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Biomedical subjects

Michael T Longaker

Publications and source records attributed to Michael T Longaker.

At least 109 records · Page 6Linked to original sources
PubMed2003

The dorsal scapular island flap: an alternative for head, neck, and chest reconstruction.

The back has become an increasingly popular donor site for flaps because it can provide thin, pliable tissue, with minimal bulk, and the scar can be easily hidden under clothing. The authors performed a cadaveric and clinical study to evaluate the anatomy of the dorsal scapular vessels and their vascular contribution to the skin, fascia, and muscles of the back. On the basis of anatomical studies in 28 cadavers and clinical experience with 32 cases, it was concluded that the dorsal scapular vessels provide a reliable blood supply to the skin of the medial back, making it a versatile flap to use as an island flap. A flap raised on the dorsal scapular vessels can be harvested with a long pedicle and can be rotated to reach as far as the anterior regions of the head, neck, and chest wall. Delaying and expanding the flap may help to facilitate venous drainage. The authors recommend the use of this versatile island pedicle flap as an alternative to microvascular free-tissue transfer for the reconstruction of defects in the head, neck, and anterior chest.

Adolescent↗
PubMed2003

FGF-2 stimulation affects calvarial osteoblast biology: quantitative analysis of nine genes important for cranial suture biology by real-time reverse transcription polymerase chain reaction.

Appropriately timed closure of the cranial sutures is a critical factor in normal postnatal morphogenesis of the cranial vault. Suture patency is necessary to permit rapid neonatal expansion of the cerebral hemispheres, and later ossification is important for bony protection of the cerebrum. Premature suture ossification (craniosynostosis) leads to myriad adverse functional and developmental consequences. Several murine studies have implicated dura-derived fibroblast growth factor-2 (FGF-2) paracrine signaling as a critical factor promoting physiologic posterior frontal suture fusion. In this study, the authors used real-time reverse transcription polymerase chain reaction (RT-PCR) to study an in vitro system that models the in vivo stimulation of suture calvarial osteoblasts by dura-derived FGF-2. The authors advocate real-time RT-PCR as a powerful and rapid technique that offers advantages in the highly sensitive, specific, and reproducible analyses of nine genes known to be important in cranial suture biology. The genes studied were growth factors [FGF-2, transforming growth factor (TGF)-beta 1, TGF-beta 2, and TGF-beta 3], growth factor receptors (FGF-R1, FGF-R2, TGF-beta RI, and TGF-beta RII), and a marker of osteoblast differentiation (Co1-I alpha I). These analyses provide a "snapshot" of several important genes involved in suture fusion that is more inclusive and quantitative than that which has been previously reported.

Animals↗
PubMed2003

Markers of osteoblast differentiation in fusing and nonfusing cranial sutures.

Accumulating clinical genetic data support the hypothesis that alterations in osteoblast differentiation are closely associated with craniosynostoses. Gain-of-function mutations in FGFR1, FGFR2, FGFR3, and Msx2 and loss-of-function mutations in Twist are examples of such alterations. Several studies have examined how these mutations alter the expression patterns for transcription factors such as Runx2 and noncollagenous extracellular matrix molecules such as osteopontin and osteocalcin. One limitation of such studies is that they examine samples derived from craniosynostotic patients with sutures that have already fused, thus missing the dynamic osteogenic process of suture fusion. In this study, in situ hybridization was used to localize Runx2, osteopontin, and osteocalcin expression in the sagittal and posterior frontal sutures in mice (n = 20), before (day 13), during (days 23, 33, and 43), and after (day 53) the period of physiological posterior frontal suture fusion. The data demonstrated similar patterns of expression in fusing (posterior frontal) and nonfusing (sagittal) sutures. The expression of all three genes was primarily concentrated in the osteogenic fronts of both sutures and decreased with time. Notably, none of the three genes was expressed in the mesenchyme of either fusing or nonfusing sutures. The data suggest that the molecular signals leading to bone formation along the osteogenic fronts in fusing and nonfusing sutures are similar, raising the possibility that other factors, such as antagonists of osteogenesis, might have a role in maintaining suture patency.

