Chronic Proliferative Dermatitis in Mice: NFκB Activation Autoinflammatory Disease

SHARPIN: Role in Finding NEMO and in Amyloid-Beta Clearance and Degradation (ABCD) Pathway in Alzheimer's Disease?

SHANK- associated RH domain-interacting protein (SHARPIN) is a multifunctional protein associated with numerous physiological functions and many diseases. The primary role of the protein as a LUBAC-dependent component in regulating the activation of the transcription factor NF-κB accounts to its role in inflammation and antiapoptosis. Hence, an alteration of SHARPIN expression or genetic mutations or polymorphisms leads to the alteration of the above-mentioned primary physiological functions contributing to inflammation-associated diseases and cancer, respectively. However, there are complications of targeting SHARPIN as a therapeutic approach, which arises from the wide-range of LUBAC-independent functions and yet unknown roles of SHARPIN including neuronal functions. The identification of SHARPIN as a postsynaptic protein and the emerging studies indicating its role in several neurodegenerative diseases including Alzheimer's disease suggests a strong role of SHARPIN in neuronal functioning. This review summarizes the functional roles of SHARPIN in normal physiology and disease pathogenesis and strongly suggests a need for concentrating more studies on identifying the unknown neuronal functions of SHARPIN and hence its role in neurodegenerative diseases.

Chemokines and cytokines profile in whole saliva of patients with periodontitis

Clinical features suggest differences in immune response among periodontitis forms, albeit a large number of cytokines and chemokines remain to be evaluated. The saliva is an available source of mediators and its analysis would be valuable in order to understand pathophysiological differences. The objective of this study was analyze chemokines/cytokines profile in whole saliva of individuals with severe periodontitis (Stage III) presenting moderate [Grade B; GB] or rapid progression rate with a localized incisor-molar pattern [Grade C; GC/IMP]. A case-control study was designed for each periodontitis group. GB (n = 9) and GC/IMP (n = 7) patients and their healthy controls (C-GB, n = 9 and C-GC, n = 7) were evaluated. Non-stimulated saliva samples were assessed by a multiplex assay for a total of 40 cytokines, C-C and C-X-C motif chemokines. GC/IMP group presented higher levels of CCL17 and CCL27 (p = 0.04, FDR > 0.05), and lower levels of CCL2 (p = 0.04, FDR > 0.05) and CCL25 (p = 0.006, FDR < 0.05) when compared to its control. GB patients had higher levels of IL-6, IL-1β (p = 0.04, FDR > 0.05), and elevated pro-inflammatory (TNF-α,IL-1β,INF-γ,IL-6, IL-16): anti-inflammatory (IL-2, IL-4, IL-10) ratio (p = 0.01, FDR < 0.05) compared to its control [p-values by Mann-Whitney test, and False Discovery Rate (FDR) by Benjamini-Hochburg corrections]. CCL-chemokines and cytokines contributed to differences between GC/C-GC and GB/C-GB, respectively (p < 0.05, PERMANOVA test). These preliminary data revealed that each periodontitis phenotype presented distinct immune profiles differentially expressed in saliva compared to their related controls, suggesting differences in the etiopathogenesis of GB and GC/IMP.

Sharpin suppresses β1-integrin activation by complexing with the β1 tail and kindlin-1

Background

Previously sharpin has been identified as an endogenous inhibitor of β1-integrin activation by directly binding to a conserved region in the cytoplasmic tails (CTs) of the integrin β1-associated α subunits.

Methods

Here we employed biochemical approaches and cellular analyses to evaluate the function and molecular mechanism of the sharpin-kindlin-1 complex in regulating β1-integrin activation.

Results

In this study, we found that although the inhibition of sharpin on β1-integrin activation could be confirmed, sharpin had no apparent effect on integrin αIIbβ3 activation in CHO cell system. Notably, a direct interaction between sharpin and the integrin β1 CT was detected, while the interaction of sharpin with the integrin αIIb and the β3 CTs were substantially weaker. Importantly, sharpin was able to inhibit the talin head domain binding to the integrin β1 CT, which can mechanistically contribute to inhibiting β1-integrin activation. Interestingly, we also found that sharpin interacted with kindlin-1, and the interaction between sharpin and the integrin β1 CT was significantly enhanced when kindlin-1 was present. Consistently, we observed that instead of acting as an activator, kindlin-1 actually suppressed the talin head domain mediated β1-integrin activation, indicating that kindlin-1 may facilitate recruitment of sharpin to the integrin β1 CT.

Conclusion

Taken together, our findings suggest that sharpin may complex with both kindlin-1 and the integrin β1 CT to restrict the talin head domain binding, thus inhibiting β1-integrin activation.

