Perspectives on tissue interactions in development and disease

Thinking in 3 dimensions: philosophies of the microenvironment in organoids and organs-on-chip

Organoids and organs-on-a-chip are currently the two major families of 3D advanced organotypic in vitro culture systems, aimed at reconstituting miniaturized models of physiological and pathological states of human organs. Both share the tenets of the so-called "three-dimensional thinking", a Systems Physiology approach focused on recapitulating the dynamic interactions between cells and their microenvironment. We first review the arguments underlying the "paradigm shift" toward three-dimensional thinking in the in vitro culture community. Then, through a historically informed account of the technical affordances and the epistemic commitments of these two approaches, we highlight how they embody two distinct experimental cultures. We finally argue that the current systematic effort for their integration requires not only innovative "synergistic" engineering solutions, but also conceptual integration between different perspectives on biological causality.

Canonical Wnt signaling regulates soft palate development by mediating ciliary homeostasis

Craniofacial morphogenesis requires complex interactions involving different tissues, signaling pathways, secreted factors and organelles. The details of these interactions remain elusive. In this study, we have analyzed the molecular mechanisms and homeostatic cellular activities governing soft palate development to improve regenerative strategies for individuals with cleft palate. We have identified canonical Wnt signaling as a key signaling pathway primarily active in cranial neural crest (CNC)-derived mesenchymal cells surrounding soft palatal myogenic cells. Using Osr2-Cre;β-cateninfl/fl mice, we show that Wnt signaling is indispensable for mesenchymal cell proliferation and subsequently for myogenesis through mediating ciliogenesis. Specifically, we have identified that Wnt signaling directly regulates expression of the ciliary gene Ttll3. Impaired ciliary disassembly leads to differentiation defects in mesenchymal cells and indirectly disrupts myogenesis through decreased expression of Dlk1, a mesenchymal cell-derived pro-myogenesis factor. Moreover, we show that siRNA-mediated reduction of Ttll3 expression partly rescues mesenchymal cell proliferation and myogenesis in the palatal explant cultures from Osr2-Cre;β-cateninfl/fl embryos. This study highlights the role of Wnt signaling in palatogenesis through the control of ciliary homeostasis, which establishes a new mechanism for Wnt-regulated craniofacial morphogenesis.

Architects of Pituitary Tumour Growth

The pituitary is a master gland responsible for the modulation of critical endocrine functions. Pituitary neuroendocrine tumours (PitNETs) display a considerable prevalence of 1/1106, frequently observed as benign solid tumours. PitNETs still represent a cause of important morbidity, due to hormonal systemic deregulation, with surgical, radiological or chronic treatment required for illness management. The apparent scarceness, uncommon behaviour and molecular features of PitNETs have resulted in a relatively slow progress in depicting their pathogenesis. An appropriate interpretation of different phenotypes or cellular outcomes during tumour growth is desirable, since histopathological characterization still remains the main option for prognosis elucidation. Improved knowledge obtained in recent decades about pituitary tumorigenesis has revealed that this process involves several cellular routes in addition to proliferation and death, with its modulation depending on many signalling pathways rather than being the result of abnormalities of a unique proliferation pathway, as sometimes presented. PitNETs can display intrinsic heterogeneity and cell subpopulations with diverse biological, genetic and epigenetic particularities, including tumorigenic potential. Hence, to obtain a better understanding of PitNET growth new approaches are required and the systematization of the available data, with the role of cell death programs, autophagy, stem cells, cellular senescence, mitochondrial function, metabolic reprogramming still being emerging fields in pituitary research. We envisage that through the combination of molecular, genetic and epigenetic data, together with the improved morphological, biochemical, physiological and metabolically knowledge on pituitary neoplastic potential accumulated in recent decades, tumour classification schemes will become more accurate regarding tumour origin, behaviour and plausible clinical results.

