Inhibition of fibroblast activation protein ameliorates cartilage matrix degradation and osteoarthritis progression

Fibroblast activation protein(Fap)is a serine protease that degrades denatured type I collagen,α2-antiplasmin and FGF21.Fap is highly expressed in bone marrow stromal cells and functions as an osteogenic suppressor and can be inhibited by the bone growth factor Osteolectin(Oln).Fap is also expressed in synovial fibroblasts and positively correlated with the severity of rheumatoid arthritis(RA).However,whether Fap plays a critical role in osteoarthritis(OA)remains poorly understood.Here,we found that Fap is significantly elevated in osteoarthritic synovium,while the genetic deletion or pharmacological inhibition of Fap significantly ameliorated posttraumatic OA in mice.Mechanistically,we found that Fap degrades denatured type II collagen(Col II)and Mmp13-cleaved native Col II.Intra-articular injection of r Fap significantly accelerated Col II degradation and OA progression.In contrast,Oln is expressed in the superficial layer of articular cartilage and is significantly downregulated in OA.Genetic deletion of Oln significantly exacerbated OA progression,which was partially rescued by Fap deletion or inhibition.Intra-articular injection of r Oln significantly ameliorated OA progression.Taken together,these findings identify Fap as a critical pathogenic factor in OA that could be targeted by both synthetic and endogenous inhibitors to ameliorate articular cartilage degradation.

Loss of Tet hydroxymethylase activity causes mouse embryonic stem cell differentiation bias and developmental defects

The TET family is well known for active DNA demethylation and plays important roles in regulating transcription,the epigenome and development.Nevertheless,previous studies using knockdown(KD)or knockout(KO)models to investigate the function of TET have faced challenges in distinguishing its enzymatic and nonenzymatic roles,as well as compensatory effects among TET family members,which has made the understanding of the enzymatic role of TET not accurate enough.To solve this problem,we successfully generated mice catalytically inactive for specific Tet members(Tetm/m).We observed that,compared with the reported KO mice,mutant mice exhibited distinct developmental defects,including growth retardation,sex imbalance,infertility,and perinatal lethality.Notably,Tetm/mmouse embryonic stem cells(mESCs)were successfully established but entered an impaired developmental program,demonstrating extended pluripotency and defects in ectodermal differentiation caused by abnormal DNA methylation.Intriguingly,Tet3,traditionally considered less critical for m ESCs due to its lower expression level,had a significant impact on the global hydroxymethylation,gene expression,and differentiation potential of mESCs.Notably,there were common regulatory regions between Tet1 and Tet3 in pluripotency regulation.In summary,our study provides a more accurate reference for the functional mechanism of Tet hydroxymethylase activity in mouse development and ESC pluripotency regulation.

Primary cilia support cartilage regeneration after injury

In growing children,growth plate cartilage has limited self-repair ability upon fracture injury always leading to limb growth arrest.Interestingly,one type of fracture injuries within the growth plate achieve amazing self-healing,however,the mechanism is unclear.Using this type of fracture mouse model,we discovered the activation of Hedgehog(Hh)signaling in the injured growth plate,which could activate chondrocytes in growth plate and promote cartilage repair.

Liver cell therapies:cellular sources and grafting strategies

The liver has a complex cellular composition and a remarkable regenerative capacity.The primary cell types in the liver are two parenchymal cell populations,hepatocytes and cholangiocytes,that perform most of the functions of the liver and that are helped through interactions with non-parenchymal cell types comprising stellate cells,endothelia and various hemopoietic cell populations.The regulation of the cells in the liver is mediated by an insoluble complex of proteins and carbohydrates,the extracellular matrix,working synergistically with soluble paracrine and systemic signals.In recent years,with the rapid development of genetic sequencing technologies,research on the liver’s cellular composition and its regulatory mechanisms during various conditions has been extensively explored.Meanwhile breakthroughs in strategies for cell transplantation are enabling a future in which there can be a rescue of patients with end-stage liver diseases,offering potential solutions to the chronic shortage of livers and alternatives to liver transplantation.This review will focus on the cellular mechanisms of liver homeostasis and how to select ideal sources of cells to be transplanted to achieve liver regeneration and repair.Recent advances are summarized for promoting the treatment of end-stage liver diseases by forms of cell transplantation that now include grafting strategies.

Single-cell transcriptomics of cardiac progenitors reveals functional subpopulations and their cooperative crosstalk in cardiac repair

Dear Editor,Myocardial infarction is one of the leading causes of morbidity and mortality.Stem/progenitor cells therapy has emerged as a promising strategy for the cardiac repair,especially those derived from cardiac tissue,have attracted worldwide attention(Tompkins et al.,2018).However,challenges and controversies remain in characterizing functional progenitors and explaining their mechanisms of action.

