Ali Modarressi

The Role of Reactive Oxygen Species in Mesenchymal Stem Cell Adipogenic and Osteogenic Differentiation: A Review

Mesenchymal stromal cells (MSCs) are promising candidates for tissue engineering and regenerative medicine. The multipotent stem cell component of MSC isolates is able to differentiate into derivatives of the mesodermal lineage including adipocytes, osteocytes, chondrocytes, and myocytes. Many common pathways have been described in the regulation of adipogenesis and osteogenesis. However, stimulation of osteogenesis appears to suppress adipogenesis and vice-versa. Increasing evidence implicates a tight regulation of these processes by reactive oxygen species (ROS). ROS are short-lived oxygen-containing molecules that display high chemical reactivity toward DNA, RNA, proteins, and lipids. Mitochondrial complexes I and III, and the NADPH oxidase isoform NOX4 are major sources of ROS production during MSC differentiation. ROS are thought to interact with several pathways that affect the transcription machinery required for MSC differentiation including the Wnt, Hedgehog, and FOXO signaling cascades. On the other hand, elevated levels of ROS, defined as oxidative stress, lead to arrest of the MSC cell cycle and apoptosis. Tightly regulated levels of ROS are therefore critical for MSC terminal differentiation, although the precise sources, localization, levels and the exact species of ROS implicated remain to be determined. This review provides a detailed overview of the influence of ROS on adipogenic and osteogenic differentiation in MSCs.

Hypoxia Impairs Skin Myofibroblast Differentiation and Function

Ischemic wounds are characterized by oxygen levels lower than that of healthy skin (hypoxia) and poor healing. To better understand the pathophysiology of impaired wound healing, we investigated how switching from high (21%) to low (2%) oxygen levels directly affects cultured skin myofibroblasts, essential cells for the normal wound repair process. Myofibroblast differentiation and function were assessed by quantifying α-smooth muscle actin expression and cell contraction in collagen gels and on wrinkling silicone substrates. Culture for 5 days at 2% oxygen is perceived as hypoxia and significantly reduced myofibroblast differentiation and contraction despite high levels of the profibrotic transforming growth factor-β1. Analysis of α-smooth muscle actin expression on wrinkling substrates over time showed that reduced myofibroblast contraction preceded α-smooth muscle actin disassembly from stress fibers after switching from 21 to 2% oxygen. These effects were reversible by restoring high oxygen conditions and by applying mechanical stress. We suggest that mechanical challenge is a clinical relevant strategy to improve ischemic and chronic wound healing by supporting myofibroblast formation.

Nonactivated versus thrombin-activated platelets on wound healing and fibroblast-to-myofibroblast differentiation in vivo and in vitro.

Background: Platelet preparations for tissue healing are usually preactivated before application to deliver concentrated growth factors. In this study, the authors investigated the differences between nonactivated and thrombin-activated platelets in wound healing. Methods: The healing effects (i.e., wound closure, myofibroblast formation, and angiogenesis) of nonactivated and thrombin-activated platelets were compared in experimental wounds in diabetic (db/db) animals. In vitro, fibroblast phenotype and function were tested in response to platelets and activated platelets. No treatment served as a negative control. Results: Wounds treated with platelets reached 90 percent closure after 15 days, faster than activated platelets (26 days), and with higher levels of myofibroblasts and angiogenesis. In vitro, platelets enhanced cell migration and induced two-fold higher myofibroblast differentiation and contraction compared with activated platelets. Conclusions: Platelets stimulate wound healing more efficiently compared with activated platelets by enhancing fibroblast differentiation and contractile function. Similar levels of growth factors may induce different biological effects when delivered “on demand” rather than in an initial bolus.

Plastic surgery improves long-term weight control after bariatric surgery.

