans-resveratrol as low as 10 μM notably suppressed the mRNA and protein levels of different fibrotic mediators namely alpha-smooth muscle actin, type I collagen and fibronectin in the LTC-14 cells stimulated with transforming growth factor-beta, a well recognized pro-fibrotic inducer. Importantly, the mechanism of the anti-fibrotic action of trans-resveratrol was associated with a decrease in nuclear factor-kappaB activation and protein kinase B phosphorylation. In conclusion, our finding suggests that trans-resveratrol may serve as a therapeutic or an adjuvant agent in anti-fibrotic approaches and/or PSC-relating pathologies.

Molecular control of capillary morphogenesis and maturation by recognition and remodeling of the extracellular matrix: functional roles of endothelial cells and pericytes in health and disease

This review addresses fundamental mechanisms underlying how capillaries form in three-dimensional extracellular matrices and how endothelial cells (ECs) and pericytes co-assemble to form capillary networks. In addition to playing a critical role in supplying oxygen and nutrients to tissues, recent work suggests that blood vessels supply important signals to facilitate tissue development. Here, we hypothesize that another major function of capillaries is to supply signals to suppress major disease mechanisms including inflammation, infection, thrombosis, hemorrhage, edema, ischemic injury, fibrosis, autoimmune disease and tumor growth/progression. Capillary dysfunction plays a key pathogenic role in many human diseases, and thus, this suppressing function may be attenuated and central toward the initiation and progression of disease. We describe how capillaries form through creation of EC-lined tube networks and vascular guidance tunnels in 3D extracellular matrices. Pericytes recruit to the abluminal EC tube surface within these tunnel spaces, and work together to assemble the vascular basement membrane matrix. These processes occur under serum-free conditions in 3D collagen or fibrin matrices and in response to five key growth factors which are stem cell factor, interleukin-3, stromal-derived factor-1α, fibroblast growth factor-2 and insulin. In addition, we identified a key role for EC-derived platelet-derived growth factor-BB and heparin-binding epidermal growth factor in pericyte recruitment and proliferation to promote EC-pericyte tube co-assembly and vascular basement membrane matrix deposition. A molecular understanding of capillary morphogenesis and maturation should lead to novel therapeutic strategies to repair capillary dysfunction in major human disease contexts including cancer and diabetes.

Hepatic stellate cells and liver fibrosis

Hepatic stellate cells are resident perisinusoidal cells distributed throughout the liver, with a remarkable range of functions in normal and injured liver. Derived embryologically from septum transversum mesenchyme, their precursors include submesothelial cells that invade the liver parenchyma from the hepatic capsule. In normal adult liver, their most characteristic feature is the presence of cytoplasmic perinuclear droplets that are laden with retinyl (vitamin A) esters. Normal stellate cells display several patterns of intermediate filaments expression (e.g., desmin, vimentin, and/or glial fibrillary acidic protein) suggesting that there are subpopulations within this parental cell type. In the normal liver, stellate cells participate in retinoid storage, vasoregulation through endothelial cell interactions, extracellular matrix homeostasis, drug detoxification, immunotolerance, and possibly the preservation of hepatocyte mass through secretion of mitogens including hepatocyte growth factor. During liver injury, stellate cells activate into alpha smooth muscle actin-expressing contractile myofibroblasts, which contribute to vascular distortion and increased vascular resistance, thereby promoting portal hypertension. Other features of stellate cell activation include mitogen-mediated proliferation, increased fibrogenesis driven by connective tissue growth factor, and transforming growth factor beta 1, amplified inflammation and immunoregulation, and altered matrix degradation. Evolving areas of interest in stellate cell biology seek to understand mechanisms of their clearance during fibrosis resolution by either apoptosis, senescence, or reversion, and their contribution to hepatic stem cell amplification, regeneration, and hepatocellular cancer.

