Development of an improved inhibitor of Lats kinases to promote regeneration of mammalian organs

Comparing Molecules Generated by MMPDB and REINVENT4 with Ideas from Drug Discovery Design Teams

This study compares molecules designed by drug discovery project teams from the Sanders Tri-Institutional Therapeutics Discovery Institute with molecules generated by two computational tools: MMPDB and REINVENT4. Seven different test cases with diverse chemotypes are studied in order to explore the potential of these computational tools in complementing human expertise in the early stages of drug discovery. By comparing the molecular structures and properties generated by MMPDB and REINVENT4 to those designed by project design teams, we aim to assess the value of such tools. The results indicate that MMPDB and REINVENT4 cover regions of chemical space larger than those covered by ideas from the drug discovery project teams. However, the chemical spaces covered by the two methods are quite different, and neither method completely covers the chemical space identified by the drug discovery project teams. Thus, the computational methods are complementary to one another and to drug discovery project team ideation. Effective application of generative molecule design tools has the potential to accelerate the identification of novel therapeutic candidates by expanding the chemical space explored during drug discovery and enabling optimal exploration.

Disrupting bile acid metabolism by suppressing Fxr causes hepatocellular carcinoma induced by YAP activation

Disruption of bile acid (BA) metabolism causes various liver diseases including hepatocellular carcinoma (HCC). However, the underlying molecular mechanism remains elusive. Here, we report that BA metabolism is directly controlled by a repressor function of YAP, which induces cholestasis by altering BA levels and composition via inhibiting the transcription activity of Fxr, a key physiological BA sensor. Elevated BA levels further activate hepatic YAP, resulting in a feedforward cycle leading to HCC. Mechanistically, Teads are found to bind Fxr in a DNA-binding-independent manner and recruit YAP to epigenetically suppress Fxr. Promoting BA excretion, or alleviating YAP repressor function by pharmacologically activating Fxr and inhibiting HDAC1, or overexpressing an Fxr target gene Bsep to promote BA exportation, alleviate cholestasis and HCC caused by YAP activation. Our results identify YAP's transcriptional repressor role in BA metabolism as a key driver of HCC and suggest its potential as a therapeutic target.

The Hippo pathway and p27Kip1 cooperate to suppress mitotic regeneration in the organ of Corti and the retina

The mature mammalian auditory sensory organ, the organ of Corti (OC), lacks the capacity for regenerating hair cells, leading to permanent hearing impairment. In contrast, the vestibular system has a limited capacity for hair cell regeneration, which we have shown to be further enhanced by inhibiting the Hippo pathway. Here, we demonstrate that, despite similar transcriptional responses, only vestibular and not auditory supporting cells proliferate as a result of Yap activation following Hippo inhibition. Mechanistically, we identify p27Kip1, a cell cycle kinase inhibitor encoded by Cdkn1b, as an additional barrier preventing cell cycle reentry specifically in the OC. We show that while in both systems Yap stimulates p27Kip1 degradation through activation of its direct target gene Skp2, this protein-level control is antagonized by an unusually high level of Cdkn1b transcription in the cochlea. Consequently, p27Kip1 activity is maintained in the OC even in the presence of constitutively active Yap5SA, counteracting its mitogenic effects. Supporting this model, inactivation of the Hippo pathway in the Cdkn1b-deficient background is sufficient to induce adult auditory supporting cell proliferation in vivo. Furthermore, we show that the synergistic interaction between Hippo and p27Kip1 is conserved in the retina where inhibition of both pathways potently induces Müller glia proliferation and initiates neuronal regeneration. Our work uncovers the molecular mechanism preventing quiescent adult sensory progenitor cells, supporting cells in the ear and Müller glia in the eye, from reentering the cell cycle after damage-the key step toward sensory receptor regeneration blocked in mammals.

