Yap- and Cdc42-dependent nephrogenesis and morphogenesis during mouse kidney development

WW domains form a folded type of nuclear localization signal to guide YAP1 nuclear import

The nuclear translocation of YAP1 is significantly implicated in the proliferation, stemness, and metastasis of cancer cells. Although the molecular basis underlying YAP1 subcellular distribution has been extensively explored, it remains to be elucidated how the nuclear localization signal guides YAP1 to pass through the nuclear pore complex. Here, we define a globular type of nuclear localization signal composed of folded WW domains, named as WW-NLS. It directs YAP1 nuclear import through the heterodimeric nuclear transport receptors KPNA-KPNB1, bypassing the canonical nuclear localization signal that has been well documented in KPNA/KPNB1-mediated nuclear import. Strikingly, competitive interference with the function of the WW-NLS significantly attenuates YAP1 nuclear translocation and damages stemness gene activation and sphere formation in malignant breast cancer cells. Our findings elucidate a novel globular type of nuclear localization signal to facilitate nuclear entry of WW-containing proteins including YAP1.

Inhibition of transcriptional coactivator YAP Impairs the expression and function of transcription factor WT1 in diabetic podocyte injury

Podocyte injury and loss are hallmarks of diabetic nephropathy (DN). However, the molecular mechanisms underlying these phenomena remain poorly understood. YAP (Yes-associated protein) is an important transcriptional coactivator that binds with various other transcription factors, including the TEAD family members (nuclear effectors of the Hippo pathway), that regulate cell proliferation, differentiation, and apoptosis. The present study found an increase in YAP phosphorylation at S127 of YAP and a reduction of nuclear YAP localization in podocytes of diabetic mouse and human kidneys, suggesting dysregulation of YAP may play a role in diabetic podocyte injury. Tamoxifen-inducible podocyte-specific Yap gene knockout mice (YappodKO) exhibited accelerated and worsened diabetic kidney injury. YAP inactivation decreased transcription factor WT1 expression with subsequent reduction of Tead1 and other well-known targets of WT1 in diabetic podocytes. Thus, our study not only sheds light on the pathophysiological roles of the Hippo pathway in diabetic podocyte injury but may also lead to the development of new therapeutic strategies to prevent and/or treat DN by targeting the Hippo signaling pathway.

Emerging role of YAP/TAZ in vascular mechanotransduction and disease

Cells have an incredible ability to physically interact with neighboring cells and their environment. They can detect and respond to mechanical forces by converting mechanical stimuli into biochemical signals in a process known as mechanotransduction. This is a key process for the adaption of vascular smooth muscle and endothelial cells to altered flow and pressure conditions. Mechanical stimuli, referring to a physical force exerted on cells, are primarily sensed by transmembrane proteins and the actin cytoskeleton, which initiate a cascade of intracellular events, including the activation of signaling pathways, ion channels, and transcriptional regulators. Recent work has highlighted an important role of the transcriptional coactivators YAP/TAZ for mechanotransduction in vascular cells. Interestingly, the activity of YAP/TAZ decreases with age, providing a potential mechanism for the detrimental effects of aging in the vascular wall. In this review, we summarize the current knowledge on the functional role of YAP and TAZ in vascular endothelial and smooth muscle cells for mechanotransduction in homeostasis and disease. In particular, the review is focused on in vivo observations from conditional knockout (KO) models of YAP/TAZ and the potential implications these studies may have for our understanding of vascular disease development.

Measurement of adhesion and traction of cells at high yield (MATCHY) reveals an energetic ratchet driving nephron condensation

Engineering of embryonic strategies for tissue-building has extraordinary promise for regenerative medicine. This has led to a resurgence in interest in the relationship between cell biophysical properties and morphological transitions. However, mapping gene or protein expression data to cell biophysical properties to physical morphogenesis remains challenging with current techniques. Here we present MATCHY (multiplexed adhesion and traction of cells at high yield). MATCHY advances the multiplexing and throughput capabilities of existing traction force and cell-cell adhesion assays using microfabrication and an automated computation scheme with machine learning-driven cell segmentation. Both biophysical assays are coupled with serial downstream immunofluorescence to extract cell type/signaling state information. MATCHY is especially suited to complex primary tissue-, organoid-, or biopsy-derived cell mixtures since it does not rely on a priori knowledge of cell surface markers, cell sorting, or use of lineage-specific reporter animals. We first validate MATCHY on canine kidney epithelial cells engineered for RET tyrosine kinase expression and quantify a relationship between downstream signaling and cell traction. We go on to create a biophysical atlas of primary cells dissociated from the mouse embryonic kidney and use MATCHY to identify distinct biophysical states along the nephron differentiation trajectory. Our data complement expression-level knowledge of adhesion molecule changes that accompany nephron differentiation with quantitative biophysical information. These data reveal an 'energetic ratchet' that explains spatial nephron progenitor cell condensation from the niche as they differentiate, which we validate through agent-based computational simulation. MATCHY offers automated cell biophysical characterization at >104-cell throughput, a highly enabling advance for fundamental studies and new synthetic tissue design strategies for regenerative medicine.

The YAP1/TAZ-TEAD transcriptional network regulates gene expression at neuromuscular junctions in skeletal muscle fibers

We examined YAP1/TAZ-TEAD signaling pathway activity at neuromuscular junctions (NMJs) of skeletal muscle fibers in adult mice. Our investigations revealed that muscle-specific knockouts of Yap1 or Taz, or both, demonstrate that these transcriptional coactivators regulate synaptic gene expression, the number and morphology of NMJs, and synaptic nuclei. Yap1 or Taz single knockout mice display reduced grip strength, fragmentation of NMJs, and accumulation of synaptic nuclei. Yap1/Taz muscle-specific double knockout mice do not survive beyond birth and possess almost no NMJs, the few detectable show severely impaired morphology and are organized in widened endplate bands; and with motor nerve endings being mostly absent. Myogenic gene expression is significantly impaired in the denervated muscles of knockout mice. We found that Tead1 and Tead4 transcription rates were increased upon incubation of control primary myotubes with AGRN-conditioned medium. Reduced AGRN-dependent acetylcholine receptor clustering and synaptic gene transcription were observed in differentiated primary Tead1 and Tead4 knockout myotubes. In silico analysis of previously reported genomic occupancy sites of TEAD1/4 revealed evolutionary conserved regions of potential TEAD binding motifs in key synaptic genes, the relevance of which was functionally confirmed by reporter assays. Collectively, our data suggest a role for YAP1/TAZ-TEAD1/TEAD4 signaling, particularly through TAZ-TEAD4, in regulating synaptic gene expression and acetylcholine receptor clustering at NMJs.

Nephron progenitors rhythmically alternate between renewal and differentiation phases that synchronize with kidney branching morphogenesis

The mammalian kidney achieves massive parallelization of function by exponentially duplicating nephron-forming niches during development. Each niche caps a tip of the ureteric bud epithelium (the future urinary collecting duct tree) as it undergoes branching morphogenesis, while nephron progenitors within niches balance self-renewal and differentiation to early nephron cells. Nephron formation rate approximately matches branching rate over a large fraction of mouse gestation, yet the nature of this apparent pace-maker is unknown. Here we correlate spatial transcriptomics data with branching 'life-cycle' to discover rhythmically alternating signatures of nephron progenitor differentiation and renewal across Wnt, Hippo-Yap, retinoic acid (RA), and other pathways. We then find in human stem-cell derived nephron progenitor organoids that Wnt/β-catenin-induced differentiation is converted to a renewal signal when it temporally overlaps with YAP activation. Similar experiments using RA activation indicate a role in setting nephron progenitor exit from the naive state, the spatial extent of differentiation, and nephron segment bias. Together the data suggest that nephron progenitor interpretation of consistent Wnt/β-catenin differentiation signaling in the niche may be modified by rhythmic activity in ancillary pathways to set the pace of nephron formation. This would synchronize nephron formation with ureteric bud branching, which creates new sites for nephron condensation. Our data bring temporal resolution to the renewal vs. differentiation balance in the nephrogenic niche and inform new strategies to achieve self-sustaining nephron formation in synthetic human kidney tissues.

