Deletion of frizzled-related protein reduces voluntary running exercise performance in mice

Serum proteomic profiling of physical activity reveals CD300LG as a novel exerkine with a potential causal link to glucose homeostasis

Background

Physical activity has been associated with preventing the development of type 2 diabetes and atherosclerotic cardiovascular disease. However, our understanding of the precise molecular mechanisms underlying these effects remains incomplete and good biomarkers to objectively assess physical activity are lacking.

Methods

We analyzed 3072 serum proteins in 26 men, normal weight or overweight, undergoing 12 weeks of a combined strength and endurance exercise intervention. We estimated insulin sensitivity with hyperinsulinemic euglycemic clamp, maximum oxygen uptake, muscle strength, and used MRI/MRS to evaluate body composition and organ fat depots. Muscle and subcutaneous adipose tissue biopsies were used for mRNA sequencing. Additional association analyses were performed in samples from up to 47,747 individuals in the UK Biobank, as well as using two-sample Mendelian randomization and mice models.

Results

Following 12 weeks of exercise intervention, we observed significant changes in 283 serum proteins. Notably, 66 of these proteins were elevated in overweight men and positively associated with liver fat before the exercise regimen, but were normalized after exercise. Furthermore, for 19.7 and 12.1% of the exercise-responsive proteins, corresponding changes in mRNA expression levels in muscle and fat, respectively, were shown. The protein CD300LG displayed consistent alterations in blood, muscle, and fat. Serum CD300LG exhibited positive associations with insulin sensitivity, and to angiogenesis-related gene expression in both muscle and fat. Furthermore, serum CD300LG was positively associated with physical activity and negatively associated with glucose levels in the UK Biobank. In this sample, the association between serum CD300LG and physical activity was significantly stronger in men than in women. Mendelian randomization analysis suggested potential causal relationships between levels of serum CD300LG and fasting glucose, 2 hr glucose after an oral glucose tolerance test, and HbA1c. Additionally, Cd300lg responded to exercise in a mouse model, and we observed signs of impaired glucose tolerance in male, but not female, Cd300lg knockout mice.

Conclusions

Our study identified several novel proteins in serum whose levels change in response to prolonged exercise and were significantly associated with body composition, liver fat, and glucose homeostasis. Serum CD300LG increased with physical activity and is a potential causal link to improved glucose levels. CD300LG may be a promising exercise biomarker and a therapeutic target in type 2 diabetes.

Funding

South-Eastern Norway Regional Health Authority, Simon Fougners Fund, Diabetesforbundet, Johan Selmer Kvanes' legat til forskning og bekjempelse av sukkersyke. The UK Biobank resource reference 53641. Australian National Health and Medical Research Council Investigator Grant (APP2017942). Australian Research Council Discovery Early Career Award (DE220101226). Research Council of Norway (Project grant: 325640 and Mobility grant: 287198). The Medical Student Research Program at the University of Oslo. Novo Nordisk Fonden Excellence Emerging Grant in Endocrinology and Metabolism 2023 (NNF23OC0082123).

Clinical trial number

clinicaltrials.gov: NCT01803568.

Hypoxia and Wnt signaling inversely regulate expression of chondroprotective molecule ANP32A in articular cartilage

OBJECTIVES

ANP32A is a key protector of cartilage health, via preventing oxidative stress and Wnt hyper-activation. We aimed to unravel how ANP32A is regulated in cartilage.

METHODS

A bioinformatics pipeline was applied to identify regulators of ANP32A. Pathways of interest were targeted to study their impact on ANP32A in in vitro cultures of the human chondrocyte C28/I2 cell-line and primary human articular chondrocytes (hACs) from up to five different donors, using Wnt-activator CHIR99021, hypoxia-mimetic IOX2 and a hypoxia chamber. ANP32A was evaluated using real-time quantitative polymerase chain reaction (RT-qPCR) and Western blot. In vivo, the effect of hypoxia was examined by immunohistochemistry in mice injected intra-articularly with IOX2 after destabilization of the medial meniscus. Effects of Wnt hyper-activation were investigated using Frzb-knockout mice and wild-type mice treated intra-articularly with CHIR99021. Wnt inhibition effects were assessed upon intra-articular injection of XAV939.

