Inflammation caused by the hyper-activation of innate immunity due to genetic factors occasionally leads to inflammatory keratinization diseases of the skin. Such inflammatory keratinization diseases with genetic autoinflammatory pathogeneses are called “autoinflammatory keratinization diseases” (AiKD). AiKD also includes diseases with mixed pathological mechanisms of autoinflammation and autoimmunity.
AiKD have primary genetic causative factors associated with autoinflammation mainly in the epidermis and the upper dermis. Autoinflammation in the epidermis and the upper dermis leads to hyperkeratosis in the skin, resulting in further skin inflammatory symptoms of AiKD.
Common clinical features of AiKD are hyperkeratotic skin lesions with inflammation, although clinical phenotypes of AiKD are inconsistent and some diseases have unique characteristic manifestations. Most AiKD patients have recurrent and persistent skin symptoms which are refractory to standard treatments for inflammatory keratinization diseases.
Initially, AiKD encompassed (i) IL-36 receptor antagonist (IL-36Ra)-related pustulosis, (ii) CARD14-mediated pustular psoriasis, pityriasis rubra pilaris (PRP), and (iii) familial keratosis lichenoides chronica. Patients with generalized pustular psoriasis (GPP), impetigo herpetiformis and acrodermatitis continua are thought to be part of IL-36Ra-related AiKD cases. CARD14-mediated pustular psoriasis includes a subset of GPP and palmoplantar pustular psoriasis patients. Most cases of PRP type V have CARD14 mutations and are included in AiKD, and a small number of patients with other types of PRP have CARD14 variants and are also classified as AiKD.
Recently, patients with (iv) hidradenitis suppurativa (HS), especially familial cases, have been proposed to have AiKD. Hyperkeratosis of the follicular epithelia and keratin plug formation are thought to play important roles in the primary stage of the autoinflammatory pathogenesis of HS.
In addition, we have proposed that (v) porokeratosis be categorized as an AiKD. Mutations in four mevalonate pathway genes (MVK, MVD, PMVK and FDPS) have been reported in porokeratosis cases, and defective mevalonate metabolism is speculated to be a pathogenetic mechanism leading to abnormal growth and differentiation of epidermal keratinocytes and autoinflammation in porokeratosis.
To date, the CARD14-NFkB pathway, IL-36 pathway, inflammasome-IL-1b pathway, mevalonate pathway and g-secretase-Notch signaling-hair follicle keratinization pathway have been discussed as inflammatory pathways involved in the pathogenesis of AiKD. We assume that additional inflammatory keratinization diseases will be recognized as AiKD from novel insights into their underlying pathogenic mechanisms.
The concept of AiKD has opened a window onto a better understanding of the pathogenesis of various inflammatory keratinization disorders. Further discussion among researchers in various research fields is required to identify the perception of the roles of autoinflammation in skin diseases. This Research Topic aims to coordinate a discussion on the pathological mechanisms of, and innovative therapeutic strategies for, AiKD and to provide wide-ranging and divergent insights into the role of autoinflammation in skin disorders.
We welcome the submission of Original Research, Review, Mini-Review, Perspective and Commentary articles that include, but are not restricted to, the following topics:
1. Medical genetics and mutation search in AiKD patients
2. Cell biology studies on effects of underlining autoinflammation upon proliferation and differentiation of epidermal keratinocytes: especially roles of keratinocytes themselves as immune cells, and skin-associated inflammatory cells, such as neutrophils, dendritic cells including TIP-DC, Th17 cells, Th1 cells.
3. Genetic studies focusing on autoinflammatory pathways in the skin, including: CARD14-NFkB, IL-36, inflammasome-IL-1b, mevalonate and g-secretase-Notch signaling-hair follicle keratinization pathways.
