Oligonucleotide Therapeutics for Age-Related Musculoskeletal Disorders: Successes and Challenges

Age-related disorders of the musculoskeletal system including sarcopenia, osteoporosis and arthritis represent some of the most common chronic conditions worldwide, for which there remains a great clinical need to develop safer and more efficacious pharmacological treatments. Collectively, these conditions involve multiple tissues, including skeletal muscle, bone, articular cartilage and the synovium within the joint lining. In this review, we discuss the potential for oligonucleotide therapies to combat the unmet clinical need in musculoskeletal disorders by evaluating the successes of oligonucleotides to modify candidate pathological gene targets and cellular processes in relevant tissues and cells of the musculoskeletal system. Further, we discuss the challenges that remain for the clinical development of oligonucleotides therapies for musculoskeletal disorders and evaluate some of the current approaches to overcome these.

miR-486-5p and miR-22-3p Enable Megakaryocytic Differentiation of Hematopoietic Stem and Progenitor Cells without Thrombopoietin

Megakaryocytes release submicron size microparticles (MkMPs) in circulation. We have shown that MkMPs target CD34+ hematopoietic stem/progenitor cells (HSPCs) to induce megakaryocytic differentiation, and that small RNAs in MkMPs play an important role in the development of this phenotype. Here, using single-molecule real-time (SMRT) RNA sequencing (RNAseq), we identify the synergetic effect of two microRNAs (miRs), miR-486-5p and miR-22-3p (highly enriched in MkMPs), in driving the Mk differentiation of HSPCs in the absence of thrombopoietin (TPO). Separately, our data suggest that the MkMP-induced Mk differentiation of HSPCs is enabled through JNK and PI3K/Akt/mTOR signaling. The interaction between the two signaling pathways is likely mediated by a direct target of miR-486-5p and a negative regulator of PI3K/Akt signaling, the phosphatase and tensin homologue (PTEN) protein. Our data provide a possible mechanistic explanation of the biological effect of MkMPs in inducing megakaryocytic differentiation of HSPCs, a phenotype of potential physiological significance in stress megakaryopoiesis.

A Head-to-Head Comparison of a Free Fatty Acid Formulation of Omega-3 Pentaenoic Acids Versus Icosapent Ethyl in Adults With Hypertriglyceridemia: The ENHANCE-IT Study

Background MAT9001 is an omega-3 free fatty acid (FFA) formulation containing mainly eicosapentaenoic acid (EPA) and docosapentaenoic acid (DPA). Compared with icosapent ethyl (EPA-ethyl esters [EE]), EPA+DPA-FFA previously showed enhanced triglyceride lowering and higher plasma EPA when both were administered once daily with a very-low fat diet. This trial compared pharmacodynamic responses and plasma omega-3 levels following twice daily dosing, with meals, of EPA+DPA-FFA and EPA-EE in hypertriglyceridemic subjects consuming a Therapeutic Lifestyle Changes diet. Methods and Results This open-label, randomized, 2-way crossover trial, with 28-day treatment periods separated by ≥28-day washout, was conducted at 8 US centers and included 100 subjects with fasting triglycerides 1.70 to 5.64 mmol/L (150-499 mg/dL) (median 2.31 mmol/L [204 mg/dL]; 57% women, average age 60.3 years). The primary end point was least squares geometric mean percent change from baseline plasma triglycerides. In the 94 subjects with analyzable data for both treatment periods, EPA+DPA-FFA and EPA-EE reduced least squares geometric mean triglycerides from baseline: 20.9% and 18.3%, respectively (P=not significant). EPA+DPA-FFA reduced least squares geometric mean high-sensitivity C-reactive protein by 5.8%; EPA-EE increased high-sensitivity C-reactive protein by 8.5% (P=0.034). EPA+DPA-FFA increased least squares geometric mean plasma EPA, DPA, and total omega-3 (EPA+docosahexaenoic acid+DPA) concentrations by 848%, 177%, and 205%, respectively, compared with corresponding changes with EPA-EE of 692%, 140%, and 165% (all P<0.001). EPA+DPA-FFA increased docosahexaenoic acid by 1.7%; EPA-EE decreased docosahexaenoic acid by 3.3% (P=0.011). Lipoprotein cholesterol and apolipoprotein responses did not differ between treatments. Conclusions EPA+DPA-FFA raised plasma EPA, DPA, and total omega-3 significantly more than did EPA-EE. EPA+DPA-FFA also reduced triglycerides and high-sensitivity C-reactive protein without increasing low-density lipoprotein cholesterol. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT04177680.

