Research Projects:

The Delaware Center for Musculoskeletal Research Projects Awards offer needed assistance to early-career investigators on the path to research independence.

Summary: Temporomandibular joint disorder (TMJD) is a heterogeneous disease which is characterized by severe pain that negatively affects masticatory function. In the United States, TMJDs affect over 10 million individuals predominantly in middle-aged adults (20-40 years-of-age) with a higher prevalence in women than in men (NIDCR). Treatment outcomes for TMJDs are highly variable which may be attributed to the gap in knowledge of the underlying pathogenic mechanisms. Hence, a better understanding of the major contributors and causative mechanisms in TMJD may significantly improve outcome following therapeutic and/or surgical intervention. Whereas the contribution of disc degeneration in TMJD is well established, the functional consequence of impaired tendon and tendon-bone insertion in TMJD is poorly understood. Recent studies have shown that defects in tendon and tendon-bone insertion development as well as dysregulated cell signaling that negatively affect these tissues can cause deformities in TMJ (Roberts et al., 2019). Jaw movement creates biomechanical forces that are generated by the pterygoid and masseter muscles which are transmitted across tendon and tendon-bone insertion and connect to the mandibular condyle. Our preliminary studies have shown that impaired telopeptide lysyl hydroxylation and cross-linking due to Fkbp10-deficiency induces heterotopic ossification (HO) in TMJ and substantially increases mandibular condyle length and width in postnatal mice. In addition, we found that Fkbp10 deletion induces aberrant aSMA-expressing cells in the tendon and tendon-bone insertion concomitant with an increase in ectopic bone formation in the medial condyle of TMJ. Preliminary data also showed enhanced pSmad1/5 expression in the tendon and tendon-bone insertion in TMJ, indicating dysregulated BMP signaling. Based on these preliminary data, we will test the hypothesis that alterations in telopeptide lysyl hydroxylation in tendons of TMJ causes HO and functional defects due to abnormal differentiation of aSMA-expressing progenitor cells that is dependent on aberrant BMP signaling. Specifically, we will (Aim 1) determine the functional consequence of impaired procollagen I telopeptide lysyl hydroxylation and cross-linking in TMJ homeostasis, (Aim 2) determine if Fkbp10 deletion triggers tissue injury and alters aSMA-expressing progenitor cell populations, and (Aim 3) determine if pharmacological inhibition of aberrant BMP signaling can prevent HO in TMJ of Fkbp10-deficient mice. The proposed studies will provide the foundational basis and additional preliminary data to develop a competitive investigator-initiated R01 or equivalent NIH research proposal.​

Summary: Currently, there are no lasting treatments to restore degenerated articular cartilage in people with osteoarthritis. Many treatment strategies for osteoarthritis attempt to restore the extracellular matrix (ECM) to its native stiffness, but these approaches have not been successful. Instead, this project focuses on the ability for healthy cartilage to swell, which in conjunction with the stiffness of the ECM, helps support load and lower friction. The ability for cartilage to swell, or its osmotic pressure, is derived from the negatively charged sidechains of proteoglycans (aggrecan). These negatively charged groups (glycosaminoglycans) are lost in osteoarthritis. To restore the osmotic pressure, often measured as the fixed charge density, we propose developing synthetic aggrecan mimics made from polystyrene sulfonate. In conjunction with this treatment, we will develop a platform capable of resolving cartilage swelling in situ, which will help determine our treatment efficacy, while also contributing to a timeline of mechanical changes in the cartilage. To facilitate physiological relevance, our platform will evaluate swelling on full-stack equine explants. This project will first establish how typical OA-like processes, like enzymatic digestion, impact the in situ swelling in our cartilage explants. Then, we will test how more physiologically relevant OA precursors, such as mechanical injury or inflammation, lead to aberrant swelling behavior. Due to the orthogonal nature of swelling measurements to standard mechanical testing, we will be able to decouple mechanical changes derived by the osmotic pressure of the cartilage from those resulting from matrix damage. Finally, after synthesis of our polymer aggrecan mimics, we will test if our intervention can revert the swelling behavior of damaged cartilage into the swelling behavior seen in native cartilage. The impact of this work is a new treatment strategy based on the swelling behavior of cartilage: while swelling is equally important to the mechanical function of cartilage, it has not seen a similar level of research as an intervention target. We hypothesize that without restoring the swelling behavior, current OA treatment strategies are unlikely to be successful in the long term.

