AKAP12 mediates barrier functions of fibrotic scars during CNS repair

Novel insight into the role of A-kinase anchoring proteins (AKAPs) in ischemic stroke and therapeutic potentials

Ischemic stroke, a devastating disease associated with high mortality and disability worldwide, has emerged as an urgent public health issue. A-kinase anchoring proteins (AKAPs) are a group of signal-organizing molecules that compartmentalize and anchor a wide range of receptors and effector proteins and have a major role in stabilizing mitochondrial function and promoting neurodevelopmental development in the central nervous system (CNS). Growing evidence suggests that dysregulation of AKAPs expression and activity is closely associated with oxidative stress, ion disorder, mitochondrial dysfunction, and blood-brain barrier (BBB) impairment in ischemic stroke. However, the underlying mechanisms remain inadequately understood. This review provides a comprehensive overview of the composition and structure of A-kinase anchoring protein (AKAP) family members, emphasizing their physiological functions in the CNS. We explored in depth the molecular and cellular mechanisms of AKAP complexes in the pathological progression and risk factors of ischemic stroke, including hypertension, hyperglycemia, lipid metabolism disorders, and atrial fibrillation. Herein, we highlight the potential of AKAP complexes as a pharmacological target against ischemic stroke in the hope of inspiring translational research and innovative clinical approaches.

Prognostic Value of Galectin-3 after Left Atrial Appendage Occlusion for Predicting Peri-Device Leakage

Echocardiographic detection of residual peri-device leakage (PDL) after percutaneous left atrial appendage occlusion (LAAO) is crucial for managing anticoagulation. Galectin-3, a protein involved in tissue-foreign body interactions, may hold significance in understanding PDL and cardiac tissue remodeling after LAAO. This study aimed to analyze galectin-3 serum levels in relation to PDL using a novel echo-morphological classification. LAAO eligible patients were included in the study. Galectin-3 serum levels were measured before LAAO, at 45 days (45D), and at 6 months (6M) after the procedure. Transesophageal echocardiography was used to assess LAAO success. A new echo-morphological classification categorized the degree of LAAO into three different types (A: homogenous echodensity, indicating completely thrombosed device; B: inhomogeneous echolucencies (<50% of device); and C: partially thrombosed device with echolucencies > 50%). Among 47 patients, complete LAAO was achieved in 60% after 45D and in 74% after 6M. We observed a significant increase and distribution of serum levels of galectin-3 [ng/mL] after 45D among the three types (baseline: 13.1 ± 5.8 ng/mL; 45D: 16.3 ± 7.2 ng/mL (Type A) vs. 19.2 ± 8.6 ng/mL (Type B) vs. 25.8 ± 9.4 ng/mL (Type C); p = 0.031), followed by a drop in galectin-3 for Types A and B after 6M toward and below the baseline levels (6M: 8.9 ± 3.1 ng/mL (Type A) vs. 12.4 ± 5.5 ng/mL (Type B)), whereas Type C persisted in showing elevated galectin-3 levels compared to all other types (6M: 17.5 ± 4.5 ng/mL (Type C); p < 0.01). Increased galectin-3 serum levels after LAAO likely reflect the transition from thrombus formation to fibrotic scar development in the LAA lumen. Successful occlusion is associated with a time-restricted decrease in galectin-3 levels after 6 months, while relevant PDL leads to persistently elevated levels, making galectin-3 a potential predictor of occlusion success.

Inference of differential key regulatory networks and mechanistic drug repurposing candidates from scRNA-seq data with SCANet

MOTIVATION

The reconstruction of small key regulatory networks that explain the differences in the development of cell (sub)types from single-cell RNA sequencing is a yet unresolved computational problem.

RESULTS

To this end, we have developed SCANet, an all-in-one package for single-cell profiling that covers the whole differential mechanotyping workflow, from inference of trait/cell-type-specific gene co-expression modules, driver gene detection, and transcriptional gene regulatory network reconstruction to mechanistic drug repurposing candidate prediction. To illustrate the power of SCANet, we examined data from two studies. First, we identify the drivers of the mechanotype of a cytokine storm associated with increased mortality in patients with acute respiratory illness. Secondly, we find 20 drugs for eight potential pharmacological targets in cellular driver mechanisms in the intestinal stem cells of obese mice.

AVAILABILITY AND IMPLEMENTATION

SCANet is a free, open-source, and user-friendly Python package that can be seamlessly integrated into single-cell-based systems medicine research and mechanistic drug discovery.