Pharmacological regulators of Hippo pathway: Advances and challenges of drug development

The Hippo signaling pathway is crucial in regulating organ size, tumor progression, tissue regeneration, and bone homeostasis. Inactivation of the Hippo pathway results in the nuclear translocation and activation of YAP/TAZ. This activation not only promotes tumor progression but also enhances tissue regeneration, wound healing, and maintenance of bone stability Although its discovery occurred over two decades ago, developing effective inhibitors or activators for the Hippo pathway remains challenging. Recently, however, the pace of advancements in developing Hippo signaling-related agonists and antagonists has accelerated, with some drugs that target TEAD advancing to clinical trials and showing promise for treating related diseases. This review summarizes the progress in research on Hippo signaling-related agonists and inhibitors, offering an in-depth analysis of their regulatory mechanisms, pharmacological properties, and potential in vivo applications.

LATS1-modulated ZBTB20 perturbing cartilage matrix homeostasis contributes to early-stage osteoarthritis

Osteoarthritis (OA) is one of the most common degenerative joint diseases in the elderly, increasing in prevalence and posing a substantial socioeconomic challenge, while no disease-modifying treatments available. Better understanding of the early molecular events will benefit the early-stage diagnosis and clinical therapy. Here, we observed the nucleus accumulation of ZBTB20, a member of ZBTB-protein family, in the chondrocytes of early-stage OA. Chondrocytes-specific depletion of Zbtb20 in adult mice attenuated DMM-induced OA progress, restored the balance of extracellular matrix anabolism and catabolism. The NF-κB signaling mediated disturbance of ECM maintenance by ZBTB20 requires its suppression of Pten and consequent PI3K-Akt signaling activation. Furthermore, the subcellular localization of ZBTB20 was modulated by the kinase LATS1. Independent approaches to modulating ZBTB20 via utilizing TRULI and DAPA can restore ECM homeostasis, improving the abnormal behavior and moderating cartilage degeneration. The compounds TRULI and DAPA modulating ZBTB20 may serve as anti-OA drugs.

The Hippo pathway: Organ size control and beyond

The Hippo signaling pathway is a highly conserved signaling network for controlling organ size, tissue homeostasis, and regeneration. It integrates a wide range of intracellular and extracellular signals, such as cellular energy status, cell density, hormonal signals, and mechanical cues, to modulate the activity of YAP/TAZ transcriptional coactivators. A key aspect of Hippo pathway regulation involves its spatial organization at the plasma membrane, where upstream regulators localize to specific membrane subdomains to regulate the assembly and activation of the pathway components. This spatial organization is critical for the precise control of Hippo signaling, as it dictates the dynamic interactions between pathway components and their regulators. Recent studies have also uncovered the role of biomolecular condensation in regulating Hippo signaling, adding complexity to its control mechanisms. Dysregulation of the Hippo pathway is implicated in various pathological conditions, particularly cancer, where alterations in YAP/TAZ activity contribute to tumorigenesis and drug resistance. Therapeutic strategies targeting the Hippo pathway have shown promise in both cancer treatment, by inhibiting YAP/TAZ signaling, and regenerative medicine, by enhancing YAP/TAZ activity to promote tissue repair. The development of small molecule inhibitors targeting the YAP-TEAD interaction and other upstream regulators offers new avenues for therapeutic intervention. SIGNIFICANCE STATEMENT: The Hippo signaling pathway is a key regulator of organ size, tissue homeostasis, and regeneration, with its dysregulation linked to diseases such as cancer. Understanding this pathway opens new possibilities for therapeutic approaches in regenerative medicine and oncology, with the potential to translate basic research into improved clinical outcomes.

Decoding the Impact of the Hippo Pathway on Different Cell Types in Heart Failure

The evolutionarily conserved Hippo pathway plays a pivotal role in governing a variety of biological processes. Heart failure (HF) is a major global health problem with a significant risk of mortality. This review provides a contemporary understanding of the Hippo pathway in regulating different cell types during HF. Through a systematic analysis of each component's regulatory mechanisms within the Hippo pathway, we elucidate their specific effects on cardiomyocytes, fibroblasts, endothelial cells, and macrophages in response to various cardiac injuries. Insights gleaned from both in vitro and in vivo studies highlight the therapeutic promise of targeting the Hippo pathway to address cardiovascular diseases, particularly HF.