Graded and pan-neural disease phenotypes of Rett Syndrome linked with dosage of functional MeCP2

Rett syndrome(RTT)is a progressive neurodevelop-mental disorder,mainly caused by mutations in MeCP2 and currently with no cure.We report here that neurons from R106W MeCP2 RTT human iPSCs as well as human embryonic stem cells after MeCP2 knockdown exhibit consistent and long-lasting impairment in maturation as indicated by impaired action potentials and passive membrane properties as well as reduced soma size and spine density.Moreover,RTT-inherent defects in neuronal maturation could be pan-neuronal and occurred in neurons with both dorsal and ventral forebrain features.Knockdown of MeCP2 led to more severe neuronal deficits as compared to RTT iPSC-derived neurons,which appeared to retain partial function.Strikingly,consistent deficits in nuclear size,dendritic complexity and circuitry-dependent spontaneous postsynaptic currents could only be observed in MeCP2 knockdown neurons but not RTT iPSC-derived neurons.Both neuron-intrinsic and circuitry-dependent deficits of MeCP2-deficient neurons could be fully or partially rescued by re-expression of wild type or T158M MeCP2,strengthening the dosage dependency of MeCP2 on disease phenotypes and also the partial function of the mutant.Our findings thus reveal stable neuronal maturation deficits and unexpectedly,graded sensitivities of neuron-inherent and neural transmission phenotypes towards the extent of MeCP2 deficiency,which is informative for future therapeutic development.

miRNA in cardiac development and regeneration

Ischemic heart disease is one of the main causes of morbidity and mortality in the world. In adult mammalianhearts, most cardiomyocytes are terminally differentiated and have extremely limited capacity of proliferation,making it impossible to regenerate the heart after injuries such as myocardial infarction. MicroRNAs (miRNAs), aclass of non-coding single-stranded RNA, which are involved in mRNA silencing and the regulation of posttranscriptionalgene expression, have been shown to play a crucial role in cardiac development and cardiomyocyteproliferation. Muscle specific miRNAs such as miR-1 are key regulators of cardiomyocyte maturation and growth,while miR-199-3p and other miRNAs display potent activity to induce proliferation of cardiomyocytes. Given theirsmall size and relative pleiotropic effects, miRNAs have gained significant attraction as promising therapeutic targetsor tools in cardiac regeneration. Increasing number of studies demonstrated that overexpression or inhibition ofspecific miRNAs could induce cardiomyocyte proliferation and cardiac regeneration. Some common targets of proproliferationmiRNAs, such as the Hippo-Yap signaling pathway, were identified in multiple species, highlighting thepower of miRNAs as probes to dissect core regulators of biological processes. A number of miRNAs have beenshown to improve heart function after myocardial infarction in mice, and one trial in swine also demonstratedpromising outcomes. However, technical difficulties, especially in delivery methods, and adverse effects, such asuncontrolled proliferation, remain. In this review, we summarize the recent progress in miRNA research in cardiacdevelopment and regeneration, examine the mechanisms of miRNA regulating cardiomyocyte proliferation, anddiscuss its potential as a new strategy for cardiac regeneration therapy.

Chronic spinal cord injury repair by NT3-chitosan only occurs after clearance of the lesion scar

Spinal cord injury(SCI)is a severe damage usually leading to limb dysesthesia,motor dysfunction,and other physiological disability.We have previously shown that NT3-chitosan could trigger an acute SCI repairment in rats and non-human primates.Due to the negative effect of inhibitory molecules in glial scar on axonal regeneration,however,the role of NT3-chitosan in the treatment of chronic SCI remains unclear.Compared with the fresh wound of acute SCI,how to handle the lesion core and glial scars is a major issue related to chronic-SCI repair.Here we report,in a chronic complete SCI rat model,establishment of magnetic resonancediffusion tensor imaging(MR-DTI)methods to monitor spatial and temporal changes of the lesion area,which matched well with anatomical analyses.Clearance of the lesion core via suction of cystic tissues and trimming of solid scar tissues before introducing NT3-chitosan using either a rigid tubular scaffold or a soft gel form led to robust neural regeneration,which interconnected the severed ascending and descending axons and accompanied with electrophysiological and motor functional recovery.In contrast,cystic tissue extraction without scar trimming followed by NT3-chitosan injection,resulted in little,if any regeneration.Taken together,after lesion core clearance,NT3-chitosan can be used to enable chronic-SCI repair and MR-DTI-based mapping of lesion area and monitoring of ongoing regeneration can potentially be implemented in clinical studies for subacute/chronic-SCI repair.

β-Catenin Deletion in Regional Neural Progenitors Leads to Congenital Hydrocephalus in Mice

Congenital hydrocephalus is a major neurological disorder with high rates of morbidity and mortality;however,the underlying cellular and molecular mechanisms remain largely unknown.Reproducible animal models mirroring both embryonic and postnatal hydrocephalus are also limited.Here,we describe a new mouse model of congenital hydrocephalus through knockout ofβ-catenin in Nkx2.1-expressing regional neural progenitors.Progressive ventriculomegaly and an enlarged brain were consistently observed in knockout mice from embryonic day 12.5 through to adulthood.Transcriptome profiling revealed severe dysfunctions in progenitor maintenance in the ventricular zone and therefore in cilium biogenesis afterβ-catenin knockout.Histological analyses also revealed an aberrant neuronal layout in both the ventral and dorsal telencephalon in hydrocephalic mice at both embryonic and postnatal stages.Thus,knockout ofβ-catenin in regional neural progenitors leads to congenital hydrocephalus and provides a reproducible animal model for studying pathological changes and developing therapeutic interventions for this devastating disease.