Halofuginone for fibrosis, regeneration and cancer in the gastrointestinal tract

Organ fibrosis and architectural remodeling can severely disrupt tissue function, often with fatal consequences. Fibrosis is the end result of chronic inflammatory reactions induced by a variety of stimuli, and the key cellular mediator of fibrosis comprises the myofibroblasts which, when activated, serve as the primary collagen-producing cells. Complex links exist between fibrosis, regeneration and carcinogenesis, and the concept that all organs contain common tissue fibrosis pathways that could be potential therapeutic targets is an attractive one. Because of the major impact of fibrosis on human health there is an unmet need for safe and effective therapies that directly target fibrosis. Halofuginone inhibits tissue fibrosis and regeneration, and thereby affects the development of tumors in various tissues along the gastrointestinal tract. The high efficacy of halofuginone in reducing the fibrosis that affects tumor growth and tissue regeneration is probably due to its dual role in inhibiting the signaling pathway of transforming growth factor β, on the one hand, and inhibiting the development of Th17 cells, on the other hand. At present halofuginone is being evaluated in a clinical trial for other fibrotic indication, and any clinical success in that trial would allow the use of halofuginone, also for all other fibrotic indications, including those of the gastrointestinal tract.

Collagen type V promotes the malignant phenotype of pancreatic ductal adenocarcinoma

Excessive matrix production by pancreatic stellate cells promotes local growth and metastasis of pancreatic ductal adenocarcinoma and provides a barrier for drug delivery. Collagen type V is a fibrillar, regulatory collagen up-regulated in the stroma of different malignant tumors. Here we show that collagen type V is expressed by pancreatic stellate cells in the stroma of pancreatic ductal adenocarcinoma and affects the malignant phenotype of various pancreatic cancer cell lines by promoting adhesion, migration and viability, also after treatment with chemotherapeutic drugs. Pharmacological and antibody-mediated inhibition of β1-integrin signaling abolishes collagen type V-induced effects on pancreatic cancer cells. Ablation of collagen type V secretion of pancreatic stellate cells by siRNA reduces invasion and proliferation of pancreatic cancer cells and tube formation of endothelial cells. Moreover, stable knock-down of collagen type V in pancreatic stellate cells reduces metastasis formation and angiogenesis in an orthotopic mouse model of ductal adenocarcinoma. In conclusion, paracrine loops involving cancer and stromal elements and mediated by collagen type V promote the malignant phenotype of pancreatic ductal adenocarcinoma and underline the relevance of epithelial-stromal interactions in the progression of this aggressive neoplasm.

Genome-wide DNA methylation patterns in pancreatic ductal adenocarcinoma reveal epigenetic deregulation of SLIT-ROBO, ITGA2 and MET signaling

The importance of epigenetic modifications such as DNA methylation in tumorigenesis is increasingly being appreciated. To define the genome-wide pattern of DNA methylation in pancreatic ductal adenocarcinomas (PDAC), we captured the methylation profiles of 167 untreated resected PDACs and compared them to a panel of 29 adjacent nontransformed pancreata using high-density arrays. A total of 11,634 CpG sites associated with 3,522 genes were significantly differentially methylated (DM) in PDAC and were capable of segregating PDAC from non-malignant pancreas, regardless of tumor cellularity. As expected, PDAC hypermethylation was most prevalent in the 5' region of genes (including the proximal promoter, 5'UTR and CpG islands). Approximately 33% DM genes showed significant inverse correlation with mRNA expression levels. Pathway analysis revealed an enrichment of aberrantly methylated genes involved in key molecular mechanisms important to PDAC: TGF-β, WNT, integrin signaling, cell adhesion, stellate cell activation and axon guidance. Given the recent discovery that SLIT-ROBO mutations play a clinically important role in PDAC, the role of epigenetic perturbation of axon guidance was pursued in more detail. Bisulfite amplicon deep sequencing and qRT-PCR expression analyses confirmed recurrent perturbation of axon guidance pathway genes SLIT2, SLIT3, ROBO1, ROBO3, ITGA2 and MET and suggests epigenetic suppression of SLIT-ROBO signaling and up-regulation of MET and ITGA2 expression. Hypomethylation of MET and ITGA2 correlated with high gene expression, which was associated with poor survival. These data suggest that aberrant methylation plays an important role in pancreatic carcinogenesis affecting core signaling pathways with potential implications for the disease pathophysiology and therapy.