Model construction and clinical therapeutic potential of engineered cardiac organoids for cardiovascular diseases

Cardiovascular diseases cause significant morbidity and mortality worldwide. Engineered cardiac organoids are being developed and used to replicate cardiac tissues supporting cardiac morphogenesis and development. These organoids have applications in drug screening, cardiac disease models and regenerative medicine. Therefore, a thorough understanding of cardiac organoids and a comprehensive overview of their development are essential for cardiac tissue engineering. This review summarises different types of cardiac organoids used to explore cardiac function, including those based on co-culture, aggregation, scaffolds, and geometries. The self-assembly of monolayers, multilayers and aggravated cardiomyocytes forms biofunctional cell aggregates in cardiac organoids, elucidating the formation mechanism of scaffold-free cardiac organoids. In contrast, scaffolds such as decellularised extracellular matrices, three-dimensional hydrogels and bioprinting techniques provide a supportive framework for cardiac organoids, playing a crucial role in cardiac development. Different geometries are engineered to create cardiac organoids, facilitating the investigation of intrinsic communication between cardiac organoids and biomechanical pathways. Additionally, this review emphasises the relationship between cardiac organoids and the cardiac system, and evaluates their clinical applications. This review aims to provide valuable insights into the study of three-dimensional cardiac organoids and their clinical potential.

Transient proliferation by reversible YAP and mitogen-control of the cyclin D1/p27 ratio

Hippo-YAP signaling orchestrates epithelial tissue repair and is therefore an attractive target in regenerative medicine. Yet it is unresolved how YAP integrates with mitogen signaling and contact inhibition to control the underlying transient proliferative response. Here we show that reduced contact inhibition, increased mitogen signaling, and YAP-TEAD activation converge on increasing the nuclear cyclin D1/p27 protein ratio during G1 phase, towards a threshold ratio that dictates whether individual cells enter or exit the cell cycle. YAP increases this ratio indirectly, in concert with mitogen signaling, by increasing EGFR and other receptors that signal primarily through ERK. After a delay, contact inhibition suppresses YAP activity which gradually downregulates mitogen signaling and the cyclin D1/p27 ratio. Increasing YAP activity by ablating the suppressor Merlin/NF2 reveals a balancing mechanism in which YAP suppression and contact inhibition of proliferation can be recovered but only at higher local cell density. Thus, critical for tissue repair, robust proliferation responses result from the YAP-induced and receptor-mediated prolonged increase in the cyclin D1/p27 ratio, which is only reversed by delayed suppression of receptor signaling after contact inhibition of YAP.

Liver mechanosignaling as a natural anti-hepatitis B virus mechanism

The mechanisms underlying the natural control of hepatitis B virus (HBV) infection have long been an intriguing question. Given the wide physiological range of liver stiffness and the growing attention to the role of mechanical microenvironment in homeostasis and diseases, we investigated how physical matrix cues impact HBV replication. High matrix stiffness significantly inhibited HBV replication and activated YAP in primary hepatocyte culture system, a key molecule in mechanosignaling. YAP activation notably suppressed HBV transcription and antigen expression. Several YAP-induced genes exhibited strong anti-HBV effects. Single-cell analysis of liver tissue from male individuals with active HBV replication revealed a strong significant negative correlation between YAP signature activation and HBV transcript levels. Intraperitoneal administration of YAP small molecule agonist potently controls HBV in male mouse models. These findings unveil a mechanism that involves the mechanical environment of hepatocytes and YAP to clear hepatotropic viral infection in the liver, providing new perspectives for HBV cure studies and antiviral development.

Discovery of selective LATS inhibitors via scaffold hopping: enhancing drug-likeness and kinase selectivity for potential applications in regenerative medicine

Due to its essential roles in cell proliferation and apoptosis, the precise regulation of the Hippo pathway through LATS presents a viable biological target for developing new drugs for cancer and regenerative diseases. However, currently available probes for selective and highly drug-like inhibition of LATS require further improvement in terms of both activity, selectivity and drug-like properties. Through scaffold hopping aided by docking studies and AI-assisted prediction of metabolic stabilities, we successfully identified an advanced LATS inhibitor demonstrating potent kinase activity, exceptional selectivity against other kinases, and superior oral pharmacokinetic profiles.