RESULTS

The hypoxia and Wnt signaling pathways were identified as networks controlling ANP32A expression. In vitro and in vivo experiments demonstrated increases in ANP32A upon hypoxic conditions (1.3-fold in hypoxia in C28/I2 cells with 95% confidence interval (CI) [1.11-1.54] and 1.90-fold in hACs [95% CI: 1.56-2] and 1.67-fold in ANP32A protein levels after DMM surgery with IOX2 injections [95% CI: 1.33-2.08]). Wnt hyper-activation decreased ANP32A in chondrocytes in vitro (1.23-fold decrease [95% CI: 1.02-1.49]) and in mice (1.45-fold decrease after CHIR99021 injection [95% CI: 1.22-1.72] and 1.41-fold decrease in Frzb-knockout mice [95% CI: 1.00-1.96]). Hypoxia and Wnt modulated ataxia-telangiectasia mutated serine/threonine kinase (ATM), an ANP32A target gene, in hACs (1.89-fold increase [95% CI: 1.38-2.60] and 1.41-fold decrease [95% CI: 1.02-1.96]).

CONCLUSIONS

Maintaining hypoxia and limiting Wnt activation sustain ANP32A and protect against osteoarthritis.

ROR2 blockade as a therapy for osteoarthritis

Osteoarthritis is characterized by the loss of the articular cartilage, bone remodeling, pain, and disability. No pharmacological intervention can currently halt progression of osteoarthritis. Here, we show that blocking receptor tyrosine kinase-like orphan receptor 2 (ROR2) improves cartilage integrity and pain in osteoarthritis models by inhibiting yes-associated protein (YAP) signaling. ROR2 was up-regulated in the cartilage in response to inflammatory cytokines and mechanical stress. The main ligand for ROR2, WNT5A, and the targets YAP and connective tissue growth factor were up-regulated in osteoarthritis in humans. In vitro, ROR2 overexpression inhibited chondrocytic differentiation. Conversely, ROR2 blockade triggered chondrogenic differentiation of C3H10T¹/₂ cells and suppressed the expression of the cartilage-degrading enzymes a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4 and ADAMTS-5. The chondrogenic effect of ROR2 blockade in the cartilage was independent of WNT signaling and was mediated by down-regulation of YAP signaling. ROR2 signaling induced G protein and Rho-dependent nuclear accumulation of YAP, and YAP inhibition was required but not sufficient for ROR2 blockade-induced chondrogenesis. ROR2 silencing protected mice from instability-induced osteoarthritis with improved structural outcomes, sustained pain relief, and without apparent side effects or organ toxicity. Last, ROR2 silencing in human articular chondrocytes transplanted in nude mice led to the formation of cartilage organoids with more and better differentiated extracellular matrix, suggesting that the anabolic effect of ROR2 blockade is conserved in humans. Thus, ROR2 blockade is efficacious and well tolerated in preclinical animal models of osteoarthritis.

Secreted Frizzled Related Proteins in Cardiovascular and Metabolic Diseases

Abnormal gene expression and secreted protein levels are accompanied by extensive pathological changes. Secreted frizzled related protein (SFRP) family members are antagonistic inhibitors of the Wnt signaling pathway, and they were recently found to be involved in the pathogenesis of a variety of metabolic diseases, which has led to extensive interest in SFRPs. Previous reports highlighted the importance of SFRPs in lipid metabolism, obesity, type 2 diabetes mellitus and cardiovascular diseases. In this review, we provide a detailed introduction of SFRPs, including their structural characteristics, receptors, inhibitors, signaling pathways and metabolic disease impacts. In addition to summarizing the pathologies and potential molecular mechanisms associated with SFRPs, this review further suggests the potential future use of SFRPs as disease biomarkers therapeutic targets.