Inducible tricolor reporter mouse for parallel imaging of lysosomes, mitochondria, and microtubules

Cell type-specific use of the same DNA blueprint generates diverse cell types. Such diversity must also be executed via differential deployment of the same subcellular machinery. However, our understanding of the size, distribution, and dynamics of subcellular machinery in native tissues and their connection to cellular diversity remains limited. We generate and characterize an inducible tricolor reporter mouse, dubbed "Kaleidoscope," for simultaneous imaging of lysosomes, mitochondria, and microtubules in any cell type and at a single-cell resolution. The expected subcellular compartments are labeled in culture and in tissues with no impact on cellular and organismal viability. Quantitative and live imaging of the tricolor reporter captures cell type-specific organelle features and kinetics in the lung, as well as their changes after Sendai virus infection. Yap/Taz mutant lung epithelial cells undergo accelerated lamellar body maturation, a subcellular manifestation of their molecular defects. A comprehensive toolbox of reporters for all subcellular structures is expected to transform our understanding of cell biology in tissues.

YAP and TAZ regulate remyelination in the central nervous system

Myelinating cells are sensitive to mechanical stimuli from their extracellular matrix. Ablation of YAP and TAZ mechanotransducers in Schwann cells abolishes the axon-Schwann cell recognition, myelination, and remyelination in the peripheral nervous system. It was unknown if YAP and TAZ are also required for myelination and remyelination in the central nervous system. Here we define the importance of oligodendrocyte (OL) YAP and TAZ in vivo, by specific deletion in oligodendroglial cells in adult OLs during myelin repair. Blocking YAP and TAZ expression in OL lineage cells did not affect animal viability or any major defects on OL maturation and myelination. However, using a mouse model of demyelination/remyelination, we demonstrate that YAP and TAZ modulate the capacity of OLs to remyelinate axons, particularly during the early stage of the repair process, when OL proliferation is most important. These results indicate that YAP and TAZ signaling is necessary for effective remyelination of the mouse brain.

YAP targetome reveals activation of SPEM in gastric pre-neoplastic progression and regeneration

Peptic ulcer disease caused by environmental factors increases the risk of developing gastric cancer (GC), one of the most common and deadly cancers in the world. However, the mechanisms underlying this association remain unclear. A major type of GC uniquely undergoes spasmolytic polypeptide-expressing metaplasia (SPEM) followed by intestinal metaplasia. Notably, intestinal-type GC patients with high levels of YAP signaling exhibit a lower survival rate and poor prognosis. YAP overexpression in gastric cells induces atrophy, metaplasia, and hyperproliferation, while its deletion in a Notch-activated gastric adenoma model suppresses them. By defining the YAP targetome genome-wide, we demonstrate that YAP binds to active chromatin elements of SPEM-related genes, which correlates with the activation of their expression in both metaplasia and ulcers. Single-cell analysis combined with our YAP signature reveals that YAP signaling is activated during SPEM, demonstrating YAP as a central regulator of SPEM in gastric neoplasia and regeneration.

Wnt16 Promotes Vascular Smooth Muscle Contractile Phenotype and Function via Taz (Wwtr1) Activation in Male LDLR-/- Mice

Wnt16 is expressed in bone and arteries, and maintains bone mass in mice and humans, but its role in cardiovascular physiology is unknown. We show that Wnt16 protein accumulates in murine and human vascular smooth muscle (VSM). WNT16 genotypes that convey risk for bone frailty also convey risk for cardiovascular events in the Dallas Heart Study. Murine Wnt16 deficiency, which causes postnatal bone loss, also reduced systolic blood pressure. Electron microscopy demonstrated abnormal VSM mitochondrial morphology in Wnt16-null mice, with reductions in mitochondrial respiration. Following angiotensin-II (AngII) infusion, thoracic ascending aorta (TAA) dilatation was greater in Wnt16-/- vs Wnt16+/+ mice (LDLR-/- background). Acta2 (vascular smooth muscle alpha actin) deficiency has been shown to impair contractile phenotype and worsen TAA aneurysm with concomitant reductions in blood pressure. Wnt16 deficiency reduced expression of Acta2, SM22 (transgelin), and other contractile genes, and reduced VSM contraction induced by TGFβ. Acta2 and SM22 proteins were reduced in Wnt16-/- VSM as was Ankrd1, a prototypic contractile target of Yap1 and Taz activation via TEA domain (TEAD)-directed transcription. Wnt16-/- VSM exhibited reduced nuclear Taz and Yap1 protein accumulation. SiRNA targeting Wnt16 or Taz, but not Yap1, phenocopied Wnt16 deficiency, and Taz siRNA inhibited contractile gene upregulation by Wnt16. Wnt16 incubation stimulated mitochondrial respiration and contraction (reversed by verteporfin, a Yap/Taz inhibitor). SiRNA targeting Taz inhibitors Ccm2 and Lats1/2 mimicked Wnt16 treatment. Wnt16 stimulated Taz binding to Acta2 chromatin and H3K4me3 methylation. TEAD cognates in the Acta2 promoter conveyed transcriptional responses to Wnt16 and Taz. Wnt16 regulates cardiovascular physiology and VSM contractile phenotype, mediated via Taz signaling.

Control of stem cell renewal and fate by YAP and TAZ

Complex physiological processes control whether stem cells self-renew, differentiate or remain quiescent. Two decades of research have placed the Hippo pathway, a highly conserved kinase signalling cascade, and its downstream molecular effectors YAP and TAZ at the nexus of this decision. YAP and TAZ translate complex biological cues acting on stem cells - from mechanical forces to cellular metabolism - into genome-wide effects to mediate stem cell functions. While aberrant YAP/TAZ activity drives stem cell dysfunction in ageing, tumorigenesis and disease, therapeutic targeting of Hippo signalling and YAP/TAZ can boost stem cell activity to enhance regeneration. In this Review, we discuss how YAP/TAZ control the self-renewal, fate and plasticity of stem cells in different contexts, how dysregulation of YAP/TAZ in stem cells leads to disease, and how therapeutic modalities targeting YAP/TAZ may benefit regenerative medicine and cancer therapy.

The L27 Domain of MPP7 enhances TAZ-YY1 Cooperation to Renew Muscle Stem Cells

Stem cells regenerate differentiated cells to maintain and repair tissues and organs. They also replenish themselves, i.e. self-renewal, for the regenerative process to last a lifetime. How stem cells renew is of critical biological and medical significance. Here we use the skeletal muscle stem cell (MuSC) to study this process. Using a combination of genetic, molecular, and biochemical approaches, we show that MPP7, AMOT, and TAZ/YAP form a complex that activates a common set of target genes. Among these targets, Carm1 can direct MuSC renewal. In the absence of MPP7, TAZ can support regenerative progenitors and activate Carm1 expression, but not to a level needed for self-renewal. Facilitated by the actin polymerization-responsive AMOT, TAZ recruits the L27 domain of MPP7 to up-regulate Carm1 to the level necessary to drive MuSC renewal. The promoter of Carm1, and those of other common downstream genes, also contain binding site(s) for YY1. We further demonstrate that the L27 domain of MPP7 enhances the interaction between TAZ and YY1 to activate Carm1. Our results define a renewal transcriptional program embedded within the progenitor program, by selectively up-regulating key gene(s) within the latter, through the combination of protein interactions and in a manner dependent on the promoter context.

Rho/ROCK activity tunes cell compartment segregation and differentiation in nephron-forming niches

Controlling the time and place of nephron formation in vitro would improve nephron density and connectivity in next-generation kidney replacement tissues. Recent developments in kidney organoid technology have paved the way to achieving self-sustaining nephrogenic niches in vitro. The physical and geometric structure of the niche are key control parameters in tissue engineering approaches. However, their relationship to nephron differentiation is unclear. Here we investigate the relationship between niche geometry, cell compartment mixing, and nephron differentiation by targeting the Rho/ROCK pathway, a master regulator of the actin cytoskeleton. We find that the ROCK inhibitor Y-27632 increases mixing between nephron progenitor and stromal compartments in native mouse embryonic kidney niches, and also increases nephrogenesis. Similar increases are also seen in reductionist mouse primary cell and human induced pluripotent stem cell (iPSC)-derived organoids perturbed by Y-27632, dependent on the presence of stromal cells. Our data indicate that niche organization is a determinant of nephron formation rate, bringing renewed focus to the spatial context of cell-cell interactions in kidney tissue engineering efforts.

