Mechanical stress through growth on stiffer substrates impacts animal health and longevity in C. elegans

Mechanical stress is a measure of internal resistance exhibited by a body or material when external forces, such as compression, tension, bending, etc. are applied. The study of mechanical stress on health and aging is a continuously growing field, as major changes to the extracellular matrix and cell-to-cell adhesions can result in dramatic changes to tissue stiffness during aging and diseased conditions. For example, during normal aging, many tissues including the ovaries, skin, blood vessels, and heart exhibit increased stiffness, which can result in a significant reduction in function of that organ. As such, numerous model systems have recently emerged to study the impact of mechanical and physical stress on cell and tissue health, including cell-culture conditions with matrigels and other surfaces that alter substrate stiffness and ex vivo tissue models that can apply stress directly to organs like muscle or tendons. Here, we sought to develop a novel method in an in vivo, model organism setting to study the impact of mechanical stress on aging, by increasing substrate stiffness in solid agar medium of C. elegans . To our surprise, we found shockingly limited impact of growth of C. elegans on stiffer substrates, including limited effects on cellular health, gene expression, organismal health, stress resilience, and longevity. Overall, our studies reveal that altering substrate stiffness of growth medium for C. elegans have only mild impact on animal health and longevity; however, these impacts were not nominal and open up important considerations for C. elegans biologists in standardizing agar medium choice for experimental assays.

The microenvironment dictates glycocalyx construction and immune surveillance

Efforts to identify anti-cancer therapeutics and understand tumor-immune interactions are built with in vitro models that do not match the microenvironmental characteristics of human tissues. Using in vitro models which mimic the physical properties of healthy or cancerous tissues and a physiologically relevant culture medium, we demonstrate that the chemical and physical properties of the microenvironment regulate the composition and topology of the glycocalyx. Remarkably, we find that cancer and age-related changes in the physical properties of the microenvironment are sufficient to adjust immune surveillance via the topology of the glycocalyx, a previously unknown phenomenon observable only with a physiologically relevant culture medium.

Uptake of tumor-derived microparticles induces metabolic reprogramming of macrophages in the early metastatic lung

Pre-metastatic niche formation is a critical step during the metastatic spread of cancer. One way by which primary tumors prime host cells at future metastatic sites is through the shedding of tumor-derived microparticles as a consequence of vascular sheer flow. However, it remains unclear how the uptake of such particles by resident immune cells affects their phenotype and function. Here, we show that ingestion of tumor-derived microparticles by macrophages induces a rapid metabolic and phenotypic switch that is characterized by enhanced mitochondrial mass and function, increased oxidative phosphorylation, and upregulation of adhesion molecules, resulting in reduced motility in the early metastatic lung. This reprogramming event is dependent on signaling through the mTORC1, but not the mTORC2, pathway and is induced by uptake of tumor-derived microparticles. Together, these data support a mechanism by which uptake of tumor-derived microparticles induces reprogramming of macrophages to shape their fate and function in the early metastatic lung.

Allosteric HSP70 inhibitors perturb mitochondrial proteostasis and overcome proteasome inhibitor resistance in multiple myeloma

Proteasome inhibitor (PI) resistance remains a central challenge in multiple myeloma. To identify pathways mediating resistance, we first mapped proteasome-associated genetic co-dependencies. We identified heat shock protein 70 (HSP70) chaperones as potential targets, consistent with proposed mechanisms of myeloma cells overcoming PI-induced stress. We therefore explored allosteric HSP70 inhibitors (JG compounds) as myeloma therapeutics. JG compounds exhibited increased efficacy against acquired and intrinsic PI-resistant myeloma models, unlike HSP90 inhibition. Shotgun and pulsed SILAC mass spectrometry demonstrated that JGs unexpectedly impact myeloma proteostasis by destabilizing the 55S mitoribosome. Our data suggest JGs have the most pronounced anti-myeloma effect not through inhibiting cytosolic HSP70 proteins but instead through mitochondrial-localized HSP70, HSPA9/mortalin. Analysis of myeloma patient data further supports strong effects of global proteostasis capacity, and particularly HSPA9 expression, on PI response. Our results characterize myeloma proteostasis networks under therapeutic pressure while motivating further investigation of HSPA9 as a specific vulnerability in PI-resistant disease.