Endothelial deletion of EPH receptor A4 alters single-cell profile and Tie2/Akap12 signaling to preserve blood-brain barrier integrity

Neurobiological consequences of traumatic brain injury (TBI) result from a complex interplay of secondary injury responses and sequela that mediates chronic disability. Endothelial cells are important regulators of the cerebrovascular response to TBI. Our work demonstrates that genetic deletion of endothelial cell (EC)-specific EPH receptor A4 (EphA4) using conditional EphA4f/f/Tie2-Cre and EphA4f/f/VE-Cadherin-CreERT2 knockout (KO) mice promotes blood-brain barrier (BBB) integrity and tissue protection, which correlates with improved motor function and cerebral blood flow recovery following controlled cortical impact (CCI) injury. scRNAseq of capillary-derived KO ECs showed increased differential gene expression of BBB-related junctional and actin cytoskeletal regulators, namely, A-kinase anchor protein 12, Akap12, whose presence at Tie2 clustering domains is enhanced in KO microvessels. Transcript and protein analysis of CCI-injured whole cortical tissue or cortical-derived ECs suggests that EphA4 limits the expression of Cldn5, Akt, and Akap12 and promotes Ang2. Blocking Tie2 using sTie2-Fc attenuated protection and reversed Akap12 mRNA and protein levels cortical-derived ECs. Direct stimulation of Tie2 using Vasculotide, angiopoietin-1 memetic peptide, phenocopied the neuroprotection. Finally, we report a noteworthy rise in soluble Ang2 in the sera of individuals with acute TBI, highlighting its promising role as a vascular biomarker for early detection of BBB disruption. These findings describe a contribution of the axon guidance molecule, EphA4, in mediating TBI microvascular dysfunction through negative regulation of Tie2/Akap12 signaling.

Role of A-Kinase Anchoring Protein 12 in the Central Nervous System

A-kinase anchoring protein (AKAP) 12 is a scaffolding protein that anchors various signaling proteins to the plasma membrane. These signaling proteins include protein kinase A, protein kinase C, protein phosphatase 2B, Src-family kinases, cyclins, and calmodulin, which regulate their respective signaling pathways. AKAP12 expression is observed in the neurons, astrocytes, endothelial cells, pericytes, and oligodendrocytes of the central nervous system (CNS). Its physiological roles include promoting the development of the blood-brain barrier, maintaining white-matter homeostasis, and even regulating complex cognitive functions such as long-term memory formation. Under pathological conditions, dysregulation of AKAP12 expression levels may be involved in the pathology of neurological diseases such as ischemic brain injury and Alzheimer's disease. This minireview aimed to summarize the current literature on the role of AKAP12 in the CNS.

Physiologic and pathophysiologic roles of AKAP12

A kinase anchoring protein (AKAP) 12 is a scaffolding protein that improves the specificity and efficiency of spatiotemporal signal through assembling intracellular signal proteins into a specific complex. AKAP12 is a negative mitogenic regulator that plays an important role in controlling cytoskeletal architecture, maintaining endothelial integrity, regulating glial function and forming blood-brain barrier (BBB) and blood retinal barrier (BRB). Moreover, elevated or reduced AKAP12 contributes to a variety of diseases. Complex connections between AKAP12 and various diseases including chronic liver diseases (CLDs), inflammatory diseases and a series of cancers will be tried to delineate in this paper. We first describe the expression, distribution and physiological function of AKAP12. Then we summarize the current knowledge of different connections between AKAP12 expression and various diseases. Some research groups have found paradoxical roles of AKAP12 in different diseases and further confirmation is needed. This paper aims to assess the role of AKAP12 in physiology and diseases to help lay the foundation for the design of small molecules for specific AKAP12 to correct the pathological signal defects.

Reversible lysine fatty acylation of an anchoring protein mediates adipocyte adrenergic signaling

N-myristoylation on glycine is an irreversible modification that has long been recognized to govern protein localization and function. In contrast, the biological roles of lysine myristoylation remain ill-defined. We demonstrate that the cytoplasmic scaffolding protein, gravin-α/A kinase-anchoring protein 12, is myristoylated on two lysine residues embedded in its carboxyl-terminal protein kinase A (PKA) binding domain. Histone deacetylase 11 (HDAC11) docks to an adjacent region of gravin-α and demyristoylates these sites. In brown and white adipocytes, lysine myristoylation of gravin-α is required for signaling via β₂- and β₃-adrenergic receptors (β-ARs), which are G protein-coupled receptors (GPCRs). Lysine myristoylation of gravin-α drives β-ARs to lipid raft membrane microdomains, which results in PKA activation and downstream signaling that culminates in protective thermogenic gene expression. These findings define reversible lysine myristoylation as a mechanism for controlling GPCR signaling and highlight the potential of inhibiting HDAC11 to manipulate adipocyte phenotypes for therapeutic purposes.