Summary: Chronic and acute inflammation are significant contributors to skeletal muscle pathology in multiple diseases. Severe inflammation associated with sepsis has profound short- and long-term effects on muscle. Sepsis is characterized by a dysregulated immune response to infection that can alter muscle force generation, wasting, and bioenergetics. Survivors of sepsis have increased risk for the development of persistent acquired weakness syndromes. The inflammatory response in sepsis is mediated by the release of pro-inflammatory cytokines, including tumor necrosis factor-alpha (TNF-α) and interleukin 1 beta (IL-1β). While we know that sepsis-induced changes in skeletal muscle are associated with inflammation, the mechanisms underlying muscle dysfunction in sepsis are not well understood, and there is a significant need to capture the evolution of these impairments to establish effective treatment strategies. Harnessing in vitro models of cytokine-induced myopathy in human skeletal muscle can inform and elucidate fundamental mechanisms of pathology in sepsis enabling development of effective treatments. Resistance training is a widely accepted prescriptive treatment for rebuilding muscle strength and mass. However, post-recovery resistance training has minimal long-term effects in many sepsis patients, and recent studies suggest that early (pre-recovery) physical therapy may preserve muscle fiber cross-sectional area though not strength, indicating a need for further analysis of the complex evolution of sepsis. This evidence formed the cornerstone of our hypothesis that inflammation limits the therapeutic effects of resistance training, which will be tested in a 3D in vitro organoid model.

Summary: Osteoarthritis (OA) is an irreversible, debilitating, and chronic disease. Current OA treatments are either surgical or aimed at pain with poor long-term reparative outcomes. Thus, there is a need to develop new OA treatments. Targeting the actin cytoskeleton in chondrocytes may be a promising strategy for treatments against OA. Actin is an abundant, ubiquitously expressed protein in cells that exists as globular (G-) molecules which polymerize to form filamentous (F-) actin. Proper F-actin organization into diverse higher order structures is required for the maintenance of chondrocyte morphology which determines phenotype. Despite strong links between actin reorganization and the chondrocyte phenotype it remains unclear if targeting actin reorganization is a feasible strategy against OA. This is due in large part to two critical knowledge gaps: 1) It remains unclear how specific deregulated F-actin populations (i.e. stress fibers) can be abolished, while retaining other vital F-actin networks (i.e. cortical actin). To fill this knowledge gap, a greater understanding on the regulation of F-actin networks by actin binding proteins is needed. 2) It is unclear if F-actin reorganization occurs and plays a role in OA pathogenesis in native chondrocytes. Previous studies have determined that treatment of chondrocyte with inflammatory mediators results in reorganization of cortical F-actin networks into stress fibers. However, these studies were performed on in vitro cultured cells. It is unknown if F-actin occurs in vivo. To assess actin reorganization in cartilage, the development of new high-to-super resolution imaging methodology of chondrocytes within native cartilage is required. Our long-term goal is to enable actin-based interventions against OA.

