Roles of Chondroitin Sulfate Proteoglycans as Regulators of Skeletal Development

Chondroitin sulfate: From bioactive molecule to versatile drug delivery system for advancing regenerative medicine

Regenerative medicine, a rapidly advancing field, holds immense promise for restoring and revitalizing damaged tissues and organs resulting from aging, diseases, or injuries, ultimately improving patient well-being. Chondroitin Sulfate (CS), a naturally occurring glycosaminoglycan, is a compelling biomaterial due to its natural origin, well-established biocompatibility, and structural complexity. Renowned for its biocompatibility, structural complexity, and varied bioactivities, CS provides significant applications beyond its recognized function in joint health and osteoarthritis treatment. Recent breakthroughs demonstrate its potential in treating complicated disorders such as interstitial cystitis, psoriasis, dry eye syndrome, and cardiovascular diseases by controlling inflammation, facilitating wound healing, and improving tissue repair. Notwithstanding its therapeutic potential, CS remains inadequately investigated in regenerative medicine and tissue engineering. Its capacity to modulate cellular signaling, promote extracellular matrix remodeling, and improve scaffold integration establishes it as a crucial facilitator of sophisticated therapeutic approaches. This review elucidates the progression of CS-based drug delivery systems, encompassing hydrogels, microparticles, nanoparticles, composites, and beads while underscoring their effectiveness in addressing conventional drug delivery obstacles such as non-specific targeting and off-target effects. Integrating CS into advanced platforms enables regulated drug release, accurate targeting, and enhanced cellular absorption while maintaining biodegradability and compatibility with tissue engineering scaffolds. Its inherent antioxidant, anti-inflammatory, and immune-modulating characteristics augment its attractiveness for individualized therapeutic applications. Recent studies highlight the adaptability of CS in developing multimodal drug delivery systems designed for regenerative medicine. Nonetheless, substantial deficiencies persist, especially in clinical validation and extensive applications. Overcoming these hurdles may fully realize CS's potential in transforming drug delivery, establishing a solid basis for the progression of regenerative therapies. By integrating biomaterial science with clinical medicine, CS-based systems are set to transform treatment approaches in regenerative medicine, providing precision, efficiency, and adaptability for individualized care.

FAM20B-Catalyzed Glycosylation Regulates the Chondrogenic and Osteogenic Differentiation of the Embryonic Condyle by Controlling IHH Diffusion and Release

Although the roles of proteoglycans (PGs) have been well documented in the development and homeostasis of the temporomandibular joint (TMJ), how the glycosaminoglycan (GAG) chains of PGs contribute to TMJ chondrogenesis and osteogenesis still requires explication. In this study, we found that FAM20B, a hexokinase essential for attaching GAG chains to the core proteins of PGs, was robustly activated in the condylar mesenchyme during TMJ development. The inactivation of Fam20b in craniofacial neural crest cells (CNCCs) dramatically reduced the synthesis and accumulation of GAG chains rather than core proteins in the condylar cartilage, which resulted in a hypoplastic condylar cartilage by severely promoting chondrocyte hypertrophy and perichondral ossification. In the condyles of Wnt1-Cre;Fam20bf/f mouse embryos, enlarged Ihh- and COL10-expressing domains indicated premature hypertrophy resulting from an attenuated IHH-PTHRP negative feedback in condylar chondrocytes, while increased osteogenic markers, canonical Wnt activity, and type-H angiogenesis verified the enhanced osteogenesis in the perichondrium. Further ex vivo investigations revealed that the loss of Fam20b decreased the domain area but increased the activity of HH signaling in the embryonic condylar mesenchyme. Moreover, the abrogation of GAG chains in heparan sulfate and chondroitin sulfate proteoglycans led to a rapid up- and then downregulation of HH signaling in condylar chondrocytes, implicating a "slow-release" manner of growth factors controlled by GAG chains. Overall, this study revealed a comprehensive role of the FAM20B-catalyzed GAG chain synthesis in the chondrogenic and osteogenic differentiation of the embryonic TMJ condyle.

Sulfate: a neglected (but potentially highly relevant) anion

Sulfate is an important anion as sulfonation is essential in modulation of several compounds, such as exogens, polysaccharide chains of proteoglycans, cholesterol or cholesterol derivatives and tyrosine residues of several proteins. Sulfonation requires the presence of both the sulfate donor 3'-phosphoadenosine-5'-phosphosulfate (PAPS) and a sulfotransferase. Genetic disorders affecting sulfonation, associated with skeletal abnormalities, impaired neurological development and endocrinopathies, demonstrate the importance of sulfate. Yet sulfate is not measured in clinical practice. This review addresses sulfate metabolism and consequences of sulfonation defects, how to measure sulfate and why we should measure sulfate more often.

Biomimetic Proteoglycans for Intervertebral Disc (IVD) Regeneration

Intervertebral disc degeneration, which leads to low back pain, is the most prevalent musculoskeletal condition worldwide, significantly impairing quality of life and imposing substantial socioeconomic burdens on affected individuals. A major impediment to the development of any prospective cell-driven recovery of functional properties in degenerate IVDs is the diminishing IVD cell numbers and viability with ageing which cannot sustain such a recovery process. However, if IVD proteoglycan levels, a major functional component, can be replenished through an orthobiological process which does not rely on cellular or nutritional input, then this may be an effective strategy for the re-attainment of IVD mechanical properties. Furthermore, biomimetic proteoglycans (PGs) represent an established polymer that strengthens osteoarthritis cartilage and improves its biomechanical properties, actively promoting biological repair processes. Biomimetic PGs have superior water imbibing properties compared to native aggrecan and are more resistant to proteolytic degradation, increasing their biological half-life in cartilaginous tissues. Methods have also now been developed to chemically edit the structure of biomimetic proteoglycans, allowing for the incorporation of bioactive peptide modules and equipping biomimetic proteoglycans as delivery vehicles for drugs and growth factors, further improving their biotherapeutic credentials. This article aims to provide a comprehensive overview of prospective orthobiological strategies that leverage engineered proteoglycans, paving the way for novel therapeutic interventions in IVD degeneration and ultimately enhancing patient outcomes.