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Striae distensae are common disfiguring cutaneous lesions but lack effective treatments because of an incomplete understanding of their pathophysiology. Dermal fibroblasts likely play an important role. The authors investigate the cellular-molecular features distinguishing fibroblasts from human striae distensae and normal skin. The authors also develop a mouse model of striae distensae.Human striae distensae and normal skin samples were compared for tensile strength and histologic structure. Fibroblasts from striae distensae and normal skin were isolated by fluorescence-activated cell sorting for gene expression analysis. Immunofluorescence staining and fluorescence-activated cell sorting were used to confirm gene expression data at the protein level. A mouse model of striae distensae formation was created by administering corticosteroids and mechanically loading the dorsal skin.Human striae distensae exhibited reduced tensile strength, more disordered collagen fibers, and epidermal atrophy compared to human normal skin. There were 296 up-regulated genes in striae distensae fibroblasts, including the profibrotic lineage and surface marker CD26. Up-regulated genes were involved in profibrotic and mechanoresponsive signaling pathways (TGFβ and FAK-PI3-AKT-signaling). In contrast, 571 genes were down-regulated, including CD74 and genes of the AMPK pathway. Increased CD26 and decreased CD74 expression was confirmed by fluorescence-activated cell sorting and immunofluorescence. Similar cutaneous histologic and gene expression changes were induced in hypercortisolemic mice by mechanically loading the dorsal skin.Fibroblasts from human striae distensae exhibit increased profibrotic and decreased antifibrotic signaling. CD26 and CD74 are promising surface markers that may be targeted therapeutically. The authors' mouse model of striae distensae can be used as a platform to test the efficacy of potential therapeutic agents.Striae distensae are common disfiguring cutaneous lesions whose etiology remains elusive, which has hindered development of effective treatment strategies. Dermal fibroblasts likely play an important role. The authors sought to elucidate the key cellular-molecular pathways distinguishing fibroblasts in striae distensae from those in normal skin.

Purpose: Crohn’s disease (CD) is a subtype of inflammatory bowel disease (IBD) characterized by patchy, transmural inflammation throughout the digestive tract and creeping fat formation. Thirty percent of CD patients develop strictures, eighty percent of which will require surgery. Creeping fat is associated with stricture formation, but its role in intestinal fibrosis remains unclear. Here, we present a novel surgical model of intestinal fibrosis and show by lineage tracing that creeping fat adipocytes convert to fibroblasts that contribute to fibrosis. Methods: We developed a novel surgical model of IBD that avoids the chronic use of caustic agents by creating a longitudinal, anti-mesenteric colotomy in the mouse transverse colon that is closed transversally. We performed Masson’s trichrome staining to assess collagen deposition. Finally, we performed lineage tracing of mature adipocytes in Adiponectin-Cre; mTmG mice and characterized adipocyte-derived cells by immunostaining. Results: Our surgical model mimics key features of human strictures, including the formation of creeping fat around the injury site, increased bowel wall thickness, collagen deposition, and transmural adipocyte infiltration by post-operative day (POD) 7. Immunostaining for adipocyte and fibroblast markers confirmed the presence of transmural adipocytes adjacent to fibroblasts. Lineage tracing of mature adipocytes in Adiponectin-Cre; mTmG mice revealed adipocyte-derived cells that infiltrate the wound site that lose expression of adipocyte lineage markers, gain expression of fibroblast markers, produce collagen, and respond to TGF-β signaling. Conclusions: Our novel surgical colotomy model represents a viable approach to study intestinal fibrosis and creeping fat without the long-term use of caustic agents. Lineage tracing of mature creeping fat adipocytes demonstrates that adipocytes convert to fibroblasts that infiltrate the injury site and participate in fibrotic responses. Taken together, these findings suggest that creeping fat contributes to intestinal fibrosis in part through the local conversion of adipocytes to fibroblasts.

Purpose: Fat grafting is known to rejuvenate and improve fibrosis in irradiated skin, but the underlying mechanisms behind these effects are poorly understood. We have previously identified the Engrailed-1 fibroblast sub-population as having a role in post-natal dorsal skin fibrosis in mice. Using a radiation model to the scalp of Engrailed-1 mice, we sought to better understand the regenerative effects of fat grafting in irradiated tissue. Methods: Adult (60-day old) En1Cre;R26mTmG transgenic mice (n=5) underwent total body irradiation with 9 Gy for immunodepletion. Mice were then immediately reconstituted with 2 million nucleated bone marrow cells from donor NSG(NOD.CB17-Prkdcsscid/J) mice via retro-orbital injections. Reconstitution was confirmed with fluorescence-activated cell sorting (FACS) 2 weeks after whole body irradiation. Mice scalps were then irradiated with 5 Gy every other day for 12 days (30 Gy total) and allowed to recover for 4 weeks to facilitate fibrotic conversion. Irradiated scalps were grafted with 200μL of fresh human lipoaspirate. Graph retention was measured in-vivo for 8 weeks using Micro-Computed Tomography Scanner (Bruker SkyScan 1726™) and scalp skin was harvest for histology. Results: Two weeks post bone-marrow transplant, >90% of circulating hematopoietic cells (CD45+) cells in En1Cre;R26mTmG reporter mice were non-fluorescent, signifying successful reconstitution. Volumetric analysis of fat grafting in-vivo was performed using 3-dimensional reconstruction. At 8 weeks post-grafting, 4 of the 5 grafts demonstrated >50% graft retention, confirming successful grafting. Histological sections of scalp skin 8 weeks post-grafting demonstrated significantly less En1+GFP cells compared to non-grafted scalp skin, signifying less presence of En1+ fibroblasts. Furthermore, histology demonstrated significantly less dermal thickening, epidermal thinning, and collagen deposition and disorganization in fat grafted irradiated scalp skin compared to non-grafted scalp skin. Conclusion: Fat grafting mitigates radiation-induced fibrosis in scalp skin by decreasing collagen deposition, remodeling collagen formation, decreasing epidermal thinning, and reducing presence of pro-fibrotic fibroblast sub-populations.

OBJECTIVE: To investigate the effects of local doxycycline administration on skin scarring. BACKGROUND: Skin scarring represents a major source of morbidity for surgical patients. Doxycycline, a tetracycline antibiotic with off-target effects on the extracellular matrix, has demonstrated antifibrotic effects in multiple organs. However, doxycycline’s potential effects on skin scarring have not been explored in vivo. METHODS: Female C57BL/6J mice underwent dorsal wounding following an established splinted excisional skin wounding model. Doxycycline was administered by local injection into the wound base following injury. Wounds were harvested upon complete wound closure (postoperative day 15) for histological examination and biomechanical testing of scar tissue. RESULTS: A one-time dose of 3.90mM doxycycline (2mg/mL) within 12 hours of injury was found to significantly reduce scar thickness by 24.8% (*P < 0.0001) without compromising tensile strength. The same effect could not be achieved by oral dosing. In doxycycline-treated scar matrices, collagen I content was significantly reduced (*P = 0.0317) and fibers were favorably arranged with significantly increased fiber randomness (*P = 0.0115). Common culprits of altered wound healing mechanics, including angiogenesis and inflammation, were not impacted by doxycycline treatment. However, engrailed1 profibrotic fibroblasts, responsible for scar extracellular matrix deposition, were significantly reduced with doxycycline treatment (*P = 0.0005). CONCLUSIONS: Due to the substantial improvement in skin scarring and well-established clinical safety profile, locally administered doxycycline represents a promising vulnerary agent. As such, we favor rapid translation to human patients as an antiscarring therapy.