Faculty Bibliography

Aging populations worldwide face an increasing burden of age-related chronic conditions, necessitating a deeper understanding of the underlying mechanisms. Purine metabolism has emerged as a crucial player in the pathophysiology of aging, affecting various tissues and organs. Dysregulation of purine metabolism, particularly alterations in extracellular adenosine levels and adenosine receptor signaling, contributes to age-related musculoskeletal problems, cardiovascular diseases, inflammation, and impaired immune responses. Changes in purine metabolism are associated with diminished tissue repair and regeneration, altered bone density, and impaired muscle regeneration. Mechanistically, age-related alterations in purine metabolism involve reductions in extracellular adenosine production, impaired autocrine signaling, and dysregulated expression of CD73 and CD39. Targeting adenosine receptors, such as A_2A and A_2B receptors, emerges as a promising therapeutic approach to mitigate age-related conditions, including sarcopenia, obesity, osteoarthritis, and impaired wound healing. Since we cannot reverse time, understanding the intricate molecular interplay between purine metabolism and aging-related pathologies holds significant potential for developing novel therapeutic strategies to improve the health and quality of life of aging populations. In this review, we compile the findings related to purine metabolism during aging in several tissues and organs and provide insights into how these signals can be manipulated to circumvent the deleterious effects of the passage of time on our body.

It has been well established that adenosine plays a key role in the control of inflammation through G protein coupled receptors and recently shown that it can regulate thermogenesis. Here we investigated the specific requirements of the adenosine A2A receptor (A2AR) in mature adipocytes for thermogenic functionality and metabolic homeostasis. We generated fat tissue-specific adenosine A2AR KO mice to assess the influence of signaling through this receptor on brown and beige fat functionality, obesity, insulin sensitivity, inflammation, and liver function. Fat-specific A2AR KO and WT littermate mice were compared for potential differences in cold tolerance and energy metabolism. In addition, we measured glucose metabolism, AT inflammation, and liver phenotypes in mice of the two genotypes after exposure to a diet rich in fat. Our results provide novel evidence indicating that loss of the adenosine A2AR specifically in adipocytes is associated with cold intolerance and decreased oxygen consumption. Furthermore, mice with fat specific ablation of the A2AR exposed to a diet rich in fat showed increased propensity to obesity, decreased insulin sensitivity, elevated adipose tissue inflammation, and hepato-steatosis and hepato-steatitis. Overall, our data provide novel evidence that A2AR in mature adipocytes safeguards metabolic homeostasis, suggesting the possibility of targeting this receptor selectively in fat for the treatment of metabolic disease.

Hair follicle neogenesis (HFN) occurs following large skin excisions in mice, serving as a rare regenerative model in mammalian wound healing. Wound healing typically results in fibrosis in mice and humans. We previously showed small skin excisions in mice result in scarring devoid of HFN, displaying features of non-regenerative healing, and Hedgehog (Hh) activation in the dermis of such wounds can induce HFN. In this study, we sought to verify the role of dermal Wnt/β-catenin signaling in HFN, as this pathway is essential for HF development, but is also paradoxically well-characterized in fibrosis of adult wounds. By deletion of β-catenin in large wound myofibroblasts, we show Wnt/β-catenin signaling is required for endogenous mechanisms of HFN. Through utilizing a combined mouse model that simultaneously induces deletion of β-catenin and constitutive activation of Smoothened (Smo) in myofibroblasts, we also found β-catenin is required for Hh-driven DP formation. Transcriptome analysis confirms Wnt/β-catenin and Hh pathways are activated in dermal papilla (DP) cells. Our results indicate that Wnt-active fibrotic status may also create a permissive state for the regenerative function of Hh, suggesting that activation of both Wnt and Hh pathways in skin wound fibroblasts must be ensured in future strategies to promote HFN.

Bone regeneration remains a significant clinical challenge, often necessitating surgical approaches when healing bone defects and fracture nonunions. Within this context, the modulation of adenosine signaling pathways has emerged as a promising therapeutic option, encouraging osteoblast activation and tempering osteoclast differentiation. A literature review of the PubMed database with relevant keywords was conducted. The search criteria involved in vitro or in vivo models, with clear methodological descriptions. Only studies that included the use of indirect adenosine agonists, looking at the effects of bone regeneration, were considered relevant according to the eligibility criteria. A total of 29 articles were identified which met the inclusion and exclusion criteria, and they were reviewed to highlight the preclinical translation of adenosine agonists. While preclinical studies demonstrate the therapeutic potential of adenosine signaling in bone regeneration, its clinical application remains unrealized, underscoring the need for further clinical trials. To date, only large, preclinical animal models using indirect adenosine agonists have been successful in stimulating bone regeneration. The adenosine receptors (A₁, A_2A, A_2B, and A₃) stimulate various pathways, inducing different cellular responses. Specifically, indirect adenosine agonists act to increase the extracellular concentration of adenosine, subsequently agonizing the respective adenosine receptors. The agonism of each receptor is dependent on its expression on the cell surface, the extracellular concentration of adenosine, and its affinity for adenosine. This comprehensive review analyzed the multitude of indirect agonists currently being studied preclinically for bone regeneration, discussing the mechanisms of each agonist, their cellular responses in vitro, and their effects on bone formation in vivo.