Amphiregulin orchestrates the paracrine immune-suppressive function of amniotic-derived cells through its interplay with COX-2/PGE2/EP4 axis

The paracrine crosstalk between amniotic-derived membranes (AMs)/epithelial cells (AECs) and immune cells is pivotal in tissue healing following inflammation. Despite evidence collected to date, gaps in understanding the underlying molecular mechanisms have hindered clinical applications. The present study represents a significant step forward demonstrating that amphiregulin (AREG) orchestrates the native immunomodulatory functions of amniotic derivatives via the COX-2/PGE2/EP4 axis. The results highlight the immunosuppressive efficacy of PGE2-dependent AREG release, dampening PBMCs' activation, and NFAT pathway in Jurkat reporter cells via TGF-β signaling. Moreover, AREG emerges as a key protein mediator by attenuating acute inflammatory response in Tg(lysC:DsRed2) zebrafish larvae. Notably, the interplay of diverse COX-2/PGE2 pathway activators enables AM/AEC to adapt rapidly to external stimuli (LPS and/or stretching) through a responsive positive feedback loop on the AREG/EGFR axis. These findings offer valuable insights for developing innovative cell-free therapies leveraging the potential of amniotic derivatives in immune-mediated diseases and regenerative medicine.

Hippo signaling pathway regulates Ebola virus transcription and egress

Filovirus-host interactions play important roles in all stages of the virus lifecycle. Here, we identify LATS1/2 kinases and YAP, key components of the Hippo pathway, as critical regulators of EBOV transcription and egress. Specifically, we find that when YAP is phosphorylated by LATS1/2, it localizes to the cytoplasm (Hippo "ON") where it sequesters VP40 to prevent egress. In contrast, when the Hippo pathway is "OFF", unphosphorylated YAP translocates to the nucleus where it transcriptionally activates host genes and promotes viral egress. Our data reveal that LATS2 indirectly modulates filoviral VP40-mediated egress through phosphorylation of AMOTp130, a positive regulator of viral egress, but more surprisingly that LATS1/2 kinases directly modulate EBOV transcription by phosphorylating VP30, an essential regulator of viral transcription. In sum, our findings highlight the potential to exploit the Hippo pathway/filovirus axis for the development of host-oriented countermeasures targeting EBOV and related filoviruses.

Exploring the effects of Hippo signaling pathway on rumen epithelial proliferation

BACKGROUND

The current understanding to the mechanism of rumen development is limited. We hypothesized that the Hippo signaling pathway controlled the proliferation of rumen epithelium (RE) during postnatal development. In the present study, we firstly tested the changes of the Hippo signaling pathway in the RE during an early growing period from d5 to d25, and then we expanded the time range to the whole preweaning period (d10-38) and one week post weaning (d45). An in vitro experiment was also carried out to verify the function of Hippo signaling pathway during RE cell proliferation.

RESULTS

In the RE of lambs from d5 to d25, the expression of baculoviral IAP repeat containing (BIRC3/5) was increased, while the expressions of large tumor suppressor kinase 2 (LATS2), TEA domain transcription factor 3 (TEAD3), axin 1 (AXIN1), and MYC proto-oncogene (MYC) were decreased with rumen growth. From d10 to d38, the RE expressions of BIRC3/5 were increased, while the expressions of LATS2 and MYC were decreased, which were similar with the changes in RE from d5 to d25. From d38 to d45, different changes were observed, with the expressions of LATS1/2, MOB kinase activator 1B (MOB1B), and TEAD1 increased, while the expressions of MST1 and BIRC5 decreased. Correlation analysis showed that during the preweaning period, the RE expressions of BIRC3/5 were positively correlated with rumen development variables, while LAST2 was negatively correlated with rumen development variables. The in vitro experiment validated the changes of LATS2 and BIRC3/5 in the proliferating RE cells, which supported their roles in RE proliferation during preweaning period.

