Plasma Membrane Factor XIIIA Transglutaminase Activity Regulates Osteoblast Matrix Secretion and Deposition by Affecting Microtubule Dynamics

Transglutaminase activity, arising potentially from transglutaminase 2 (TG2) and Factor XIIIA (FXIIIA), has been linked to osteoblast differentiation where it is required for type I collagen and fibronectin matrix deposition. In this study we have used an irreversible TG-inhibitor to ‘block –and-track’ enzyme(s) targeted during osteoblast differentiation. We show that the irreversible TG-inhibitor is highly potent in inhibiting osteoblast differentiation and mineralization and reduces secretion of both fibronectin and type I collagen and their release from the cell surface. Tracking of the dansyl probe by Western blotting and immunofluorescence microscopy demonstrated that the inhibitor targets plasma membrane-associated FXIIIA. TG2 appears not to contribute to crosslinking activity on the osteoblast surface. Inhibition of FXIIIA with NC9 resulted in defective secretory vesicle delivery to the plasma membrane which was attributable to a disorganized microtubule network and decreased microtubule association with the plasma membrane. NC9 inhibition of FXIIIA resulted in destabilization of microtubules as assessed by cellular Glu-tubulin levels. Furthermore, NC9 blocked modification of Glu-tubulin into 150 kDa high-molecular weight Glu-tubulin form which was specifically localized to the plasma membrane. FXIIIA enzyme and its crosslinking activity were colocalized with plasma membrane-associated tubulin, and thus, it appears that FXIIIA crosslinking activity is directed towards stabilizing the interaction of microtubules with the plasma membrane. Our work provides the first mechanistic cues as to how transglutaminase activity could affect protein secretion and matrix deposition in osteoblasts and suggests a novel function for plasma membrane FXIIIA in microtubule dynamics

Recent advances in bone regeneration: The role of adipose tissue-derived stromal vascular fraction and mesenchymal stem cells

The management of large bone defects, atrophic nonunions, and other conditions with poor bone formation presents a formidable challenge to the treating physician, as all available techniques of bone reconstruction have drawbacks. Recent advances in stem cell biology, specifically adipose tissue-derived mesenchymal stem cells (ASCs) and adipose tissue stromal vascular fraction (SVF), have opened up new horizons by providing a reliable and abundant source of stem cells with osteogenic potential that can be used in various bone tissue engineering techniques. In this review, several aspects related to the use of ASCs are addressed, such as harvesting and processing of adipose tissue, advantages of ASCs over bone marrow-derived mesenchymal stem cells, mechanism of action and safety of ASCs, and factors affecting the differentiation of ASCs. Published reports on the use of ASCs in critical size defects, nonunions, and distraction osteogenesis are also reviewed. Innovative trends in stem cell research on musculoskeletal pathologies are highlighted, with special emphasis on the increasing evidence that the direct application of freshly prepared SVF processed from adipose tissue into the bone defect to be treated without a prior differentiation or an ex vivo expansion and culture is possible. This highly promising approach may lead to the development of a one-step intraoperative cell therapy