Cell type-specific targeting dissociates the therapeutic from the adverse effects of protein kinase inhibition in allergic skin disease

Interactions between skin-resident dendritic and Langerhans cells and pain-sensing neurons

Various immune cells in the skin contribute to its function as a first line of defense against infection and disease, and the skin's dense innervation by pain-sensing sensory neurons protects the host against injury or damage signals. Dendritic cells (DCs) are a heterogeneous population of cells that link the innate immune response to the adaptive response by capturing, processing, and presenting antigens to promote T-cell differentiation and activation. DCs are abundant across peripheral tissues, including the skin, where they are found in the dermis and epidermis. Langerhans cells (LCs) are a DC subset located only in the epidermis; both populations of cells can migrate to lymph nodes to contribute to broad immune responses. Dermal DCs and LCs are found in close apposition with sensory nerve fibers in the skin and express neurotransmitter receptors, allowing them to communicate directly with the peripheral nervous system. Thus, neuroimmune signaling between DCs and/or LCs and sensory neurons can modulate physiologic and pathophysiologic pathways, including immune cell regulation, host defense, allergic response, homeostasis, and wound repair. Here, we summarize the latest discoveries on DC- and LC-neuron interaction with neurons while providing an overview of gaps and areas not previously explored. Understanding the interactions between these 2 defence systems may provide key insight into developing therapeutic targets for treating diseases such as psoriasis, neuropathic pain, and lupus.

Gene, cell type, and drug prioritization analysis suggest genetic basis for the utility of diuretics in treating Alzheimer disease

We introduce a user-friendly tool for risk gene, cell type, and drug prioritization for complex traits: GCDPipe. It uses gene-level GWAS-derived data and gene expression data to train a model for the identification of disease risk genes and relevant cell types. Gene prioritization information is then coupled with known drug target data to search for applicable drug agents based on their estimated functional effects on the identified risk genes. We illustrate the utility of our approach in different settings: identification of the cell types, implicated in disease pathogenesis, was tested in inflammatory bowel disease (IBD) and Alzheimer disease (AD); gene target and drug prioritization was tested in IBD and schizophrenia. The analysis of phenotypes with known disease-affected cell types and/or existing drug candidates shows that GCDPipe is an effective tool to unify genetic risk factors with cellular context and known drug targets. Next, analysis of the AD data with GCDPipe suggested that gene targets of diuretics, as an Anatomical Therapeutic Chemical drug subgroup, are significantly enriched among the genes prioritized by GCDPipe, indicating their possible effect on the course of the disease.

The kinase p38α functions in dendritic cells to regulate Th2-cell differentiation and allergic inflammation

Dendritic cells (DCs) play a critical role in controlling T helper 2 (Th2) cell-dependent diseases, but the signaling mechanism that triggers this function is not fully understood. We showed that p38α activity in DCs was decreased upon HDM stimulation and dynamically regulated by both extrinsic signals and Th2-instructive cytokines. p38α-specific deletion in cDC1s but not in cDC2s or macrophages promoted Th2 responses under HDM stimulation. Further study showed that p38α in cDC1s regulated Th2-cell differentiation by modulating the MK2−c-FOS−IL-12 axis. Importantly, crosstalk between p38α-dependent DCs and Th2 cells occurred during the sensitization phase, not the effector phase, and was conserved between mice and humans. Our results identify p38α signaling as a central pathway in DCs that integrates allergic and parasitic instructive signals with Th2-instructive cytokines from the microenvironment to regulate Th2-cell differentiation and function, and this finding may offer a novel strategy for the treatment of allergic diseases and parasitic infection.

The Developmental Transcription Factor p63 Is Redeployed to Drive Allergic Skin Inflammation through Phosphorylation by p38α

Keratinocytes, the epithelial cells of the skin, reprogram their gene expression and produce immune effector molecules when exposed to environmental and endogenous triggers of inflammation. It remains unclear how keratinocytes process physiological signals generated during skin irritation and switch from a homeostatic to an inflammatory state. In this article, we show that the stress-activated protein kinase p38α is crucial for keratinocytes to prompt changes in their transcriptome upon cytokine stimulation and drive inflammation in allergen-exposed skin. p38α serves this function by phosphorylating p63, a transcription factor essential for the lineage identity and stemness of the skin epithelium. Phosphorylation by p38α alters the activity of p63 and redeploys this developmental transcription factor to a gene expression program linked to inflammation. Genetic ablation and pharmacological inhibition of p38α or the p38α-p63 target gene product MMP13 attenuate atopic dermatitis-like disease in mice. Our study reveals an epithelial molecular pathway promoting skin inflammation and actionable through treatment with topical small-molecule therapeutics.