CONCLUSIONS

Our results suggest that the LATS2-YAP1-BIRC3/5 axis participates in the RE cell proliferation and promotes rumen growth during the preweaning period.

Generation of human alveolar epithelial type I cells from pluripotent stem cells

Alveolar epithelial type I cells (AT1s) line the gas exchange barrier of the distal lung and have been historically challenging to isolate or maintain in cell culture. Here, we engineer a human in vitro AT1 model system via directed differentiation of induced pluripotent stem cells (iPSCs). We use primary adult AT1 global transcriptomes to suggest benchmarks and pathways, such as Hippo-LATS-YAP/TAZ signaling, enriched in these cells. Next, we generate iPSC-derived alveolar epithelial type II cells (AT2s) and find that nuclear YAP signaling is sufficient to promote a broad transcriptomic shift from AT2 to AT1 gene programs. The resulting cells express a molecular, morphologic, and functional phenotype reminiscent of human AT1 cells, including the capacity to form a flat epithelial barrier producing characteristic extracellular matrix molecules and secreted ligands. Our results provide an in vitro model of human alveolar epithelial differentiation and a potential source of human AT1s.

Molecular Pathways Governing the Termination of Liver Regeneration

The liver has the unique capacity to regenerate, and up to 70% of the liver can be removed without detrimental consequences to the organism. Liver regeneration is a complex process involving multiple signaling networks and organs. Liver regeneration proceeds through three phases: the initiation phase, the growth phase, and the termination phase. Termination of liver regeneration occurs when the liver reaches a liver-to-body weight that is required for homeostasis, the so-called "hepatostat." The initiation and growth phases have been the subject of many studies. The molecular pathways that govern the termination phase, however, remain to be fully elucidated. This review summarizes the pathways and molecules that signal the cessation of liver regrowth after partial hepatectomy and answers the question, "What factors drive the hepatostat?" SIGNIFICANCE STATEMENT: Unraveling the pathways underlying the cessation of liver regeneration enables the identification of druggable targets that will allow us to gain pharmacological control over liver regeneration. For these purposes, it would be useful to understand why the regenerative capacity of the liver is hampered under certain pathological circumstances so as to artificially modulate the regenerative processes (e.g., by blocking the cessation pathways) to improve clinical outcomes and safeguard the patient's life.

Single-cell analyses reveal transient retinal progenitor cells in the ciliary margin of developing human retina

The emergence of retinal progenitor cells and differentiation to various retinal cell types represent fundamental processes during retinal development. Herein, we provide a comprehensive single cell characterisation of transcriptional and chromatin accessibility changes that underline retinal progenitor cell specification and differentiation over the course of human retinal development up to midgestation. Our lineage trajectory data demonstrate the presence of early retinal progenitors, which transit to late, and further to transient neurogenic progenitors, that give rise to all the retinal neurons. Combining single cell RNA-Seq with spatial transcriptomics of early eye samples, we demonstrate the transient presence of early retinal progenitors in the ciliary margin zone with decreasing occurrence from 8 post-conception week of human development. In retinal progenitor cells, we identified a significant enrichment for transcriptional enhanced associate domain transcription factor binding motifs, which when inhibited led to loss of cycling progenitors and retinal identity in pluripotent stem cell derived organoids.

Cysteine and glycine-rich protein 2 retards platelet-derived growth factor-BB-evoked phenotypic transition of airway smooth muscle cells by decreasing YAP/TAZ activity

