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Photoaging is an accelerated form of aging resulting from skin exposure to ultraviolet (UV) radiation. UV-A radiation deeply penetrates the dermis and triggers the generation of reactive oxygen species (ROS) which promotes damage to DNA, lipids and proteins. Lipid peroxidation results from the oxidative attack of polyunsaturated fatty acids which generate a huge amount of lipid peroxidation products, among them reactive carbonyl species (RCS) such as α, β-unsaturated hydroxyalkenals (e.g., 4-hydroxynonenal), acrolein or malondialdehyde. These highly reactive agents form adducts on free NH2 groups and thiol residues on amino acids in proteins and can also modify DNA and phospholipids. The accumulation of RCS-adducts leads to carbonyl stress characterized by progressive cellular and tissular dysfunction, inflammation and toxicity. RCS-adducts are formed in the dermis of skin exposed to UV-A radiation. Several RCS targets have been identified in the dermis, such as collagen and elastin in the extracellular matrix, whose modification could contribute to actinic elastosis lesions. RCS-adducts may play a role in fibroblast senescence via the modification of histones, and the sirtuin SIRT1, leading to an accumulation of acetylated proteins. The cytoskeleton protein vimentin is modified by RCS, which could impair fibroblast motility. A better identification of protein modification and carbonyl stress in the dermis may help to develop new treatment approaches for preventing photoaging.

Summary: Endogenous PIEZO1 channels of native endothelium lack the hallmark inactivation often seen when these channels are overexpressed in cell lines. Because prior work showed that the force of shear stress activates sphingomyelinase in endothelium, we considered if sphingomyelinase is relevant to endogenous PIEZO1. Patch clamping was used to quantify PIEZO1-mediated signals in freshly isolated murine endothelium exposed to the mechanical forces caused by shear stress and membrane stretch. Neutral sphingomyelinase inhibitors and genetic disruption of sphingomyelin phosphodiesterase 3 (SMPD3) cause PIEZO1 to switch to profoundly inactivating behavior. Ceramide (a key product of SMPD3) rescues non-inactivating channel behavior. Its co-product, phosphoryl choline, has no effect. In contrast to ceramide, sphingomyelin (the SMPD3 substrate) does not affect inactivation but alters channel force sensitivity. The data suggest that sphingomyelinase activity, ceramide, and sphingomyelin are determinants of native PIEZO gating that enable sustained activity.

Solar ultraviolet A (UV-A) radiation promotes a huge variety of damages on connective tissues and dermal fibroblasts, including cellular senescence, a major contributor of skin photoaging. The mechanisms of skin photoaging evoked by UV-A partly involve the generation of reactive oxygen species and lipid peroxidation. We previously reported that 4-hydroxynonenal (HNE), a lipid peroxidation-derived aldehyde, forms adducts on elastin in the skins of UV-A irradiated hairless mice, possibly contributing to actinic elastosis. In the present study, we investigated whether and how HNE promotes fibroblast senescence in skin photoaging. Dermal fibroblasts of skins from UV-A-exposed hairless mice exhibited an increased number of γH2AX foci characteristic of cell senescence, together with an accumulation of HNE adducts partly colocalizing with the cytoskeletal protein vimentin. Murine fibroblasts exposed to UV-A radiation (two cycles of 15 J/cm2), or HNE (30 µM, 4 h), exhibited senescence patterns characterized by an increased γH2AX foci expression, an accumulation of acetylated proteins, and a decreased expression of the sirtuin SIRT1. HNE adducts were detected on vimentin in cultured fibroblasts irradiated by UV-A or incubated with HNE. The HNE scavenger carnosine prevented both vimentin modification and fibroblast senescence evoked by HNE in vitro and in the skins of UV-A-exposed mice. Altogether, these data emphasize the role of HNE and lipid peroxidation-derived aldehydes in fibroblast senescence, and confirm the protective effect of carnosine in skin photoaging.

The balance between vascular cell proliferation vs apoptosis plays a key role in vessel wall remodeling. Intimal migration and proliferation of smooth muscle cells (SMC), and secretion of extracellular matrix are involved in fibrous cap formation and plaque stability, whereas apoptosis of vascular cells may contribute to the erosion and instability of the plaque leading to its rupture and subsequent thrombus formation. LDL become atherogenic after undergoing oxidation within the vascular wall. Oxidized LDL (oxLDL) and oxidized lipids exhibit complex biological properties involved in endothelial dysfunction, SMC migration and proliferation, inflammation, and apoptosis. Oxidized LDL-induced apoptosis involves the extrinsic propapoptotic pathway (linked to Fas/Fas ligand) in lymphocytes, and the intrinsic mitochondrial apoptotic pathway, involving bcl-2 family members, cytochrome C release, and the terminal executive caspase-3 pathway, as well as the mitochondrial apoptotic factor AIF, in vascular cells. The apoptotic signaling of oxLDL is mediated in part by an intense and sustained rise of cytosolic calcium. The mechanisms regulating the balance between proliferation and apoptosis triggered by oxLDL and their role in vivo in atherosclerotic plaque progression remains to be clarified.

Oxidative stress play a major role in the genesis and the evolution of vascular pathologies. Recent data suggest that redox mechanisms are involved in the signaling network of vascular cells and the physiology of the vascular wall. Experimental cell models allow to analyse the biological effect of pro-oxidants, and the regulation exerted by antioxidants and cytoprotective agents. Fatty acids play a complex role in atherosclerosis, since they exhibit both anti and proatherogenic properties, as function of their concentration and insaturation level. Beside their role in cell metabolism and mitochondrial b-oxidation, fatty acids activate various signaling pathways, and could modulate intracellular oxidative stress via an uncoupling effect on mitochondria. We report here that fatty acids protect against mitochondrial oxidative stress by activating cellular glutathione peroxidase (GPX) activity. This effect is independent of the chain length and unsaturation level. EGF receptor is activated by fatty acids and involved in their protective effect against mitochondrial oxidative stress and GPX activation, and similar protective results are observed with EGF. Oleic acid and EGF protect DNA against the formation of 8oxodG lesions occurring subsequently to oxidative stress. Taken together, this new ‘antioxidant’ and cytoprotective property of fatty acids and EGF could participate to the stabilization of atherosclerotic plaque, and the more general anti-atherogenic properties of oleic acid.

Scrapie-infected mice are considered a model for study in prion diseases, which are characterized by the progressive accumulation in the brain of an abnormal isoform (PrPsc) of the normal cellular prion protein (PrPc). Increasing data suggest that the neurodegenerative process in prion diseases may result, at least partially, from a defect in antioxidant function, but so far in vivo oxidative stress remains poorly documented. We report here that 4-hydroxynonenal, a lipid peroxidation by-product, forms protein adducts in brains of scrapie-infected mice and of Creutzfeldt–Jakob disease affected patients. In scrapie mice, studies on the progression of PrPsc accumulation, glial activation, ubiquitin deposition, and 4-HNE adduct formation allowed us to conclude the late occurrence of oxidative damage in the course of the disease. Massive 4-HNE accumulation was identified in astrocytes, but not in neurons or microglial cells. These findings suggest an important oxidative stress (and subsequent lipid peroxidation) in astrocytes, with possible consequences on their neuronal trophic function.