Cross-species screening platforms identify EPS-8 as a critical link for mitochondrial stress and actin stabilization

The dysfunction of mitochondria is associated with the physiological consequences of aging and many age-related diseases. Therefore, critical quality control mechanisms exist to protect mitochondrial functions, including the unfolded protein response of the mitochondria (UPRMT). However, it is still unclear how UPRMT is regulated in mammals with mechanistic discrepancies between previous studies. Here, we reasoned that a study of conserved mechanisms could provide a uniquely powerful way to reveal previously uncharacterized components of the mammalian UPRMT. We performed cross-species comparison of genetic requirements for survival under—and in response to—mitochondrial stress between karyotypically normal human stem cells and the nematode Caenorhabditis elegans. We identified a role for EPS-8/EPS8 (epidermal growth factor receptor pathway substrate 8), a signaling protein adaptor, in general mitochondrial homeostasis and UPRMT regulation through integrin-mediated remodeling of the actin cytoskeleton. This study also highlights the use of cross-species comparisons in genetic screens to interrogate cellular pathways.

Adhesion-mediated mechanosignaling forces mitohormesis

Mitochondria control eukaryotic cell fate by producing the energy needed to support life and the signals required to execute programed cell death. The biochemical milieu is known to affect mitochondrial function and contribute to the dysfunctional mitochondrial phenotypes implicated in cancer and the morbidities of aging. However, the physical characteristics of the extracellular matrix are also altered in cancerous and aging tissues. Here, we demonstrate that cells sense the physical properties of the extracellular matrix and activate a mitochondrial stress response that adaptively tunes mitochondrial function via solute carrier family 9 member A1-dependent ion exchange and heat shock factor 1-dependent transcription. Overall, our data indicate that adhesion-mediated mechanosignaling may play an unappreciated role in the altered mitochondrial functions observed in aging and cancer.

Mitohormesis reprogrammes macrophage metabolism to enforce tolerance

Macrophages generate mitochondrial reactive oxygen species and mitochondrial reactive electrophilic species as antimicrobials during Toll-like receptor (TLR)-dependent inflammatory responses. Whether mitochondrial stress caused by these molecules impacts macrophage function is unknown. Here, we demonstrate that both pharmacologically driven and lipopolysaccharide (LPS)-driven mitochondrial stress in macrophages triggers a stress response called mitohormesis. LPS-driven mitohormetic stress adaptations occur as macrophages transition from an LPS-responsive to LPS-tolerant state wherein stimulus-induced pro-inflammatory gene transcription is impaired, suggesting tolerance is a product of mitohormesis. Indeed, like LPS, hydroxyoestrogen-triggered mitohormesis suppresses mitochondrial oxidative metabolism and acetyl-CoA production needed for histone acetylation and pro-inflammatory gene transcription, and is sufficient to enforce an LPS-tolerant state. Thus, mitochondrial reactive oxygen species and mitochondrial reactive electrophilic species are TLR-dependent signalling molecules that trigger mitohormesis as a negative feedback mechanism to restrain inflammation via tolerance. Moreover, bypassing TLR signalling and pharmacologically triggering mitohormesis represents a new anti-inflammatory strategy that co-opts this stress response to impair epigenetic support of pro-inflammatory gene transcription by mitochondria.