The Diagnostic and Therapeutic Potential of Galectin-3 in Cardiovascular Diseases

Galectin-3 plays a prominent role in chronic inflammation and has been implicated in the development of many disease conditions, including heart disease. Galectin-3, a regulatory protein, is elevated in both acute and chronic heart failure and is involved in the inflammatory pathway after injury leading to myocardial tissue remodelling. We discussed the potential utility of galectin-3 as a diagnostic and disease severity/prognostic biomarker in different cardio/cerebrovascular diseases, such as acute ischemic stroke, acute coronary syndromes, heart failure and arrhythmogenic cardiomyopathy. Over the last decade there has been a marked increase in the understanding the role of galectin-3 in myocardial fibrosis and inflammation and as a therapeutic target for the treatment of heart failure and myocardial infarction.

Recent insights on astrocyte mechanisms in CNS homeostasis, pathology, and repair

Astrocytes play essential roles in development, homeostasis, injury, and repair of the central nervous system (CNS). Their development is tightly regulated by distinct spatial and temporal cues during embryogenesis and into adulthood throughout the CNS. Astrocytes have several important responsibilities such as regulating blood flow and permeability of the blood-CNS barrier, glucose metabolism and storage, synapse formation and function, and axon myelination. In CNS pathologies, astrocytes also play critical parts in both injury and repair mechanisms. Upon injury, they undergo a robust phenotypic shift known as "reactive astrogliosis," which results in both constructive and deleterious outcomes. Astrocyte activation and migration at the site of injury provides an early defense mechanism to minimize the extent of injury by enveloping the lesion area. However, astrogliosis also contributes to the inhibitory microenvironment of CNS injury and potentiate secondary injury mechanisms, such as inflammation, oxidative stress, and glutamate excitotoxicity, which facilitate neurodegeneration in CNS pathologies. Intriguingly, reactive astrocytes are increasingly a focus in current therapeutic strategies as their activation can be modulated toward a neuroprotective and reparative phenotype. This review will discuss recent advancements in knowledge regarding the development and role of astrocytes in the healthy and pathological CNS. We will also review how astrocytes have been genetically modified to optimize their reparative potential after injury, and how they may be transdifferentiated into neurons and oligodendrocytes to promote repair after CNS injury and neurodegeneration.

Central Nervous System Fibroblast-Like Cells in Stroke and Other Neurological Disorders

Fibroblasts are the most common cell type of connective tissues. In the central nervous system (CNS), fibroblast-like cells are mainly located in the meninges and perivascular Virchow-Robin space. The origins of these fibroblast-like cells and their functions in both CNS development and pathological conditions remain largely unknown. In this review, we first introduce the anatomic location and molecular markers of CNS fibroblast-like cells. Next, the functions of fibroblast-like cells in CNS development and neurological disorders, including stroke, CNS traumatic injuries, and other neurological diseases, are discussed. Third, current challenges and future directions in the field are summarized. We hope to provide a synthetic review that stimulates future research on CNS fibroblast-like cells.

Temporal dynamics of cells expressing NG2 and platelet-derived growth factor receptor-β in the fibrotic scar formation after 3-nitropropionic acid-induced acute brain injury

Neuron-glia antigen 2 (NG2) proteoglycan and platelet-derived growth factor receptor beta (PDGFR-β) are widely used markers of pericytes, which are considered cells that form fibrotic scars in response to central nervous system insults. However, the exact phenotypes of NG2- and PDGFR-β-expressing cells, as well as the origin of the fibrotic scar after central nervous system insults, are still elusive. In the present study, we directly examined the identities and distributions of NG2- and PDGFR-β-positive cells in the control and lesioned striatum injured by the mitochondrial toxin 3-nitropropionic acid. Immunoelectron microscopy and correlative light and electron microscopy clearly distinguished NG2 and PDGFR-β expression in the vasculature during the post-injury period. Vascular smooth muscle cells and pericytes expressed NG2, which was prominently increased after the injury. NG2 expression was restricted to these vascular mural cells until 14 days post-lesion. By contrast, PDGFR-β-positive cells were perivascular fibroblasts located abluminal to smooth muscle cells or pericytes. These PDGFR-β-expressing cells formed extravascular networks associated with collagen fibrils at 14 days post-lesion. We also found that in the injured striatal parenchyma, PDGFR-β could be used as a complementary marker of resting and reactive NG2 glia because activated microglia/macrophages shared only the NG2 expression with NG2 glia in the lesioned striatum. These data indicate that NG2 and PDGFR-β label different vascular mural and parenchymal cells in the healthy and injured brain, suggesting that fibrotic scar-forming cells most likely originate in PDGFR-β-positive perivascular fibroblasts rather than in NG2-positive pericytes.