1. Balagué N, Combescure C, Huber O, Pittet-Cuénod B, Modarressi A. Plastic surgery improves long-term weight control after bariatric surgery. Plast Reconstr Surg. 2013;132: 826–833. 2. American Society of Plastic Surgeons. 2012 Plastic Surgery Statistics Report. Available at: http://www.plasticsurgery. org/Documents/news-resources/statistics/2012-PlasticSurgery-Statistics/body-contouring-after-massive-weight-loss. pdf. Accessed October 9, 2013. 3. Sarwer DB, Fabricatore AN. Psychiatric considerations of the massive weight loss patient. Clin Plast Surg. 2008;35:1–10. 4. Coon D, Michaels J V, Gusenoff JA, Purnell C, Friedman T, Rubin JP. Multiple procedures and staging in the massive weight loss population. Plast Reconstr Surg. 2010;125:691–698. 5. Coon D, Gusenoff JA, Kannan N, El Khoudary SR, Naghshineh N, Rubin JP. Body mass and surgical complications in the postbariatric reconstructive patient: Analysis of 511 cases. Ann Surg. 2009;249:397–401.

Persistent ischemia impairs myofibroblast development in wound granulation tissue : A new model of delayed wound healing

We describe a new animal model designed to assess the impact of ischemia on wound healing. Eight patterns of arterial lesion in the limb were first tested in 24 Wistar rats. Resection of the external iliac artery down to the femoral artery at the level of the knee was chosen as the reference model and performed on the left limb of 45 rats; the right limb was used as the control. Skin wounds measuring 1.2 × 0.8 cm were created on both feet. Ischemia was assessed by blood flow measurement, which decreases dramatically in the ischemic limb. A significant delay in wound closure with a decrease in wound contraction was observed in the ischemic limb. Myofibroblast quantification showed a significant delay in appearance as well as a decrease in the number of these cells in the ischemic wound. Vascular endothelial growth factor‐A appearance and evolution were qualitatively similar in both situations. However, collagen type I mRNA was markedly decreased in ischemic granulation tissue 10 days after wounding. These findings suggest that decreased wound contraction plays an important role in delayed ischemic wound healing, probably due to reduced myofibroblast development and activity.

Hyperglycemia Increases Susceptibility to Ischemic Necrosis

Diabetic patients are at risk for spontaneous foot ulcers, chronic wounds, infections, and tissue necrosis. Current theories suggest that the development and progression of diabetic foot ulcers are mainly caused by arteriosclerosis and peripheral neuropathy. Tissue necrosis plays a primordial role in the progression of diabetic foot ulcers but the underlying mechanisms are poorly understood. The aim of the present study was to investigate the effects of hyperglycemia per se on the susceptibility of ischemic tissue to necrosis, using a critical ischemic hind limb animal model. We inflicted the same degree of ischemia in both euglycemic and streptozotocin-induced hyperglycemic rats by resecting the external iliac, the femoral, and the saphenous arteries. Postoperative laser Doppler flowmetry of the ischemic feet showed the same degree of reduction in skin perfusion in both hyperglycemic and euglycemic animals. Nevertheless, we found a significantly higher rate of limb necrosis in hyperglycemic rats compared to euglycemic rats (71% versus 29%, resp.). In this study, we revealed that hyperglycemia per se increases the susceptibility to limb necrosis in ischemic conditions. Our results may help to better understand the physiopathology of progressive diabetic wounds and underline the importance of strict glycemic control in patients with critical limb ischemia.

NADPH oxidase 4 deficiency leads to impaired wound repair and reduced dityrosine-crosslinking, but does not affect myofibroblast formation.

NADPH oxidases (NOX) mediate redox signaling by generating superoxide and/or hydrogen peroxide, which are involved in biosynthetic pathways, e.g. thyroid hormone generation, dityrosine crosslinking, as well as bacterial killing. Data investigating the role of NOX enzymes in cutaneous wound repair is limited and specifically their function in skin myofibroblast expression is unknown. The isoform NOX4 was recently shown to be a pre-requisite for the differentiation of cardiac and pulmonary myofibroblasts. In this study we investigate the role of NOX4 in wound repair using a wound model in NOX4 knockout mice (n=16) and wildtype mice (n=16). Wounds were photographed daily until complete wound closure. Mice were sacrificed at day 3, 7, 14; wound tissue was harvested. NOX4-deficient mice healed significantly slower (22 days, SD=1.9) than wild-type mice (17 days, SD=1.4, p<0.005). However, there was no difference in myofibroblast expression. Strong dityrosine formation was observed, but was significantly weaker in NOX4-/- mice (p<0.05). NOX2, HIF1α and CD31 expression was significantly weaker in NOX4-/- mice (p<0.05). In this study we show for the first time that NOX4 plays a role in cutaneous wound repair. Our data suggests that NOX4 mediates HIF1α expression and neoangiogenesis during wound repair. NOX4 deletion led to a decreased expression of NOX2, implying a role of NOX4 in phagocytic cell recruitment. NOX4 was required for effective wound contraction but not myofibroblast expression. We suggest that myofibroblast contraction in NOX4-deficient mice is less effective in contracting the wound because of insufficient dityrosine-crosslinking of the ECM, providing the first indication for a physiological function of dityrosine crosslinking in higher animals.