Pancreatic cancer and its stroma: A conspiracy theory

Pancreatic cancer is characterised by a prominent desmoplastic/stromal reaction that has received little attention until recent times. Given that treatments focusing on pancreatic cancer cells alone have failed to significantly improve patient outcome over many decades, research efforts have now moved to understanding the pathophysiology of the stromal reaction and its role in cancer progression. In this regard, our Group was the first to identify the cells (pancreatic stellate cells, PSCs) that produced the collagenous stroma of pancreatic cancer and to demonstrate that these cells interacted closely with cancer cells to facilitate local tumour growth and distant metastasis. Evidence is accumulating to indicate that stromal PSCs may also mediate angiogenesis, immune evasion and the well known resistance of pancreatic cancer to chemotherapy and radiotherapy. This review will summarise current knowledge regarding the critical role of pancreatic stellate cells and the stroma in pancreatic cancer biology and the therapeutic approaches being developed to target the stroma in a bid to improve the outcome of this devastating disease.

Chronic stress accelerates pancreatic cancer growth and invasion: a critical role for beta-adrenergic signaling in the pancreatic microenvironment

Pancreatic cancer cells intimately interact with a complex microenvironment that influences pancreatic cancer progression. The pancreas is innervated by fibers of the sympathetic nervous system (SNS) and pancreatic cancer cells have receptors for SNS neurotransmitters which suggests that pancreatic cancer may be sensitive to neural signaling. In vitro and non-orthotopic in vivo studies showed that neural signaling modulates tumour cell behavior. However the effect of SNS signaling on tumor progression within the pancreatic microenvironment has not previously been investigated. To address this, we used in vivo optical imaging to non-invasively track growth and dissemination of primary pancreatic cancer using an orthotopic mouse model that replicates the complex interaction between pancreatic tumor cells and their microenvironment. Stress-induced neural activation increased primary tumor growth and tumor cell dissemination to normal adjacent pancreas. These effects were associated with increased expression of invasion genes by tumor cells and pancreatic stromal cells. Pharmacological activation of β-adrenergic signaling induced similar effects to chronic stress, and pharmacological β-blockade reversed the effects of chronic stress on pancreatic cancer progression. These findings indicate that neural β-adrenergic signaling regulates pancreatic cancer progression and suggest β-blockade as a novel strategy to complement existing therapies for pancreatic cancer.

The complex landscape of pancreatic cancer metabolism

Pancreatic ductal adenocarcinomas (PDA) are extremely aggressive cancers and currently available therapies are only minimally effective in treating this disease. Tackling this devastating cancer has been a major challenge to the scientific and medical communities, in part due to its intense therapeutic resistance. One of the aspects of this tumor that contributes to its aggressive behavior is its altered cellular metabolism. Indeed, PDA cells seem to possess the ability to adapt their metabolism to the particular environment to which they are exposed, including utilizing diverse fuel sources depending on their availability. Moreover, PDA tumors are efficient at recycling various metabolic substrates through activation of different salvage pathways such as autophagy and macropinocytosis. Together, these diverse metabolic adaptations allow PDA cells to survive and thrive in harsh environments that may lack nutrients and oxygen. Not surprisingly, given its central role in the pathogenesis of this tumor, oncogenic Kras plays a critical role in much of the metabolic reprogramming seen in PDA. In this review, we discuss the metabolic landscape of PDA tumors, including the molecular underpinnings of the key regulatory nodes, and describe how such pathways can be exploited for future diagnostic and therapeutic approaches.

Inhibitory effects of prostaglandin E2 on collagen synthesis and cell proliferation in human stellate cells from pancreatic head adenocarcinoma

BACKGROUND

Several studies have described an increased cyclooxygenase-2 (COX-2) expression in pancreatic cancer, but the role of COX-2 in tumour development and progression is not clear. The aim of the present study was to examine expression of COX-2 in cancer cells and stromal cells in pancreatic cancer specimens, and to explore the role of PGE2 in pancreatic stellate cell proliferation and collagen synthesis.