Roles of A-kinase Anchor Protein 12 in Astrocyte and Oligodendrocyte Precursor Cell in Postnatal Corpus Callosum

The formation of the corpus callosum in the postnatal period is crucial for normal neurological function, and clinical genetic studies have identified an association of 6q24-25 microdeletion in this process. However, the mechanisms underlying corpus callosum formation and its critical gene(s) are not fully understood or identified. In this study, we examined the roles of AKAP12 in postnatal corpus callosum formation by focusing on the development of glial cells, because AKAP12 is coded on 6q25.1 and has recently been shown to play roles in the regulations of glial function. In mice, the levels of AKAP12 expression was confirmed to be larger in the corpus callosum compared to the cortex, and AKAP12 levels decreased with age both in the corpus callosum and cortex regions. In addition, astrocytes expressed AKAP12 in the corpus callosum after birth, but oligodendrocyte precursor cells (OPCs), another major type of glial cell in the developing corpus callosum, did not. Furthermore, compared to wild types, Akap12 knockout mice showed smaller numbers of both astrocytes and OPCs, along with slower development of corpus callosum after birth. These findings suggest that AKAP12 signaling may be required for postnatal glial formation in the corpus callosum through cell- and non-cell autonomous mechanisms.

Single-Cell Transcriptomic Analyses of the Developing Meninges Reveal Meningeal Fibroblast Diversity and Function

The meninges are a multilayered structure composed of fibroblasts, blood and lymphatic vessels, and immune cells. Meningeal fibroblasts secrete a variety of factors that control CNS development, yet strikingly little is known about their heterogeneity or development. Using single-cell sequencing, we report distinct transcriptional signatures for fibroblasts in the embryonic dura, arachnoid, and pia. We define new markers for meningeal layers and show conservation in human meninges. We find that embryonic meningeal fibroblasts are transcriptionally distinct between brain regions and identify a regionally localized pial subpopulation marked by the expression of μ-crystallin. Developmental analysis reveals a progressive, ventral-to-dorsal maturation of telencephalic meninges. Our studies have generated an unparalleled view of meningeal fibroblasts, providing molecular profiles of embryonic meningeal fibroblasts by layer and yielding insights into the mechanisms of meninges development and function.

AKAP12 Supports Blood-Brain Barrier Integrity against Ischemic Stroke

A-kinase anchor protein 12 (AKAP12) is a scaffolding protein that associates with intracellular molecules to regulate multiple signal transductions. Although the roles of AKAP12 in the central nervous system are still relatively understudied, it was previously shown that AKAP12 regulates blood-retinal barrier formation. In this study, we asked whether AKAP12 also supports the function and integrity of the blood-brain barrier (BBB). In a mouse model of focal ischemia, the expression level of AKAP12 in cerebral endothelial cells was upregulated during the acute phase of stroke. Also, in cultured cerebral endothelial cells, oxygen-glucose deprivation induced the upregulation of AKAP12. When AKAP12 expression was suppressed by an siRNA approach in cultured endothelial cells, endothelial permeability was increased along with the dysregulation of ZO-1/Claudin 5 expression. In addition, the loss of AKAP12 expression caused an upregulation/activation of the Rho kinase pathway, and treatment of Rho kinase inhibitor Y-27632 mitigated the increase of endothelial permeability in AKAP12-deficient endothelial cell cultures. These in vitro findings were confirmed by our in vivo experiments using Akap12 knockout mice. Compared to wild-type mice, Akap12 knockout mice showed a larger extent of BBB damage after stroke. However, the inhibition of rho kinase by Y-27632 tightened the BBB in Akap12 knockout mice. These data may suggest that endogenous AKAP12 works to alleviate the damage and dysfunction of the BBB caused by ischemic stress. Therefore, the AKAP12-rho-kinase signaling pathway represents a novel therapeutic target for stroke.