The L27 Domain of MPP7 enhances TAZ-YY1 Cooperation to Renew Muscle Stem Cells

Stem cells regenerate differentiated cells to maintain and repair tissues and organs. They also replenish themselves, i.e. self-renewal, for the regenerative process to last a lifetime. How stem cells renew is of critical biological and medical significance. Here we use the skeletal muscle stem cell (MuSC) to study this process. Using a combination of genetic, molecular, and biochemical approaches, we show that MPP7, AMOT, and TAZ/YAP form a complex that activates a common set of target genes. Among these targets, Carm1 can direct MuSC renewal. In the absence of MPP7, TAZ can support regenerative progenitors and activate Carm1 expression, but not to a level needed for self-renewal. Facilitated by the actin polymerization-responsive AMOT, TAZ recruits the L27 domain of MPP7 to up-regulate Carm1 to the level necessary to drive MuSC renewal. The promoter of Carm1, and those of other common downstream genes, also contain binding site(s) for YY1. We further demonstrate that the L27 domain of MPP7 enhances the interaction between TAZ and YY1 to activate Carm1. Our results define a renewal transcriptional program embedded within the progenitor program, by selectively up-regulating key gene(s) within the latter, through the combination of protein interactions and in a manner dependent on the promoter context.

Genetic interactions between polycystin-1 and Wwtr1 in osteoblasts define a novel mechanosensing mechanism regulating bone formation in mice

Molecular mechanisms transducing physical forces in the bone microenvironment to regulate bone mass are poorly understood. Here, we used mouse genetics, mechanical loading, and pharmacological approaches to test the possibility that polycystin-1 and Wwtr1 have interdependent mechanosensing functions in osteoblasts. We created and compared the skeletal phenotypes of control Pkd1flox/+;Wwtr1flox/+, Pkd1Oc-cKO, Wwtr1Oc-cKO, and Pkd1/Wwtr1Oc-cKO mice to investigate genetic interactions. Consistent with an interaction between polycystins and Wwtr1 in bone in vivo, Pkd1/Wwtr1Oc-cKO mice exhibited greater reductions of BMD and periosteal MAR than either Wwtr1Oc-cKO or Pkd1Oc-cKO mice. Micro-CT 3D image analysis indicated that the reduction in bone mass was due to greater loss in both trabecular bone volume and cortical bone thickness in Pkd1/Wwtr1Oc-cKO mice compared to either Pkd1Oc-cKO or Wwtr1Oc-cKO mice. Pkd1/Wwtr1Oc-cKO mice also displayed additive reductions in mechanosensing and osteogenic gene expression profiles in bone compared to Pkd1Oc-cKO or Wwtr1Oc-cKO mice. Moreover, we found that Pkd1/Wwtr1Oc-cKO mice exhibited impaired responses to tibia mechanical loading in vivo and attenuation of load-induced mechanosensing gene expression compared to control mice. Finally, control mice treated with a small molecule mechanomimetic, MS2 that activates the polycystin complex resulted in marked increases in femoral BMD and periosteal MAR compared to vehicle control. In contrast, Pkd1/Wwtr1Oc-cKO mice were resistant to the anabolic effects of MS2. These findings suggest that PC1 and Wwtr1 form an anabolic mechanotransduction signaling complex that mediates mechanical loading responses and serves as a potential novel therapeutic target for treating osteoporosis.

The spatiotemporal heterogeneity of the biophysical microenvironment during hematopoietic stem cell development: from embryo to adult

Hematopoietic stem cells (HSCs) with the ability to self-renew and differentiate are responsible for maintaining the supply of all types of blood cells. The complex and delicate microenvironment surrounding HSCs is called the HSC niche and can provide physical, chemical, and biological stimuli to regulate the survival, maintenance, proliferation, and differentiation of HSCs. Currently, the exploration of the biophysical regulation of HSCs remains in its infancy. There is evidence that HSCs are susceptible to biophysical stimuli, suggesting that the construction of engineered niche biophysical microenvironments is a promising way to regulate the fate of HSCs in vitro and ultimately contribute to clinical applications. In this review, we introduced the spatiotemporal heterogeneous biophysical microenvironment during HSC development, homeostasis, and malignancy. Furthermore, we illustrated how these biophysical cues contribute to HSC behaviors, as well as the possible mechanotransduction mechanisms from the extracellular microenvironment into cells. Comprehending the important functions of these biophysical regulatory factors will provide novel approaches to resolve clinical problems.

Vascular smooth muscle-specific YAP/TAZ deletion triggers aneurysm development in mouse aorta

Inadequate adaption to mechanical forces, including blood pressure, contributes to development of arterial aneurysms. Recent studies have pointed to a mechanoprotective role of YAP and TAZ in vascular smooth muscle cells (SMCs). Here, we identified reduced expression of YAP1 in human aortic aneurysms. Vascular SMC-specific knockouts (KOs) of YAP/TAZ were thus generated using the integrin α8-Cre (Itga8-Cre) mouse model (i8-YT-KO). i8-YT-KO mice spontaneously developed aneurysms in the abdominal aorta within 2 weeks of KO induction and in smaller arteries at later times. The vascular specificity of Itga8-Cre circumvented gastrointestinal effects. Aortic aneurysms were characterized by elastin disarray, SMC apoptosis, and accumulation of proteoglycans and immune cell populations. RNA sequencing, proteomics, and myography demonstrated decreased contractile differentiation of SMCs and impaired vascular contractility. This associated with partial loss of myocardin expression, reduced blood pressure, and edema. Mediators in the inflammatory cGAS/STING pathway were increased. A sizeable increase in SOX9, along with several direct target genes, including aggrecan (Acan), contributed to proteoglycan accumulation. This was the earliest detectable change, occurring 3 days after KO induction and before the proinflammatory transition. In conclusion, Itga8-Cre deletion of YAP and TAZ represents a rapid and spontaneous aneurysm model that recapitulates features of human abdominal aortic aneurysms.

Loss of TAZ after YAP deletion severely impairs foregut development and worsens cholestatic hepatocellular injury

BACKGROUND

We previously showed that loss of yes-associated protein 1 (YAP) in early liver development (YAPKO) leads to an Alagille syndrome-like phenotype, with failure of intrahepatic bile duct development, severe cholestasis, and chronic hepatocyte adaptations to reduce liver injury. TAZ, a paralog of YAP, was significantly upregulated in YAPKO hepatocytes and interacted with TEA domain family member (TEAD) transcription factors, suggesting possible compensatory activity.

METHODS

We deleted both Yap1 and Wwtr1 (which encodes TAZ) during early liver development using the Foxa3 promoter to drive Cre expression, similar to YAPKO mice, resulting in YAP/TAZ double knockout (DKO) and YAPKO with TAZ heterozygosity (YAPKO TAZHET). We evaluated these mice using immunohistochemistry, serum biochemistry, bile acid profiling, and RNA sequencing.

RESULTS

DKO mice were embryonic lethal, but their livers were similar to YAPKO, suggesting an extrahepatic cause of death. Male YAPKO TAZHET mice were also embryonic lethal, with insufficient samples to determine the cause. However, YAPKO TAZHET females survived and were phenotypically similar to YAPKO mice, with increased bile acid hydrophilicity and similar global gene expression adaptations but worsened the hepatocellular injury. TAZ heterozygosity in YAPKO impacted the expression of canonical YAP targets Ctgf and Cyr61, and we found changes in pathways regulating cell division and inflammatory signaling correlating with an increase in hepatocyte cell death, cell cycling, and macrophage recruitment.

CONCLUSIONS

YAP loss (with or without TAZ loss) aborts biliary development. YAP and TAZ play a codependent critical role in foregut endoderm development outside the liver, but they are not essential for hepatocyte development. TAZ heterozygosity in YAPKO livers increased cell cycling and inflammatory signaling in the setting of chronic injury, highlighting genes that are especially sensitive to TAZ regulation.