Frizzled related protein deficiency impairs muscle strength, gait and calpain 3 levels

Background

Limb-girdle muscular dystrophy recessive 1 calpain3-related (LGMDR1), previously known as LGMD2A, is a disease caused by mutations in the CAPN3 gene. It is characterized by progressive weakness and muscle degeneration. Frizzled related protein (FRZB), upregulated in LGMDR1, was identified as a key regulator of the crosstalk between Wnt and integrin signalling pathways. FRZB gene silencing showed a recovery in the expression of some of the costamere protein levels in myotubes.

Results

Here, we performed a comprehensive characterization of Frzb^−/− mice muscles to study the absence of Frzb in skeletal muscle and eventual links with the molecular characteristics of LGMDR1 patient muscles. Frzb^−/− mice showed reduced muscle size and strength. Gait analysis showed that Frzb^−/− mice moved more slowly but no impaired regeneration capacity was observed after muscle injury. Additionally, Frzb^−/− mice muscle showed an increased number of mesoangioblasts. Lack of Frzb gene in Frzb^−/− mice and its increased expression in LGMDR1 patients, showed contrary regulation of Rora, Slc16a1, Tfrc and Capn3 genes. The reciprocal regulation of Frzb and Capn3 genes further supports this axis as a potential target for LGMDR1 patients.

Conclusions

Our data confirm a role for Frzb in the regulation of Rora, Slc16a1, Tfrc, and Capn3 genes in muscle cells. In vivo, reduced muscle strength and gait in the Frzb^−/− mice are intriguing features. The reciprocal relationship between FRZB and CAPN3 further supports a key role for this axis in patients with LGMDR1.

Sex Specific Determinants in Osteoarthritis: A Systematic Review of Preclinical Studies

Osteoarthritis (OA) is a highly prevalent joint disease that primarily affects about 10% of the world's population over 60 years old. The purpose of this study is to systematically review the preclinical studies regarding sex differences in OA, with particular attention to the molecular aspect and gene expression, but also to the histopathological aspects. Three databases (PubMed, Scopus, and Web of Knowledge) were screened for eligible studies. In vitro and in vivo papers written in English, published in the last 11 years (2009-2020) were eligible. Participants were preclinical studies, including cell cultures and animal models of OA, evaluating sex differences. Independent extraction of articles and quality assessments were performed by two authors using predefined data fields and specific tools (Animals in Research Reporting In Vivo Experiments (ARRIVE) guideline and Systematic Review Centre for Laboratory animal Experimentation (SYRCLE) tool). Twenty-three studies were included in the review: 4 in vitro studies, 18 in vivo studies, and 1 both in vitro and in vivo study. From in vitro works, sex differences were found in the gene expression of inflammatory molecules, hormonal receptors, and in responsiveness to hormonal stimulation. In vivo research showed a great heterogeneity of animal models mainly focused on the histopathological aspects rather than on the analysis of sex-related molecular mechanisms. This review highlights that many gaps in knowledge still exist; improvementsin the selection and reporting of animal models, the use of advanced in vitro models, and multiomics analyses might contribute to developing a personalized gender-based medicine.

Review Article: Is Wnt Signaling an Attractive Target for the Treatment of Osteoarthritis?

Osteoarthritis is the most common chronic joint disease affecting millions of people worldwide and a leading cause of pain and disability. Increasing incidence of obesity and aging of the population are two factors that suggest that the impact of osteoarthritis will further increase at the society level. Currently, there are no drugs available that can manage both structural damage to the joint or the associated pain. Increasing evidence supports the view that the Wnt signaling pathway plays an important role in this disease. The current concept, based on genetic and functional studies, indicates that tight regulation of Wnt signaling in cartilage is essential to keep the joint healthy. In this review, we discuss how this concept has evolved, provide insights into the regulation of Wnt signaling, in particular by Wnt modulators such as frizzled-related protein and DOT1-like histone lysine methyltransferase, and summarize preclinical evidence and molecular mechanisms of lorecivivint, the first Wnt antagonist in clinical development for osteoarthritis.