Akap12beta supports asymmetric heart development via modulating the Kupffer’s vesicle formation in zebrafish

The vertebrate body plan is accomplished by left-right asymmetric organ development and the heart is a representative asymmetric internal organ which jogs to the left-side. Kupffer’s vesicle (KV) is a spherical left-right organizer during zebrafish embryogenesis and is derived from a cluster of dorsal forerunner cells (DFCs). Cadherin1 is required for collective migration of a DFC cluster and failure of DFC collective migration by Cadherin1 decrement causes KV malformation which results in defective heart laterality. Recently, loss of function mutation of A-kinase anchoring protein 12 (AKAP12) is reported as a high-risk gene in congenital heart disease patients. In this study, we demonstrated the role of akap12β in asymmetric heart development. The akap12β, one of the akap12 isoforms, was expressed in DFCs which give rise to KV and akap12β-deficient zebrafish embryos showed defective heart laterality due to the fragmentation of DFC clusters which resulted in KV malformation. DFC-specific loss of akap12β also led to defective heart laterality as a consequence of the failure of collective migration by cadherin1 reduction. Exogenous akap12β mRNA not only restored the defective heart laterality but also increased cadherin1 expression in akap12β morphant zebrafish embryos. Taken together, these findings provide the first experimental evidence that akap12β regulates heart laterality via cadherin1.

Defining a role for lung function associated gene GSTCD in cell homeostasis

Genome wide association (GWA) studies have reproducibly identified signals on chromosome 4q24 associated with lung function and COPD. GSTCD (Glutathione S-transferase C-terminal domain containing) represents a candidate causal gene in this locus, however little is currently known about the function of this protein. We set out to further our understanding of the role of GSTCD in cell functions and homeostasis using multiple molecular and cellular approaches in airway relevant cells. Recombinant expression of human GSTCD in conjunction with a GST activity assay did not identify any enzymatic activity for two GSTCD isoforms questioning the assignment of this protein to this family of enzymes. Protein structure analyses identified a potential methyltransferase domain contained within GSTCD, with these enzymes linked to cell viability and apoptosis. Targeted knockdown (siRNA) of GSTCD in bronchial epithelial cells identified a role for GSTCD in cell viability as proliferation rates were not altered. To provide greater insight we completed transcriptomic analyses on cells with GSTCD expression knocked down and identified several differentially expressed genes including those implicated in airway biology; fibrosis e.g. TGFBR1 and inflammation e.g. IL6R. Pathway based transcriptomic analyses identified an over-representation of genes related to adipogenesis which may suggest additional functions for GSTCD. These findings identify potential additional functions for GSTCD in the context of airway biology beyond the hypothesised GST activity and warrant further investigation.

PDGFR-β-Positive Perivascular Adventitial Cells Expressing Nestin Contribute to Fibrotic Scar Formation in the Striatum of 3-NP Intoxicated Rats

Perivascular cells expressing platelet-derived growth factor receptor beta (PDGFR-β) have recently been implicated in fibrotic scar formation after acute brain injury, but their precise identity and detailed morphological characteristics remain elusive. This study sought to characterize and define the cellular phenotype of vascular-associated cells expressing PDGFR-β in the striatum of rats treated with the mitochondrial toxin 3-nitropropionic acid (3-NP). In the control striatum, PDGFR-β-positive cells were invariably localized on the abluminal side of smooth muscle cells of larger caliber vessels, and demonstrated morphological features typical of perivascular fibroblasts. PDGFR-β expression increased and expanded to almost all vessels, including microvessels in the lesion core, at 7 days after 3-NP injection. The cells expressing PDGFR-β had ultrastructural features of fibroblasts undergoing active collagen synthesis: large euchromatic nuclei with a prominent nucleolus, well-developed rough endoplasmic reticulum (rER) with dilated cisterns and extracellular collagen fibrils. By 14 days, PDGFR-β-positive cells had somata located at a distance from the vasculature, and their highly ramified, slender processes overlapped with those from other cells, thus forming a plexus of processes in the extravascular space of the lesion core. In addition, their ultrastructural morphology and spatial correlation with activated microglia/macrophages were elaborated by three-dimensional reconstruction. Using a correlative light- and electron-microscopy technique, we found that the intermediate filament proteins nestin and vimentin were induced in PDGFRβ-positive fibroblasts in the lesion core. Collectively, our data suggest that perivascular PDGFR-β-positive fibroblasts are distinct from other vascular cell types, including pericytes and contribute to fibrotic scar formation in the lesion core after acute brain injury. Nestin and vimentin play critical roles in the structural dynamics of these reactive fibroblasts.

