No abstract

Summary The skin is a unique immune organ that constitutes a complex network of physical, chemical and microbiological barriers against external insults. Keratinocytes are the most abundant cell type in the epidermis. These cells form the physical skin barrier and represent the first line of the host defense system by sensing pathogens via innate immune receptors, initiating anti‐microbial responses and producing various cytokines, chemokines and anti‐microbial peptides, which are important events in immunity. A damaged epidermal barrier in atopic dermatitis allows the penetration of potential allergens and pathogens to activate keratinocytes. Among the dysregulation of immune responses in atopic dermatitis, activated keratinocytes play a role in several biological processes that contribute to the pathogenesis of atopic dermatitis. In this review, we summarize the current understanding of the innate immune functions of keratinocytes in the pathogenesis of atopic dermatitis, with a special emphasis on skin‐derived anti‐microbial peptides and atopic dermatitis‐related cytokines and chemokines in keratinocytes. An improved understanding of the innate immunity mediated by keratinocytes can provide helpful insight into the pathophysiological processes of atopic dermatitis and support new therapeutic efforts.

The conformational properties of an active-site loop segment, defined by residues Ser161-Glu162-Asn163-Ser164, have been shown to be important for modulating the intrinsic reactivity of Mn(II) in the active site of Bacillus subtilis oxalate decarboxylase. We now detail the functional and structural consequences of removing a conserved Arg/Thr hydrogen bonding interaction by site-specific mutagenesis. Hence, substitution of Thr-165 by a valine residue gives an OxDC variant (T165V) that exhibits impaired catalytic activity. Heavy-atom isotope effect measurements, in combination with the X-ray crystal structure of the T165V OxDC variant, demonstrate that the conserved Arg/Thr hydrogen bond is important for correctly locating the side chain of Glu-162, which mediates a proton-coupled electron transfer (PCET) step prior to decarboxylation in the catalytically competent form of OxDC. In addition, we show that the T165V OxDC variant exhibits a lower level of oxalate consumption per dioxygen molecule, consistent with the predictions of recent spin-trapping experiments (Imaram et al., 2011, Free Rad. Biol. Med. 50, 1009–1015). This finding implies that dioxygen might participate as a reversible electron sink in two putative PCET steps and is not merely used to generate a protein-based radical or oxidized metal center.

Twice-daily plasma exchange was typically considered in acutely ill patients who had initially responded but then severe thrombocytopenia recurred, often with new neurologic abnormalities, while continuing daily plasma exchange. In three patients, twice-daily plasma exchange appeared to be beneficial. In most patients, a benefit of twice-daily plasma exchange could not be clearly documented because other treatments were initiated or intensified.

The transcription factor nuclear factor E2-related factor 2 (Nrf2) induces the expression of antioxidant gene products that neutralize reactive oxygen species and restore redox homeostasis. Nrf2 is constitutively degraded by the ubiquitin proteolytic system in unperturbed cells, but this turnover is arrested in response to oxidative stress, thereby leading to Nrf2 accumulation. Yet, a mechanistic understanding of how Nrf2 stabilization and transcriptional activation are coupled remains to be determined. We have discovered that the ubiquitin-conjugating enzyme UbcM2 is a novel regulator of Nrf2. Recombinant Nrf2 and UbcM2 form a complex upon alkylation of a non-catalytic cysteine in UbcM2, Cys-136. Substitution of this cysteine with a phenylalanine (C136F) to mimic cysteine oxidation/alkylation results in constitutive binding of UbcM2 to Nrf2 and an increased half-life of the transcription factor in vivo. We provide evidence that UbcM2 and Nrf2 form a nuclear complex utilizing the DNA binding, Neh1 domain, of Nrf2. Finally, we demonstrate that UbcM2 can enhance the transcriptional activity of endogenous Nrf2 and that Cys-136 and the active-site cysteine, Cys-145, jointly contribute to this regulation. Collectively, these data identify UbcM2 as a novel component of the Nrf2 regulatory circuit and position cysteine 136 as a putative redox sensor in this signaling pathway. This work implicates UbcM2 in the restoration of redox homeostasis following oxidative stress.