Transcriptomic analysis reveals that BMP4 sensitizes glioblastoma tumor-initiating cells to mechanical cues

The poor prognosis of glioblastoma (GBM) is associated with a highly invasive stem-like subpopulation of tumor-initiating cells (TICs), which drive recurrence and contribute to intra-tumoral heterogeneity through differentiation. These TICs are better able to escape extracellular matrix-imposed mechanical restrictions on invasion than their more differentiated progeny, and sensitization of TICs to extracellular matrix mechanics extends survival in preclinical models of GBM. However, little is known about the molecular basis of the relationship between TIC differentiation and mechanotransduction. Here we explore this relationship through a combination of transcriptomic analysis and studies with defined-stiffness matrices. We show that TIC differentiation induced by bone morphogenetic protein 4 (BMP4) suppresses expression of proteins relevant to extracellular matrix signaling and sensitizes TIC spreading to matrix stiffness. Moreover, our findings point towards a previously unappreciated connection between BMP4-induced differentiation, mechanotransduction, and metabolism. Notably, stiffness and differentiation modulate oxygen consumption, and inhibition of oxidative phosphorylation influences cell spreading in a stiffness- and differentiation-dependent manner. Our work integrates bioinformatic analysis with targeted molecular measurements and perturbations to yield new insight into how morphogen-induced differentiation influences how GBM TICs process mechanical inputs.

Modeling Tissue Polarity in Context

Polarity is critical for development and tissue-specific function. However, the acquisition and maintenance of tissue polarity is context dependent. Thus, cell and tissue polarity depend on cell adhesion which is regulated by the cytoskeleton and influenced by the biochemical composition of the extracellular microenvironment and modified by biomechanical cues within the tissue. These biomechanical cues include fluid flow induced shear stresses, cell-density and confinement-mediated compression, and cellular actomyosin tension intrinsic to the tissue or induced in response to morphogens or extracellular matrix stiffness. Here, we discuss how extracellular matrix stiffness and fluid flow influence cell-cell and cell-extracellular matrix adhesion and alter cytoskeletal organization to modulate cell and tissue polarity. We describe model systems that when combined with state of the art molecular screens and high-resolution imaging can be used to investigate how force modulates cell and tissue polarity.

Actomyosin-Mediated Tension Orchestrates Uncoupled Respiration in Adipose Tissues

The activation of brown/beige adipose tissue (BAT) metabolism and the induction of uncoupling protein 1 (UCP1) expression are essential for BAT-based strategies to improve metabolic homeostasis. Here, we demonstrate that BAT utilizes actomyosin machinery to generate tensional responses following adrenergic stimulation, similar to muscle tissues. The activation of actomyosin mechanics is critical for the acute induction of oxidative metabolism and uncoupled respiration in UCP1+ adipocytes. Moreover, we show that actomyosin-mediated elasticity regulates the thermogenic capacity of adipocytes via the mechanosensitive transcriptional co-activators YAP and TAZ, which are indispensable for normal BAT function. These biomechanical signaling mechanisms may inform future strategies to promote the expansion and activation of brown/beige adipocytes.

Amplification of Adipogenic Commitment by VSTM2A

Despite progress in our comprehension of the mechanisms regulating adipose tissue development, the nature of the factors that functionally characterize adipose precursors is still elusive. Defining the early steps regulating adipocyte development is needed for the generation of tools to control adipose tissue size and function. Here, we report the discovery of V-set and transmembrane domain containing 2A (VSTM2A) as a protein expressed and secreted by committed preadipocytes. VSTM2A expression is elevated in the early phases of adipogenesis in vitro and adipose tissue development in vivo. We show that VSTM2A-producing cells associate with the vasculature and express the common surface markers of adipocyte progenitors. Overexpression of VSTM2A induces adipogenesis, whereas its depletion impairs this process. VSTM2A controls preadipocyte determination at least in part by modulating BMP signaling and PPARγ2 activation. We propose a model in which VSTM2A is produced to preserve and amplify the adipogenic capability of adipose precursors.

LSD1 Interacts with Zfp516 to Promote UCP1 Transcription and Brown Fat Program

Zfp516, a brown fat (BAT)-enriched and cold-inducible transcription factor, promotes transcription of UCP1 and other BAT-enriched genes for non-shivering thermogenesis. Here, we identify lysine-specific demethylase 1 (LSD1) as a direct binding partner of Zfp516. We show that, through interaction with Zfp516, LSD1 is recruited to UCP1 and other BAT-enriched genes, such as PGC1α, to function as a coactivator by demethylating H3K9. We also show that LSD1 is induced during brown adipogenesis and that LSD1 and its demethylase activity is required for the BAT program. Furthermore, we show that LSD1 ablation in mice using Myf5-Cre alters embryonic BAT development. Moreover, BAT-specific deletion of LSD1 via the use of UCP1-Cre impairs the BAT program and BAT development, making BAT resemble WAT, reducing thermogenic activity and promoting obesity. Finally, we demonstrate an in vivo requirement of the Zfp516-LSD1 interaction for LSD1 function in BAT gene activation.