Risks and benefits of using an absorbable mesh in one-stage immediate breast reconstruction: a comparative study

Background: Complete implant coverage by pectoralis major muscle in immediate breast reconstruction prevents implant exposure but restricts implant volume, increases the risk of a high-riding implant, and prevents natural ptosis. The authors hypothesized that extension of the subpectoral pocket with Vicryl mesh may produce more satisfactory results. The safety and efficiency of this technique were assessed by comparing complication rates and clinical results of the two reconstruction techniques: with and without mesh. Methods: The authors reviewed 161 immediate breast reconstructions in 139 patients from 2002 to 2010. A complete submuscular pocket was performed in 46 breasts and a partial submuscular pocket with Vicryl mesh extension was performed in 115 breasts. Complications, surgical revisions rates, implant size, and contralateral breast procedures were compared between the two groups. Results: Early and late surgical revisions were similar between the mesh and nonmesh groups (11.6 percent versus 4.3 percent at 90 days, p = 0.09; and 34.3 percent versus 41.4 percent at 5 years, p = 0.41). There were fewer revisions for implant malposition in the mesh group (8.9 percent versus 21.7 percent, p = 0.05). Patients with mesh could have a larger implant in comparison with those without mesh (329 g versus 284 g, p = 0.01) and had fewer contralateral mastopexies (12 percent versus 30 percent, p = 0.01). Conclusions: Larger implants and perhaps better control of implant position were possible using the Vicryl mesh extension without increasing complications. Because the mesh technique also recreates a slightly ptotic breast, fewer contralateral mastopexies were needed. The Vicryl mesh extension is a low-cost alternative to biological matrices or tissue expanders. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, III.

Reactive oxygen species and NOX enzymes are emerging as key players in cutaneous wound repair

Our understanding of the role of oxygen in cell physiology has evolved from its long-recognized importance as an essential factor in oxidative metabolism to its recognition as an important player in cell signaling. With regard to the latter, oxygen is needed for the generation of reactive oxygen species (ROS), which regulate a number of different cellular functions including differentiation, proliferation, apoptosis, migration, and contraction. Data specifically concerning the role of ROS-dependent signaling in cutaneous wound repair are very limited, especially regarding wound contraction. In this review we provide an overview of the current literature on the role of molecular and reactive oxygen in the physiology of wound repair as well as in the pathophysiology and therapy of chronic wounds, especially under ischemic and hyperglycemic conditions.

Breast lesions in reduction mammaplasty specimens: a histopathological pattern in 534 patients

Background:The prevalence of breast lesions (benign, precancerous and cancer lesions) in reduction mammaplasty (RM) specimens has rarely been reported in Europe and never in the Swiss population.Methods:Personal and histopathological data from 534 female patients who underwent RM were reviewed.Results:Benign and/or malignant lesions were detected in 76.2% of all patients. Benign breast lesions associated with an increased risk of developing breast cancer represented 2.8% of all lesions. Breast cancer in situ was identified in 5 (0.9%) patients. Patient age and previous history of breast cancer were risk factors for incidental breast cancer.Conclusion:The rate of incidental carcinoma in situ was higher for patients with breast cancer history. Probably due to preoperative breast cancer investigation, no occult invasive breast cancer was found in reduction mammary specimens. Therefore before RM, breast cancer evaluation should be considered for all patients, especially for those with breast cancer risk factors (e.g., patient age, personal history of breast cancer).