Animals↗
PubMed2003

Mechanical strain affects dura mater biological processes: implications for immature calvarial healing.

The human brain grows rapidly during the first 2 years of life. This growth generates tensile strain in the overlying dura mater and neurocranium. Interestingly, it is largely during this 2-year growth period that infants are able to reossify calvarial defects. This clinical observation is important because it suggests that calvarial healing is most robust during the period of active intracranial volume expansion. With a rat model, it was previously demonstrated that immature dura mater proliferates more rapidly and produces more osteogenic cytokines and markers of osteoblast differentiation than does mature dura mater. It was therefore hypothesized that mechanical strain generated by the growing brain induces immature dura mater proliferation and increases osteogenic cytokine expression necessary for growth and healing of the overlying calvaria. Human and rat (n = 40) intracranial volume expansion was calculated as a function of age. These calculations demonstrated that 83 percent of human intracranial volume expansion is complete by 2 years of age and 90 percent of Sprague-Dawley rat intracranial volume expansion is achieved by 2 months of age. Next, the maximal daily circumferential tensile strains that could be generated in immature rat dura mater were calculated, and the corresponding daily biaxial tensile strains in the dura mater during this 2-month period were determined. With the use of a three-parameter monomolecular growth curve, it was calculated that rat dura mater experiences daily equibiaxial strains of at most 9.7 percent and 0.1 percent at birth (day 0) and 60 days of age, respectively. Because it was noted that immature dural cells may experience tensile strains as high as approximately 10 percent, neonatal rat dural cells were subjected to 10 percent equibiaxial strain in vitro, and dural cell proliferation and gene expression profiles were analyzed. When exposed to mechanical strain, immature dural cells rapidly proliferated (5.8-fold increase in proliferating cell nuclear antigen expression at 24 hours). Moreover, mechanical strain induced marked up-regulation of dural cell osteogenic cytokine production; transforming growth factor-beta1 messenger RNA levels increased 3.4-fold at 3 hours and fibroblast growth factor-2 protein levels increased 4.5-fold at 24 hours and 5.6-fold at 48 hours. Finally, mechanical strain increased dural cell expression of markers of osteoblast differentiation (2.8-fold increase in osteopontin levels at 3 hours). These findings suggest that mechanical strain can induce changes in dura mater biological processes and gene expression that may play important roles in coordinating the growth and healing of the neonatal calvaria.

Animals↗
PubMed2002

Matrix metalloproteinases and the ontogeny of scarless repair: the other side of the wound healing balance.

Early gestation mammalian fetuses possess the remarkable ability to heal cutaneous wounds in a scarless fashion. Over the past 20 years, scientists have been working to decipher the mechanisms underlying this phenomenon. Much of the research to date has focused on fetal correlates of adult wound healing that promote fibrosis and granulation tissue formation. It is important to remember, however, that wound repair consists of a balance between tissue synthesis, deposition, and degradation. Relatively little attention has been paid to this latter component of the fetal wound healing process. In this study, we examined the ontogeny of ten matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) in nonwounded fetal rat skin and fibroblasts as a function of gestational age. We used a semiquantitative polymerase chain reaction protocol to analyze these important enzymes at time points that represent both the scarless and scar-forming periods of rat gestation. The enzymes evaluated were collagenase-1 (MMP-1), stromelysin-1 (MMP-3), gelatinase A (MMP-2), gelatinase B (MMP-9), membrane-type matrix metalloproteinases (MT-MMPs) 1, 2, and 3, and TIMPs 1, 2, and 3. Results demonstrated marked increases in gene expression for MMP-1, MMP-3 and MMP-9 that correlated with the onset of scar formation in nonwounded fetal skin. Similar results were noted in terms of MMP-9 gene expression in fetal fibroblasts. These results suggest that differences in the expression of these matrix metalloproteinases may have a role in the scarless wound healing phenotype observed early in fetal rat gestation. Furthermore, our data suggest that the differential expression of gelatinase B (MMP-9) may be mediated by the fetal fibroblasts themselves.