Differential requirement for de novo lipogenesis in cholangiocarcinoma and hepatocellular carcinoma of mice and humans

Hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC) are the most prevalent types of primary liver cancer. These malignancies have limited treatment options, resulting in poor patient outcomes. Metabolism reprogramming, including increased de novo lipogenesis, is one of the hallmarks of cancer. Fatty acid synthase (FASN) catalyzes the de novo synthesis of long-chain fatty acids from acetyl-coenzyme A and malonyl-coenzyme A. Increased FASN expression has been reported in multiple tumor types, and inhibition of FASN expression has been shown to have tumor-suppressing activity. Intriguingly, we found that while FASN is up-regulated in human HCC samples, its expression is frequently low in human ICC specimens. Similar results were observed in mouse ICC models induced by different oncogenes. Ablating FASN in the mouse liver did not affect activated AKT and Notch (AKT/Notch intracellular domain 1) induced ICC formation in vivo. Furthermore, while both HCC and ICC lesions develop in mice following hydrodynamic injection of AKT and neuroblastoma Ras viral oncogene homolog oncogenes (AKT/Ras), deletion of FASN in AKT/Ras mice triggered the development almost exclusively of ICCs. In the absence of FASN, ICC cells might receive lipids for membrane synthesis through exogenous fatty acid uptake. In accordance with the latter hypothesis, ICC cells displayed high expression of fatty acid uptake-related proteins and robust long-chain fatty acid uptake.

CONCLUSION

Our data demonstrate that FASN dependence is not a universal feature of liver tumors: while HCC development is highly dependent of FASN and its mediated lipogenesis, ICC tumorigenesis can be insensitive to FASN deprivation; our study supports novel therapeutic approaches to treat this pernicious tumor type with the inhibition of exogenous fatty acid uptake. (Hepatology 2016;63:1900-1913).

Prevention of gallbladder hypomotility via FATP2 inhibition protects from lithogenic diet-induced cholelithiasis

Gallstone disease is a widespread disorder costing billions for annual treatment in the United States. The primary mechanisms underlying gallstone formation are biliary cholesterol supersaturation and gallbladder hypomotility. The relative contribution of these two processes has been difficult to dissect, as experimental lithogenic diets cause both bile supersaturation and alterations in gallbladder motility. Importantly, there is no mechanistic explanation for obesity as a major risk factor for cholelithiasis. We discovered that lithogenic diets induce ectopic triacylglycerol (TAG) accumulation, a major feature of obesity and a known muscle contraction impairing condition. We hypothesized that prevention of TAG accumulation in gallbladder walls may prevent gallbladder contractile dysfunction without impacting biliary cholesterol saturation. We utilized adeno-associated virus-mediated knock down of the long-chain fatty acid transporter 2 (FATP2; Slc27A2), which is highly expressed by gallbladder epithelial cells, to downregulate lithogenic diet-associated TAG accumulation. FATP2-knockdown significantly reduced gallbladder TAG, but did not affect key bile composition parameters. Importantly, measurements with force displacement transducers showed that contractile strength in FATP2-knockdown gallbladders was significantly greater than in control gallbladders following lithogenic diet administration, and the magnitude of this effect was sufficient to prevent the formation of gallstones. FATP2-driven fatty acid uptake and the subsequent TAG accumulation in gallbladder tissue plays a pivotal role in cholelithiasis, and prevention of this process can protect from gallstone formation, even in the context of supersaturated bile cholesterol levels, thus pointing to new treatment approaches and targets.