Building consensus on definition and nomenclature of hepatic, pancreatic, and biliary organoids

Hepatic, pancreatic, and biliary (HPB) organoids are powerful tools for studying development, disease, and regeneration. As organoid research expands, the need for clear definitions and nomenclature describing these systems also grows. To facilitate scientific communication and consistent interpretation, we revisit the concept of an organoid and introduce an intuitive classification system and nomenclature for describing these 3D structures through the consensus of experts in the field. To promote the standardization and validation of HPB organoids, we propose guidelines for establishing, characterizing, and benchmarking future systems. Finally, we address some of the major challenges to the clinical application of organoids.

Pancreatic Adenocarcinoma Invasiveness and the Tumor Microenvironment: From Biology to Clinical Trials

Pancreatic adenocarcinoma (PDAC) originates in the glandular compartment of the exocrine pancreas. Histologically, PDAC tumors are characterized by a parenchyma that is embedded in a particularly prominent stromal component or desmoplastic stroma. The unique characteristics of the desmoplastic stroma shape the microenvironment of PDAC and modulate the reciprocal interactions between cancer and stromal cells in ways that have profound effects in the pathophysiology and treatment of this disease. Here, we review some of the most recent findings regarding the regulation of PDAC cell invasion by the unique microenvironment of this tumor, and how new knowledge is being translated into novel therapeutic approaches.

Can Environmental Manipulation Help Suppress Cancer? Non-Linear Competition Among Tumor Cells in Periodically Changing Conditions

It has been shown that the tumor population growth dynamics in a periodically varying environment can drastically differ from the one in a fixed environment. Thus, the environment of a tumor can potentially be manipulated to suppress cancer progression. Diverse evolutionary processes play vital roles in cancer progression and accordingly, understanding the interplay between these processes is essential in optimizing the treatment strategy. Somatic evolution and genetic instability result in intra-tumor cell heterogeneity. Various models have been developed to analyze the interactions between different types of tumor cells. Here, models of density-dependent interaction between different types of tumor cells under fast periodical environmental changes are examined. It is illustrated that tumor population densities, which vary on a slow time scale, are affected by fast environmental variations. Finally, the intriguing density-dependent interactions in metastatic castration-resistant prostate cancer (mCRPC) in which the different types of tumor cells are defined with respect to the production of and dependence on testosterone are discussed.

Self-Organized Liver Microtissue on a Bio-Functional Surface: The Role of Human Adipose-Derived Stromal Cells in Hepatic Function

The maintenance of hepatocyte function is a critical research topic in liver tissue engineering. Although an increasing number of strategies have been developed, liver tissue engineering using hepatocytes as a therapeutic alternative remains challenging owing to its poor efficacy. In this study, we developed a multicellular hepatic microtissue to enhance the function of induced hepatic precursor cells. Mouse induced hepatic precursor cells (miHeps) were self-organized in 3D with human adipose-derived stem cells (hASCs) on a bio-functional matrix. We found that hepatic phenotypes, such as levels of albumin, asialoglycoprotein receptor-1, and cytochrome P450, were enhanced in miHeps-hASC microtissue comprising miHeps and hASCs relative to two-dimensional-cultured miHeps-hASCs. Additionally, the secretome of 3D-cultured hASCs increased the hepatic function of mature miHeps. Furthermore, hepatic gene expression was reduced in mature miHeps treated with conditioned media of hypoxia-inducible factor 1α (HIF1α)-depleted hASCs relative to that with conditioned media of control hASCs. Our results suggested that the hepatic function of 3D-co-cultured miHeps could be enhanced by HIF1α-dependent factors secreted from stromal cells. This study provides an insight into the factors regulating hepatic function and shows that self-organized hepatic microtissue could act as liver spheroids for liver regenerative medicine and liver toxicity tests.