Cancer Stem Cells in Renal Cell Carcinoma: Origins and Biomarkers

The term "cancer stem cell" (CSC) refers to a cancer cell with the following features: clonogenic ability, the expression of stem cell markers, differentiation into cells of different lineages, growth in nonadhesive spheroids, and the in vivo ability to generate serially transplantable tumors that reflect the heterogeneity of primary cancers (tumorigenicity). According to this model, CSCs may arise from normal stem cells, progenitor cells, and/or differentiated cells because of striking genetic/epigenetic mutations or from the fusion of tissue-specific stem cells with circulating bone marrow stem cells (BMSCs). CSCs use signaling pathways similar to those controlling cell fate during early embryogenesis (Notch, Wnt, Hedgehog, bone morphogenetic proteins (BMPs), fibroblast growth factors, leukemia inhibitory factor, and transforming growth factor-β). Recent studies identified a subpopulation of CD133+/CD24+ cells from ccRCC specimens that displayed self-renewal ability and clonogenic multipotency. The development of agents targeting CSC signaling-specific pathways and not only surface proteins may ultimately become of utmost importance for patients with RCC.

Spontaneous urinary bladder regeneration after subtotal cystectomy increases YAP/WWTR1 signaling and downstream BDNF expression: Implications for smooth muscle injury responses

Rodents have the capacity for spontaneous bladder regeneration and bladder smooth muscle cell (BSMC) migration following a subtotal cystectomy (STC). YAP/WWTR1 and BDNF (Brain-derived neurotrophic factor) play crucial roles in development and regeneration. During partial bladder outlet obstruction (PBO), excessive YAP/WWTR1 signaling and BDNF expression increases BSMC hypertrophy and dysfunction. YAP/WWTR1 and expression of BDNF and CYR61 were examined in models of regeneration and wound repair. Live cell microscopy was utilized in an ex vivo model of STC to visualize cell movement and division. In Sprague-Dawley female rats, STC was performed by resection of the bladder dome sparing the trigone, followed by closure of the bladder. Smooth muscle migration and downstream effects on signaling and expression were also examined after scratch wound of BSMC with inhibitors of YAP and BDNF signaling. Sham, PBO and incision (cystotomy) were comparators for the STC model. Scratch wound in vitro increased SMC migration and expression of BDNF, CTGF and CYR61 in a YAP/WWTR1-dependent manner. Inhibition of YAP/WWTR1 and BDNF signaling reduced scratch-induced migration. BDNF and CYR61 expression was elevated during STC and PBO. STC induces discrete genes associated with endogenous de novo cell regeneration downstream of YAP/WWTR1 activation.

Engineering Strategies to Move from Understanding to Steering Renal Tubulogenesis

Rebuilding the kidney in the context of tissue engineering offers a major challenge as the organ is structurally complex and has a high variety of specific functions. Recreation of kidney function is inherently connected to the formation of tubules since the functional subunit of the kidney, the nephron, is based on tubular structures. In vivo, tubulogenesis culminates in a perfectly shaped, patterned, and functional renal tubule via different morphogenic processes that depend on delicately orchestrated chemical, physical, and mechanical interactions between cells and between cells and their microenvironment. This review summarizes the current understanding of the role of the microenvironment in the morphogenic processes involved in in vivo renal tubulogenesis. We highlight the current state-of-the-art of renal tubular engineering and provide a view on the design elements that can be extracted from these studies. Next, we discuss how computational modeling can aid in specifying and identifying design parameters and provide directions on how these design parameters can be incorporated in biomaterials for the purpose of engineering renal tubulogenesis. Finally, we propose that a step-by-step reciprocal interaction between understanding and engineering is necessary to effectively guide renal tubulogenesis. Impact statement Tubular tissue engineering lies at the foundation of regenerating kidney tissue function, as the functional subunit of the kidney, the nephron, is based on tubular structures. Guiding renal tubulogenesis toward functional renal tubules requires in-depth knowledge of the developmental processes that lead to the formation of native tubules as well as engineering approaches to steer these processes. In this study, we review the role of the microenvironment in the developmental processes that lead to functional renal tubules and give directions how this knowledge can be harnessed for biomaterial-based tubular engineering using computational models.

An inducible tricolor reporter mouse for simultaneous imaging of lysosomes, mitochondria and microtubules

Cell-type-specific use of the same DNA blueprint generates diverse cell types. Such diversity must also be executed via differential deployment of the same subcellular machinery. However, our understanding of the size, distribution, and dynamics of subcellular machinery in native tissues, and their connection to cellular diversity, remain limited. We generate and characterize an inducible tricolor reporter mouse, dubbed "kaleidoscope", for simultaneous imaging of lysosomes, mitochondria and microtubules in any cell type and at a single cell resolution. The expected subcellular compartments are labeled in culture and in tissues with no impact on cellular and organismal viability. Quantitative and live imaging of the tricolor reporter captures cell-type-specific organelle features and kinetics in the lung, as well as their changes after Sendai virus infection. Yap/Taz mutant lung epithelial cells undergo accelerated lamellar body maturation, a subcellular manifestation of their molecular defects. A comprehensive toolbox of reporters for all subcellular structures is expected to transform our understanding of cell biology in tissues.

Cell response to mechanical microenvironment cues via Rho signaling: From mechanobiology to mechanomedicine

Mechanical cues in the cell microenvironment such as those from extracellular matrix properties, stretching, compression and shear stress, play a critical role in maintaining homeostasis. Upon sensing mechanical stimuli, cells can translate these external forces into intracellular biochemical signals to regulate their cellular behaviors, but the specific mechanisms of mechanotransduction at the molecular level remain elusive. As a subfamily of the Ras superfamily, Rho GTPases have been recognized as key intracellular mechanotransduction mediators that can regulate multiple cell activities such as proliferation, migration and differentiation as well as biological processes such as cytoskeletal dynamics, metabolism, and organ development. However, the upstream mechanosensors for Rho proteins and downstream effectors that respond to Rho signal activation have not been well illustrated. Moreover, Rho-mediated mechanical signals in previous studies are highly context-dependent. In this review, we systematically summarize the types of mechanical cues in the cell microenvironment and provide recent advances on the roles of the Rho-based mechanotransduction in various cell activities, physiological processes and diseases. Comprehensive insights into the mechanical roles of Rho GTPase partners would open a new paradigm of mechanomedicine for a variety of diseases. STATEMENT OF SIGNIFICANCE: In this review, we highlight the critical role of Rho GTPases as signal mediators to respond to physical cues in microenvironment. This article will add a distinct contribution to this set of knowledge by intensively addressing the relationship between Rho signaling and mechanobiology/mechanotransduction/mechanomedcine. This topic has not been discussed by the journal, nor has it yet been developed by the field. The comprehensive picture that will develop, from molecular mechanisms and engineering methods to disease treatment strategies, represents an important and distinct contribution to the field. We hope that this review would help researchers in various fields, especially clinicians, oncologists and bioengineers, who study Rho signal pathway and mechanobiology/mechanotransduction, understand the critical role of Rho GTPase in mechanotransduction.

YAP/TAZ as master regulators in cancer: modulation, function and therapeutic approaches

Our understanding of the function of the transcriptional regulators YAP and TAZ (YAP/TAZ) in cancer is advancing. In this Review, we provide an update on recent progress in YAP/TAZ biology, their regulation by Hippo signaling and mechanotransduction and highlight open questions. YAP/TAZ signaling is an addiction shared by multiple tumor types and their microenvironments, providing many malignant attributes. As such, it represents an important vulnerability that may offer a broad window of therapeutic efficacy, and here we give an overview of the current treatment strategies and pioneering clinical trials.