Animals↗
PubMed2002

The course of the inferior alveolar nerve in craniofacial microsomia: virtual dissection using three-dimensional computed tomography image analysis.

Computer-assisted medical imaging was used to locate the mandibular foramen and the portion of the inferior alveolar nerve canal at the level of the angle of the mandible in 19 hemimandibles of patients with craniofacial microsomia. The distance from each of these two points to the borders of the mandible was measured. The ratios of these distances to the height, anteroposterior, and buccolingual extents of the mandibular ramus were calculated. These ratios were compared among affected hemimandibles (Pruzansky classification I, n = 4; and Pruzansky classification II, n = 10), unaffected hemimandibles (n = 9), and the hemimandibles of patients with nonsyndromic, sutural synostosis (n = 7). Comparison of mean distance ratios showed that the mandibular foramen was located significantly more proximally in the affected cohort than in either the unaffected or synostosis control groups. The mandibular foramen was also located significantly closer to the buccal cortex of the mandible in the affected cohort when compared with unaffected patients. The distance from the mandibular foramen to the anterior or posterior tables of the mandible divided by the total anteroposterior distance did not vary among the three groups studied. The distance ratios between the inferior alveolar nerve canal at the level of the angle of the mandible and the mandibular borders also did not vary significantly among the groups studied. An inferior alveolar nerve canal could not be identified in any patient with Pruzansky grade III mandibular deficiency. This quantitative, three-dimensional description of points along the proximal path of the inferior alveolar nerve canal in patients with craniofacial microsomia provides useful information to assist the surgeon during osteotomy planning and may help in avoiding injury to the nerve at the time of surgery.

Child↗
PubMed2002

Differences in collagen production between normal and keloid-derived fibroblasts in serum-media co-culture with keloid-derived keratinocytes.

Keloids are characterized by the deposition of excessive extracellular-matrix collagen by abnormal fibroblasts in response to cutaneous injury. Studies to date have largely concentrated on the role of the keloid fibroblast in the pathogenesis of this lesion. Recent studies have highlighted the important concept of epithelial-mesenchymal interactions in normal skin biology. Extrapolating this to keloids in two recent serum-free in vitro studies, we demonstrated increased growth and proliferation, as well as induction of keloid-like collagen secretory characteristics in normal fibroblasts co-cultured with keloid-derived keratinocytes. Most fibroblast culture work to date has been performed in nutrient and growth factor-rich serum media. To investigate how a serum co-culture system might influence epithelial-mesenchymal interactions, [3H] proline incorporation was examined in normal and keloid fibroblasts co-cultured in serum with keratinocytes derived either from normal skin or keloid tissue. Results showed increased [3H] proline incorporation when normal fibroblasts were co-cultured with keloid keratinocytes, which was significantly increased when keloid fibroblasts were co-cultured with keloid keratinocytes. Taken with previous results, this study demonstrates a good correlation between both serum and serum-free co-culture systems, and supports the significance of epithelial-mesenchymal interactions in keloid pathogenesis.

Cells, Cultured↗
PubMed2002

Flexor tendon healing in vitro: effects of TGF-beta on tendon cell collagen production.