Stromal reactivity differentially drives tumour cell evolution and prostate cancer progression

Prostate cancer (PCa) progression is a complex eco-evolutionary process driven by the feedback between evolving tumour cell phenotypes and microenvironmentally driven selection. To better understand this relationship, we used a multiscale mathematical model that integrates data from biology and pathology on the microenvironmental regulation of PCa cell behaviour. Our data indicate that the interactions between tumour cells and their environment shape the evolutionary dynamics of PCa cells and explain overall tumour aggressiveness. A key environmental determinant of this aggressiveness is the stromal ecology, which can be either inhibitory, highly reactive (supportive) or non-reactive (neutral). Our results show that stromal ecology correlates directly with tumour growth but inversely modulates tumour evolution. This suggests that aggressive, environmentally independent PCa may be a result of poor stromal ecology, supporting the concept that purely tumour epithelium-centric metrics of aggressiveness may be incomplete and that incorporating markers of stromal ecology would improve prognosis.

Long circulating liposomes: challenges and opportunities

The poor pharmacokinetic parameters and low solubility of many anticancer therapeutics have warranted the use of drug-delivery systems such as liposomes. Overcoming some drawbacks of the conventional liposomes, targeted liposomal delivery by longer circulation time by addition of poly(ethylene glycol) to the liposomal surface and further adding specific ligands to achieve ligand selective retention and uptake has been introduced. PEGylated liposomes are the only second-generation liposomal formulations in clinical use and are now being challenged with the allergenic response they pose even in the treatment of naive patients. This article will review the challenges and hindrances in the use of long circulating liposomes and explore the opportunities to overcome this issue.

Homeostasis Back and Forth: An Ecoevolutionary Perspective of Cancer

The role of genetic mutations in cancer is indisputable: They are a key source of tumor heterogeneity and drive its evolution to malignancy. But, the success of these new mutant cells relies on their ability to disrupt the homeostasis that characterizes healthy tissues. Mutated clones unable to break free from intrinsic and extrinsic homeostatic controls will fail to establish a tumor. Here, we will discuss, through the lens of mathematical and computational modeling, why an evolutionary view of cancer needs to be complemented by an ecological perspective to understand why cancer cells invade and subsequently transform their environment during progression. Importantly, this ecological perspective needs to account for tissue homeostasis in the organs that tumors invade, because they perturb the normal regulatory dynamics of these tissues, often coopting them for its own gain. Furthermore, given our current lack of success in treating advanced metastatic cancers through tumor-centric therapeutic strategies, we propose that treatments that aim to restore homeostasis could become a promising venue of clinical research. This ecoevolutionary view of cancer requires mechanistic mathematical models to both integrate clinical with biological data from different scales but also to detangle the dynamic feedback between the tumor and its environment. Importantly, for these models to be useful, they need to embrace a higher degree of complexity than many mathematical modelers are traditionally comfortable with.

Heterocellular cadherin connections: coordinating adhesive cues in homeostasis and cancer

This short insight covers some of the recent topics relevant to the field of cadherin-catenin adhesion in mediating connections between different cell types, so-called heterotypic or heterocellular connections, in both homeostasis and cancer. These scientific discoveries are increasing our understanding of how multiple cells residing in complex tissues can be instructed by cadherin adhesion receptors to regulate tissue architecture and function and how these cadherin-mediated heterocellular connections spur tumor growth and the acquisition of malignant characteristics in tumor cells. Overall, the findings that have emerged over the past few years are elucidating the complexity of the functional roles of the cadherin-catenin complexes. Future exciting research lies ahead in order to understand the physical basis of these heterotypic interactions and their influence on the behavior of heterogeneous cellular populations as well as their roles in mediating phenotypic and genetic changes as cells evolve through complex environments during morphogenesis and cancer.

Isolation and analysis of discreet human prostate cellular populations

The use of lineage tracing in transgenic mouse models has revealed an abundance of subcellular phenotypes responsible for maintaining prostate homeostasis. The ability to use fresh human tissues to examine the hypotheses generated by these mouse experiments has been greatly enhanced by technical advances in tissue processing, flow cytometry and cell culture. We describe in detail the optimization of protocols for each of these areas to facilitate research on solving human prostate diseases through the analysis of human tissue.