Aldosterone Impairs Mitochondrial Function in Human Cardiac Fibroblasts via A-Kinase Anchor Protein 12

Aldosterone (Aldo) contributes to mitochondrial dysfunction and cardiac oxidative stress. Using a proteomic approach, A-kinase anchor protein (AKAP)-12 has been identified as a down-regulated protein by Aldo in human cardiac fibroblasts. We aim to characterize whether AKAP-12 down-regulation could be a deleterious mechanism which induces mitochondrial dysfunction and oxidative stress in cardiac cells. Aldo down-regulated AKAP-12 via its mineralocorticoid receptor, increased oxidative stress and induced mitochondrial dysfunction characterized by decreased mitochondrial-DNA and Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) expressions in human cardiac fibroblasts. CRISPR/Cas9-mediated knock-down of AKAP-12 produced similar deleterious effects in human cardiac fibroblasts. CRISPR/Cas9-mediated activation of AKAP-12 blunted Aldo effects on mitochondrial dysfunction and oxidative stress in human cardiac fibroblasts. In Aldo-salt-treated rats, cardiac AKAP-12, mitochondrial-DNA and PGC-1α expressions were decreased and paralleled increased oxidative stress. In myocardial biopsies from patients with aortic stenosis (AS, n = 26), AKAP-12, mitochondrial-DNA and PGC-1α expressions were decreased as compared to Controls (n = 13). Circulating Aldo levels inversely correlated with cardiac AKAP-12. PGC-1α positively associated with AKAP-12 and with mitochondrial-DNA. Aldo decreased AKAP-12 expression, impairing mitochondrial biogenesis and increasing cardiac oxidative stress. AKAP-12 down-regulation triggered by Aldo may represent an important event in the development of mitochondrial dysfunction and cardiac oxidative stress.

Altered AKAP12 expression in portal fibroblasts and liver sinusoids mediates transition from hepatic fibrogenesis to fibrosis resolution

Liver fibrosis can be reversed by removing its causative injuries; however, the molecular mechanisms mediating the resolution of liver fibrogenesis are poorly understood. We investigate the role of a scaffold protein, A-Kinase Anchoring Protein 12 (AKAP12), during liver fibrosis onset, and resolution. Biliary fibrogenesis and fibrosis resolution was induced in wild-type (WT) or AKAP12-deficient C57BL/6 mice through different feeding regimens with 0.1% 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-containing chow. AKAP12 expression in portal fibroblasts (PFs) and liver sinusoidal endothelial cells (LSECs) gradually decreased as fibrosis progressed but was restored after cessation of the fibrotic challenge. Histological analysis of human liver specimens with varying degrees of fibrosis of different etiologies revealed that AKAP12 expression diminishes in hepatic fibrosis from its early stages onward. AKAP12 KO mice displayed reduced fibrosis resolution in a DDC-induced biliary fibrosis model, which was accompanied by impaired normalization of myofibroblasts and capillarized sinusoids. RNA sequencing of the liver transcriptome revealed that genes related to ECM accumulation and vascular remodeling were mostly elevated in AKAP12 KO samples. Gene ontology (GO) and bioinformatic pathway analyses identified that the differentially expressed genes were significantly enriched in GO categories and pathways, such as the adenosine 3′,5′-cyclic monophosphate (cAMP) pathway. Knockdown of the AKAP12 gene in cultured primary PFs revealed that AKAP12 inhibited PF activation in association with the adenosine 3′,5′-cyclic monophosphate (cAMP) pathway. Moreover, AKAP12 knockdown in LSECs led to enhanced angiogenesis, endothelin-1 expression and alterations in laminin composition. Collectively, this study demonstrates that AKAP12-mediated regulation of PFs and LSECs has a central role in resolving hepatic fibrosis.

A scaffolding protein that modulates cell signaling pathways contributes to reverse liver scarring. Liver fibrosis is caused by a build-up of scar tissue that interferes with liver function. However, the damage is reversed when the cause of injury is removed. Kyu-Won Kim at Seoul National University, South Korea, and colleagues examined the levels of A-Kinase Anchoring Protein 12 (AKAP12), a scaffolding protein that regulates the subcellular location of signaling proteins, in mouse and human livers. Levels of AKAP12 were reduced in fibrotic livers but restored when fibrosis was reversed. Mice lacking AKAP12 were unable to effectively repair the damage caused by fibrosis. Genetic analyses suggest that AKAP12 stimulates signaling through the adenosine 3′,5′-cyclic monophosphate (cAMP) pathway, which can inhibit fibrosis. These findings highlight a key role for AKAP12 in accelerating liver recovery.