Flexor tendon healing is complicated by adhesions to the surrounding sheath. Transforming growth factor beta (TGF-beta) is a cytokine with numerous activities related to wound healing. We examined the effects of TGF-beta-1, -2 and -3 on tendon cell proliferation and collagen production. Three separate cell lines--sheath fibroblasts, epitenon and endotenon tenocytes--were isolated from rabbit flexor tendons and cultured separately. Cell culture media was supplemented with 1 or 5 ng/mL of TGF-beta-1, -2, or -3. Cell number and collagen I and III production were measured and compared with unsupplemented control cultures. The addition of TGF-beta to cell culture media resulted in a decrease in cell number in all 3 lines that did not reach statistical significance. There was a significant increase (p <.05) in collagen I and III production with the addition of all 3 TGF-beta isoforms. Modulation of TGF-beta production may provide a mechanism to modulate adhesion formation clinically.

Animals↗
PubMed2002

The molecular biology of distraction osteogenesis.

Distraction osteogenesis has become a mainstay in bone tissue engineering and has significantly improved our armamentarium for reconstructive craniomaxillofacial procedures. However, although the biomechanical, histological, and ultrastructural changes associated with distraction osteogenesis have been widely described, the molecular mechanisms governing the formation of new bone in the interfragmental gap of gradually distracted bone segments remain largely unclear. Recently, a rat model of mandibular distraction was described that provides an excellent environment for deciphering the molecular mechanisms that mediate distraction osteogenesis. This article presents the hypotheses and current research that have furthered knowledge of the molecular mechanisms that govern distraction osteogenesis. Recent studies have implicated a growing number of cytokines that are intimately involved in the regulation of bone synthesis and turnover. The gene regulation of numerous cytokines (transforming growth factor-beta1, -beta2, -beta3, bone morphogenetic proteins, insulin-like growth factor-1, fibroblast growth factor-2) and extracellular matrix proteins (osteonectin, osteopontin) during distraction osteogenesis have been best characterized and are discussed in this article. It is believed that understanding the biomolecular mechanisms that mediate membranous distraction osteogenesis may guide the development of targeted strategies designed to improve distraction osteogenesis and accelerate bone healing.

Animals↗
PubMed2002

Granulation tissue regression induced by musculocutaneous advancement flap coverage.

BACKGROUND: Clinical experience suggests that granulation tissue may be inhibited by coverage with a musculocutaneous flap. We hypothesized that coverage of an open wound with a musculocutaneous flap would result in regression and apoptosis of the wound's granulation tissue. METHODS: In the first experiment, 32 rats underwent excisional wounding; 16 underwent musculocutaneous flap coverage of their granulation tissue on postwounding day 8, and then 16 rats (8 controls + 8 flaps) were killed on both postwounding days 10 and 12 (2 and 4 days after the flap procedure, respectively). In the second experiment, 18 rats were wounded, and on postwounding day 5 the rats underwent flap coverage (n = 6), wound edge release/mobilization (the first step of the flap procedure) without flap coverage (n = 6), or dressing change only (n = 6); all rats were killed on postwounding day 6 (24 hours after the secondary intervention). Apoptosis was quantified with the terminal deoxynucleotidyl transferase-mediated nick-end labeling assay. RESULTS: Placement of a musculocutaneous flap over an 8-day-old excisional wound in the first experiment increased the apoptotic rate in the granulation tissue from 0% to 1% (controls) to 5% to 10% at both 2 and 4 days after flap coverage (P <.05). Cell population density decreased 50% in the flap-covered granulation tissue compared with the controls (P <.05). In the second experiment, circumferential release of the granulation tissue resulted in an equivalent increase in granulation tissue apoptosis over controls compared to that induced by the full flap procedure. CONCLUSIONS: Coverage of established granulation tissue with a musculocutaneous flap resulted in histologic regression of the wound's granulation tissue after 2 to 4 days of flap coverage and induced at least a 5-fold increase in the apoptotic rate of the granulation tissue. Releasing the wound edge increased granulation tissue apoptosis to a level equivalent to that produced by the musculocutaneous flap procedure, suggesting that alteration of the wound's mechanical environment is responsible for the acute induction of apoptosis in this model.

Animals↗
PubMed2002

The subunit approach to nasal tip hemangiomas.