Autophagy, apoptosis, and neurodevelopmental genes might underlie selective brain region vulnerability in attention-deficit/hyperactivity disorder

Large-scale brain imaging studies by the ENIGMA Consortium identified structural changes associated with attention-deficit/hyperactivity disorder (ADHD). It is not clear why some brain regions are impaired and others spared by the etiological risks for ADHD. We hypothesized that spatial variation in brain cell organization and/or pathway expression levels contribute to selective brain region vulnerability (SBRV) in ADHD. In this study, we used the largest available collection of magnetic resonance imaging (MRI) results from the ADHD ENIGMA Consortium (subcortical MRI n = 3242; cortical MRI n = 4180) along with high-resolution postmortem brain microarray data from Allen Brain Atlas (donors n = 6) from 22 brain regions to investigate our SBRV hypothesis. We performed deconvolution of the bulk transcriptomic data to determine abundances of neuronal and nonneuronal cells in the brain. We assessed the relationships between gene-set expression levels, cell abundance, and standardized effect sizes representing regional changes in brain sizes in cases of ADHD. Our analysis yielded significant correlations between apoptosis, autophagy, and neurodevelopment genes with smaller brain sizes in ADHD, along with associations to regional abundances of astrocytes and oligodendrocytes. The lack of enrichment of common genetic risk variants for ADHD within implicated gene sets suggests an environmental etiology to these differences. This work provides novel mechanistic clues about SBRV in ADHD.

Comparison Study of Stem Cell-Derived Extracellular Vesicles for Enhanced Osteogenic Differentiation

Stem cell-derived extracellular vesicles (EVs) have shown great promise in the field of regenerative medicine and tissue engineering. Recently, human bone marrow-derived mesenchymal stem cell (BMSC)-derived EVs have been considered for bone tissue engineering applications. In this study, we evaluated the osteogenic capability of placental stem cell (PSC)-derived EVs and compared them to the well-characterized BMSC-derived EVs. EVs were extracted from three designated time points (0, 7, and 21 days) after osteogenic differentiation. The results showed that the PSC-derived EVs had much higher protein and lipid concentrations than EVs derived from BMSCs. The extracted EVs were characterized by observing their morphology and size distribution before utilizing next-generation sequencing to determine their microRNA (miRNA) profiles. A total of 306 miRNAs within the EVs were identified, of which 64 were significantly expressed in PSC-derived EVs that related to osteogenic differentiation. In vitro osteogenic differentiation study indicated the late-stage (21-day extracted)-derived EVs higher osteogenic enhancing capability when compared with the early stage-derived EVs. We demonstrated that EVs derived from PSCs could be a new source of EVs for bone tissue engineering applications.

Muscle fibrosis in the soft palate: Delivery of cells, growth factors and anti-fibrotics

The healing of skeletal muscle injuries after major trauma or surgical reconstruction is often complicated by the development of fibrosis leading to impaired function. Research in the field of muscle regeneration is mainly focused on the restoration of muscle mass while far less attention is paid to the prevention of fibrosis. In this review, we take as an example the reconstruction of the muscles in the soft palate of cleft palate patients. After surgical closure of the soft palate, muscle function during speech is often impaired by a shortage of muscle tissue as well as the development of fibrosis. We will give a short overview of the most common approaches to generate muscle mass and then focus on strategies to prevent fibrosis. These include anti-fibrotic strategies that have been developed for muscle and other organs by the delivery of small molecules, decorin and miRNAs. Anti-fibrotic compounds should be delivered in aligned constructs in order to obtain the organized architecture of muscle tissue. The available techniques for the preparation of aligned muscle constructs will be discussed. The combination of approaches to generate muscle mass with anti-fibrotic components in an aligned muscle construct may greatly improve the functional outcome of regenerative therapies for muscle injuries.

Use of uniformly sized muscle fiber fragments for restoration of muscle tissue function

Treatment of extensive muscle loss due to traumatic injury, congenital defects, or tumor ablations is clinically challenging. The current treatment standard is grafting of autologous muscle flaps; however, significant donor site morbidity and graft tissue availability remain a problem. Alternatively, muscle fiber therapy has been attempted to treat muscle injury by transplanting single fibers into the defect site. However, irregularly organized long fibers resulted in low survivability due to delay in vascular and neural integration, thus limiting the therapeutic efficacy. Therefore, no effective method is available to permanently restore extensive muscle injuries. To address the current limitations, we developed a novel method that produces uniformly sized native muscle fiber fragments (MFFs) for muscle transplantation. We hypothesized that fragmentation of muscle fibers into small and uniformly sized fragments would allow for rapid reassembly and efficient engraftment within the defect site, resulting in accelerated recovery of muscle function. Our results demonstrate that the processed MFFs have a dimension of approximately 100 μm and contain living muscle cells on extracellular matrices. In preclinical animal studies using volumetric defect and urinary incontinence models, histological and functional analyses confirmed that the transplanted MFFs into the injury sites were able to effectively integrate with host muscle tissue, vascular, and neural systems, which resulted in significant improvement of muscle function and mass. These results indicate that the MFF technology platform is a promising therapeutic option for the restoration of muscle function and can be applied to various muscle defect and injury cases.