Pilots 2024-25:

Summary: Anterior cruciate ligament (ACL) injuries and subsequent reconstruction surgery (ACLR) have an incidence rate of approximately 200,000 a year in the United States. One of the most used graft types especially among young athletes is the bone-patellar tendon-bone (BTPB) autograft, but the post operative healing of this graft site is not well understood. Objectives of this proposed project are to investigate the changes in patellar tendon morphology (B-mode ultrasound imaging, MRI) and mechanical properties (shear wave elastography and shear wave tensiometry) of the patellar tendon throughout the first six months of healing after BPTB graft harvest.​

Summary: While skeletal muscle spontaneously regenerates in response to minor injuries, more severe muscle injuries undergo irreversible damage due to prolonged and degenerating pro-inflammatory responses. Anti-inflammatory immune cells, such as regulatory T-cells (Tregs), can suppress these pro-inflammatory responses and secrete factors that stimulate muscle repair. However, the recruitment of Tregs to severe muscle injury sites is impaired. There is a critical need for approaches to enhance anti-inflammatory responses in severe muscle injuries. Cytokine-releasing biomaterials offer a means to control the number of anti-inflammatory immune cells at muscle injury sites. Our central hypothesis is that an injectable, alginate biomaterial providing sustained delivery of interleukin-33 (IL-33) to recruit Tregs and interleukin-2 (IL-2) to induce Treg proliferation can enhance the number of Tregs at sites of ischemic muscle injury in vivo; the enhanced presence of Tregs will reduce pro-inflammatory muscle degeneration and directly stimulate blood vessel, nerve, and muscle regeneration. This central hypothesis will be tested with the following aims: 1) engineer an injectable, alginate hydrogel that provides controlled delivery of IL-33 and IL-2 in vitro and 2) evaluate the ability of the engineered hydrogel to enhance the number of Tregs and promote regeneration in ischemic muscle in vivo. In Aim 1, we will utilize our established injectable alginate delivery system and modify it to provide sustained release of IL-2 and IL-33 for at least two weeks, which is the time scale of inflammation in severe muscle injury. The alginate modifications include regulating the degradation and net charge within the hydrogel. In Aim 2, we will collect preliminary data to evaluate how the hydrogel can enhance the number of Tregs at muscle injury sites and promote functional regeneration in vivo in a murine model of hindlimb ischemia. This model will involve ligating the femoral and iliac artery and vein in BALB/c mice, which results in ischemia in the downstream muscle. We will inject our alginate biomaterial into the ischemic muscle and evaluate both functional and histological blood vessel, nerve, muscle regeneration. We will also quantify different types of immune cells recruited to the ischemic muscle. This proposal is innovative because it develops a novel biomaterial to regulate adaptive immune responses in muscle injuries. Furthermore, success of the proposal will yield an off-the-shelf immunotherapy for reducing inflammation and promoting wound healing in muscle injuries.

Summary: Every year in the USA, one out of every 33 babies is born with birth defects. Of these, craniosynostosis (CS) is among the most prevalent, affecting ~1:2500 live births. CS is characterized by premature closure of the cranial sutures, the fibrous joints between the osteogenic fronts (OF) of cranial bones. Recently, a clinical study reported CS, particularly affecting the sagittal suture, in individuals carrying SIX1 variants that are predicted to produce haploinsufficiency (p.Q11X and p.Q22X) or a dominant negative action (p.R110W). Interestingly, these variants are linked to branchio-oto-renal syndrome (BOR), another prevalent craniofacial defect, suggesting that CS may be an undiagnosed feature of BOR. To test the impact of decreased Six1 dosage (Six1 haploinsufficiency in mouse) on cranial bone and suture morphology, and on suture patency maintenance, I will perform quantitative morphological (Aim 1) and histological (Aim 2) analyses using Six1-het mice (modeling reduced Six1 dosage). Results will characterize the cranial bone and suture phenotype (Aim 1) and will initiate to dissect the mechanism(s) leading to CS in patients with SIX1 variants (Aim 2). Data generated in this proposal will be crucial for the characterization of Six1-het mice as a novel disease model for CS and for proposing future mechanistic experiments. These data and mice will be included in future grant applications in which I will continue to dissect in mice the cellular and molecular mechanisms leading to CS in patients with BOR SIX1 variants, and to develop corrective strategies with clinicians and biomedical engineers for SIX1-associated craniosynostosis.