Muscle and Bone: Combating the Evil Side of the Connection

Novel insights from human induced pluripotent stem cells on origins and roles of fibro/adipogenic progenitors as heterotopic ossification precursors

Fibro/adipogenic progenitors (FAPs) that reside in muscle tissue are crucial for muscular homeostasis and regeneration as they secrete signaling molecules and components of the extracellular matrix. During injury or disease, FAPs differentiate into different cell types and significantly modulate muscular function. Recent advances in lineage tracing and single-cell transcriptomics have proven that FAPs are heterogeneous both in resting and post-injury or disease states. Their heterogeneity may be owing to the varied tissue microenvironments and their diverse developmental origins. Therefore, understanding FAPs' developmental origins can help predict their characteristics and behaviors under different conditions. FAPs are thought to be the major cell populations in the muscle connective tissue (MCT). During embryogenesis, the MCT directs muscular development throughout the body and serves as a prepattern for muscular morphogenesis. The developmental origins of FAPs as stromal cells in the MCT were studied previously. In adult tissues, FAPs are important precursors for heterotopic ossification, especially in the context of the rare genetic disorder fibrodysplasia ossificans progressiva. A new developmental origin for FAPs have been suggested that differs from conventional developmental perspectives. In this review, we summarize the developmental origins and functions of FAPs as stromal cells of the MCT and present novel insights obtained by using patient-derived induced pluripotent stem cells and mouse models of heterotopic ossification. This review broadens the current understanding of FAPs and suggests potential avenues for further investigation.

Bone construction surgery: A case report using recombinant human platelet-derived growth factor-BB

BACKGROUND

The position and condition of bone largely sets the stage for functional and esthetic implant success. In bone construction surgery, creating a sustainable functional matrix is complex, but necessary, to enable long-term mechanotransduction and maintenance of soft tissue support.

METHODS

A patient with a severe peri-implantitis ridge defect in the anterior maxilla underwent bone construction surgery simultaneous with implant removal using a composite bone graft (mineralized freeze dried bone allograft + xenograft) enhanced with recombinant human platelet-derived growth factor (rhPDGF-BB). Space maintenance for bone construct immobility and unimpeded wound healing was ensured via a nonresorbable titanium reinforced polytetrafluoroethylene membrane and an absorbable porcine collagen membrane.

RESULTS

Primary closure was maintained throughout the 6 month healing process at which time implant diagnostics commenced for prosthetically directed implant placement using dynamic navigation and involving soft tissue augmentation. Uncovery was performed 3 months thereafter leading to provisionalization and prosthetic phase completion.

CONCLUSION

This case report highlights a severe maxillary anterior ridge defect secondary to advanced peri-implantitis in a systemically healthy Caucasian male patient. The surgical outcome success, both clinically and radiographically, underscores the complexities of complete regional anatomy rehabilitation after suffering catastrophic and debilitating bone loss from inflammatory peri-implantitis. Further, it demonstrates the importance of incorporating optimized angiogenetic therapeutics to help establish a vascularized functional bone matrix for implant success.