Publications

<title>Abstract</title> The skin’s barrier function relies on the epidermis, whose structural integrity is maintained by basal stem cells that continuously renew and differentiate to form the multilayered epidermal architecture. Disruptions in epidermal differentiation underlie numerous hyperproliferative and inflammatory skin disorders. While transcriptional and epigenetic mechanisms are known to regulate the late stages of this process, the molecular events driving the early commitment to differentiation remain elusive. Here, we reveal that early mitochondrial reprogramming, characterized by the activation of oxidative phosphorylation (OXPHOS), is a critical determinant of differentiation initiation. Our findings identify fatty acid oxidation (FAO) as the primary metabolic pathway fueling OXPHOS during this process. Pharmacological and genetic inhibition of FAO, both in vitro and in vivo, disrupts differentiation and compromises the regeneration of the epidermal barrier, causing defective responses to physical insults. Mechanistically, FAO enables ATP production in committed epidermal cells to support the high energy demand of the differentiation process, establishing a direct link between lipid metabolism and epidermal homeostasis. These results uncover a previously unrecognized role for metabolic reprogramming in epidermal stem cell fate and highlight FAO as a novel target for therapeutic interventions to restore barrier function in pathological conditions.

High-fat diet obesity is linked to increased lung injury and bronchoalveolar lavage fluid (BALF) fatty acids in a hyperoxic ARDS model. In the present study, obesity not only upregulated intracellular lipids and effectors of fatty acid mitochondrial import but also was associated with downregulated fatty acid oxidation and reduced ATP production in alveolar epithelial type 2 cells after injury. Hyperoxic AEC2 from obese mice had reduced phospholipids, and obese mice had increased BALF surface tension after injury.

Recent gene targeting studies indicate that the plasminogen system is implicated in cell migration and matrix degradation during arterial neointima formation and atherosclerotic aneurysm formation. This study examined whether plasmin proteolysis is involved in accelerated posttransplant arteriosclerosis (graft arterial disease). Donor carotid arteries from wild-type B10.A2R mice were transplanted into either plasminogen wild-type (Plg+/+) or homozygous plasminogen-deficient (Plg-/-) recipient mice with a genetic background of 75% C57BL/6 and 25% 129. Within 15 d after allograft transplantation, leukocytes and macrophages infiltrated the graft intima in Plg+/+ and Plg-/- recipient mice to a similar extent. In Plg+/+ recipients, the elastic laminae in the transplant media exhibited breaks through which macrophages infiltrated before smooth muscle cell proliferation, whereas in Plg-/- recipients, macrophages failed to infiltrate the transplant media which remained structurally more intact. After 45 d of transplantation, a multilayered smooth muscle cell-rich transplant neointima developed in Plg+/+ hosts, in contrast to Plg-/- recipients, in which the transplants contained a smaller intima, predominantly consisting of leukocytes, macrophages, and thrombus. Media necrosis, fragmentation of the elastic laminae, and adventitial remodeling were more pronounced in Plg+/+ than in Plg-/- recipient mice. Expression of the plasminogen activators (PA), urokinase-type PA (u-PA) and tissue-type PA (t-PA), and expression of the matrix metalloproteinases (MMPs), MMP-3, MMP-9, MMP-12, and MMP-13, were significantly increased within 15 d of transplantation when cells actively migrate. These data indicate that plasmin proteolysis plays a major role in allograft arteriosclerosis by mediating elastin degradation, macrophage infiltration, media remodeling, medial smooth muscle cell migration, and formation of a neointima.

Mitochondrial oxidative phosphorylation (OXPHOS) generates ATP, but OXPHOS also supports biosynthesis during proliferation. In contrast, the role of OXPHOS during quiescence, beyond ATP production, is not well understood. Using mouse models of inducible OXPHOS deficiency in all cell types or specifically in the vascular endothelium that negligibly relies on OXPHOS-derived ATP, we show that selectively during quiescence OXPHOS provides oxidative stress resistance by supporting macroautophagy/autophagy. Mechanistically, OXPHOS constitutively generates low levels of endogenous ROS that induce autophagy via attenuation of ATG4B activity, which provides protection from ROS insult. Physiologically, the OXPHOS-autophagy system (i) protects healthy tissue from toxicity of ROS-based anticancer therapy, and (ii) provides ROS resistance in the endothelium, ameliorating systemic LPS-induced inflammation as well as inflammatory bowel disease. Hence, cells acquired mitochondria during evolution to profit from oxidative metabolism, but also built in an autophagy-based ROS-induced protective mechanism to guard against oxidative stress associated with OXPHOS function during quiescence.<b>Abbreviations</b>: AMPK: AMP-activated protein kinase; AOX: alternative oxidase; Baf A: bafilomycin A₁; CI, respiratory complexes I; DCF-DA: 2',7'-dichlordihydrofluorescein diacetate; DHE: dihydroethidium; DSS: dextran sodium sulfate; ΔΨmi: mitochondrial inner membrane potential; EdU: 5-ethynyl-2'-deoxyuridine; ETC: electron transport chain; FA: formaldehyde; HUVEC; human umbilical cord endothelial cells; IBD: inflammatory bowel disease; LC3B: microtubule associated protein 1 light chain 3 beta; LPS: lipopolysaccharide; MEFs: mouse embryonic fibroblasts; MTORC1: mechanistic target of rapamycin kinase complex 1; mtDNA: mitochondrial DNA; NAC: N-acetyl cysteine; OXPHOS: oxidative phosphorylation; PCs: proliferating cells; PE: phosphatidylethanolamine; PEITC: phenethyl isothiocyanate; QCs: quiescent cells; ROS: reactive oxygen species; PLA2: phospholipase A2, WB: western blot.

&lt;p&gt;Supplementary Figure legends&lt;/p&gt;