Sox2 controls Schwann cell self-organization through fibronectin fibrillogenesis.

The extracellular matrix is known to modulate cell adhesion and migration during tissue regeneration. However, the molecular mechanisms that fine-tune cells to extra-cellular matrix dynamics during regeneration of the peripheral nervous system remain poorly understood. Using the RSC96 Schwann cell line, we show that Sox2 directly controls fibronectin fibrillogenesis in Schwann cells in culture, to provide a highly oriented fibronectin matrix, which supports their organization and directional migration. We demonstrate that Sox2 regulates Schwann cell behaviour through the upregulation of multiple extracellular matrix and migration genes as well as the formation of focal adhesions during cell movement. We find that mouse primary sensory neurons and human induced pluripotent stem cell-derived motoneurons require the Sox2-dependent fibronectin matrix in order to migrate along the oriented Schwann cells. Direct loss of fibronectin in Schwann cells impairs their directional migration affecting the alignment of the axons in vitro. Furthermore, we show that Sox2 and fibronectin are co-expressed in proregenerative Schwann cells in vivo in a time-dependent manner during sciatic nerve regeneration. Taken together, our results provide new insights into the mechanisms by which Schwann cells regulate their own extracellular microenvironment in a Sox2-dependent manner to ensure the proper migration of neurons.

Perfusion Controlled Mobilization after Lower Extremity Free Flaps-Pushing the Limits of Time and Intensity.

Background The current standard to gradually adapt the fragile perfusion in lower extremity free flaps to an upright posture is the dangling maneuver. This type of flap training neither fits the orthostatic target load of an upright posture, nor does it assist in mobilizing the patients effectively. In this study, we quantitatively analyzed training effects of an early and full mobilization on flap perfusion. Methods A total of 15 patients with gracilis flaps for distal lower extremity reconstruction were included. Flap training was performed daily by mobilizing the patients on a tilt table into a fully upright posture for 5 minutes between the third and fifth postop days (PODs). Changes in micro- and macrocirculation were analyzed by laser Doppler flowmetry, remission spectroscopy, and an implanted Doppler probe. Results All flaps healed without complications. Yet, in three patients, the increased orthostatic load required an adjustment of the training duration due to a critical blood flow. The others showed an increasing compensation in the microcirculation. When tilting the patients, blood flow and oxygen saturation dropped significantly less on POD5 than on POD3. Furthermore, a significant increase of the blood flow was noted after an initial decrease during the mobilization on all days. An increasing compensation in the macrocirculation could not be determined. Conclusion Full mobilization of patients with lower extremity free flaps can be performed safely under perfusion monitoring, already starting on POD3. Additionally, monitoring allows a consideration of the individual orthostatic competence and therefore, exploitation of the maximum mobilization potential.

Less Is More? Impact of Single Venous Anastomosis on the Intrinsic Transit Time of Free Flaps.

Background The number of venous anastomoses advisable for a free flap continues to be controversial. Intrinsic transit time (ITT) is the time it takes dye during indocyanine green (ICG) microangiography to travel from the arterial to the venous anastomosis. ITT provides information on blood flow velocity and can predict postoperative circulatory complications. This study investigated the effect of the number of venous anastomoses on ITT. Methods The study enrolled 126 patients who had undergone microsurgical reconstruction and intraoperative ICG microangiography. Selection was limited to free gracilis and anterolateral thigh flaps as flaps with a single venous system. The retrospective assessment included reconstruction characteristics of the flaps, clinical outcome, ITT, and the number of venous anastomoses. Results The two groups were homogenous in terms of reconstruction characteristics. The single-venous anastomosis group (n = 75) had a reduced ITT (23.6 ± 11.7 vs. 43.8 ± 23.7 seconds; p < 0.001) compared with the double-anastomosis group (n = 51). A shorter ITT resulted in a significant reduction in the risk of reexploration for anastomotic thrombosis (OR 0.96; p = 0.024). Despite this, a higher reexploration rate tended to occur in the single-venous anastomosis group (9.3 vs. 7.8%; p = 1.0). Conclusion The results highlight the effect of shortening the ITT (thromboprotective blood flow acceleration) by using only one venous anastomosis. However, if the ITT is already at a low enough level with two veins, restriction to one vein does not appear to result in a reduced reexploration rate. For these flaps, the advantages of double-venous anastomosis prevail in terms of a backup drainage.

Arteriovenous Loop-Independent Free Flap Reconstruction of Sternal Defects after Cardiac Surgery.

Background Sternal defects following deep wound infections are predominantly reconstructed using local and regional flaps. The lack of appropriate recipient vessels after cardiac surgery may explain the minor role of free flaps. To date, arteriovenous loops have been the leading solution to enable microsurgical closure of these defects. However, the related surgical effort and the risk of flap failure are increased. We reviewed our experiences with the right gastroepiploic vessels as alternative recipient vessels for free flap reconstructions. Methods Between September 2010 and July 2015, 12 patients suffering deep wound infection after cardiac surgery underwent sternal reconstruction with free flaps anastomosed to the right gastroepiploic vessels. Gracilis flaps (n = 8) and anterolateral thigh perforator flaps (n = 4) were used for sternal reconstruction. Recipient vessels were harvested by laparoscopic dissection in five patients. Half of the free flaps were variably combined with omental flow-through flaps. Results Healing of all flaps was uneventful with no partial or total flap loss. Simultaneous interdisciplinary harvesting of recipient vessels by laparoscopy significantly shortened mean operative time from 313 to 216 minutes (p = 0.018). One incisional hernia was observed in the laparotomy group. Revision of a gracilis donor site was necessary in another patient due to postoperative bleeding. No recurrent sternal infection occurred during a mean follow-up of 20 months (range, 3-59 months). Conclusions The concept of gastroepiploic recipient vessels allows reliable free flap reconstructions of sternal defects in such high-risk patients without the need for arteriovenous loops.