Immune-Regulatory and Molecular Effects of Antidepressants on the Inflamed Human Keratinocyte HaCaT Cell Line

Allergic contact dermatitis (ACD) is a T cell-mediated type of skin inflammation resulting from contact hypersensitivity (CHS) to antigens. There is strong comorbidity between ACD and major depression. Keratinocytes release immunomodulatory mediators including pro-inflammatory cytokines and chemokines, which modulate skin inflammation and are crucial cell type for the development of CHS. Our previous studies showed that fluoxetine and desipramine were effective in suppressing CHS in different mouse strains. However, the immune and molecular mechanisms underlying this effect remain to be explored. The aim of the current study was to determine the immune and molecular mechanisms of action of antidepressant drugs engaged in the inhibition of CHS response in the stimulated keratinocyte HaCaT cell line. The results show that LPS, TNF-α/IFN-γ, and DNFB stimulate HaCaT cells to produce large amounts of pro-inflammatory factors including IL-1β, IL-6, CCL2, and CXCL8. HaCaT stimulation was associated with increased expression of ICAM-1, a cell adhesion molecule, and decreased expression of E-cadherin. Imipramine, desipramine, and fluoxetine suppress the production of IL-1β, CCL2, as well as the expression of ICAM-1. LPS and TNF-α/IFN-γ activate p-38 kinase, but antidepressants do not regulate this pathway. LPS decreases E-cadherin protein expression and fluoxetine normalizes these effects. In summary, the antidepressant drugs examined in this study attenuate the stimulated secretion of pro-inflammatory cytokines, chemokines, and modulate adhesion molecule expression by the HaCaT cell line. Therefore, antidepressants may have some clinical efficacy in patients with ACD and patients with comorbid depression and contact allergy.

Deciphering cell-type specific signal transduction in the brain: Challenges and promises

Signal transduction designates the set of molecular events that take place within a cell upon extracellular stimulation to mediate a functional outcome. Decades after the discovery that dopamine triggers opposing signaling pathways in D1- and D2-expressing medium spiny neurons, it is now clear that there are as many different flavors of signaling pathways in the brain as there are neuron types. One of the biggest challenges in molecular neuroscience is to elucidate cell-type specific signaling, in order to understand neurological diseases with regional vulnerability, but also to identify targets for precision drugs devoid of off-target effects. Here, we make a case for the importance of the study of neuron-type specific molecular characteristics. We then review the technologies that exist to study neurons in their full diversity and highlight their disease-relevant idiosyncrasies.

The sex-specific role of p38 MAP kinase in CNS autoimmunity is regulated by estrogen receptor alpha

Biological sex is a critical factor in regulating immune function. A striking example of this is the higher prevalence of autoimmune diseases such as multiple sclerosis (MS) and lupus in females compared to males. While many studies have implicated the role of sex hormones such as estrogens and androgens in these sex differences, surprisingly little is known about other molecular pathways that underlie sex differences or interact with sex hormones. We have previously shown that conditional ablation of p38α MAP kinase signaling in myeloid cells (p38αCKO) was protective in a mouse model of MS, experimental autoimmune encephalomyelitis (EAE), in female but not male mice. This sex difference was dependent on the presence of sex hormones, leading us to hypothesize that the pathogenic function of p38α in EAE depends on estrogen signaling via one of the two nuclear estrogen receptors, encoded by Esr1 and Esr2 . To test this hypothesis, we performed experiments with p38αCKO macrophages, which demonstrated that the effects of estradiol and p38α were independent of one another in vitro . Since many sex hormone effects are lost in vitro, we generated p38αCKO mice lacking either Esr1 or Esr2 , and evaluated their EAE susceptibility in vivo . Myeloid-specific deletion of Esr1 abrogated protection in p38αCKO females, although global deletion of Esr1 and Esr2 did not. Moreover, global or myeloid-specific disruption of Esr1 unexpectedly promoted protection from EAE in p38αCKO males. Mechanistically, Esr1 deletion resulted in partial reprogramming of p38α-dependent transcriptional modules in male macrophages, in particular those regulated by TGFβ, BRD4, and SMARCA4. These results demonstrate that estrogen signaling in myeloid cells plays an important sex-specific role in programming their dependence on specific intracellular signaling pathways in the context of autoimmune disease pathogenesis, suggesting potential avenues for sex-specific therapeutics or combinatorial approaches for the treatment of such diseases.