Myogenic regulatory factors: The orchestrators of myogenesis after 30 years of discovery

Prenatal and postnatal myogenesis share many cellular and molecular aspects. Myogenic regulatory factors are basic Helix-Loop-Helix transcription factors that indispensably regulate both processes. These factors (Myf5, MyoD, Myogenin, and MRF4) function as an orchestrating cascade, with some overlapped actions. Prenatally, myogenic regulatory factors are restrictedly expressed in somite-derived myogenic progenitor cells and their derived myoblasts. Postnatally, myogenic regulatory factors are important in regulating the myogenesis process via satellite cells. Many positive and negative regulatory mechanisms exist either between myogenic regulatory factors themselves or between myogenic regulatory factors and other proteins. Upstream factors and signals are also involved in the control of myogenic regulatory factors expression within different prenatal and postnatal myogenic cells. Here, the authors have conducted a thorough and an up-to-date review of the myogenic regulatory factors since their discovery 30 years ago. This review discusses the myogenic regulatory factors structure, mechanism of action, and roles and regulations during prenatal and postnatal myogenesis. Impact statement Myogenic regulatory factors (MRFs) are key players in the process of myogenesis. Despite a considerable amount of literature regarding these factors, their exact mechanisms of actions are still incompletely understood with several overlapped functions. Herein, we revised what has hitherto been reported in the literature regarding MRF structures, molecular pathways that regulate their activities, and their roles during pre- and post-natal myogenesis. The work submitted in this review article is considered of great importance for researchers in the field of skeletal muscle formation and regeneration, as it provides a comprehensive summary of all the biological aspects of MRFs and advances a better understanding of the cellular and molecular mechanisms regulating myogenesis. Indeed, attaining a better understanding of MRFs could be utilized in developing novel therapeutic protocols for multiple myopathies.

MicroRNA Dysregulation in Aging and Pathologies of the Skeletal Muscle

Skeletal muscle is one of the biggest organs of the body with important mechanistic and metabolic functions. Muscle homeostasis is controlled by environmental, genetic, and epigenetic factors. Indeed, MiRNAs, small noncoding RNAs robust regulators of gene expression, have and have been shown to regulate muscle homeostasis on several levels: through controlling myogenesis, muscle growth (hypertrophy) and atrophy, as well as interactions of muscle with other tissues. Given the large number of MiRNA target genes and the important role of MiRNAs in most physiological processes and various diseases, MiRNAs may have an enormous potential as therapeutic targets against numerous disorders, including pathologies of muscle. The purpose of this review is to present the current knowledge of the role of MiRNAs in skeletal muscle homeostasis and pathologies and the potential of MiRNAs as therapeutics for skeletal muscle wasting, with particular focus on the age- and disease-related loss of muscle mass and function.

Muscle-specific microRNA-206 targets multiple components in dystrophic skeletal muscle representing beneficial adaptations

Over the last several years, converging lines of evidence have indicated that miR-206 plays a pivotal role in promoting muscle differentiation and regeneration, thereby potentially impacting positively on the progression of neuromuscular disorders, including Duchenne muscular dystrophy (DMD). Despite several studies showing the regulatory function of miR-206 on target mRNAs in skeletal muscle cells, the effects of overexpression of miR-206 in dystrophic muscles remain to be established. Here, we found that miR-206 overexpression in mdx mouse muscles simultaneously targets multiple mRNAs and proteins implicated in satellite cell differentiation, muscle regeneration, and at the neuromuscular junction. Overexpression of miR-206 also increased the levels of several muscle-specific mRNAs/proteins, while enhancing utrophin A expression at the sarcolemma. Finally, we also observed that the increased expression of miR-206 in dystrophin-deficient mouse muscle decreased the production of proinflammatory cytokines and infiltration of macrophages. Taken together, our results show that miR-206 acts as a pleiotropic regulator that targets multiple key mRNAs and proteins expected to provide beneficial adaptations in dystrophic muscle, thus highlighting its therapeutic potential for DMD.