Many surgeons who operate on nasal tip hemangiomas find a central vertical scar frustrating. Alternatives such as open rhinoplasty provide great exposure, but the redraping leaves unsightly scars along the alar rim and columella. Therefore, a new aesthetic incision was needed to allow hemangioma reduction in both the horizontal and vertical dimensions while providing adequate access to the lower lateral cartilage for soft-tissue reduction and/or suturing. The subunit incision, based on the pioneering work of Burget and Menick, was developed to provide both excellent exposure and cosmesis. By designing the incision to lie along the contour lines of the nasal subunits, the senior author (B.M.Z.) believed that the border scars would reflect lines of light and cast linear shadows that would mimic the normal ridges and valleys that separate the topographic subunits of the nose. Based on the results of nine recent cases, the authors believe the subunit incision is currently the best approach to correcting nasal tip hemangiomas.

Child, Preschool↗
PubMed2002

Co-culture of osteoblasts with immature dural cells causes an increased rate and degree of osteoblast differentiation.

For decades surgeons have exploited the ability of infants to reossify large calvarial defects. To demonstrate the role of dura mater-osteoblast communication during the process of calvarial reossification, the authors used a novel in vitro system that recapitulates the in vivo anatomic relationship of these cell populations. Primary cultures of osteoblast cells from 2-day-old Sprague-Dawley rat pups were grown on six-well plates, and cultures of immature, non-suture-associated dura mater cells from 6-day-old Sprague-Dawley rat pups were grown on Transwell inserts. When the osteoblast and dura mater cell cultures reached confluence, they were combined. This Transwell co-culture system permitted the two cell populations to grow together in the same well, but it prevented direct cell-to-cell contact. Therefore, the authors were able to determine, for the first time, whether paracrine signaling from immature, non-suture-associated dura mater could influence the biologic activity of osteoblasts. Osteoblasts co-cultured with dural cells proliferated significantly faster after 2 days (2.1 x 10(5) +/- 2.4 x 10(4) versus 1.4 x 10(5) +/- 2.2 x 10(4), p < or = 0.05) and 4 days (3.1 x 10(5) +/- 5 x 10(4) versus 2.2 x 10(5) +/- 4.0 x 10(4), p < or = 0.01) than did osteoblasts cultured alone. After 20 days, co-cultured osteoblasts expressed greater amounts of mRNA for several markers of osteoblast differentiation, including collagen I alpha I (4-fold), alkaline phosphatase (2.5-fold), osteopontin (3-fold), and osteocalcin (4-fold), than did osteoblasts cultured alone. After 30 days, co-cultured osteoblasts produced bone nodules that were significantly greater both in number (324 +/- 29 nodules versus 252 +/- 29 nodules per well, p , < or = 0.04) and total area of nodules (65 +/- 11 mm(2) versus 24 +/- 1.6 mm(2), p < or = 0.003) than osteoblasts cultured alone. To begin to understand how dural cells effect changes in osteoblast gene expression, the authors compared the expression of candidate genes, transforming growth factor beta 1 and fibroblast growth factor 2, in dural cells and osteoblasts before and after 5 days of culture. Interestingly, the dura mater produced marked amounts of these osteogenic cytokines compared with osteoblasts.The described co-culture system demonstrated that co-cultured osteoblasts proliferated more rapidly and experienced an increased rate and degree of cellular maturation than did osteoblasts cultured alone. The authors hypothesize that this effect was due to paracrine signaling (e.g., transforming growth factor beta 1 and fibroblast growth factor 2) from the dura mater, and they are investigating those mechanisms in ongoing experiments. Collectively these data verify that immature, non-suture-associated dura mater can influence the biologic activity of osteoblasts. Moreover, the production of cytokines derived from the dura mater (e.g., transforming growth factor beta 1 and fibroblast growth factor 2), and they may begin to explain why immature animals and infants with intact dura mater can reossify large calvarial defects.

Alkaline Phosphatase↗