The regulation of skeletal muscle fiber-type composition by betaine is associated with NFATc1/MyoD

Increasing evidence indicates that muscular dysfunction or alterations in skeletal muscle fiber-type composition not only are involved in muscle metabolism and function but also can limit functional capacity. Therefore, understanding the mechanisms regulating key events during skeletal myogenesis is necessary. Betaine is a naturally occurring component of commonly eaten foods. Here, we showed that 10 mM betaine supplementation in vitro significantly repressed myoblast proliferation and enhanced myoblast differentiation. This effect can be mediated by regulation of miR-29b-3p. Further analysis showed that betaine supplementation in vitro regulated skeletal muscle fiber-type composition through the induction of NFATc1 and the negative regulation of MyoD expression. Furthermore, mice fed with 10 mM betaine in water for 133 days showed no impairment in overall health. Consistently, betaine supplementation increased muscle mass, promoted muscle formation, and modulated the ratio of fiber types in skeletal muscle in vivo. These findings shed light on the diverse biological functions of betaine and indicate that betaine supplementation may lead to new therapies for diseases such as muscular dystrophy or other diseases related to muscle dysfunction. KEY MESSAGES: Betaine supplementation inhibits proliferation and promotes differentiation of C2C12 myoblasts. Betaine supplementation regulates fast to slow muscle fiber-type conversion and is associated with NFATc1/MyoD. Betaine supplementation enhances skeletal myogenesis in vivo. Betaine supplementation does not impair health of mice.

Cushioning the cartilage: a canonical Wnt restricting matter

Wnt signalling pathways have key roles in joint development, homeostasis and disease, particularly in osteoarthritis. New data is starting to reveal the importance of tightly regulating canonical Wnt signalling pathway activation to maintain homeostasis and health in articular cartilage. In addition to the presence of different Wnt antagonists that limit pathway activation in articular cartilage, the reciprocal crosstalk between the canonical and non-canonical cascades and competitive antagonism between different Wnt ligands seem to be critical in restraining excessive Wnt pathway activation. Changes in transcriptional complex assembly upon Wnt pathway activation, epigenetic modulation of target gene transcription, in particular through histone modifications, and complex interactions between the Wnt signalling pathway and other signalling pathways, are also instrumental in adjusting Wnt signalling. In this Review, the cellular and molecular mechanisms involved in fine-tuning canonical Wnt signalling in the joint are updated, with a focus on the articular cartilage. The interventions for preventing or treating osteoarthritis are also discussed, which should aim to limit disease-associated excessive canonical Wnt activity to avoid joint damage.

FRZB and melusin, overexpressed in LGMD2A, regulate integrin β1D isoform replacement altering myoblast fusion and the integrin-signalling pathway

Limb-girdle muscular dystrophy type 2A (LGMD2A) is characterised by muscle wasting and progressive degeneration of proximal muscles because of mutations in the CAPN3 gene. However, the underlying pathophysiological mechanisms of muscle degeneration are still not well understood. The objective of this study was to assess the relevance of genes with differential expression in the muscle of LGMD2A patients. For this purpose, we analysed their in vitro expression in primary cultures of human myoblasts and myotubes. Abnormal fusion was observed in the myotubes of these patients, which may be explained by the lack of physiological replacement of integrin β1D. Owing to this observation, we focused on deregulated genes coding proteins that directly interact with integrin, ITGB1BP2 and CD9, as well as FRZB gene, because of its in vitro upregulation in myotubes. Silencing studies established that these genes are closely regulated, CD9 and FRZB being positive regulators of the expression of ITGB1BP2, and in turn, this gene being a negative regulator of the expression of FRZB. Interestingly, we observed that FRZB regulates integrin β1D expression, its silencing increasing integrin β1D expression to levels similar to those in controls. Finally, the administration of LiCl, an enhancer of the Wnt-signalling pathway showed similar experimentally beneficial effects, suggesting FRZB silencing or LiCl administration as potential therapeutic targets, though further studies are required.