METHODS

Immunohistochemistry and immunofluorescence was performed on slides from whole sections of tissue blocks using antibodies against COX-2 and α-smooth muscle actin (αSMA). Pancreatic stellate cells (PSC) were isolated from surgically resected tumour tissue by the outgrowth method. Cells were used between passages 4 and 8. Collagen synthesis was determined by [(3)H]-proline incorporation, or by enzyme immunoassay measurement of collagen C-peptide. DNA synthesis was measured by incorporation of [(3)H]-thymidine in DNA. Cyclic AMP (cAMP) was determined by radioimmunoassay. Collagen 1A1 mRNA was determined by RT-qPCR.

RESULTS

Immunohistochemistry staining showed COX-2 in pancreatic carcinoma cells, but not in stromal cells. All tumours showed positive staining for αSMA in the fibrotic stroma. Cultured PSC expressed COX-2, which could be further induced by interleukin-1β (IL-1β), epidermal growth factor (EGF), thrombin, and PGE2, but not by transforming growth factor-β1 (TGFβ). Indirect coculture with the adenocarcinoma cell line BxPC-3, but not HPAFII or Panc-1, induced COX-2 expression in PSC. Treatment of PSC with PGE2 strongly stimulated cAMP accumulation, mediated by EP2 receptors, and also stimulated phosphorylation of extracellular signal-regulated kinase (ERK). Treatment of PSC with PGE2 or forskolin suppressed both TGFβ-stimulated collagen synthesis and PDGF-stimulated DNA synthesis.

CONCLUSIONS

The present results show that COX-2 is mainly produced in carcinoma cells and suggest that the cancer cells are the main source of PGE2 in pancreatic tumours. PGE2 exerts a suppressive effect on proliferation and fibrogenesis in pancreatic stellate cells. These effects of PGE2 are mediated by the cAMP pathway and suggest a role of EP2 receptors.

Human Pancreatic Cancer-Associated Stellate Cells Remain Activated after in vivo Chemoradiation

Pancreatic ductal adenocarcinoma (PDAC) is characterized by an extensive fibrotic reaction or desmoplasia and complex involvement of the surrounding tumor microenvironment. Pancreatic stellate cells are a key mediator of the pancreatic matrix and they promote progression and invasion of pancreatic cancer by increasing cell proliferation and offering protection against therapeutic interventions. Our study utilizes human tumor-derived pancreatic stellate cells (HTPSCs) isolated from fine needle aspirates of pancreatic cancer tissue from patients with locally advanced, unresectable pancreatic adenocarcinoma before and after treatment with full-dose gemcitabine plus concurrent hypo-fractionated stereotactic radiosurgery. We show that HTPSCs survive in vivo chemotherapy and radiotherapy treatment and display a more activated phenotype post-therapy. These data support the idea that stellate cells play an essential role in supporting and promoting pancreatic cancer and further research is needed to develop novel treatments targeting the pancreatic tumor microenvironment.

Stars and stripes in pancreatic cancer: role of stellate cells and stroma in cancer progression

Pancreatic cancer is a devastating disease with an unacceptably high mortality to incidence ratio. Traditional therapeutic approaches such as surgery in combination with chemo- or radiotherapy have had limited efficacy in improving the outcome of this disease. Up until just under a decade ago, the prominent desmoplastic reaction which is a characteristic of the majority of pancreatic ductal adenocarcinomas (PDAC) had been largely ignored. However, since the identification of the pancreatic stellate cell (PSC) as the key cell responsible for the production of the collagenous stroma in PDAC, increasing attention has been paid to the role of the stromal reaction in pancreatic cancer pathobiology. There is now compelling evidence that PSCs interact not only with cancer cells themselves, but with several other cell types in the stroma (endothelial cells, immune cells, and possibly neuronal cells) to promote cancer progression. This review summarizes current knowledge in the field about the influence of PSCs and the stromal microenvironment on cancer behavior and discusses novel therapeutic approaches which reflect an increasing awareness amongst clinicians and researchers that targeting cancer cells alone is no longer sufficient to improve patient outcome and that combinatorial treatments targeting the stroma as well as the cancer cells will be required to change the clinical course of this disease.