BACKGROUND/UNASSIGNED:β-tricalcium phosphate (β-TCP) has been successfully utilized as a 3D printed ceramic scaffold in the repair of non-healing bone defects; however, it requires the addition of growth factors to augment its regenerative capacity. Synthetic bone mineral (SBM) is a novel and extrudable carbonate hydroxyapatite with ionic substitutions known to facilitate bone healing. However, its efficacy as a 3D printed scaffold for hard tissue defect repair has not been explored. OBJECTIVE/UNASSIGNED:To evaluate the biocompatibility and cell viability of human osteoprecursor (hOP) cells seeded on 3D printed SBM scaffolds via in vitro analysis. METHODS/UNASSIGNED:SBM and β-TCP scaffolds were fabricated via 3D printing and sintered at various temperatures. Scaffolds were then subject to qualitative cytotoxicity testing and cell proliferation experiments utilizing (hOP) cells. RESULTS/UNASSIGNED:SBM scaffolds sintered at lower temperatures (600 °C and 700 °C) induced greater levels of acute cellular stress. At higher sintering temperatures (1100 °C), SBM scaffolds showed inferior cellular viability relative to β-TCP scaffolds sintered to the same temperature (1100 °C). However, qualitative analysis suggested that β-TCP presented no evidence of morphological change, while SBM 1100 °C showed few instances of acute cellular stress. CONCLUSION/UNASSIGNED:Results demonstrate SBM may be a promising alternative to β-TCP for potential applications in bone tissue engineering.

OA is a common and debilitating condition that restricts mobility and diminishes the quality of life. Recent work indicates that the generation of adenosine at the cell surface is an important mediator of chondrocyte homeostasis, and topical application of adenosine in a slow-release form (liposomes) can halt the progression of OA and diminish the pain associated with OA. Here, we review the evidence indicating that adenosine, acting at A_2A receptors, plays a critical role in endogenous and exogenous treatment and reversal of OA.

Periprocedural inflammation is associated with major adverse cardiovascular events in patients who undergo percutaneous coronary intervention (PCI). In the contemporary era, 5% to 10% of patients develop restenosis, and in the acute coronary syndrome cohort, there remains a 20% major adverse cardiovascular events rate at 3 years, half of which are culprit-lesion related. In patients at risk of restenosis, colchicine has been shown to reduce restenosis when started within 24 hours of PCI and continued for 6 months thereafter, compared with placebo. The Colchicine-PCI trial, which randomized patients to a 1-time loading dose of colchicine or placebo 1 to 2 hours before PCI, showed a dampening of the inflammatory response to PCI but no difference in postprocedural myocardial injury. On mean follow-up of 3.3 years, the incidence of major adverse cardiovascular events did not differ between colchicine and placebo groups (32.5% vs 34.9%; hazard ratio 0.95 [0.68 to 1.34]).

BACKGROUND:3D-printed bioceramic scaffolds composed of 100% beta(β)-tricalcium phosphate augmented with dipyridamole (3DPBC-DIPY) can regenerate bone across critically sized defects in skeletally mature and immature animal models. Prior to human application, safe and effective bone formation should be demonstrated in a large translational animal model. This study evaluated the ability of 3DPBC-DIPY scaffolds to restore critically sized calvarial defects in a skeletally immature, growing minipig. METHODS:Unilateral calvarial defects (~1.4cm) were created in six-week-old Göttingen minipigs (n=12). Four defects were filled with a 1000µ M 3DPBC-DIPY scaffold with a cap (a solid barrier on the ectocortical side of the scaffold to prevent soft tissue infiltration), four defects were filled with a 1000µM 3DPBC-DIPY scaffold without a cap, and four defects served as negative controls (no scaffold). Animals were euthanized 12-weeks post-operatively. Calvaria were subjected to micro-computed tomography, 3D-reconstruction with volumetric analysis, qualitative histologic analysis, and nanoindentation. RESULTS:Scaffold-induced bone growth was statistically greater than negative controls (p≤0.001) and the scaffolds with caps produced significantly more bone generation compared to the scaffolds without caps (p≤0.001). Histological analysis revealed woven and lamellar bone with the presence of haversian canals throughout the regenerated bone. Additionally, cranial sutures were observed to be patent and there was no evidence of ectopic bone formation or excess inflammatory response. Reduced elastic modulus (Er) and hardness (H) of scaffold-regenerated bone were found to be statistically equivalent to native bone (p = 0.148 for Er of scaffolds with and without caps, and p = 0.228 and p = 0.902, for H of scaffolds with and without caps, respectively). CONCLUSION/CONCLUSIONS:3DPBC-DIPY scaffolds have the capacity to regenerate bone across critically sized calvarial defects in a skeletally immature translational pig model.