Lipid Raft Facilitated Receptor Organization and Signaling: A Functional Rheostat in Embryonic Development, Stem Cell Biology and Cancer

Molecular views of plasma membrane organization and dynamics are gradually changing over the past fifty years. Dynamics of plasma membrane instigate several signaling nexuses in eukaryotic cells. The striking feature of plasma membrane dynamics is that, it is internally transfigured into various subdomains of clustered macromolecules. Lipid rafts are nanoscale subdomains, enriched with cholesterol and sphingolipids, reside as floating entity mostly on the exoplasmic leaflet of the lipid bilayer. In terms of functionality, lipid rafts are unique among other membrane subdomains. Herein, advances on the roles of lipid rafts in cellular physiology and homeostasis are discussed, precisely, on how rafts dynamically harbor signaling proteins, including GPCRs, catalytic receptors, and ionotropic receptors within it and orchestrate multiple signaling pathways. In the developmental proceedings signaling are designed for patterning of overall organism and they differ from the somatic cell physiology and signaling of fully developed organisms. Some of the developmental signals are characteristic in maintenance of stemness and activated during several types of tumor development and cancer progression. The harmony between extracellular signaling and lineage specific transcriptional programs are extremely important for embryonic development. The roles of plasma membrane lipid rafts mediated signaling in lineage specificity, early embryonic development, stem cell maintenance are emerging. In view of this, we have highlighted and analyzed the roles of lipid rafts in receptor organization, cell signaling, and gene expression during embryonic development; from pre-implantation through the post-implantation phase, in stem cell and cancer biology.

Inactivation of LATS1/2 drives luminal-basal plasticity to initiate basal-like mammary carcinomas

Basal-like breast cancers, an aggressive breast cancer subtype that has poor treatment options, are thought to arise from luminal mammary epithelial cells that undergo basal plasticity through poorly understood mechanisms. Using genetic mouse models and ex vivo primary organoid cultures, we show that conditional co-deletion of the LATS1 and LATS2 kinases, key effectors of Hippo pathway signaling, in mature mammary luminal epithelial cells promotes the development of Krt14 and Sox9-expressing basal-like carcinomas that metastasize over time. Genetic co-deletion experiments revealed that phenotypes resulting from the loss of LATS1/2 activity are dependent on the transcriptional regulators YAP/TAZ. Gene expression analyses of LATS1/2-deleted mammary epithelial cells notably revealed a transcriptional program that associates with human basal-like breast cancers. Our study demonstrates in vivo roles for the LATS1/2 kinases in mammary epithelial homeostasis and luminal-basal fate control and implicates signaling networks induced upon the loss of LATS1/2 activity in the development of basal-like breast cancer.

A Genome-Wide Association Study into the Aetiology of Congenital Solitary Functioning Kidney

Congenital solitary functioning kidney (CSFK) is a birth defect that occurs in 1:1500 children and predisposes them to kidney injury. Its aetiology is likely multifactorial. In addition to known monogenic causes and environmental risk factors, common genetic variation may contribute to susceptibility to CSFK. We performed a genome-wide association study among 452 patients with CSFK and two control groups of 669 healthy children and 5363 unaffected adults. Variants in two loci reached the genome-wide significance threshold of 5 × 10^-8, and variants in 30 loci reached the suggestive significance threshold of 1 × 10^-5. Of these, an identified locus with lead single nucleotide variant (SNV) rs140804918 (odds ratio 3.1, p-value = 1.4 × 10^-8) on chromosome 7 was most promising due to its close proximity to HGF, a gene known to be involved in kidney development. Based on their known molecular functions, both KCTD20 and STK38 could explain the suggestive significant association with lead SNV rs148413365 on chromosome 6. Our findings need replication in an independent cohort of CSFK patients before they can be established definitively. However, our analysis suggests that common variants play a role in CSFK aetiology. Future research could enhance our understanding of the molecular mechanisms involved.

The Hippo signalling pathway and its implications in human health and diseases

As an evolutionarily conserved signalling network, the Hippo pathway plays a crucial role in the regulation of numerous biological processes. Thus, substantial efforts have been made to understand the upstream signals that influence the activity of the Hippo pathway, as well as its physiological functions, such as cell proliferation and differentiation, organ growth, embryogenesis, and tissue regeneration/wound healing. However, dysregulation of the Hippo pathway can cause a variety of diseases, including cancer, eye diseases, cardiac diseases, pulmonary diseases, renal diseases, hepatic diseases, and immune dysfunction. Therefore, therapeutic strategies that target dysregulated Hippo components might be promising approaches for the treatment of a wide spectrum of diseases. Here, we review the key components and upstream signals of the Hippo pathway, as well as the critical physiological functions controlled by the Hippo pathway. Additionally, diseases associated with alterations in the Hippo pathway and potential therapies targeting Hippo components will be discussed.

Targeted Disruption of Lats1 and Lats2 in Mice Impairs Testis Development and Alters Somatic Cell Fate

Hippo signaling plays an essential role in the development of numerous tissues. Although it was previously shown that the transcriptional effectors of Hippo signaling Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) can fine-tune the regulation of sex differentiation genes in the testes, the role of Hippo signaling in testis development remains largely unknown. To further explore the role of Hippo signaling in the testes, we conditionally deleted the key Hippo kinases large tumor suppressor homolog kinases 1 and -2 (Lats1 and Lats2, two kinases that antagonize YAP and TAZ transcriptional co-regulatory activity) in the somatic cells of the testes using an Nr5a1-cre strain (Lats1flox/flox;Lats2flox/flox;Nr5a1-cre). We report here that early stages of testis somatic cell differentiation were not affected in this model but progressive testis cord dysgenesis was observed starting at gestational day e14.5. Testis cord dysgenesis was further associated with the loss of polarity of the Sertoli cells and the loss of SOX9 expression but not WT1. In parallel with testis cord dysgenesis, a loss of steroidogenic gene expression associated with the appearance of myofibroblast-like cells in the interstitial space was also observed in mutant animals. Furthermore, the loss of YAP phosphorylation, the accumulation of nuclear TAZ (and YAP) in both the Sertoli and interstitial cell populations, and an increase in their transcriptional co-regulatory activity in the testes suggest that the observed phenotype could be attributed at least in part to YAP and TAZ. Taken together, our results suggest that Hippo signaling is required to maintain proper differentiation of testis somatic cells.

The Regulation of the Hippo Pathway by Intercellular Junction Proteins

The Hippo pathway is an evolutionarily conserved pathway that serves to promote cell death and differentiation while inhibiting cellular proliferation across species. The downstream effectors of this pathway, yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), are considered vital in promoting the output of the Hippo pathway, with activation of upstream kinases negatively regulating YAP/TAZ activity. The upstream regulation of the Hippo pathway is not entirely understood on a molecular level. However, several studies have shown that numerous cellular and non-cellular mechanisms such as cell polarity, contact inhibition, soluble factors, mechanical forces, and metabolism can convey external stimuli to the intracellular kinase cascade, promoting the activation of key components of the Hippo pathway and therefore regulating the subcellular localisation and protein activity of YAP/TAZ. This review will summarise what we have learnt about the role of intercellular junction-associated proteins in the activation of this pathway, including adherens junctions and tight junctions, and in particular our latest findings about the desmosomal components, including desmoglein-3 (DSG3), in the regulation of YAP signalling, phosphorylation, and subcellular translocation.

Early developmental plasticity enables the induction of an intermediate extraembryonic cell state

Two fundamental elements of pre-implantation embryogenesis are cells' intrinsic self-organization program and their developmental plasticity, which allows embryos to compensate for alterations in cell position and number; yet, these elements are still poorly understood. To be able to decipher these features, we established culture conditions that enable the two fates of blastocysts' extraembryonic lineages-the primitive endoderm and the trophectoderm-to coexist. This plasticity emerges following the mechanisms of the first lineage segregation in the mouse embryo, and it manifests as an extended potential for extraembryonic chimerism during the pre-implantation embryogenesis. Moreover, this shared state enables robust assembly into higher-order blastocyst-like structures, thus combining both the cell fate plasticity and self-organization features of the early extraembryonic lineages.

FGF8 induces chemokinesis and regulates condensation of mouse nephron progenitor cells

Kidneys develop via iterative branching of the ureteric epithelial tree and subsequent nephrogenesis at the branch points. Nephrons form in the cap mesenchyme as the metanephric mesenchyme (MM) condenses around the epithelial ureteric buds (UBs). Previous work has demonstrated that FGF8 is important for the survival of nephron progenitor cells (NPCs), and early deletion of Fgf8 leads to the cessation of nephron formation, which results in post-natal lethality. We now reveal a previously unreported function of FGF8. By combining transgenic mouse models, quantitative imaging assays and data-driven computational modelling, we show that FGF8 has a strong chemokinetic effect and that this chemokinetic effect is important for the condensation of NPCs to the UB. The computational model shows that the motility must be lower close to the UB to achieve NPC attachment. We conclude that the FGF8 signalling pathway is crucial for the coordination of NPC condensation at the UB. Chemokinetic effects have also been described for other FGFs and may be generally important for the formation of mesenchymal condensates.