Using mouse models to investigate the pathophysiology, treatment, and prevention of post-traumatic osteoarthritis

Post-traumatic osteoarthritis (PTOA) is defined by its development after joint injury. Factors contributing to the risk of PTOA occurring, the rate of progression, and degree of associated disability in any individual, remain incompletely understood. What constitutes an "OA-inducing injury" is not defined. In line with advances in the traumatic brain injury field, we propose the scope of PTOA-inducing injuries be expanded to include not only those causing immediate structural damage and instability (Type I), but also those without initial instability/damage from moderate (Type II) or minor (Type III) loading severity. A review of the literature revealed this full spectrum of potential PTOA subtypes can be modeled in mice, with 27 Type I, 6 Type II, and 4 Type III models identified. Despite limitations due to cartilage anatomy, joint size, and bio-fluid availability, mice offer advantages as preclinical models to study PTOA, particularly genetically modified strains. Histopathology was the most common disease outcome, cartilage more frequently studied than bone or synovium, and meniscus and ligaments rarely evaluated. Other methods used to examine PTOA included gene expression, protein analysis, and imaging. Despite the major issues reported by patients being pain and biomechanical dysfunction, these were the least commonly measured outcomes in mouse models. Informative correlations of simultaneously measured disease outcomes in individual animals, was rarely done in any mouse PTOA model. This review has identified knowledge gaps that need to be addressed to increase understanding and improve prevention and management of PTOA. Preclinical mouse models play a critical role in these endeavors. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:424-439, 2017.

Diametrical diseases reflect evolutionary-genetic tradeoffs: Evidence from psychiatry, neurology, rheumatology, oncology and immunology

Tradeoffs centrally mediate the expression of human adaptations. We propose that tradeoffs also influence the prevalence and forms of human maladaptation manifest in disease. By this logic, increased risk for one set of diseases commonly engenders decreased risk for another, diametric, set of diseases. We describe evidence for such diametric sets of diseases from epidemiological, genetic and molecular studies in four clinical domains: (i) psychiatry (autism vs psychotic-affective conditions), (ii) rheumatology (osteoarthritis vs osteoporosis), (iii) oncology and neurology (cancer vs neurodegenerative disorders) and (iv) immunology (autoimmunity vs infectious disease). Diametric disorders are important to recognize because genotypes or environmental factors that increase risk for one set of disorders protect from opposite disorders, thereby providing novel and direct insights into disease causes, prevention and therapy. Ascertaining the mechanisms that underlie disease-related tradeoffs should also indicate means of circumventing or alleviating them, and thus reducing the incidence and impacts of human disease in a more general way.

Reduced expression of Sfrp1 during chondrogenesis and in articular chondrocytes correlates with osteoarthritis in STR/ort mice

To circumvent the problems of genetic and environmental diversity hampering the analysis in humans, we turned to a murine model for human knee osteoarthritis (OA) and fine mapped a previously defined OA-quantitative trait locus (QTL). We here focused on one of the candidate genes within the OA-QTL encoding the Wnt antagonist secreted frizzled related protein 1 (Sfrp1). Sequence analysis of the Sfrp1 gene in the OA strain STR/ort revealed 23 polymorphic changes with a potential to alter the gene expression. Indeed, a reduced expression in STR/ort mice was demonstrated for articular chondrocytes and hypertrophic chondrocytes of the femoral growth plate as shown by immunohistochemistry. RT-PCR of in vitro generated mesenchymal stem cells (MSC) and chondrogenically differentiated MSC (cMSC) confirmed the reduced Sfrp1 expression in STR/ort mice. This reduced Sfrp1 expression in MSC correlated with an increased amount of cytoplasmic β-catenin, a downregulation of the Wnt target gene PPARγ and an upregulation of Runx2 as well as a preferential differentiation of the MSC along the osteoblasts lineage. Given the role of Wnt signalling during chondrogenesis and in maintaining the integrity of the long lived articular chondrocytes, we conclude from our results that the reduced Sfrp1 expression in STR/ort mice not only leads to an increased activation of the Wnt/β-catenin signalling early in life but also renders the articular cartilage prone to premature ageing and to the development of OA.

