Substance P alterations in skin and brain of chronically stressed atopic-like mice

Psychological Stress and Atopic Dermatitis: A Focus Group Study

BACKGROUND

Atopic dermatitis (AD) is a chronic inflammatory skin disorder. It is often reported to be worsened by psychological stress.

OBJECTIVE

To explore the role of psychological stress and related triggers in AD, and its connection to worsening of this disease, focusing on patients' perspectives.

METHODS

In total, 28 patients with AD were included in focus groups. Topics regarding psychological stress and psychological triggers were discussed.

RESULTS

The hypothesis that psychological stress may have impact on eczema and its pruritus was supported by all of the patients. Distinguishing the worsening effect of psychological stress from effects of physiological triggers, such as infection, climate and allergic factors, was claimed to be difficult by many patients. Most of the patients thought that chronic stress affected the AD more when compared to acute stress. Family problems, financial problems, work overload, school exam periods, lack of structure at work, and unforeseen events were identified as important psychological triggers. Conventional treatment/therapy with topical corticosteroids and emollients, UV light treatment, were suggested as possible treatments, as well as psychological intervention and physical exercise.

CONCLUSION

Psychological stress is an important factor to consider in the management of patients with AD. In particular, chronic stress tends to worsen AD. The type of stress can possibly also affect the quality of the pruritus experienced by the patients. Unforeseen events and decision making were frequently mentioned as important triggers. Furthermore, physical exercise was reported to provide beneficial effects.

Tachykinin upregulation in atopic dermatitis

Context: Atopic dermatitis (AD) is a chronic, inflammatory, itching skin disorder, which may worsen due to stress, depression and anxiety. Tachykinins may be involved in inflammation signaling as well as they may have a role in stress, depression and anxiety. Objective: This study aimed to measure the expression of tachykinin markers, in the skin of patients with AD, and the correlation of these tachykinins with clinical and psychodemographic parameters. Materials and methods: Twenty-eight adult patients with AD were investigated regarding tachykinin expression in skin biopsies, using an immunohistochemical technique. The patients were characterized with clinical and psychodemographic parameters. Results: The number of substance P and neurokinin (NK)A positive nerve fibers, as well as NKA positive mononuclear dermal cells, was increased in lesional compared to non-lesional skin. Interestingly, the depression score and the number of dermal NK-1 receptor (R) positive cells in lesional as well as in non-lesional skin showed a correlation. Conclusion: These findings indicate an upregulation of the tachykinergic system in the inflamed skin of AD.

Substance P restores normal skin architecture and reduces epidermal infiltration of sensory nerve fiber in TNCB-induced atopic dermatitis-like lesions in NC/Nga mice

BACKGROUND

Atopic dermatitis (AD) is a chronic inflammatory skin disorder characterized by intense pruritus and eczematous lesion. Substance P (SP) is an 11-amino-acid endogenous neuropeptide that belongs to the tachykinin family and several reports recently have supported the anti-inflammatory and tissue repairing roles of SP.

OBJECTIVE

In this study, we investigated whether SP can improve AD symptoms, especially the impaired skin barrier function, in 2, 4, 6-trinitrochlorobenzene (TNCB)-induced chronic dermatitis of NC/Nga mice or not.

METHOD

AD-like dermatitis was induced in NC/Nga mice by repeated sensitization with TNCB for 5 weeks. The experimental group designations and topical treatments were as follows: vehicle group (AD-VE); SP group (AD-SP); and SP with NK1R antagonist CP99994 (AD-SP-A) group. Histological analysis was performed to evaluate epidermal differentiation, dermal integrity, and epidermal nerve innervation in AD-like lesions. The skin barrier functions and pruritus of NC/Nga mice were evaluated by measuring transepidermal water loss (TEWL) and scratching behavior, respectively.

RESULT

Topical SP treatment resulted in significant down-regulation of Ki67 and the abnormal-type keratins (K) K6, K16, and K17, restoration of filaggrin and claudin-1, marked reduction of TEWL, and restoration of basement membrane and dermal collagen deposition, even under continuous sensitization of low dose TNCB. In addition, SP significantly reduced innervation of itch-evoking nerve fibers, gelatinase activity and nerve growth factor (NGF) expression in the epidermis but upregulated semaphorin-3A (Sema3A) expression in the epidermis, along with reduced scratching behavior in TNCB-treated NC/Nga mice. All of these effects were completely reversed by co-treatment with the NK1R antagonist CP99994. In cultured human keratinocytes, SP treatment reduced expression of TGF-α, but upregulated TGF-β and Sema3A.

CONCLUSION

Topically administered SP can restore normal skin barrier function, reduce epidermal infiltration of itch-evoking nerve fibers in the AD-like skin lesions, and alleviate scratching behavior. Thus, SP may be proposed as a potential medication for chronic dermatitis and AD.

Atopic dermatitis: allergic dermatitis or neuroimmune dermatitis?