Cysteine and glycine-rich protein 2 (Csrp2) has emerged as a key factor in controlling the phenotypic modulation of smooth muscle cells. The phenotypic transition of airway smooth muscle cells (ASMCs) is a pivotal step in developing airway remodeling during the onset of asthma. However, whether Csrp2 mediates the phenotypic transition of ASMCs in airway remodeling during asthma onset is undetermined. This work aimed to address the link between Csrp2 and the phenotypic transition of ASMCs evoked by platelet-derived growth factor (PDGF)-BB in vitro. The overexpression or silencing of Csrp2 in ASMCs was achieved through adenovirus-mediated gene transfer. The expression of mRNA was measured by quantitative real-time-PCR. Protein levels were determined through Western blot analysis. Cell proliferation was detected by EdU assay and Calcein AM assays. Cell cycle distribution was assessed via fluorescence-activated cell sorting assay. Cell migration was evaluated using the scratch-wound assay. The transcriptional activity of Yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ) was measured using the luciferase reporter assay. A decline in Csrp2 level occurred in PDGF-BB-stimulated ASMCs. Increasing Csrp2 expression repressed the PDGF-BB-evoked proliferation and migration of ASMCs. Moreover, increasing Csrp2 expression impeded the phenotypic change of PDGF-BB-stimulated ASMCs from a contractile phenotype into a synthetic/proliferative phenotype. On the contrary, the opposite effects were observed in Csrp2-silenced ASMCs. The activity of YAP/TAZ was elevated in PDGF-BB-stimulated ASMCs, which was weakened by Csrp2 overexpression or enhanced by Csrp2 silencing. The YAP/TAZ activator could reverse Csrp2-overexpression-mediated suppression of the PDGF-BB-evoked phenotypic switching of ASMCs, while the YAP/TAZ suppressor could dimmish Csrp2-silencing-mediated enhancement on PDGF-BB-evoked phenotypic switching of ASMCs. In summary, Csrp2 serves as a determinant for the phenotypic switching of ASMCs. Increasing Csrp2 is able to impede PDGF-BB-evoked phenotypic change of ASMCs from a synthetic phenotype into a synthetic/proliferative phenotype through the effects on YAP/TAZ. This work implies that Csrp2 may be a key player in airway remodeling during the onset of asthma.

Obtaining High-Quality Cryosections of Whole Rabbit Eye

This protocol describes how to obtain high-quality retinal cryosections in larger animals, such as rabbits. After enucleation, the eye is briefly immersed in the fixative. Then, the cornea and iris are removed and the eye is left overnight for additional fixation at 4 °C. Following fixation, the lens is removed. The eye is then placed in a cryomold and filled with an embedding medium. By removing the lens, the embedding medium has better access to the vitreous and leads to better retinal stability. Importantly, the eye should be incubated in embedding medium overnight to allow complete infiltration throughout the vitreous. Following overnight incubation, the eye is frozen on dry ice and sectioned. Whole retinal sections may be obtained for use in immunohistochemistry. Standard staining protocols may be utilized to study the localization of antigens within the retinal tissue. Adherence to this protocol results in high-quality retinal cryosections that may be used in any experiment utilizing immunohistochemistry.

Recent advances in regulating the proliferation or maturation of human-induced pluripotent stem cell-derived cardiomyocytes

In the last decade, human-induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM)-based cell therapy has drawn broad attention as a potential therapy for treating injured hearts. However, mass production of hiPSC-CMs remains challenging, limiting their translational potential in regenerative medicine. Therefore, multiple strategies including cell cycle regulators, small molecules, co-culture systems, and epigenetic modifiers have been used to improve the proliferation of hiPSC-CMs. On the other hand, the immaturity of these proliferative hiPSC-CMs could lead to lethal arrhythmias due to their limited ability to functionally couple with resident cardiomyocytes. To achieve functional maturity, numerous methods such as prolonged culture, biochemical or biophysical stimulation, in vivo transplantation, and 3D culture approaches have been employed. In this review, we summarize recent approaches used to promote hiPSC-CM proliferation, and thoroughly review recent advances in promoting hiPSC-CM maturation, which will serve as the foundation for large-scale production of mature hiPSC-CMs for future clinical applications.

Genetic and epigenetic regulators of retinal Müller glial cell reprogramming

Background

Retinal diseases characterized with irreversible loss of retinal nerve cells, such as optic atrophy and retinal degeneration, are the main causes of blindness. Current treatments for these diseases are very limited. An emerging treatment strategy is to induce the reprogramming of Müller glial cells to generate new retinal nerve cells, which could potentially restore vision.