MitoQ alleviates carbon tetrachloride-induced liver fibrosis in mice through regulating JNK/YAP pathway

Background

Liver fibrosis is a pathological wound-healing response caused by chronic liver damage. Mitochondria regulate hepatic energy metabolism and oxidative stress. Accumulating evidence has revealed that increased mitochondrial oxidative stress contributes to the activation of fibrogenesis. However, the roles and underlying mechanisms of mitochondrial oxidative stress in liver fibrosis remain unknown.

Methods and results

In this study, C57BL/6 mice were used to establish a model of liver fibrosis via oral gavage with CCl4 treatment for 8 weeks. Furthermore, intervention experiments were achieved by CCl4 combined with the intraperitoneal injection of mitoquinone mesylate (mitoQ). We demonstrated that the chronic CCl4 exposure resulted in severe hepatic fibrogenesis and significantly promoted the production of reactive oxygen species (ROS) and mitochondrial abnormalities. Besides, JNK/YAP pathway was also activated. By contrast, the administration of mitoQ markedly inhibited the expression of pro-fibrogenic transforming growth factor-β as well as type I collagen. The antifibrotic effects of mitoQ were also confirmed by hematoxylin and eosin staining and Sirius red staining. Moreover, mitoQ substantially reduced CCl4-induced mitochondrial damage and the release of ROS. Further studies suggested that this protection against liver fibrosis was mechanistically related to the inhibition of phosphorylation of JNK and the nuclear translocation of YAP.

Conclusion

In conclusion, these findings revealed that mitoQ attenuated liver fibrosis by inhibiting ROS production and the JNK/YAP signaling pathway. Selective targeting JNK/YAP may serve as a therapeutic strategy for retarding progression of chronic liver disease.

A Stk4-Foxp3-NF-κB p65 transcriptional complex promotes Treg cell activation and homeostasis

The molecular programs involved in regulatory T (T_reg) cell activation and homeostasis remain incompletely understood. Here, we show that T cell receptor (TCR) signaling in T_reg cells induces the nuclear translocation of serine/threonine kinase 4 (Stk4), leading to the formation of an Stk4-NF-κB p65-Foxp3 complex that regulates Foxp3- and p65-dependent transcriptional programs. This complex was stabilized by Stk4-dependent phosphorylation of Foxp3 on serine-418. Stk4 deficiency in T_reg cells, either alone or in combination with its homolog Stk3, precipitated a fatal autoimmune lymphoproliferative disease in mice characterized by decreased T_reg cell p65 expression and nuclear translocation, impaired NF-κB p65-Foxp3 complex formation, and defective T_reg cell activation. In an adoptive immunotherapy model, overexpression of p65 or the phosphomimetic Foxp3^S418E in Stk3/4-deficient T_reg cells ameliorated their immune regulatory defects. Our studies identify Stk4 as an essential TCR-responsive regulator of p65-Foxp3-dependent transcription that promotes T_reg cell-mediated immune tolerance.

Disruption of adipocyte YAP improves glucose homeostasis in mice and decreases adipose tissue fibrosis

OBJECTIVE

Adipose tissue is a very dynamic metabolic organ that plays an essential role in regulating whole-body glucose homeostasis. Dysfunctional adipose tissue hypertrophy with obesity is associated with fibrosis and type 2 diabetes. Yes-associated protein 1 (YAP) is a transcription cofactor important in the Hippo signaling pathway. However, the role of YAP in adipose tissue and glucose homeostasis is unknown.

METHODS

To study the role of YAP with metabolic stress, we assessed how increased weight and insulin resistance impact YAP in humans and mouse models. To further investigate the in vivo role of YAP specifically in adipose tissue and glucose homeostasis, we developed adipose tissue-specific YAP knockout mice and placed them on either chow or high fat diet (HFD) for 12-14 weeks. To further study the direct role of YAP in adipocytes we used 3T3-L1 cells.

RESULTS

We found that YAP protein levels increase in adipose tissue from humans with type 2 diabetes and mouse models of diet-induced obesity and insulin resistance. This suggests that YAP signaling may contribute to adipocyte dysfunction and insulin resistance under metabolic stress conditions. On an HFD, adipose tissue YAP knockout mice had improved glucose tolerance compared to littermate controls. Perigonadal fat pad weight was also decreased in knockout animals, with smaller adipocyte size. Adipose tissue fibrosis and gene expression associated with fibrosis was decreased in vivo and in vitro in 3T3-L1 cells treated with a YAP inhibitor or siRNA.

CONCLUSIONS

We show that YAP is increased in adipose tissue with weight gain and insulin resistance. Disruption of YAP in adipocytes prevents glucose intolerance and adipose tissue fibrosis, suggesting that YAP plays an important role in regulating adipose tissue and glucose homeostasis with metabolic stress.

Transcription Factors YAP/TAZ and SRF Cooperate To Specify Renal Myofibroblasts in the Developing Mouse Kidney

BACKGROUND

The embryonic renal stroma consists of multiple molecularly distinct cell subpopulations, the functional significance of which is largely unknown. Previous work has demonstrated that the transcription factors YAP and TAZ play roles in the development and morphogenesis of the nephrons, collecting ducts, and nephron progenitor cells.

METHODS

In embryonic mouse kidneys, we identified a subpopulation of stromal cells with enriched activity in YAP and TAZ. To evaluate the function of these cell types, we genetically ablated both Yap and Taz from the stromal progenitor population and examined how gene activity and development of YAP/TAZ mutant kidneys are affected over a developmental time course.

RESULTS

We found that YAP and TAZ are active in a subset of renal interstitium and that stromal-specific coablation of YAP/TAZ disrupts cortical fibroblast, pericyte, and myofibroblast development, with secondary effects on peritubular capillary differentiation. We also demonstrated that the transcription factor SRF cooperates with YAP/TAZ to drive expression of at least a subset of renal myofibroblast target genes and to specify myofibroblasts but not cortical fibroblasts or pericytes.

CONCLUSIONS

These findings reveal a critical role for YAP/TAZ in specific embryonic stromal cells and suggest that interaction with cofactors, such as SRF, influence the expression of cell type-specific target genes, thus driving stromal heterogeneity. Further, this work reveals functional roles for renal stroma heterogeneity in creating unique microenvironments that influence the differentiation and maintenance of the renal parenchyma.

Expression of Key Factors of the Hippo Signaling Pathway in Yak (Bos grunniens) Mammary Gland

Simple Summary

The Hippo signaling pathway plays a significant role in regulating the organ development processes of mammals. Our research aimed to investigate the expression and distribution of key members of the Hippo signaling pathway in yak mammary glands during different stages. Using immunohistochemistry, Western blot, and relative quantitative real-time polymerase chain reaction techniques, we found that the protein and mRNA expression levels of MST1, LATS1, YAP1 and TEAD1 in the yak’s mammary gland varies with the growth, lactation, and dry periods. The differential expression in the yak’s mammary gland at different stages strongly suggests that the Hippo signaling pathway plays an important role in regulating the mammary gland development processes under different physiological conditions.

Abstract

Due to its rich nutritional value, yak milk is an important food source in the alpine pastoral areas. However, yaks have a low milk yield. The Hippo pathway participates in cell proliferation and organ development. We aimed to determine the regulatory mechanism of this pathway in yak mammary cells. A greater understanding of how the expression of its essential genes influence the reproductive cycle could lead to improvements in lactation performance. The expression levels of the key genes MST1, LATS1, YAP1, and TEAD1 were detected by quantitative real-time PCR, Western blotting, and immunohistochemistry during the growth, lactation, and dry periods (GP, LP and DP, respectively). The MST1 and LATS1 mRNA and protein expression level was highest during GP and lowest during LP. The YAP1 and TEAD1 mRNA and protein expression level decreased from GP to LP and DP. MST1 and LATS1 were expressed in the cytoplasm whereas YAP1 and TEAD1 were expressed in the nucleus and cytoplasm, respectively. The differential expression of MST1, LATS1, YAP1, and TEAD1 expression in the yak mammary gland during different developmental stages strongly suggests that they play an important role in the regulation of developmental functions under different physiological conditions.