The many ways to make a luminal cell and a prostate cancer cell

Research in the area of stem/progenitor cells has led to the identification of multiple stem-like cell populations implicated in prostate homeostasis and cancer initiation. Given that there are multiple cells that can regenerate prostatic tissue and give rise to prostate cancer, our focus should shift to defining the signaling mechanisms that drive differentiation and progenitor self-renewal. In this article, we will review the literature, present the evidence and raise important unanswered questions that will help guide the field forward in dissecting critical mechanisms regulating stem-cell differentiation and tumor initiation.

Evolutionary game theory: cells as players

In two papers we review game theory applications in biology below the level of cognitive living beings. It can be seen that evolution and natural selection replace the rationality of the actors appropriately. Even in these micro worlds, competing situations and cooperative relationships can be found and modeled by evolutionary game theory. Also those units of the lowest levels of life show different strategies for different environmental situations or different partners. We give a wide overview of evolutionary game theory applications to microscopic units. In this first review situations on the cellular level are tackled. In particular metabolic problems are discussed, such as ATP-producing pathways, secretion of public goods and cross-feeding. Further topics are cyclic competition among more than two partners, intra- and inter-cellular signalling, the struggle between pathogens and the immune system, and the interactions of cancer cells. Moreover, we introduce the theoretical basics to encourage scientists to investigate problems in cell biology and molecular biology by evolutionary game theory.

Establishment of a syngeneic orthotopic model of prostate cancer in immunocompetent rats

We previously established 3 cell lines (PLS10, PLS20 and PLS30) from a chemically-induced prostate carcinoma in F344 rats, and demonstrated high potential for metastasis in nude mice. In the present study, we investigated the feasibility of establishing an orthotopic model using the 3 rat prostate cancer cell lines in immunocompetent rats with the aim of resolving species-mismatch problems and defects of immune systems. The PLS10, PLS20 and PLS30 cell lines were injected into the ventral prostates of 6-week-old rats, which were then sacrificed at experimental weeks 4 and 8. Tumor mass formation was found in rats with PLS10, but not in those with PLS20 or PLS30. Additionally, metastatic carcinomas could be detected in lymph nodes and lungs of PLS10-inoculated rats. Genetic analysis demonstrated K-ras gene mutations in PLS10 and PLS20, but not in PLS30 cells. There were no mutations in p53 and KLF6. In conclusion, we established a syngeneic orthotopic model for prostate cancer in immunocompetent rats simulating human castration-resistant prostate cancer (CRPC), which should prove useful for development and validation of therapeutic agents, especially with immunotherapy.

The pivotal role of integrin β1 in metastasis of head and neck squamous cell carcinoma

PURPOSE

This study aimed to understand the prognostic value of integrin β1 expression in head and neck squamous cell carcinoma (HNSCC) and the mechanism underlying its association with metastatic HNSCC.

EXPERIMENTAL DESIGN

Archival HNSCC tissues including 99 nonmetastatic primary tumors and 101 metastatic primary tumors were examined for the association of integrin β1 expression with metastasis and disease prognosis by appropriate statistical methods. Fluorescence-activated cell sorting was used to separate the integrin β1(high/+) cell population from the integrin β1(low/-) population in HNSCC cell lines. These two populations and integrin β1 shRNA knockdown HNSCC cells were examined for the effect of integrin β1 on invasion in vitro and on lymph node and lung metastases in a xenograft mouse model. Expression and activation of matrix metalloproteinases (MMP) were examined by zymography.

RESULTS

Statistical analysis showed that integrin β1 expression was significantly higher in the metastatic primary tumors than in the nonmetastatic tumors (42.6% vs. 24.8%, P < 0.0001 and P < 0.0001 by univariate and multivariate analyses, respectively). In patients with lymph node metastasis, integrin β1 expression was inversely correlated with overall survival (P = 0.035). The integrin β1 knockdown or integrin β1(low/-) HNSCC cells showed a significant reduction in lymph node and lung metastases in vivo (P < 0.001 and P < 0.05, respectively). Significantly reduced Matrigel invasion capability was also found in integrin β1 knockdown or integrin β1(low/-) HNSCC cells (P < 0.01). Finally, zymography results showed integrin β1-affected HNSCC invasion by regulating MMP-2 activation.