High glucose aggravates the detrimental effects of pancreatic stellate cells on Beta-cell function

Background and Aims. We here assess the effects of PSCs on β-cell function and apoptosis in vivo and in vitro. Materials and Methods. PSCs were transplanted into Wistar and Goto-Kakizaki (GK) rats. Sixteen weeks after transplantation, β-cell function, apoptosis, and islet fibrosis were assessed. In vitro the effects of PSCs conditioned medium (PSCs-CM) and/or high concentration of glucose on INS-1 cell function was assessed by measuring insulin secretion, INS-1 cell survival, apoptosis, and endoplasmic reticulum stress (ER stress) associated CHOP expression. Results. PSCs transplantation exacerbated the impaired β-cell function in GK rats, but had no significant effects in Wistar rats. In vitro, PSCs-CM caused impaired INS-1 cell viability and insulin secretion and increased apoptosis, which were more pronounced in the presence of high glucose. Conclusion. Our study demonstrates that PSCs induce β-cell failure in vitro and in vivo.

Programming of glucose-insulin homoeostasis: long-term consequences of pre-natal versus early post-natal nutrition insults. Evidence from a sheep model

AIM

Exposure to adverse intra-uterine conditions can predispose for metabolic disorders later in life. By using a sheep model, we studied (i) how programming of glucose-insulin homoeostasis during late gestation is manifested later in life depending on the early post-natal dietary exposure and (ii) whether dietary alteration in obese individuals can prevent adverse outcomes of early life programming.

METHODS

During late gestation, twin-pregnant sheep were fed 100% (NORM) or 50% (LOW) of energy and protein requirements. After birth, offspring were exposed to a moderate (CONV) or high-carbohydrate-high-fat (HCHF) diet until around puberty. Offspring remaining thereafter (exclusively females) were fed a moderate diet until young adulthood.

RESULTS

LOW lambs had increased insulin secretory responses during intravenous glucose tolerance tests indicative of reduced insulin sensitivity. HCHF lambs were hypertriglyceridaemic, 75% had mild pancreatic collagen infiltration, and their acute insulin secretory response and insulin clearance during intravenous glucose and insulin tolerance tests, respectively, were reduced. However, NORM-HCHF in contrast to LOW-HCHF lambs had normal glucose tolerance, indicating that later health outcomes are highly influenced by pre-natal nutrition. Dietary alteration normalized glucose-insulin homoeostasis in adult HCHF females, whereas late-gestation undernutrition (LOW) permanently depressed insulin sensitivity.

CONCLUSION

Maintenance of glucose tolerance in sheep exposed to pre-natal undernutrition relied on pancreatic hypersecretion of insulin to compensate for reduced insulin sensitivity. A mismatching high-fat diet in early post-natal life interfered with this pancreatic hypersecretion resulting in reduced glucose tolerance. Early post-natal, but not late pre-natal, impacts on glucose-insulin homoeostasis could be reversed by dietary correction later in life.

Isolation and characterization of islet stellate cells in rat

The central role of PSCs in pancreatic fibrogenesis is well established. However, the mechanism responsible for the islet fibrosis presenting in the late stage of T2DM has not been fully elucidated. This study was designed to determine whether the endocrine pancreatic islets contain cells resembling PSCs. PSCs were isolated from pancreas using standard explants techniques. A similar method was used to acquire ISCs. Adherent ISCs with a stellate, angular morphology migrated from the edge of cultured islets within 48 h of primary culture. ISCs contained fewer lipid droplets than equivalent PSCs, and their rapid disappearance accompanied by the increased expression of α-SMA suggested that ISCs were more rapidly activated than PSCs in vitro. They expressed α-SMA, vimentin, GFAP and were positive for ECM components col-I, col-III and FN, all of which are characteristics of classical PSCs. However, ISCs differed from PSCs by having reduced rates of proliferation and migration in vitro. Our in vitro study shows that isolated islets contain a population of stellate cells which are phenotypically similar but not identical to PSCs. In view of the established role of PSCs in pancreatic fibrosis, we suggest that these may contribute to islet fibrosis in T2DM.