TAZ is important for maintenance of the integrity of podocytes

The podocyte is an important component of the glomerular filtration barrier, and maintenance of the integrity of its highly specified structure and function is critical for normal kidney function. Yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ) are two crucial effectors of the Hippo signaling pathway, and recent studies have shown that podocyte-specific YAP deletion causes podocyte apoptosis and the development of focal segmental glomerulosclerosis followed by progressive renal failure. In the present study, we investigated a potential role of the YAP paralog TAZ in podocytes. TAZ was found to be constitutively active in podocytes, and mice with podocyte-specific deletion of TAZ (TazpodKO) developed proteinuria starting at 4 wk of age and had increased podocyte apoptosis. Using primary cultured podocytes or immortalized mouse podocytes from Tazflox/flox mice, we found that TAZ is a transcriptional activator for TEAD-dependent expression of synaptopodin, zonula occludens-1, and zonula occludens-2. This is the first study to determine that TAZ plays an important role in the maintenance of the structure and function of podocytes.NEW & NOTEWORTHY Podocytes play an important role in maintaining the integrity of the structure and function of the kidney. We observed that mice with selective deletion of transcriptional coactivator with PDZ-binding motif (TAZ) in podocytes developed proteinuria. TAZ is constitutively active and critical for expression of synaptopodin, zonula occludens-1, and zonula occludens-2 in podocytes. The findings of this study implicate TAZ as an important mediator of podocyte structural integrity and provide further insights into the role of Hippo-Yes-associated protein/TAZ in podocyte biology.

YAP and TAZ in Vascular Smooth Muscle Confer Protection Against Hypertensive Vasculopathy

BACKGROUND

Hypertension remains a major risk factor for cardiovascular diseases, but the underlying mechanisms are not well understood. We hypothesize that appropriate mechanotransduction and contractile function in vascular smooth muscle cells are crucial to maintain vascular wall integrity. The Hippo pathway effectors YAP (yes-associated protein 1) and TAZ (WW domain containing transcription regulator 1) have been identified as mechanosensitive transcriptional coactivators. However, their role in vascular smooth muscle cell mechanotransduction has not been investigated in vivo.

METHODS

We performed physiological and molecular analyses utilizing an inducible smooth muscle-specific YAP/TAZ knockout mouse model.

RESULTS

Arteries lacking YAP/TAZ have reduced agonist-mediated contraction, decreased myogenic response, and attenuated stretch-induced transcriptional regulation of smooth muscle markers. Moreover, in established hypertension, YAP/TAZ knockout results in severe vascular lesions in small mesenteric arteries characterized by neointimal hyperplasia, elastin degradation, and adventitial thickening.

CONCLUSIONS

This study demonstrates a protective role of YAP/TAZ against hypertensive vasculopathy.

NUAK1 promotes organ fibrosis via YAP and TGF-β/SMAD signaling

Fibrosis is a central pathway that drives progression of multiple chronic diseases, yet few safe and effective clinical antifibrotic therapies exist. In most fibrotic disorders, transforming growth factor-β (TGF-β)-driven scarring is an important pathologic feature and a key contributor to disease progression. Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are two closely related transcription cofactors that are important for coordinating fibrogenesis after organ injury, but how they are activated in response to tissue injury has, so far, remained unclear. Here, we describe NUAK family kinase 1 (NUAK1) as a TGF-β-inducible profibrotic kinase that is up-regulated in multiple fibrotic organs in mice and humans. Mechanistically, we show that TGF-β induces a rapid increase in NUAK1 in fibroblasts. NUAK1, in turn, can promote profibrotic YAP and TGF-β/SMAD signaling, ultimately leading to organ scarring. Moreover, activated YAP and TAZ can induce further NUAK1 expression, creating a profibrotic positive feedback loop that enables persistent fibrosis. Using mouse models of kidney, lung, and liver fibrosis, we demonstrate that this fibrogenic signaling loop can be interrupted via fibroblast-specific loss of NUAK1 expression, leading to marked attenuation of fibrosis. Pharmacologic NUAK1 inhibition also reduced scarring, either when initiated immediately after injury or when initiated after fibrosis was already established. Together, our data suggest that NUAK1 plays a critical, previously unrecognized role in fibrogenesis and represents an attractive target for strategies that aim to slow fibrotic disease progression.

Integrating mechanical signals into cellular identity

The large arrays of cell types in a multicellular organism are defined by their stereotypic size and/or morphology, and, for cells in vivo, by their anatomic positions. Historically, this identity-structure-function correlation was conceptualized as arising from distinct gene expression programs that dictate how cells appear and behave. However, a growing number of studies suggest that a cell's mechanical state is also an important determinant of its identity, both in lineage-committed cells and in pluripotent stem cells. Defining the mechanism by which mechanical inputs influence complex cellular programs remains an area of ongoing investigation. Here, we discuss how the cytoskeleton actively participates in instructing the response of the nucleus and genome to integrate mechanical and biochemical inputs, with a primary focus on the role of the actomyosin-LINC (linker of nucleoskeleton and cytoskeleton) complex axis.

The Hippo Pathway Effectors YAP/TAZ Are Essential for Mineralized Tissue Homeostasis in the Alveolar Bone/Periodontal Complex

YAP and TAZ are essential transcriptional co-activators and downstream effectors of the Hippo pathway, regulating cell proliferation, organ growth, and tissue homeostasis. To ask how the Hippo pathway affects mineralized tissue homeostasis in a tissue that is highly reliant on a tight homeostatic control of mineralized deposition and resorption, we determined the effects of YAP/TAZ dysregulation on the periodontal tissues alveolar bone, root cementum, and periodontal ligament. Loss of YAP/TAZ was associated with a reduction of mineralized tissue density in cellular cementum and alveolar bone, a downregulation in collagen I, alkaline phosphatase, and RUNX2 gene expression, an increase in the resorption markers TRAP and cathepsin K, and elevated numbers of TRAP-stained osteoclasts. Cyclic strain applied to periodontal ligament cells resulted in YAP nuclear localization, an effect that was abolished after blocking YAP. The rescue of YAP signaling with the heparan sulfate proteoglycan agrin resulted in a return of the nuclear YAP signal. Illustrating the key role of YAP on mineralization gene expression, the YAP inhibition-related downregulation of mineralization-associated genes was reversed by the extracellular matrix YAP activator agrin. Application of the unopposed mouse molar model to transform the periodontal ligament into an unloaded state and facilitate the distal drift of teeth resulted in an overall increase in mineralization-associated gene expression, an effect that was 10–20% diminished in Wnt1Cre/YAP/TAZ mutant mice. The unloaded state of the unopposed molar model in Wnt1Cre/YAP/TAZ mutant mice also caused a significant three-fold increase in osteoclast numbers, a substantial increase in bone/cementum resorption, pronounced periodontal ligament hyalinization, and thickened periodontal fiber bundles. Together, these data demonstrated that YAP/TAZ signaling is essential for the microarchitectural integrity of the periodontium by regulating mineralization gene expression and preventing excessive resorption during bodily movement of the dentoalveolar complex.

Myofibroblast YAP/TAZ activation is a key step in organ fibrogenesis

Fibrotic diseases account for nearly half of all deaths in the developed world. Despite its importance, the pathogenesis of fibrosis remains poorly understood. Recently, the two mechanosensitive transcription cofactors YAP and TAZ have emerged as important profibrotic regulators in multiple murine tissues. Despite this growing recognition, a number of important questions remain unanswered, including which cell types require YAP/TAZ activation for fibrosis to occur and the time course of this activation. Here, we present a detailed analysis of the role that myofibroblast YAP and TAZ play in organ fibrosis and the kinetics of their activation. Using analyses of cells, as well as multiple murine and human tissues, we demonstrated that myofibroblast YAP and TAZ were activated early after organ injury and that this activation was sustained. We further demonstrated the critical importance of myofibroblast YAP/TAZ in driving progressive scarring in the kidney, lung, and liver, using multiple transgenic models in which YAP and TAZ were either deleted or hyperactivated. Taken together, these data establish the importance of early injury-induced myofibroblast YAP and TAZ activation as a key event driving fibrosis in multiple organs. This information should help guide the development of new antifibrotic YAP/TAZ inhibition strategies.

