Tissue restoration is the process whereby multiple damaged cell types are replaced to restore the histoarchitecture and function to the tissue. Several theories have been proposed to explain the phenomenon of tissue restoration in amphibians and in animals belonging to higher orders. These theories include dedifferentiation of damaged tissues, transdifferentiation of lineage-committed progenitor cells, and activation of reserve precursor cells. Studies by Young et al. and others demonstrated that connective tissue compartments throughout postnatal individuals contain reserve precursor cells. Subsequent repetitive single cell-cloning and cell-sorting studies revealed that these reserve precursor cells consisted of multiple populations of cells, including tissue-specific progenitor cells, germ-layer lineage stem cells, and pluripotent stem cells. Tissue-specific progenitor cells display various capacities for differentiation, ranging from unipotency (forming a single cell type) to multipotency (forming multiple cell types). However, all progenitor cells demonstrate a finite life span of 50 to 70 population doublings before programmed cell senescence and cell death occurs. Germ-layer lineage stem cells can form a wider range of cell types than a progenitor cell. An individual germ-layer lineage stem cell can form all cells types within its respective germ-layer lineage (i.e., ectoderm, mesoderm, or endoderm). Pluripotent stem cells can form a wider range of cell types than a single germ-layer lineage stem cell. A single pluripotent stem cell can form cells belonging to all three germ layer lineages. Both germ-layer lineage stem cells and pluripotent stem cells exhibit extended capabilities for self-renewal, far surpassing the limited life span of progenitor cells (50-70 population doublings). The authors propose that the activation of quiescent tissue-specific progenitor cells, germ-layer lineage stem cells, and/or pluripotent stem cells may be a potential explanation, along with dedifferentiation and transdifferentiation, for the process of tissue restoration. Several model systems are currently being investigated to determine the possibilities of using these adult quiescent reserve precursor cells for tissue engineering.

Human mesenchymal stem cells (MSCs) have been isolated from bone marrow and other adult tissues and are potentially useful for tissue engineering. Adipose tissue has several clear advantages as a starting material for harvesting stem cells, as it is abundant and relatively easy to procure. However, existing methods to expand adipose-derived MSCs are less than optimal. Here we describe a new cell culture method that accelerates greatly the growth rate and prolongs the lifespan of adipose MSCs. This was accomplished by using a growth medium with low calcium and supplemented with N-acetyl-L-cysteine and L-ascorbic acid-2-phosphate. Cells produced early in these cultures displayed characteristics similar to those previously reported for multipotential stem cells, including a high frequency of anchorage- independent growth in soft agar, lack of gap junctional intercellular communication in a cell type with serpiginous morphology, and the expression of Oct-4. Furthermore, these cells could readily be induced to differentiate into adipocytes, osteoblasts, and chondrocytes. Thus, modification of growth medium by reduction of calcium and addition of antioxidants greatly enhanced the growth rate and extended the lifespan of adipose-derived multipotential human MSCs.

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BackgroundNumerous techniques and materials are available for increasing the dorsal height and length of the nose. Microautologous fat transplantation (MAFT) may be an appropriate strategy for augmentation rhinoplasty.ObjectivesThe authors sought to determine the long-term results of MAFT with the so-called one-third maneuver in Asian patients who underwent augmentation rhinoplasty.MethodsA total of 198 patients who underwent primary augmentation rhinoplasty with MAFT were evaluated in a retrospective study. Fat was harvested by liposuction and was processed and refined by centrifugation. Minute parcels of purified fat were transplanted to the nasal dorsum with a MAFT-Gun. Patient satisfaction was scored with a 5-point Likert scale, and aesthetic outcomes were validated with pre- and postoperative photographs.ResultsThe mean age of the patients was 45.5 years. The mean operating time for MAFT was 25 minutes, and patients underwent 1-3 MAFT sessions. The mean volume of fat delivered per session was 3.4 mL (range, 2.0-5.5 mL). Patients received follow-up for an average of 19 months (range, 6-42 months). Overall, 125 of 198 patients (63.1%) indicated that they were satisfied with the results of 1-3 sessions of MAFT. There were no major complications.ConclusionsThe results of this study support MAFT as an appropriate fat-transfer strategy for Asian patients undergoing primary augmentation rhinoplasty.Level of Evidence: 4 Therapeutic