CONCLUSION

These findings indicate that integrin β1 has a major impact on HNSCC prognosis through its regulation of metastasis.

PPARγ isoforms differentially regulate metabolic networks to mediate mouse prostatic epithelial differentiation

Recent observations indicate prostatic diseases are comorbidities of systemic metabolic dysfunction. These discoveries revealed fundamental questions regarding the nature of prostate metabolism. We previously showed that prostate-specific ablation of PPARγ in mice resulted in tumorigenesis and active autophagy. Here, we demonstrate control of overlapping and distinct aspects of prostate epithelial metabolism by ectopic expression of individual PPARγ isoforms in PPARγ knockout prostate epithelial cells. Expression and activation of either PPARγ 1 or 2 reduced de novo lipogenesis and oxidative stress and mediated a switch from glucose to fatty acid oxidation through regulation of genes including Pdk4, Fabp4, Lpl, Acot1 and Cd36. Differential effects of PPARγ isoforms included decreased basal cell differentiation, Scd1 expression and triglyceride fatty acid desaturation and increased tumorigenicity by PPARγ1. In contrast, PPARγ2 expression significantly increased basal cell differentiation, Scd1 expression and AR expression and responsiveness. Finally, in confirmation of in vitro data, a PPARγ agonist versus high-fat diet (HFD) regimen in vivo confirmed that PPARγ agonization increased prostatic differentiation markers, whereas HFD downregulated PPARγ-regulated genes and decreased prostate differentiation. These data provide a rationale for pursuing a fundamental metabolic understanding of changes to glucose and fatty acid metabolism in benign and malignant prostatic diseases associated with systemic metabolic stress.

Exploiting evolution to treat drug resistance: combination therapy and the double bind

Although many anticancer therapies are successful in killing a large percentage of tumor cells when initially administered, the evolutionary dynamics underpinning tumor progression mean that, often, resistance is an inevitable outcome. Research in the field of ecology suggests that an evolutionary double bind could be an effective way to treat tumors. In an evolutionary double bind two therapies are used in combination such that evolving resistance to one leaves individuals more susceptible to the other. In this paper we present a general evolutionary game theory framework of a double bind to study the effect that such an approach would have in cancer. Furthermore we use this mathematical framework to understand recent experimental results that suggest a synergistic effect between a p53 cancer vaccine and chemotherapy. Our model recapitulates the latest experimental data and provides an explanation for its effectiveness based on the commensalistic relationship between the tumor phenotypes.

Investigating prostate cancer tumour-stroma interactions: clinical and biological insights from an evolutionary game

BACKGROUND

Tumours are made up of a mixed population of different types of cells that include normal structures as well as ones associated with the malignancy, and there are multiple interactions between the malignant cells and the local microenvironment. These intercellular interactions, modulated by the microenvironment, effect tumour progression and represent a largely under-appreciated therapeutic target. We use observations of primary tumour biology from prostate cancer to extrapolate a mathematical model. Specifically, it has been observed that in prostate cancer three disparate cellular outcomes predominate: (i) the tumour remains well differentiated and clinically indolent--in this case the local stromal cells may act to restrain the growth of the cancer; (ii) early in its genesis the tumour acquires a highly malignant phenotype, growing rapidly and displacing the original stromal population (often referred to as small cell prostate cancer)--these less common aggressive tumours are relatively independent of the local microenvironment and (iii) the tumour co-opts the local stroma--taking on a classic stromagenic phenotype where interactions with the local microenvironment are critical to the cancer growth.

