Akemi Ishida-Yamamoto

A molecular defect in loricrin, the major component of the cornified cell envelope, underlies Vohwinkel's syndrome

Terminal keratinocyte differentiation involves coordinated expression of several functionally interdependent genes, many of which have been mapped to the epidermal differentiation complex (EDC) on chromosome 1q21. We have identified linkage of Vohwinkels syndrome in an extended pedigree to markers flanking the EDC region with a maximum multipoint lod score of 14.3. Sequencing of the loricrin gene revealed an insertion that shifts the translation frame of the C-terminal Gly– and Gln/Lys–rich domains, and is likely to impair cornification. Our findings provide the first evidence for a defect in an EDC gene in human disease, and disclose novel insights into perturbations of cornified cell envelope formation.

Structural organization of cornified cell envelopes and alterations in inherited skin disorders

Abstract: The cornified cell envelope is a highly insoluble and extremely tough structure formed beneath the cell membrane during terminal differentiation of kerationcytes. Its main function is to provide human skin with a protective barrier against the environment. Sequential cross‐linking of several integral components catalyzed by transglutaminases leads to a gradual increase in the thickness of the envelope and underscores its rigidity. Key structural players in this cross‐linking process include involucrin, loricrin, SPRRs, elafin, cystatin A, S100 family proteins, and some desmosomal proteins. The recent identification of genetic skin diseases with mutations in the genes encoding some of these proteins, including transglutaminase 1 and loricrin, has disclosed that abnormal cornified cell envelope synthesis is significantly involved in the pathophysiology of certain inherited keratodermas and reflects perturbations in the complex yet highly orderly process of cornified cell envelope formation in normal skin biology.

Immunoelectron microscopic analysis of cornified cell envelope formation in normal and psoriatic epidermis

The cornified cell envelope (CE) is an insoluble, highly resistant structure formed beneath the plasma membrane of differentiating keratinocytes. It consists of various crosslinked precursor proteins, including involucrin and loricrin. However, neither the normal assembly process of CE nor its alteration in skin disorders has been fully characterized. In this study we analyzed CE formation in normal skin and in lesional psoriatic skin by immunoelectron microscopy. In the superficial granular cells of normal epidermis, involucrin labeling was detected along the plasma membrane, whereas loricrin staining was mostly distributed diffusely within the cells, occasionally with some additional granular aggregates within the cytoplasm and nucleus. Loricrin was also present predominantly on the desmosomal attachment plaques, colocalizing with desmoglein. In the cornified cells, involucrin labeling was reduced, whereas loricrin labeling was retained and continuously decorated the CEs, with relative sparing of the desmosomal areas. In typical psoriatic epidermis, involucrin staining was very intense but loricrin labeling was markedly reduced. The involucrin-positive CEs were formed precociously and further maturation of CE did not occur. These results suggest that formation of CE occurs sequentially, initially involving involucrin deposition and subsequently involving loricrin incorporation. Psoriatic epidermis demonstrates a lack of proper CE maturation.

Extracellular regulated kinase and c-Jun N-terminal kinase are activated in psoriatic involved epidermis.

Psoriatic skin shows markedly increased keratinocyte proliferation and altered differentiation with various abnormal signalling pathways. In the present study, we investigated the expression of mitogen-activated protein kinases in psoriatic skin. Immunohistochemical study showed increased extracellular regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) expression in the nuclei of involved epidermis. Western blot analyses confirmed the increased active phospho-ERK and phospho-JNK expression in the involved epidermis. In contrast, expression pattern of p38 was not different between the involved and uninvolved epidermis, which was confirmed by western blot analysis. These results indicate that psoriatic epidermis shows selective activation of ERK and JNK, which might be related to hyperproliferation and abnormal differentiation of psoriatic epidermis.

Similarly potent action of 1,25-dihydroxyvitamin D3 and its analogues, tacalcitol, calcipotriol, and maxacalcitol on normal human keratinocyte proliferation and differentiation