Impact of Pals1 on Expression and Localization of Transporters Belonging to the Solute Carrier Family

Pals1 is part of the evolutionary conserved Crumbs polarity complex and plays a key role in two processes, the formation of apicobasal polarity and the establishment of cell-cell contacts. In the human kidney, up to 1.5 million nephrons control blood filtration, as well as resorption and recycling of inorganic and organic ions, sugars, amino acids, peptides, vitamins, water and further metabolites of endogenous and exogenous origin. All nephron segments consist of polarized cells and express high levels of Pals1. Mice that are functionally haploid for Pals1 develop a lethal phenotype, accompanied by heavy proteinuria and the formation of renal cysts. However, on a cellular level, it is still unclear if reduced cell polarization, incomplete cell-cell contact formation, or an altered Pals1-dependent gene expression accounts for the renal phenotype. To address this, we analyzed the transcriptomes of Pals1-haploinsufficient kidneys and the littermate controls by gene set enrichment analysis. Our data elucidated a direct correlation between TGFβ pathway activation and the downregulation of more than 100 members of the solute carrier (SLC) gene family. Surprisingly, Pals1-depleted nephrons keep the SLC’s segment-specific expression and subcellular distribution, demonstrating that the phenotype is not mainly due to dysfunctional apicobasal cell polarization of renal epithelia. Our data may provide first hints that SLCs may act as modulating factors for renal cyst formation.

Therapeutic Low-Intensity Ultrasound for Peripheral Nerve Regeneration – A Schwann Cell Perspective

Peripheral nerve injuries are common conditions that can arise from trauma (e.g., compression, severance) and can lead to neuropathic pain as well as motor and sensory deficits. Although much knowledge exists on the mechanisms of injury and nerve regeneration, treatments that ensure functional recovery following peripheral nerve injury are limited. Schwann cells, the supporting glial cells in peripheral nerves, orchestrate the response to nerve injury, by converting to a “repair” phenotype. However, nerve regeneration is often suboptimal in humans as the repair Schwann cells do not sustain their repair phenotype long enough to support the prolonged regeneration times required for successful nerve regrowth. Thus, numerous strategies are currently focused on promoting and extending the Schwann cells repair phenotype. Low-intensity ultrasound (LIU) is a non-destructive therapeutic approach which has been shown to facilitate peripheral nerve regeneration following nerve injury in rodents. Still, clinical trials in humans are scarce and limited to small population sizes. The benefit of LIU on nerve regeneration could possibly be mediated through the repair Schwann cells. In this review, we discuss the known and possible molecular mechanisms activated in response to LIU in repair Schwann cells to draw support and attention to LIU as a compelling regenerative treatment for peripheral nerve injury.

Rho GTPases in kidney physiology and diseases

Rho family GTPases are molecular switches best known for their pivotal role in dynamic regulation of the actin cytoskeleton, but also of cellular morphology, motility, adhesion and proliferation. The prototypic members of this family (RhoA, Rac1 and Cdc42) also contribute to the normal kidney function and play important roles in the structure and function of various kidney cells including tubular epithelial cells, mesangial cells and podocytes. The kidney's vital filtration function depends on the structural integrity of the glomerulus, the proximal portion of the nephron. Within the glomerulus, the architecturally actin-based cytoskeleton podocyte forms the final cellular barrier to filtration. The glomerulus appears as a highly dynamic signalling hub that is capable of integrating intracellular cues from its individual structural components. Dynamic regulation of the podocyte cytoskeleton is required for efficient barrier function of the kidney. As master regulators of actin cytoskeletal dynamics, Rho GTPases are therefore of critical importance for sustained kidney barrier function. Dysregulated activities of the Rho GTPases and of their effectors are implicated in the pathogenesis of both hereditary and idiopathic forms of kidney diseases. Diabetic nephropathy is a progressive kidney disease that is caused by injury to kidney glomeruli. High glucose activates RhoA/Rho-kinase in mesangial cells, leading to excessive extracellular matrix production (glomerulosclerosis). This RhoA/Rho-kinase pathway also seems involved in the post-transplant hypertension frequently observed during treatment with calcineurin inhibitors, whereas Rac1 activation was observed in post-transplant ischaemic acute kidney injury.

Nephronophthisis-Pathobiology and Molecular Pathogenesis of a Rare Kidney Genetic Disease

The exponential rise in our understanding of the aetiology and pathophysiology of genetic cystic kidney diseases can be attributed to the identification of cystogenic genes over the last three decades. The foundation of this was laid by positional cloning strategies which gradually shifted towards next-generation sequencing (NGS) based screenings. This shift has enabled the discovery of novel cystogenic genes at an accelerated pace unlike ever before and, most notably, the past decade has seen the largest increase in identification of the genes which cause nephronophthisis (NPHP). NPHP is a monogenic autosomal recessive cystic kidney disease caused by mutations in a diverse clade of over 26 identified genes and is the most common genetic cause of renal failure in children. NPHP gene types present with some common pathophysiological features alongside a diverse range of extra-renal phenotypes associated with specific syndromic presentations. This review provides a timely update on our knowledge of this disease, including epidemiology, pathophysiology, anatomical and molecular features. We delve into the diversity of the NPHP causing genes and discuss known molecular mechanisms and biochemical pathways that may have possible points of intersection with polycystic kidney disease (the most studied renal cystic pathology). We delineate the pathologies arising from extra-renal complications and co-morbidities and their impact on quality of life. Finally, we discuss the current diagnostic and therapeutic modalities available for disease management, outlining possible avenues of research to improve the prognosis for NPHP patients.

Novel zebrafish polycystic kidney disease models reveal functions of the Hippo pathway in renal cystogenesis

The Hippo signaling pathway is a kinase cascade that plays an important role in organ size control. As the main effectors of the Hippo pathway, transcription coactivators Yap1/Wwtr1 are regulated by the upstream kinase Stk3. Recent studies in mammals have implicated the Hippo pathway in kidney development and kidney diseases. To further illustrate its roles in vertebrate kidney, we generated a series of zebrafish mutants targeting stk3, yap1 and wwtr1 genes. The stk3^−/− mutant exhibited edema, formation of glomerular cysts and pronephric tubule dilation during the larval stage. Interestingly, disruption of wwtr1, but not yap1, significantly alleviated the renal phenotypes of the stk3^−/− mutant, and overexpression of Wwtr1 with the CMV promoter also induced pronephric phenotypes, similar to those of the stk3^−/− mutant, during larval stage. Notably, adult fish with Wwtr1 overexpression developed phenotypes similar to those of human polycystic kidney disease (PKD). Overall, our analyses revealed roles of Stk3 and Wwtr1 in renal cyst formation. Using a pharmacological approach, we further demonstrated that Stk3-deficient zebrafish could serve as a PKD model for drug development.

Summary: A zebrafish stk3 mutant line and Wwtr1 overexpression line provide evidence for functions of the Hippo signaling pathway in renal cyst formation and represent potential models for polycystic kidney disease.

YAP establishes epiblast responsiveness to inductive signals for germ cell fate

The germ cell lineage in mammals is induced by the stimulation of pluripotent epiblast cells by signaling molecules. Previous studies have suggested that the germ cell differentiation competence or responsiveness of epiblast cells to signaling molecules is established and maintained in epiblast cells of a specific differentiation state. However, the molecular mechanism underlying this process has not been well defined. Here, using the differentiation model of mouse epiblast stem cells (EpiSCs), we have shown that two defined EpiSC lines have robust germ cell differentiation competence. However, another defined EpiSC line has no competence. By evaluating the molecular basis of EpiSCs with distinct germ cell differentiation competence, we identified YAP, an intracellular mediator of the Hippo signaling pathway, as crucial for the establishment of germ cell induction. Strikingly, deletion of YAP severely affected responsiveness to inductive stimuli, leading to a defect in WNT target activation and germ cell differentiation. In conclusion, we propose that the Hippo/YAP signaling pathway creates a potential for germ cell fate induction via mesodermal WNT signaling in pluripotent epiblast cells.

Summary: YAP, an intracellular mediator of the Hippo signaling pathway, establishes epiblast competency for germ cell differentiation through activation of the WNT pathway.