p38γ and p38δ Are Involved in T Lymphocyte Development

p38 mitogen-activated protein kinase (MAPK) signal transduction pathways are essential regulators of the immune response. Particularly, p38γ and p38δ regulate many immune cell functions such as cytokine production, migration, or T cell activation; however, their involvement in immune cell development is largely unknown. Here, we analysed the role of p38 MAPK isoforms p38γ and p38δ in T cell differentiation in the thymus and in lymph nodes, using mice deficient in p38γ, p38δ, or in both. We found that the T cell differentiation program in the thymus was affected at different stages in p38γ-, p38δ-, and p38γ/δ-deficient mice, and also peripheral T cell homaeostasis was compromised. Particularly, p38δ deletion affects different stages of early CD4⁻CD8⁻ double-negative thymocyte development, whereas lack of p38γ favours thymocyte positive selection from CD4⁺CD8⁺ double-positive to CD4⁺ or CD8⁺ single-positive cells. Our results identify unreported functions for p38γ and p38δ in T cells.

Anti-inflammatory roles of p38α MAPK in macrophages are context dependent and require IL-10

The p38 MAPK pathway was originally identified as a master regulator of proinflammatory cytokine production by myeloid cells. Numerous drugs targeting this kinase showed promise in preclinical models of inflammatory disease, but so far, none have shown efficacy in clinical trials. The reasons behind this are unclear, but may, in part, be explained by emerging anti-inflammatory functions of this kinase or overly refined selectivity of second-generation pharmacologic inhibitors. Here, we show that p38α signaling in macrophages plays pro- and anti-inflammatory functions in vivo and in vitro, with the outcome depending on the stimulus, output, kinetics, or mode of kinase inhibition (genetic vs. pharmacologic). Different pharmacologic inhibitors of p38 exhibit opposing effects, with second-generation inhibitors acting more specifically but inhibiting anti-inflammatory functions. Functionally, we show that the anti-inflammatory functions of p38α in macrophages are critically dependent on production of IL-10. Accordingly, in the absence of IL-10, inhibition of p38α signaling in macrophages is protective in a spontaneous model of colitis. Taken together, our results shed light on the limited clinical efficacy of drugs targeting p38 and suggest that their therapeutic efficacy can be significantly enhanced by simultaneous modulation of p38-dependent anti-inflammatory mediators, such as IL-10.

Fatsia polycarpa Triterpenoids and Acetylated Derivatives Thereof Inhibit Tumor Necrosis Factor-α-Induced Inflammation

Fatsia polycarpa Hayata is an evergreen shrub endemic to Taiwan and used locally to treat several inflammatory disorders. The crude extract of F. polycarpa has been proven to exhibit an anti-inflammatory effect in vitro and in vivo; however, which constituents of the extract confer the anti-inflammatory function remains unclear. Fatsicarpain D (Fat D) and fatsicarpain F (Fat F) are oleanane-type triterpenoids and two of the feature constituents of the F polycarpa extract. Ester substitution on C-3 has been proposed to enhance the activities of triterpenoids. Thus, this study compared and characterized the anti-inflammatory activities of Fat D, Fat F, and the C-3-acetylated derivatives thereof. These compounds were toxic to RAW 264.7 cells, but not to FL83B cells. The compounds dose-dependently inhibited tumor necrosis factor-α (TNF-α)-induced expression of inducible nitric oxide synthase in FL83B cells, with the IC50 values being Fat D 8.5 μM, acetylated Fat D 10.4 μM, acetylated Fat F 10.7 μM, and Fat F 27.4 μM, respectively. Thus, acetylation of C-3 improved the activity of Fat F. Moreover, the compounds suppressed TNF-α-induced expression of nuclear factor-κB (NF-κB) p65 subunit and protein tyrosine phosphatase-1B. Furthermore, they inhibited TNF-α-mediated activation of the inhibitor kappa B kinase (IKK), and that of the mitogen-activated protein kinases (MAPKs) extracellular-signal-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK), but promoted the activation of MAPK p38, which was found to be anti-inflammatory in certain cell types. Thus, Fat D and Fat F exhibited obvious anti-inflammatory activities in vitro and inhibited ERK, JNK, and the IKK/NF-κB pathway.