Rhein, a natural anthraquinone derivative, attenuates the activation of pancreatic stellate cells and ameliorates pancreatic fibrosis in mice with experimental chronic pancreatitis

Pancreatic fibrosis, a prominent histopathological feature of chronic pancreatitis (CP) and pancreatic ductal adenocarcinoma, is essentially a dynamic process that leads to irreversible scarring of parenchymal tissues of the pancreas. Though the exact mechanisms of its initiation and development are poorly understood, recent studies suggested that the activation of pancreatic stellate cells (PSCs) plays a critical role in eliciting such active course of fibrogenesis. Anthraquinone compounds possess anti-inflammatory bioactivities whereas its natural derivative rhein has been shown to effectively reduce tissue edema and free-radical production in rat models of inflammatory conditions. Apart from its anti-inflammatory properties, rhein actually exerts strong anti-fibrotic effects in our current in-vivo and in-vitro experiments. In the mouse model of cerulein-induced CP, prolonged administration of rhein at 50 mg/kg/day significantly decreased immunoreactivities of the principal fibrotic activators alpha-smooth muscle actin (α-SMA) and transforming growth factor-beta (TGF-β) on pancreatic sections implicating the activation of PSCs, which is the central tread to fibrogenesis, was attenuated. Consequently, the overwhelmed deposition of extracellular matrix proteins fibronectin 1 (FN1) and type I collagen (COL I-α1) in exocrine parenchyma was found accordingly reduced. In addition, the expression levels of sonic hedgehog (SHH), which plays important roles in molecular modulation of various fibrotic processes, and its immediate effector GLI1 in pancreatic tissues were positively correlated to the degree of cerulein-induced fibrosis. Such up-regulation of SHH signaling was restrained in rhein-treated CP mice. In cultured PSCs, we demonstrated that the expression levels of TGF-β-stimulated fibrogenic markers including α-SMA, FN1 and COL I-α1 as well as SHH were all notably suppressed by the application of rhein at 10 μM. The present study firstly reported that rhein attenuates PSC activation and suppresses SHH/GLI1 signaling in pancreatic fibrosis. With strong anti-fibrotic effects provided, rhein can be a potential remedy for fibrotic and/or PSC-related pathologies in the pancreas.

Pancreatic stellate cells promote hapto-migration of cancer cells through collagen I-mediated signalling pathway

Background:

Pancreatic stellate cells (PSCs) promote metastasis as well as local growth of pancreatic cancer. However, the factors mediating the effect of PSCs on pancreatic cancer cells have not been clearly identified.

Methods:

We used a modified Boyden chamber assay as an in vitro model to investigate the role of PSCs in migration of Panc1 and UlaPaCa cells and to identify the underlying mechanisms.

Results:

PSC supernatant (PSC-SN) dose-dependently induced the trans-migration of Panc1 and UlaPaCa cells, mainly via haptokinesis and haptotaxis, respectively. In contrast to poly-L-lysine or fibronectin, collagen I resembled PSC-SN with respect to its effect on cancer cell behaviours, including polarised morphology, facilitated adhesion, accelerated motility and stimulated trans-migration. Blocking antibodies against integrin α2/β1 subunits significantly attenuated PSC-SN- or collagen I-promoted cell trans-migration and adhesion. Moreover, both PSC-SN and collagen I induced the formation of F-actin and focal adhesions in cells, which was consistent with the constantly enhanced phosphorylation of focal adhesion kinase (FAK, Tyr397). Inhibition of FAK function by an inhibitor or small interference RNAs significantly diminished the effect of PSC-SN or collagen I on haptotaxis/haptokinesis of pancreatic cancer cells.

Conclusion:

Collagen I is the major mediator for PSC-SN-induced haptokinesis of Panc1 and haptotaxis of UlaPaCa by activating FAK signalling via binding to integrin α2β1.

The heparin-binding protein interactome in pancreatic diseases

BACKGROUND

The cellular microenvironment plays an important role in the regulation of homoeostasis and is a source of potential biomarkers and drug targets. In a genome-wide analysis the extracellular proteins that bind to heparin (HBPs) have been shown to form highly modular and interconnected extracellular protein regulatory networks. Using a systems biology approach, we have investigated the role of HBP networks in the normal pancreas and pancreatic digestive diseases.

METHODS

Lists of mRNAs encoding for HBPs associated with the normal pancreas (NP), acute pancreatitis (AP), chronic pancreatitis (CP) and pancreatic ductal adenocarcinoma (PDAC) were obtained using public databases and publications. Networks of the putative protein interactomes derived from mRNA expression data of HBPs were built and analysed using cluster analysis, gene ontology term enrichment and canonical pathways analysis.