Advances in knowledge of neurocellulars relations have provided new directions in the understanding and treatment of numerous conditions, including atopic dermatitis. It is known that emotional, physical, chemical or biological stimuli can generate more accentuated responses in atopic patients than in non-atopic individuals; however, the complex network of control covered by these influences, especially by neuropeptides and neurotrophins, and their genetic relations, still keep secrets to be revealed. Itching and airway hyperresponsiveness, the main aspects of atopy, are associated with disruption of the neurosensory network activity. Increased epidermal innervation and production of neurotrophins, neuropeptides, cytokines and proteases, in addition to their relations with the sensory receptors in an epidermis with poor lipid mantle, are the aspects currently covered for understanding atopic dermatitis.

Critical evaluation of the expression of gastrin-releasing peptide in dorsal root ganglia and spinal cord

There are substantial disagreements about the expression of gastrin-releasing peptide (GRP) in sensory neurons and whether GRP antibody cross-reacts with substance P (SP). These concerns necessitate a critical revaluation of GRP expression using additional approaches. Here, we show that a widely used GRP antibody specifically recognizes GRP but not SP. In the spinal cord of mice lacking SP (Tac1 KO), the expression of not only GRP but also other peptides, notably neuropeptide Y (NPY), is significantly diminished. We detected Grp mRNA in dorsal root ganglias using reverse transcription polymerase chain reaction, in situ hybridization and RNA-seq. We demonstrated that Grp mRNA and protein are upregulated in dorsal root ganglias, but not in the spinal cord, of mice with chronic itch. Few GRP⁺ immunostaining signals were detected in spinal sections following dorsal rhizotomy and GRP⁺ cell bodies were not detected in dissociated dorsal horn neurons. Ultrastructural analysis further shows that substantially more GRPergic fibers form synaptic contacts with gastrin releasing peptide receptor-positive (GRPR⁺) neurons than SPergic fibers. Our comprehensive study demonstrates that a majority of GRPergic fibers are of primary afferent origin. A number of factors such as low copy number of Grp transcripts, small percentage of cells expressing Grp, and the use of an eGFP GENSAT transgenic as a surrogate for GRP protein have contributed to the controversy. Optimization of experimental procedures facilitates the specific detection of GRP expression in dorsal root ganglia neurons.

Brain-skin connection: stress, inflammation and skin aging

The intricate relationship between stress and skin conditions has been documented since ancient times. Recent clinical observations also link psychological stress to the onset or aggravation of multiple skin diseases. However, the exact underlying mechanisms have only been studied and partially revealed in the past 20 years or so. In this review, the authors will discuss the recent discoveries in the field of “Brain-Skin Connection”, summarizing findings from the overlapping fields of psychology, endocrinology, skin neurobiology, skin inflammation, immunology, and pharmacology.

Tachykinin: recent developments and novel roles in health and disease

Over 80 years has passed since the discovery of substance P (SP), and a variety of peptides of the tachykinin (TK) family have been found and investigated. SP, neurokinin A (NKA), and neurokinin B (NKB) are representative peptides in mammalian species. SP and NKA are major excitatory neurotransmitters in the peripheral nervous system, while NKB is primarily involved in the central nervous system (CNS). Moreover, TK peptides play roles not only as neurotransmitters but also as local factors and are involved in almost all aspects of the regulation of physiological functions and pathophysiological processes. The role of SP as a mediator of pain processing and inflammation in peripheral tissues in coordination with transient receptor potential channels is well established, while novel aspects of TKs in relation to hematopoiesis, venous thromboembolism, tendinopathy, and taste perception have been clarified. In the CNS, the NKB signaling system in the hypothalamus has been shown to play a crucial role in the regulation of gonadotropin hormone secretion and the onset of puberty, and molecular biological studies have elucidated novel prophylaxic activities of TKs against neurogenic movement disorders based on their molecular structure. This review provides an overview of the novel aspects of TKs reported around the world in the last 5 years, with particular focus on nociception, inflammation, hemopoiesis, gonadotropin secretion, and CNS diseases.

Chronic mild stress modulates 5-HT1A and 5-HT2A receptor expression in the cerebellar cortex of NC/Nga atopic-like mice

Atopic eczema symptoms may worsen due to stress. In the present study, the cerebellar cortex of the atopic-like mouse NC/Nga was studied regarding the effect of chronic mild stress on expression of two well-characterized serotonergic receptors (R), 5-HT1A and 5-HT2A. In total 24 mice were used. Sixteen of these mice were subjected to unpredictable stressors for 12 weeks, and 8 mice were used as controls. In order to evoke an eczema, a mite antigen was applied to 16 mice from week 9 of the experiment. Thus, three groups of mice, stressed eczematous (SE), non-stressed eczematous (NSE) and stressed control (SC), respectively, were obtained. The expression of the 5-HT1AR was analyzed using quantitative immunohistochemistry. For evaluation of 5-HT2AR a semi-quantitative technique was used, the cell density and signal intensity being measured. The highest average value for 5-HT1AR expression, in the Purkinje cells, was recorded in the NSE group, while the lowest average was in the SC group. 5-HT1AR expression differed significantly between the groups. The highest average value for density of 5-HT2AR positive Purkinje cells was evident in the SE group, while the lowest was in the SC group, this difference between groups also being statistically significant. In addition, the signal intensity was highest in the SE group, with a difference compared to the other groups. In conclusion, chronic mild stress modulates serotonergic receptor expressions in the cerebellar cortex of atopic-like mice.