α8β1 integrin regulates nutrient absorption through an Mfge8-PTEN dependent mechanism

Coordinated gastrointestinal smooth muscle contraction is critical for proper nutrient absorption and is altered in a number of medical disorders. In this work, we demonstrate a critical role for the RGD-binding integrin α8β1 in promoting nutrient absorption through regulation of gastrointestinal motility. Smooth muscle-specific deletion and antibody blockade of α8 in mice result in enhanced gastric antral smooth muscle contraction, more rapid gastric emptying, and more rapid transit of food through the small intestine leading to malabsorption of dietary fats and carbohydrates as well as protection from weight gain in a diet-induced model of obesity. Mechanistically, ligation of α8β1 by the milk protein Mfge8 reduces antral smooth muscle contractile force by preventing RhoA activation through a PTEN-dependent mechanism. Collectively, our results identify a role for α8β1 in regulating gastrointestinal motility and identify α8 as a potential target for disorders characterized by hypo- or hyper-motility.

DOI:http://dx.doi.org/10.7554/eLife.13063.001

Animals absorb nutrients from the food they eat in a complicated process that involves multiple steps. In the mouth, teeth break down the food into smaller chunks. Then the food passes through the stomach and small intestine, where enzymes break it down into individual molecules that are small enough to be absorbed by cells that line the small intestine. These cells then package the molecules and release them into the bloodstream so that they can be distributed to the rest of the body.

Muscles in the wall of the small intestine control how quickly food travels through this part of the gut. If food moves too quickly, the cells that line the intestine have less time to absorb the food molecules and may fail to absorb enough nutrients. If the food moves too slowly, an individual may experience nausea or vomiting, or the contents of their stomach may spill into their lungs.

In 2014, researchers reported that a protein in breast milk called Mfge8 helps to boost the number of fat molecules absorbed from food. Now, Khalifeh-Soltani et al. – including some of the same researchers involved in the earlier work – show that Mfge8 also slows the rate at which food travels through the small intestine in mice. Mfge8 binds to another protein called integrin α8β1 to control how often the intestine muscles contract. Genetically engineered mice that lacked integrin α8β1 developed diarrhea and food passed through their intestines more quickly than in normal mice. Furthermore, these mice did not gain as much weight as normal mice when they were fed a high-fat diet.

Khalifeh-Soltani et al.’s findings show that Mfge8 has a dual role in controlling the absorption of food molecules in the small intestine. The next challenge is to find out whether drugs that alter the activity of integrin α8β1 could be used to help treat patients with diseases in which food moves too quickly, or too slowly, through the gut.

DOI:http://dx.doi.org/10.7554/eLife.13063.002

Matrix metalloproteinase-13 mediated degradation of hyaluronic acid-based matrices orchestrates stem cell engraftment through vascular integration

A critical design parameter for the function of synthetic extracellular matrices is to synchronize the gradual cell-mediated degradation of the matrix with the endogenous secretion of natural extracellular matrix (ECM) (e.g., creeping substitution). In hyaluronic acid (HyA)-based hydrogel matrices, we have investigated the effects of peptide crosslinkers with different matrix metalloproteinases (MMP) sensitivities on network degradation and neovascularization in vivo. The HyA hydrogel matrices consisted of cell adhesive peptides, heparin for both the presentation of exogenous and sequestration of endogenously synthesized growth factors, and MMP cleavable peptide linkages (i.e., QPQGLAK, GPLGMHGK, and GPLGLSLGK). Sca1(+)/CD45(-)/CD34(+)/CD44(+) cardiac progenitor cells (CPCs) cultured in the matrices with the slowly degradable QPQGLAK hydrogels supported the highest production of MMP-2, MMP-9, MMP-13, VEGF165, and a range of angiogenesis related proteins. Hydrogels with QPQGLAK crosslinks supported prolonged retention of these proteins via heparin within the matrix, stimulating rapid vascular development, and anastomosis with the host vasculature when implanted in the murine hindlimb.