RESULTS

The extracellular heparin-binding putative protein interactomes in the pancreas were better connected than their non heparin-binding counterparts, having higher clustering coefficients in the normal pancreas (0.273), acute pancreatitis (0.457), chronic pancreatitis (0.329) and pancreatic ductal adenocarcinoma (0.269). 'Hepatic Fibrosis/Hepatic Stellate Cell Activation' appears to be a significant canonical pathway in pancreatic homoeostasis in health and disease with a large number of important HBPs.

CONCLUSIONS

Our analyses clearly demonstrate that HBPs form disease-specific and highly connected networks that can be explored for potential biomarkers and as collective drug targets via the modification of heparin binding properties.

Proteomics as a systems approach to pancreatitis

Proteomics is an approach to looking at the identity, amount, proteolysis, compartmentalization, and posttranslational modification of a large number of proteins simultaneously in a cell or tissue. Recently, proteomics has begun to be applied to the study of pancreatitis to ascertain mechanisms of disease and search for biomarkers of disease. Most mechanistic work has been carried out in animal models of acute pancreatitis. In 8 studies, 97 proteins have been reported to increase, 55 to decrease, and 23 to undergo proteolysis. Proteins showing increases are most often related to stress, inflammation, or the cytoskeleton, whereas decreases are seen in digestive enzymes and proteins related to metabolism. Many protein changes however, are not consistent between studies and only the most recent studies are rigorous and quantitative. By contrast, biomarker studies have focused on pancreatic juice and plasma of humans with disease and often are directed at distinguishing chronic pancreatitis from cancer. Chronic pancreatitis has also been investigated in tissue sections of histological samples. In this review, the results of studies to date are described as well as coverage of the methods used and special issues that must be considered. Areas are pointed out that are worthy of future study.

A starring role for stellate cells in the pancreatic cancer microenvironment

Pancreatic ductal adenocarcinoma is a devastating disease, and patient outcomes have not improved in decades. Treatments that target tumor cells have largely failed. This could be because research has focused on cancer cells and the influence of the stroma on tumor progression has been largely ignored. The focus of pancreatic cancer research began to change with the identification of pancreatic stellate cells, which produce the pancreatic tumor stroma. There is compelling in vitro and in vivo evidence for the influence of pancreatic stellate cells on pancreatic cancer development; several recent preclinical studies have reported encouraging results with approaches designed to target pancreatic stellate cells and the stroma. We review the background and recent advances in these areas, along with important areas of future research that could improve therapy.

A Speculative Role for Stromal Gastrin Signaling in Development and Dissemination of Pancreatic Ductal Adenocarcinoma

The peptide growth factor gastrin and its receptor, the G-protein coupled cholecystokinin receptor type B (CCK_BR), play an integral role in the growth and progression of pancreatic ductal adenocarcinoma (PDAC). Gastrin immunoreactivity is found in the fetal pancreas but its expression is not detected in normal pancreas after birth, except when it is re-expressed in malignant lesions.

Tumor-stromal interactions in pancreatic cancer

Pancreatic adenocarcinoma has one of the worse prognoses of any cancer with a 5-year survival of only 3%. Pancreatic cancer displays one of the most prominent stromal reactions of all tumors and it is evident that this is a key contributing factor to disease outcome. The tumor microenvironment of pancreatic cancer harbors a wide spectrum of cell types and a complex network of mechanisms which all serve to promote tumor progression. It is clear that the symbiotic relationship between pancreatic cancer cells and stellate cells is the chief factor creating this unique tumor milieu. Pancreatic stellate cells play critical roles in evasion of cancer cell apoptosis, invasion and metastases, angiogenesis, and promotion of an immunosuppressive environment, all key hallmarks of malignancy. Existing treatments for pancreatic cancer focus on targeting the cancer cells rather than the whole tumor, of which cancer cells represent a small proportion. It is now increasingly evident that research targeted towards the interactions between these cell types, ideally at an early stage of tumor development, is imperative in order to propel the way forward to more effective treatments.