Evolutionary aspects of human exercise--born to run purposefully

This article is intended to raise awareness of the adaptive value of endurance exercise (particularly running) in the evolutionary history of humans, and the implications of the genetic disposition to exercise for the aging populations of modern technology-driven societies. The genome of Homo sapiens has evolved to support the svelte phenotype of an endurance runner, setting him/her apart from all other primates. The cellular and molecular mechanisms underlying the competitive advantages conferred by exercise capacity in youth can also provide a survival benefit beyond the reproductive period. These mechanisms include up-regulation of genes encoding proteins involved in protecting cells against oxidative stress, disposing of damaged proteins and organelles, and enhancing bioenergetics. Particularly fascinating are the signaling mechanisms by which endurance running changes the structure and functional capabilities of the brain and, conversely, the mechanisms by which the brain integrates metabolic, cardiovascular and behavioral responses to exercise. As an emerging example, I highlight the roles of brain-derived neurotrophic factor (BDNF) as a mediator of the effects of exercise on the brain, and BDNF's critical role in regulating metabolic and cardiovascular responses to endurance running. A better understanding of such 'healthspan-extending' actions of endurance exercise may lead to new approaches for improving quality of life as we advance in the coming decades and centuries.

Biological aspects of early osteoarthritis

PURPOSE

Early OA primarily affects articular cartilage and involves the entire joint, including the subchondral bone, synovial membrane, menisci and periarticular structures. The aim of this review is to highlight the molecular basis and histopathological features of early OA.

METHODS

Selective review of literature.

RESULTS

Risk factors for developing early OA include, but are not limited to, a genetic predisposition, mechanical factors such as axial malalignment, and aging. In early OA, the articular cartilage surface is progressively becoming discontinuous, showing fibrillation and vertical fissures that extend not deeper than into the mid-zone of the articular cartilage, reflective of OARSI grades 1.0-3.0. Early changes in the subchondral bone comprise a progressive increase in subchondral plate and subarticular spongiosa thickness. Early OA affects not only the articular cartilage and the subchondral bone but also other structures of the joint, such as the menisci, the synovial membrane, the joint capsule, ligaments, muscles and the infrapatellar fat pad. Genetic markers or marker combinations may become useful in the future to identify early OA and patients at risk.

CONCLUSION

The high socioeconomic impact of OA suggests that a better insight into the mechanisms of early OA may be a key to develop more targeted reconstructive therapies at this first stage of the disease.

LEVEL OF EVIDENCE

Systematic review, Level II.

Analysis of osteoarthritis in a mouse model of the progeroid human DNA repair syndrome trichothiodystrophy

The increasing average age in developed societies is paralleled by an increase in the prevalence of many age-related diseases such as osteoarthritis (OA), which is characterized by deformation of the joint due to cartilage damage and increased turnover of subchondral bone. Consequently, deficiency in DNA repair, often associated with premature aging, may lead to increased pathology of these two tissues. To examine this possibility, we analyzed the bone and cartilage phenotype of male and female knee joints derived from 52- to 104-week-old WT C57Bl/6 and trichothiodystrophy (TTD) mice, who carry a defect in the nucleotide excision repair pathway and display many features of premature aging. Using micro-CT, we found bone loss in all groups of 104-week-old compared to 52-week-old mice. Cartilage damage was mild to moderate in all mice. Surprisingly, female TTD mice had less cartilage damage, proteoglycan depletion, and osteophytosis compared to WT controls. OA severity in males did not significantly differ between genotypes, although TTD males had less osteophytosis. These results indicate that in premature aging TTD mice age-related changes in cartilage were not more severe compared to WT mice, in striking contrast with bone and many other tissues. This segmental aging character may be explained by a difference in vasculature and thereby oxygen load in cartilage and bone. Alternatively, a difference in impact of an anti-aging response, previously found to be triggered by accumulation of DNA damage, might help explain why female mice were protected from cartilage damage. These findings underline the exceptional segmental nature of progeroid conditions and provide an explanation for pro- and anti-aging features occurring in the same individual.