METHODS

We present an evolutionary game theoretical construct that models the influence of tumour-stroma interactions in driving these outcomes. We consider three characteristic and distinct cellular populations: stromal cells, tumour cells that are self-reliant in terms of microenvironmental factors and tumour cells that depend on the environment for resources, but can also co-opt stroma.

RESULTS

Using evolutionary game theory we explore a number of different scenarios that elucidate the impact of tumour-stromal interactions on the dynamics of prostate cancer growth and progression, and how different treatments in the metastatic setting can affect different types of tumours.

CONCLUSION

The tumour microenvironment has a crucial role in selecting the traits of the tumour cells that will determine prostate cancer progression. Equally important treatments like hormone therapy affect the selection of these cancer phenotypes making it very important to understand how they impact prostate cancer's somatic evolution.

Hybrid models of tumor growth

Cancer is a complex, multiscale process in which genetic mutations occurring at a subcellular level manifest themselves as functional changes at the cellular and tissue scale. The multiscale nature of cancer requires mathematical modeling approaches that can handle multiple intracellular and extracellular factors acting on different time and space scales. Hybrid models provide a way to integrate both discrete and continuous variables that are used to represent individual cells and concentration or density fields, respectively. Each discrete cell can also be equipped with submodels that drive cell behavior in response to microenvironmental cues. Moreover, the individual cells can interact with one another to form and act as an integrated tissue. Hybrid models form part of a larger class of individual-based models that can naturally connect with tumor cell biology and allow for the integration of multiple interacting variables both intrinsically and extrinsically and are therefore perfectly suited to a systems biology approach to tumor growth.

Altered TGF-β signaling in a subpopulation of human stromal cells promotes prostatic carcinogenesis

Carcinoma-associated fibroblasts (CAF) play a critical role in malignant progression. Loss of TGF-β receptor II (TGFβR2) in the prostate stroma is correlated with prostatic tumorigenesis. To determine the mechanisms by which stromal heterogeneity because of loss of TGFβR2 might contribute to cancer progression, we attenuated transforming growth factor beta (TGF-β) signaling in a subpopulation of immortalized human prostate fibroblasts in a model of tumor progression. In a tissue recombination model, loss of TGFβR2 function in 50% of the stromal cell population resulted in malignant transformation of the nontumorigenic human prostate epithelial cell line BPH1. Mixing fibroblasts expressing the empty vector and dominant negative TGFβR2 increased the expression of markers of myofibroblast differentiation [coexpression of vimentin and alpha smooth muscle actin (αSMA)] through elevation of TGF-β1 and activation of the Akt pathway. In combination, these two populations of stromal cells recapitulated the tumor inductive activity of CAFs. TGFβR2 activity in mixed stromal cell populations cultured in vitro caused secretion of factors that are known to promote tumor progression, including TGF-β1, SDF1/CXCL12, and members of the fibroblast growth factor (FGF) and bone morphogenetic protein (BMP) families. In vivo, tissue recombination of fibroblasts overexpressing TGF-β1 and SDF1/CXCL12 not only induced transformation of BPH1 cells, but also promoted a robust growth of highly invasive cells, similar to effects produced by CAFs. While the precise nature and/or origin of the particular stromal cell populations in vivo remain unknown, these findings strongly link heterogeneity in TGF-β signaling to tumor promotion by tumor stromal cells.

Modeling stromal-epithelial interactions in disease progression

The role of tumor stroma in progression to malignancy has become the subject of intense experimental and clinical interest. The stromal compartment of organs is composed of all the non-epithelial cell types and maintains the proper architecture and nutrient levels required for epithelial and, ultimately, organ function. The composition of the reactive stroma surrounding tumors is vastly different from normal stromal tissue. Stromal phenotype can be correlated with, and predictive of, disease recurrence. In addition, the stroma is now seen as a legitimate target for therapeutic intervention. Although much has been learned about the role of the stromal compartment in development and disease in recent years, a number of key questions remain. Here we review how some of these questions are beginning to be addressed using new models of stromal-epithelial interaction.