Integrin beta 1 inhibition alleviates the chronic hyperproliferative dermatitis phenotype of SHARPIN-deficient mice

SHARPIN (Shank-Associated RH Domain-Interacting Protein) is a component of the linear ubiquitin chain assembly complex (LUBAC), which enhances TNF-induced NF-κB activity. SHARPIN-deficient (Sharpincpdm/cpdm) mice display multi-organ inflammation and chronic proliferative dermatitis (cpdm) due to TNF-induced keratinocyte apoptosis. In cells, SHARPIN also inhibits integrins independently of LUBAC, but it has remained enigmatic whether elevated integrin activity levels in the dermis of Sharpincpdm/cpdm mice is due to increased integrin activity or is secondary to inflammation. In addition, the functional contribution of increased integrin activation to the Sharpincpdm/cpdm phenotype has not been investigated. Here, we find increased integrin activity in keratinocytes from Tnfr1-/- Sharpincpdm/cpdm double knockout mice, which do not display chronic inflammation or proliferative dermatitis, thus suggesting that SHARPIN indeed acts as an integrin inhibitor in vivo. In addition, we present evidence for a functional contribution of integrin activity to the Sharpincpdm/cpdm skin phenotype. Treatment with an integrin beta 1 function blocking antibody reduced epidermal hyperproliferation and epidermal thickness in Sharpincpdm/cpdm mice. Our data indicate that, while TNF-induced cell death triggers the chronic inflammation and proliferative dermatitis, absence of SHARPIN-dependent integrin inhibition exacerbates the epidermal hyperproliferation in Sharpincpdm/cpdm mice.

IFN-γ or IFN-α ameliorates chronic proliferative dermatitis by inducing expression of linear ubiquitin chain assembly complex

The linear ubiquitin chain assembly complex (LUBAC) ubiquitin ligase complex, composed of HOIL-1L-interacting protein (HOIP), heme-oxidized IRP2 ubiquitin ligase-1L (HOIL-1L), and SHANK-associated RH domain protein, specifically generates linear polyubiquitin chains and is involved in NF-κB activation. Lack of SHANK-associated RH domain protein, which drastically reduces the amount of HOIP and HOIL-1L, causes chronic proliferative dermatitis (cpdm) in mice. Impaired NF-κB activation and augmented apoptosis have been implicated in the pathogenesis of cpdm in mice. In this study, we found that IFN-γ increased the amount of LUBAC by inducing HOIP and HOIL-1L mRNA transcription and enhanced the signal-induced NF-κB activation in embryonic fibroblasts, keratinocytes, and bone marrow-derived macrophages from wild-type and/or cpdm mice; however, IFN-γ failed to augment NF-κB activation in mouse embryonic fibroblasts lacking linear polyubiquitination activity of LUBAC. Moreover, s.c. injection of IFN-γ for 3 wk into the skin of cpdm mice increased the amount of HOIP, suppressed apoptosis, and ameliorated the dermatitis. Inhibition of keratinocyte apoptosis by IFN-γ injection suppressed neutrophil, macrophage, and mast cell infiltration and the amount of TNF-α in the skin of cpdm mice. Similarly, IFN-α also enhanced the amount of HOIP as well as NF-κB activation, inhibited apoptosis, and ameliorated cpdm dermatitis. These results indicate that the IFNs enhance NF-κB activation and ameliorate cpdm dermatitis by augmenting expression of HOIP and HOIL-1L and linear polyubiquitination activity of LUBAC.

Three-dimensional model of mouse epidermis for experimental studies of psoriasis

Three-dimensional models of skin and epidermis imitate the structure of real tissues and provide accurate information about certain skin conditions, such as psoriasis. A three-dimensional model of mouse epidermis was generated from the epidermal keratinocytes of newborn mice and treated with cytokines. The aim of this study was to evaluate this model as an experimental model of psoriasis and to assess the changes occurring in its structure and gene expression after the exposure to proinflammatory cytokines. Treatment of the three-dimensional model with either interleukin 17 or a combination of tumor necrosis factor and interferon γ was shown to produce morphological changes, which were similar to acanthosis in psoriatic skin. The observed changes in gene expression of metalloproteinases and certain psoriasis biomarkers, such as mki67, krt16 and fosl1, were similar to the changes in patients' skin. Notably, changes caused by interleukin 17 were less evident than those caused by the combination of interferon γ and tumor necrosis factor. On the contrary, HaCaT cells exhibited no significant changes in the expression of fosl1 and had decreased levels of mki67 after being treated with a combination of TNF and IFNG. Moreover, treatment with IL17 had no significant effect on krt16 and mki67 expression and even reduced the fosl1 levels. The findings suggest that artificially generated three-dimensional models of murine skin can be used to study psoriasis.

SHARPIN negatively associates with TRAF2-mediated NFκB activation

NFκB is an inducible transcriptional factor controlled by two principal signaling cascades and plays pivotal roles in diverse physiological processes including inflammation, apoptosis, oncogenesis, immunity, and development. Activation of NFκB signaling was detected in skin of SHAPRIN-deficient mice and can be diminished by an NFκB inhibitor. However, in vitro studies demonstrated that SHARPIN activates NFκB signaling by forming a linear ubiquitin chain assembly complex with RNF31 (HOIP) and RBCK1 (HOIL1). The inconsistency between in vivo and in vitro findings about SHARPIN's function on NFκB activation could be partially due to SHARPIN's potential interactions with downstream molecules of NFκB pathway. In this study, 17 anti-flag immunoprecipitated proteins, including TRAF2, were identified by mass spectrum analysis among Sharpin-Flag transfected mouse fibroblasts, B lymphocytes, and BALB/c LN stroma 12 cells suggesting their interaction with SHARPIN. Interaction between SHARPIN and TRAF2 confirmed previous yeast two hybridization reports that SHARPIN was one TRAF2's partners. Furthermore, luciferase-based NFκB reporter assays demonstrated that SHARPIN negatively associates with NFκB activation, which can be partly compensated by over-expression of TRAF2. These data suggested that other than activating NFκB signaling by forming ubiquitin ligase complex with RNF31 and RBCK1, SHARPIN may also negatively associate with NFκB activation via interactions with other NFκB members, such as TRAF2.