Deduction of Novel Genes Potentially Involved in Osteoblasts of Rheumatoid Arthritis Using Next-Generation Sequencing and Bioinformatic Approaches

The role of osteoblasts in peri-articular bone loss and bone erosion in rheumatoid arthritis (RA) has gained much attention, and microRNAs are hypothesized to play critical roles in the regulation of osteoblast function in RA. The aim of this study is to explore novel microRNAs differentially expressed in RA osteoblasts and to identify genes potentially involved in the dysregulated bone homeostasis in RA. RNAs were extracted from cultured normal and RA osteoblasts for sequencing. Using the next generation sequencing and bioinformatics approaches, we identified 35 differentially expressed microRNAs and 13 differentially expressed genes with potential microRNA–mRNA interactions in RA osteoblasts. The 13 candidate genes were involved mainly in cell–matrix adhesion, as classified by the Gene Ontology. Two genes of interest identified from RA osteoblasts, A-kinase anchoring protein 12 (AKAP12) and leucin rich repeat containing 15 (LRRC15), were found to express more consistently in the related RA synovial tissue arrays in the Gene Expression Omnibus database, with the predicted interactions with miR-183-5p and miR-146a-5p, respectively. The Ingenuity Pathway Analysis identified AKAP12 as one of the genes involved in protein kinase A signaling and the function of chemotaxis, interconnecting with molecules related to neovascularization. The findings indicate new candidate genes as the potential indicators in evaluating therapies targeting chemotaxis and neovascularization to control joint destruction in RA.

SSeCKS/AKAP12 scaffolding functions suppress B16F10-induced peritoneal metastasis by attenuating CXCL9/10 secretion by resident fibroblasts

SSeCKS/Gravin/AKAP12 (SSeCKS) is a kinase scaffolding protein known to suppress metastasis by attenuating tumor-intrinsic PKC- and Src-mediated signaling pathways [1]. In addition to downregulation in metastatic cells, in silico analyses identified SSeCKS downregulation in prostate or breast cancer-derived stroma, suggesting a microenvironmental cell role in controlling malignancy. Although orthotopic B16F10 and SM1WT1[Braf^V600E] mouse melanoma tumors grew similarly in syngeneic WT or SSeCKS-null (KO) mice, KO hosts exhibited 5- to 10-fold higher levels of peritoneal metastasis, and this enhancement could be adoptively transferred by pre-injecting naïve WT mice with peritoneal fluid (PF), but not non-adherent peritoneal cells (PC), from naïve KO mice. B16F10 and SM1WT1 cells showed increased chemotaxis to KO-PF compared to WT-PF, corresponding to increased PF levels of multiple inflammatory mediators, including the Cxcr3 ligands, Cxcl9 and 10. Cxcr3 knockdown abrogated enhanced chemotaxis to KO-PF and peritoneal metastasis in KO hosts. Conditioned media from KO peritoneal membrane fibroblasts (PMF), but not from KO-PC, induced increased B16F10 chemotaxis over controls, which could be blocked with Cxcl10 neutralizing antibody. KO-PMF exhibited increased levels of the senescence markers, SA-β-galactosidase, p21^waf1 and p16^ink4a, and enhanced Cxcl10 secretion induced by inflammatory mediators, lipopolysaccharide, TNFα, IFNα and IFNγ. SSeCKS scaffolding-site mutants and small molecule kinase inhibitors were used to show that the loss of SSeCKS-regulated PKC, PKA and PI3K/Akt pathways are responsible for the enhanced Cxcl10 secretion. These data mark the first description of a role for stromal SSeCKS/AKAP12 in suppressing metastasis, specifically by attenuating signaling pathways that promote secretion of tumor chemoattractants in the peritoneum.

Structural environment built by AKAP12+ colon mesenchymal cells drives M2 macrophages during inflammation recovery

Macrophages exhibit phenotypic plasticity, as they have the ability to switch their functional phenotypes during inflammation and recovery. Simultaneously, the mechanical environment actively changes. However, how these dynamic alterations affect the macrophage phenotype is unknown. Here, we observed that the extracellular matrix (ECM) constructed by AKAP12+ colon mesenchymal cells (CMCs) generated M2 macrophages by regulating their shape during recovery. Notably, rounded macrophages were present in the linear and loose ECM of inflamed colons and polarized to the M1 phenotype. In contrast, ramified macrophages emerged in the contracted ECM of recovering colons and mainly expressed M2 macrophage markers. These contracted structures were not observed in the inflamed colons of AKAP12 knockout (KO) mice. Consequently, the proportion of M2 macrophages in inflamed colons was lower in AKAP12 KO mice than in WT mice. In addition, clinical symptoms and histological damage were more severe in AKAP12 KO mice than in WT mice. In experimentally remodeled collagen gels, WT CMCs drove the formation of a more compacted structure than AKAP12 KO CMCs, which promoted the polarization of macrophages toward an M2 phenotype. These results demonstrated that tissue contraction during recovery provides macrophages with the physical cues that drive M2 polarization.