Main text

Müller glial cells are the predominant glial cells in retinae and play multiple roles to maintain retinal homeostasis. In lower vertebrates, such as in zebrafish, Müller glial cells can undergo cell reprogramming to regenerate new retinal neurons in response to various damage factors, while in mammals, this ability is limited. Interestingly, with proper treatments, Müller glial cells can display the potential for regeneration of retinal neurons in mammalian retinae. Recent studies have revealed that dozens of genetic and epigenetic regulators play a vital role in inducing the reprogramming of Müller glial cells in vivo. This review summarizes these critical regulators for Müller glial cell reprogramming and highlights their differences between zebrafish and mammals.

Conclusions

A number of factors have been identified as the important regulators in Müller glial cell reprogramming. The early response of Müller glial cells upon acute retinal injury, such as the regulation in the exit from quiescent state, the initiation of reactive gliosis, and the re-entry of cell cycle of Müller glial cells, displays significant difference between mouse and zebrafish, which may be mediated by the diverse regulation of Notch and TGFβ (transforming growth factor-β) isoforms and different chromatin accessibility.

MAP4Ks inhibition promotes retinal neuron regeneration from Müller glia in adult mice

Mammalian Müller glia (MG) possess limited regenerative capacities. However, the intrinsic capacity of mammalian MG to transdifferentiate to generate mature neurons without transgenic manipulations remains speculative. Here we show that MAP4K4, MAP4K6 and MAP4K7, which are conserved Misshapen subfamily of ste20 kinases homologs, repress YAP activity in mammalian MG and therefore restrict their ability to be reprogrammed. However, by treating with a small molecule inhibitor of MAP4K4/6/7, mouse MG regain their ability to proliferate and enter into a retinal progenitor cell (RPC)-like state after NMDA-induced retinal damage; such plasticity was lost in YAP knockout MG. Moreover, spontaneous trans-differentiation of MG into retinal neurons expressing both amacrine and retinal ganglion cell (RGC) markers occurs after inhibitor withdrawal. Taken together, these findings suggest that MAP4Ks block the reprogramming capacity of MG in a YAP-dependent manner in adult mammals, which provides a novel avenue for the pharmaceutical induction of retinal regeneration in vivo.

CCN-Hippo YAP signaling in vision and its role in neuronal, glial and vascular cell function and behavior

The retina is a highly specialized tissue composed of a network of neurons, glia, and vascular and epithelial cells; all working together to coordinate and transduce visual signals to the brain. The retinal extracellular matrix (ECM) shapes the structural environment in the retina but also supplies resident cells with proper chemical and mechanical signals to regulate cell function and behavior and maintain tissue homeostasis. As such, the ECM affects virtually all aspects of retina development, function and pathology. ECM-derived regulatory cues influence intracellular signaling and cell function. Reversibly, changes in intracellular signaling programs result in alteration of the ECM and downstream ECM-mediated signaling network. Our functional studies in vitro, genetic studies in mice, and multi omics analyses have provided evidence that a subset of ECM proteins referred to as cellular communication network (CCN) affects several aspects of retinal neuronal and vascular development and function. Retinal progenitor, glia and vascular cells are major sources of CCN proteins particularly CCN1 and CCN2. We found that expression of the CCN1 and CCN2 genes is dependent on the activity of YAP, the core component of the hippo-YAP signaling pathway. Central to the Hippo pathway is a conserved cascade of inhibitory kinases that regulate the activity of YAP, the final transducer of this pathway. Reversibly, YAP expression and/or activity is dependent on CCN1 and CCN2 downstream signaling, which creates a positive or negative feedforward loop driving developmental processes (e.g., neurogenesis, gliogenesis, angiogenesis, barriergenesis) and, when dysregulated, disease progression in a range of retinal neurovascular disorders. Here we describe mechanistic hints involving the CCN-Hippo-YAP regulatory axis in retina development and function. This regulatory pathway represents an opportunity for targeted therapies in neurovascular and neurodegenerative diseases. The CCN-YAP regulatory loop in development and pathology.