BACKGROUND The active vitamin D3 regulates proliferation and differentiation of epidermal keratinocytes. Recently topical vitamin D3, tacalcitol, calcipotriol, and maxacalcitol are widely used for psoriasis. OBJECTIVE To examine the effect of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on cultured normal keratinocytes (NHK) and compared its effect with those of various vitamin D3 analogues. METHODS Cell proliferation of NHK cells was analyzed by MTS, BrdU and 3H-thymidine incorporation. The expression of involucrin, transglutaminase 1, keratin 5 and keratin 1 was investigated by western blot and PCR amplification and quantitative assay. Furthermore, we performed cornified cell envelope (CE) formation assay. RESULTS 1,25(OH)2D3, tacalcitol, calcipotriol, and maxacalcitol decreased NHK cell proliferation in a concentration-dependent manner and the maximal effect was observed at 10(-7) M. There was no significant difference in the anti-proliferative effect among the active vitamin D3 analogues. The expression of involucrin and transglutaminase 1 were induced by 1,25(OH)2D3 and its analogues in mRNA and protein levels. CE formation was also induced by 1,25(OH)2D3 and its analogues. There was no significant difference in the potency among these chemicals. Keratin 5 and 1 expression was not altered by these active vitamin D3 analogues. CONCLUSIONS The present study demonstrated that active vitamin D3 analogues, tacalcitol, calcipotriol, and maxacalcitol, suppress keratinocyte proliferation and induce differentiation with similar potency.

Corneodesmosin Expression in Psoriasis Vulgaris Differs from Normal Skin and Other Inflammatory Skin Disorders

Corneodesmosin (Cdsn) is a late differentiation epidermal glycoprotein putatively involved in keratinocyte adhesion. The Cdsn gene lies within the susceptibility region on chromosome 6p21.3 (PSORS1) for psoriasis, a common chronic disfiguring skin disease. A particular allelic variant of Cdsn has a strong association with psoriasis. Therefore, genetically and biologically, Cdsn is a possible candidate gene for psoriasis susceptibility. To investigate a potential role for Cdsn in psoriasis pathogenesis, protein expression studies were performed by quantitative immunohistochemistry on normal skin, psoriatic skin (lesional and nonlesional), and other skin disorders using monoclonal antibodies (G36-19 and F28-27). In normal and nonlesional skin, Cdsn was expressed in stratum corneum and one or two layers of superficial stratum granulosum. In lesional psoriasis, there was a significant increase in Cdsn expression, which was observed in multiple layers of stratum spinosum and in stratum corneum. The expression pattern varied from granular, cytoplasmic immunoreactivity to cell surface labeling with weakly immunoreactive cytoplasm. In chronic atopic dermatitis, lichen planus, mycosis fungoides, and pityriasis rubra pilaris, Cdsn immunoreactivity was confined to stratum corneum and upper stratum granulosum with no stratum spinosum immunoreactivity. Immunoelectron microscopy of normal and lesional psoriatic skin demonstrated Cdsn release concomitant with involucrin incorporation into cell envelopes and completed before mature envelope formation. Extracellular release of Cdsn occurred at a lower level of the epidermis in psoriasis than normal skin. These protein expression studies provide evidence of altered Cdsn expression in psoriasis consistent with a role of Cdsn in disease pathogenesis. Further functional and genetic studies of Cdsn are justified to determine its role as a potential psoriasis-susceptibility factor.

Psoriasis Risk Genes of the Late Cornified Envelope-3 Group Are Distinctly Expressed Compared with Genes of Other LCE Groups

Deletion of the late cornified envelope (LCE) genes LCE3B and LCE3C has recently been identified as a risk factor for psoriasis. Expression of 16 LCE genes of LCE groups 1, 2, 3, 5, and 6 was examined in vivo and in vitro. Quantitative PCR demonstrated that moderate to high LCE expression was largely confined to skin and a few oropharyngeal tissues. Genes of the LCE3 group demonstrated increased expression in lesional psoriatic epidermis and were induced after superficial injury of normal skin, whereas expression of members of other LCE groups was down-regulated under these conditions. Immunohistochemistry and immunoelectron microscopy demonstrated that LCE2 protein expression was restricted to the uppermost granular layer and the stratum corneum. Stimulation of in vitro reconstructed skin by several psoriasis-associated cytokines resulted in induction of LCE3 members. The data suggest that LCE proteins of groups 1, 2, 5, and 6 are involved in normal skin barrier function, whereas LCE3 genes encode proteins involved in barrier repair after injury or inflammation. These findings may provide clues to the mechanistic role of LCE3B/C deletion in psoriasis.