Selenoprotein MsrB1 promotes anti-inflammatory cytokine gene expression in macrophages and controls immune response in vivo

Post-translational redox modification of methionine residues often triggers a change in protein function. Emerging evidence points to this reversible protein modification being an important regulatory mechanism under various physiological conditions. Reduction of oxidized methionine residues is catalyzed by methionine sulfoxide reductases (Msrs). Here, we show that one of these enzymes, a selenium-containing MsrB1, is highly expressed in immune-activated macrophages and contributes to shaping cellular and organismal immune responses. In particular, lipopolysaccharide (LPS) induces expression of MsrB1, but not other Msrs. Genetic ablation of MsrB1 did not preclude LPS-induced intracellular signaling in macrophages, but resulted in attenuated induction of anti-inflammatory cytokines, such as interleukin (IL)-10 and the IL-1 receptor antagonist. This anomaly was associated with excessive pro-inflammatory cytokine production as well as an increase in acute tissue inflammation in mice. Together, our findings suggest that MsrB1 controls immune responses by promoting anti-inflammatory cytokine expression in macrophages. MsrB1-dependent reduction of oxidized methionine in proteins may be a heretofore unrecognized regulatory event underlying immunity and inflammatory disease, and a novel target for clinical applications.

Loss of Functionally Redundant p38 Isoforms in T Cells Enhances Regulatory T Cell Induction

The evolutionarily conserved protein kinase p38 mediates innate resistance to environmental stress and microbial infection. Four p38 isoforms exist in mammals and may have been co-opted for new roles in adaptive immunity. Murine T cells deficient in p38α, the ubiquitously expressed p38 isoform, showed no readily apparent cell-autonomous defects while expressing elevated amounts of another isoform, p38β. Mice with T cells simultaneously lacking p38α and p38β displayed lymphoid atrophy and elevated Foxp3⁺ regulatory T cell frequencies. Double deficiency of p38α and p38β in naïve CD4⁺ T cells resulted in an attenuation of MAPK-activated protein kinase (MK)-dependent mTOR signaling after T cell receptor engagement, and enhanced their differentiation into regulatory T cells under appropriate inducing conditions. Pharmacological inhibition of the p38-MK-mTOR signaling module produced similar effects, revealing potential for therapeutic applications.

p38α has an important role in antigen cross-presentation by dendritic cells

The role of the p38 signaling pathway in the innate and adaptive immune responses has been well documented, especially in inflammatory cytokine production by dendritic cells (DCs). However, whether the p38 signaling pathway affects the important antigen (Ag) presentation function of DCs remains largely unknown. In this study, we reported that the deletion of p38α resulted in an impaired cross-presentation ability of CD8⁺ conventional DCs (cDCs) and a reduction in the direct presentation ability of CD8^- cDCs ex vivo. Further study revealed that p38α had a crucial role in Ag processing by CD8⁺ cDCs but did not affect the Ag uptake or co-stimulation of T cells. Moreover, p38α deficiency led to reduced cross-priming of T cells in vivo. The production of the IL-12p40 and IL-12p70 cytokines by p38α-deficient cDCs was also significantly reduced. Our study identified a new role for p38α in modulating the important antigen cross-presentation function of DCs.

Keratinocyte p38δ loss inhibits Ras-induced tumor formation, while systemic p38δ loss enhances skin inflammation in the early phase of chemical carcinogenesis in mouse skin

p38δ expression and/or activity are increased in human cutaneous malignancies, including invasive squamous cell carcinoma (SCC) and head and neck SCC, but the role of p38δ in cutaneous carcinogenesis has not been well-defined. We have reported that mice with germline loss of p38δ exhibited a reduced susceptibility to skin tumor development compared with wild-type mice in the two-stage 7,12-dimethylbenz(a)anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA) chemical skin carcinogenesis model. Here, we report that p38δ gene ablation inhibited the growth of tumors generated from v-ras(Ha) -transformed keratinocytes in skin orthografts to nude mice, indicating that keratinocyte-intrinsic p38δ is required for Ras-induced tumorigenesis. Gene expression profiling of v-ras(Ha) -transformed p38δ-null keratinocytes revealed transcriptional changes associated with cellular responses linked to tumor suppression, such as reduced proliferation and increased differentiation, cell adhesion, and cell communications. Notably, a short-term DMBA/TPA challenge, modeling the initial stages of chemical skin carcinogenesis treatment, elicited an enhanced inflammation in p38δ-null skin compared with skin of wild-type mice, as assessed by measuring the expression of pro-inflammatory cytokines, including IL-1β, IL-6, IL-17, and TNFα. Additionally, p38δ-null skin and p38δ-null keratinocytes exhibited increased p38α activation and signaling in response to acute inflammatory challenges, suggesting a role for p38α in stimulating the elevated inflammatory response in p38δ-null skin during the initial phases of the DMBA/TPA treatment compared with similarly treated p38δ(+/+) skin. Altogether, our results indicate that p38δ signaling regulates skin carcinogenesis not only by keratinocyte cell-autonomous mechanisms, but also by influencing the interaction between between the epithelial compartment of the developing skin tumor and its stromal microenvironment.