4. Interventional studies revealing the clinical value of therapies targeting autoinflammatory pathways in the skin.
5. Perspectives on the novel roles of autoinflammation in skin diseases, and proposals for disorders to be newly included in AiKD
Inflammation caused by the hyper-activation of innate immunity due to genetic factors occasionally leads to inflammatory keratinization diseases of the skin. Such inflammatory keratinization diseases with genetic autoinflammatory pathogeneses are called “autoinflammatory keratinization diseases” (AiKD). AiKD also includes diseases with mixed pathological mechanisms of autoinflammation and autoimmunity.
AiKD have primary genetic causative factors associated with autoinflammation mainly in the epidermis and the upper dermis. Autoinflammation in the epidermis and the upper dermis leads to hyperkeratosis in the skin, resulting in further skin inflammatory symptoms of AiKD.
Common clinical features of AiKD are hyperkeratotic skin lesions with inflammation, although clinical phenotypes of AiKD are inconsistent and some diseases have unique characteristic manifestations. Most AiKD patients have recurrent and persistent skin symptoms which are refractory to standard treatments for inflammatory keratinization diseases.
Initially, AiKD encompassed (i) IL-36 receptor antagonist (IL-36Ra)-related pustulosis, (ii) CARD14-mediated pustular psoriasis, pityriasis rubra pilaris (PRP), and (iii) familial keratosis lichenoides chronica. Patients with generalized pustular psoriasis (GPP), impetigo herpetiformis and acrodermatitis continua are thought to be part of IL-36Ra-related AiKD cases. CARD14-mediated pustular psoriasis includes a subset of GPP and palmoplantar pustular psoriasis patients. Most cases of PRP type V have CARD14 mutations and are included in AiKD, and a small number of patients with other types of PRP have CARD14 variants and are also classified as AiKD.
Recently, patients with (iv) hidradenitis suppurativa (HS), especially familial cases, have been proposed to have AiKD. Hyperkeratosis of the follicular epithelia and keratin plug formation are thought to play important roles in the primary stage of the autoinflammatory pathogenesis of HS.
In addition, we have proposed that (v) porokeratosis be categorized as an AiKD. Mutations in four mevalonate pathway genes (MVK, MVD, PMVK and FDPS) have been reported in porokeratosis cases, and defective mevalonate metabolism is speculated to be a pathogenetic mechanism leading to abnormal growth and differentiation of epidermal keratinocytes and autoinflammation in porokeratosis.
To date, the CARD14-NFkB pathway, IL-36 pathway, inflammasome-IL-1b pathway, mevalonate pathway and g-secretase-Notch signaling-hair follicle keratinization pathway have been discussed as inflammatory pathways involved in the pathogenesis of AiKD. We assume that additional inflammatory keratinization diseases will be recognized as AiKD from novel insights into their underlying pathogenic mechanisms.
The concept of AiKD has opened a window onto a better understanding of the pathogenesis of various inflammatory keratinization disorders. Further discussion among researchers in various research fields is required to identify the perception of the roles of autoinflammation in skin diseases. This Research Topic aims to coordinate a discussion on the pathological mechanisms of, and innovative therapeutic strategies for, AiKD and to provide wide-ranging and divergent insights into the role of autoinflammation in skin disorders.
We welcome the submission of Original Research, Review, Mini-Review, Perspective and Commentary articles that include, but are not restricted to, the following topics:
1. Medical genetics and mutation search in AiKD patients
2. Cell biology studies on effects of underlining autoinflammation upon proliferation and differentiation of epidermal keratinocytes: especially roles of keratinocytes themselves as immune cells, and skin-associated inflammatory cells, such as neutrophils, dendritic cells including TIP-DC, Th17 cells, Th1 cells.
3. Genetic studies focusing on autoinflammatory pathways in the skin, including: CARD14-NFkB, IL-36, inflammasome-IL-1b, mevalonate and g-secretase-Notch signaling-hair follicle keratinization pathways.
4. Interventional studies revealing the clinical value of therapies targeting autoinflammatory pathways in the skin.
5. Perspectives on the novel roles of autoinflammation in skin diseases, and proposals for disorders to be newly included in AiKD