Matrix-Assisted Transplantation of Functional Beige Adipose Tissue

Novel, clinically relevant, approaches to shift energy balance are urgently needed to combat metabolic disorders such as obesity and diabetes. One promising approach has been the expansion of brown adipose tissues that express uncoupling protein (UCP) 1 and thus can uncouple mitochondrial respiration from ATP synthesis. While expansion of UCP1-expressing adipose depots may be achieved in rodents via genetic and pharmacological manipulations or the transplantation of brown fat depots, these methods are difficult to use for human clinical intervention. We present a novel cell scaffold technology optimized to establish functional brown fat-like depots in vivo. We adapted the biophysical properties of hyaluronic acid-based hydrogels to support the differentiation of white adipose tissue-derived multipotent stem cells (ADMSCs) into lipid-accumulating, UCP1-expressing beige adipose tissue. Subcutaneous implantation of ADMSCs within optimized hydrogels resulted in the establishment of distinct UCP1-expressing implants that successfully attracted host vasculature and persisted for several weeks. Importantly, implant recipients demonstrated elevated core body temperature during cold challenges, enhanced respiration rates, improved glucose homeostasis, and reduced weight gain, demonstrating the therapeutic merit of this highly translatable approach. This novel approach is the first truly clinically translatable system to unlock the therapeutic potential of brown fat-like tissue expansion.

Enhanced survival and engraftment of transplanted stem cells using growth factor sequestering hydrogels

We have generated a bioinspired tunable system of hyaluronic acid (HyA)-based hydrogels for Matrix-Assisted Cell Transplantation (MACT). With this material, we have independently evaluated matrix parameters such as adhesion peptide density, mechanical properties, and growth factor sequestering capacity, to engineer an environment that imbues donor cells with a milieu that promotes survival and engraftment with host tissues after transplantation. Using a versatile population of Sca-1(+)/CD45(-) cardiac progenitor cells (CPCs), we demonstrated that the addition of heparin in the HyA hydrogels was necessary to coordinate the presentation of TGFβ1 and to support the trophic functions of the CPCs via endothelial cell differentiation and vascular like tubular network formation. Presentation of exogenous TGFβ1 by binding with heparin improved differentiated CPC function by sequestering additional endogenously-produced angiogenic factors. Finally, we demonstrated that TGFβ1 and heparin-containing HyA hydrogels can promote CPC survival when implanted subcutaneously into murine hind-limbs and encouraged their participation in the ensuing neovascular response, which included blood vessels that had anastomosed with the host's blood vessels.

Bioengineering Beige Adipose Tissue Therapeutics

Unlocking the therapeutic potential of brown/beige adipose tissue requires technological advancements that enable the controlled expansion of this uniquely thermogenic tissue. Transplantation of brown fat in small animal model systems has confirmed the expectation that brown fat expansion could possibly provide a novel therapeutic to combat obesity and related disorders. Expansion and/or stimulation of uncoupling protein-1 (UCP1)-positive adipose tissues have repeatedly demonstrated physiologically beneficial reductions in circulating glucose and lipids. The recent discovery that brown adipose tissue (BAT)-derived secreted factors positively alter whole body metabolism further expands potential benefits of brown or beige/brite adipose expansion. Unfortunately, there are no sources of transplantable BATs for human therapeutic purposes at this time. Recent developments in bioengineering, including novel hyaluronic acid-based hydrogels, have enabled non-immunogenic, functional tissue allografts that can be used to generate large quantities of UCP1-positive adipose tissue. These sophisticated tissue-engineering systems have provided the methodology to develop metabolically active brown or beige/brite adipose tissue implants with the potential to be used as a metabolic therapy. Unlike the pharmacological browning of white adipose depots, implantation of bioengineered UCP1-positive adipose tissues offers a spatially controlled therapeutic. Moving forward, new insights into the mechanisms by which extracellular cues govern stem-cell differentiation and progenitor cell recruitment may enable cell-free matrix implant approaches, which generate a niche sufficient to recruit white adipose tissue-derived stem cells and support their differentiation into functional beige/brite adipose tissues. This review summarizes clinically relevant discoveries in tissue-engineering and biology leading toward the recent development of biomaterial supported beige adipose tissue implants and their potential for the metabolic therapies.