Galectin-3 blockade inhibits cardiac inflammation and fibrosis in experimental hyperaldosteronism and hypertension

Hypertensive cardiac remodeling is accompanied by molecular inflammation and fibrosis, 2 mechanisms that finally affect cardiac function. At cardiac level, aldosterone promotes inflammation and fibrosis, although the precise mechanisms are still unclear. Galectin-3 (Gal-3), a β-galactoside-binding lectin, is associated with inflammation and fibrosis in the cardiovascular system. We herein investigated whether Gal-3 inhibition could block aldosterone-induced cardiac inflammation and fibrosis and its potential role in cardiac damage associated with hypertension. Aldosterone-salt-treated rats presented hypertension, cardiac inflammation, and fibrosis that were prevented by the pharmacological inhibition of Gal-3 with modified citrus pectin. Cardiac inflammation and fibrosis presented in spontaneously hypertensive rats were prevented by modified citrus pectin treatment, whereas Gal-3 blockade did not modify blood pressure levels. In the absence of blood pressure modifications, Gal-3 knockout mice were resistant to aldosterone-induced cardiac inflammation. In human cardiac fibroblasts, aldosterone increased Gal-3 expression via its mineralocorticoid receptor. Gal-3 and aldosterone enhanced proinflammatory and profibrotic markers, as well as metalloproteinase activities in human cardiac fibroblasts, effects that were not observed in Gal-3-silenced cells treated with aldosterone. In experimental hyperaldosteronism, the increase in Gal-3 expression was associated with cardiac inflammation and fibrosis, alterations that were prevented by Gal-3 blockade independently of blood pressure levels. These data suggest that Gal-3 could be a new molecular mechanism linking cardiac inflammation and fibrosis in situations with high-aldosterone levels, such as hypertension.

Meteorin is upregulated in reactive astrocytes and functions as a negative feedback effector in reactive gliosis

Reactive gliosis is a glial response to a wide range of central nervous system insults, which results in cellular and molecular changes to resting glial cells. Despite its fundamental effect on neuropathologies, the identification and characterization of the molecular mechanisms underlying this process remain to be fully elucidated. The aim of the present study was to analyze the expression profile and functions of the astrocytic neurotrophic factor, meteorin, in the progression of reactive gliosis. A mouse model of photothrombotic ischemia, and a primary astrocyte culture were used in the present study. Reverse transcription quantitative polymerase chain reaction, western blotting and immunofluorescence staining were performed to examine the expression levels of meteorin and reactive gliosis markers. Increased expression levels of meteorin were observed in reactive astrocytes in a photothrombotic ischemia mouse model, as well as in cultured astrocytes, which were stimulated by transforming growth factor-β1. Exogenous treatment of the astrocytes with meteorin did not induce janus kinase-signal transducer and activator of transcription 3 signaling, however, silencing the expression of meteorin in the astrocytes resulted in an upregulation of reactive astrocyte markers, including glial fibrillary acidic protein and S100β, indicating that endogenous meteorin is required for the maintenance of astrocytic homeostasis. These results suggested a novel role for meteorin as a negative feedback effector in reactive gliosis.

Prompt meningeal reconstruction mediated by oxygen-sensitive AKAP12 scaffolding protein after central nervous system injury

The meninges forms a critical epithelial barrier, which protects the central nervous system (CNS), and therefore its prompt reconstruction after CNS injury is essential for reducing neuronal damage. Meningeal cells migrate into the lesion site after undergoing an epithelial-mesenchymal transition (EMT) and repair the impaired meninges. However, the molecular mechanisms of meningeal EMT remain largely undefined. Here we show that TGF-β1 and retinoic acid (RA) released from the meninges, together with oxygen tension, could constitute the mechanism for rapid meningeal reconstruction. AKAP12 is an effector of this mechanism, and its expression in meningeal cells is regulated by integrated upstream signals composed of TGF-β1, RA and oxygen tension. Functionally, AKAP12 modulates meningeal EMT by regulating the TGF-β1-non-Smad-SNAI1 signalling pathway. Collectively, TGF-β1, RA and oxygen tension can modulate the dynamic change in AKAP12 expression, causing prompt meningeal reconstruction after CNS injury by regulating the transition between the epithelial and mesenchymal states of meningeal cells.