Loss of epidermal p38α signaling prevents UVR-induced inflammation via acute and chronic mechanisms

Ultraviolet B radiation (UVB) is a component of solar radiation primarily responsible for causing damage and cancer in irradiated skin, and disrupting immune homeostasis. The immediate harm and long-term health risks of excessive sunlight exposure are impacting the lives of nearly all people worldwide. Inflammation is a key mechanism underlying UVB’s various detrimental effects. Here we show that activation of the protein kinase p38α is restricted to the epidermis in UVB-exposed skin, and p38α ablation targeted to the epithelial compartment is sufficient to suppress UVB-induced inflammation. Mechanistically, loss of epithelial p38α signaling attenuates the expression of genes required to induce vascular leakage and edema, and also increases the steady-state abundance of epidermal γδ T cells, which are known to promote the repair of damaged epidermis. These effects of p38α deficiency delineate a molecular network operating at the organism-environment interface, and reveal conditions crucial to preventing the pathology resulting from sun-damaged skin.

Activation of p38α in T cells regulates the intestinal host defense against attaching and effacing bacterial infections

Intestinal infections by attaching and effacing (A/E) bacterial pathogens cause severe colitis and bloody diarrhea. Although p38α in intestinal epithelial cells (IEC) plays an important role in promoting protection against A/E bacteria by regulating T cell recruitment, its impact on immune responses remains unclear. In this study, we show that activation of p38α in T cells is critical for the clearance of the A/E pathogen Citrobacter rodentium. Mice deficient of p38α in T cells, but not in macrophages or dendritic cells, were impaired in clearing C. rodentium. Expression of inflammatory cytokines such as IFN-γ by p38α-deficient T cells was reduced, which further reduced the expression of inflammatory cytokines, chemokines, and antimicrobial peptide by IECs and led to reduced infiltration of T cells into the infected colon. Administration of IFN-γ activated the mucosal immunity to C. rodentium infection by increasing the expression of inflammation genes and the recruitment of T cells to the site of infection. Thus, p38α contributes to host defense against A/E pathogen infection by regulating the expression of inflammatory cytokines that activate host defense pathways in IECs.

The emerging role of p38 mitogen-activated protein kinase in multiple sclerosis and its models

Multiple sclerosis (MS), the most common disabling neurologic disease of young adults, is considered a classical T cell-mediated disease and is characterized by demyelination, axonal damage, and progressive neurological dysfunction. The currently available disease-modifying therapies are limited in their efficacy, and improved understanding of new pathways contributing to disease pathogenesis could reveal additional novel therapeutic targets. The p38 mitogen-activated protein kinase (MAPK) signaling pathway is known to be triggered by stress stimuli and to contribute to inflammatory responses. Importantly, a number of recent studies have identified this signaling pathway as a central player in MS and its principal animal model, experimental allergic encephalomyelitis. Here, we review the evidence from mouse and human studies supporting the role of p38 MAPK in regulating key immunopathogenic mechanisms underlying autoimmune inflammatory disease of the central nervous system and the potential of targeting this pathway as a disease-modifying therapy in MS.

Tuning of protein kinase circuitry by p38α is vital for epithelial tissue homeostasis

The epithelium of mucosal and skin surfaces serves as a permeability barrier and affords mechanisms for local immune defense. Crucial to the development and maintenance of a properly functioning epithelium is the balance of cell proliferation, differentiation, and death. Here we show that this balance depends on cross-regulatory interactions among multiple protein kinase-mediated signals and their coordinated transmission. From an investigation of conditional gene knock-out mice, we find that epithelial-specific loss of the protein kinase p38α leads to aberrant activation of TAK1, JNK, EGF receptor, and ERK in distinct microanatomical areas of the intestines and skin. Consequently, the epithelial tissues display excessive proliferation, inadequate differentiation, and sensitivity to apoptosis. These anomalies leave the tissue prone to damage and collapse at the trigger of an environmental insult. The vulnerability of p38α-deficient epithelium predicts adverse effects of long term pharmacological p38α inhibition; yet such limitations could be overcome by concomitant blockade of one or more of the dysregulated protein kinase signaling pathways.