A Novel Protease Inhibitor of the α2-Macroglobulin Family Expressed in the Human Epidermis

In the course of a large scale analysis of late-expressed genes in the human epidermis, we identified a new member of the α2-macroglobulin (α2M) protease inhibitor family, A2ML1 (for α2-macroglobulin-like 1). Like A2M and PZP, A2ML1 is located on chromosome 12p13.31. A2ML1 encodes a protein of 1454 amino acids, which fits the characteristics of α2Ms: 1) strong conservation in amino acid sequence including most of cysteine positions with α2M; 2) a putative central bait domain; 3) a typical thiol ester sequence. Northern blot and reverse transcriptase-PCR studies revealed a single 5-kb A2ML1 mRNA, mainly in the epidermis granular keratinocytes. A2ML1 is also transcribed in placenta, thymus, and testis. By Western blot analysis, α2ML1 is detected as a monomeric, ∼180-kDa protein in human epidermis. In vitro keratinocyte differentiation is associated with increased expression levels. By immunohistochemistry, α2ML1 was detected within keratinosomes in the granular layer of the epidermis, and as a secreted product in the extracellular space between the uppermost granular layer and the cornified layer. Recombinant α2ML1 displayed inhibitory activity toward chymotrypsin, papain, thermolysin, subtilisin A, and to a lesser extent, elastase but not trypsin. Incubation with chymotrypsin and the chymotrypsin-like kallikrein 7 protease indicated that α2ML1 binds covalently to these proteases, a feature shared with other members of the family. Therefore, α2ML1 is the first α2M family member detected in the epidermis. It may play an important role during desquamation by inhibiting extracellular proteases.

Aberrant expression of apoptosis-related molecules in psoriatic epidermis

Apoptosis is a physiological form of cell death that is responsible for the deletion of cells. Epidermal keratinocytes are supposed to be regulated by cell proliferation and cell death leading to structural homeostasis. Psoriatic skin shows marked thickening of the epidermis, suggesting the imbalance of the homeostasis, which might be related to abnormal apoptotic process. We investigated the expression of various apoptosis-related molecules in the psoriatic hyperproliferative epidermis. Real time quantitative RT-PCR analyses revealed that mRNAs of Fas, Bcl-xL, Bax and ICAD (inhibitor of caspase 3-related DNase) of the psoriatic involved epidermis were increased by 4.2-, 2.8-, 2.6- and 5.6-fold, respectively, compared with the uninvolved epidermis. In contrast, Bcl-2 expression in the involved epidermis was one-third suppressed compared with the uninvolved epidermis. No significant difference in the expression of mRNAs of Fas ligand or CAD (caspase 3-related DNase) was detected between the involved and uninvolved epidermis. Western blot analysis and immunohistochemical studies showed compatible results obtained by RT-PCR analyses. Although active caspase 3 was slightly increased in the involved epidermis, apoptotic cells were marginally detected. These results indicate that psoriatic epidermis shows aberrant expression of apoptosis-related molecules representing suppressed apoptotic process, which might be related to characteristic histopathology.

Plasma trough levels of adalimumab and infliximab in terms of clinical efficacy during the treatment of psoriasis

We examined the relation between adalimumab and infliximab plasma trough levels, anti‐adalimumab and anti‐infliximab antibody formation. We analyzed plasma from 32 adalimumab‐treated and 20 infliximab‐treated psoriasis patients for evaluating trough levels of each drug. The presence of anti‐adalimumab and anti‐infliximab antibodies was analyzed and the severity of psoriasis was evaluated. At week 28, 25 out of 32 and at week 48, 21 out of 30 adalimumab‐treated patients maintained as more than PASI 75. At week 28, 12 out of 20 and at week 48, nine out of 18 infliximab‐treated patients were evaluated as more than PASI 75. In patients treated with 40 mg adalimumab every other week, the mean trough level was 7.62 μg/mL (range, 0.05–10.6) at week 48. In patients treated with 80 mg adalimumab every other week, the mean trough level was 8.61 μg/mL (range, 0.08–13.5) at week 48. Mean trough level of infliximab‐treated cases (4.1–5.2 mg/kg; mean, 4.6) was 4.64 μg/mL (range, 0.03–16.9) at week 48. Anti‐adalimumab antibody was detected in five out of 32 cases and anti‐infliximab antibody was detected in six out of 20 cases, respectively, at weeks 24 and 48. The optimal cut‐off values of adalimumab and infliximab concentration for more than PASI 75 were more than 7.84 μg/mL and more than 0.92 μg/mL, respectively. The trough levels of adalimumab and infliximab in psoriasis patients were positively associated with clinical response and were significantly lower in cases having anti‐adalimumab or anti‐infliximab antibodies.