Conditional targeting of plectin in prenatal and adult mouse stratified epithelia causes keratinocyte fragility and lesional epidermal barrier defects

Abstract

Plectin, a widespread intermediate filament-based cytolinker protein capable of interacting with a variety of cytoskeletal structures and plasma membrane-bound junctional complexes, serves essential functions in maintenance of cell and tissue cytoarchitecture. We have generated a mouse line bearing floxed plectin alleles and conditionally deleted plectin in stratified epithelia. This strategy enabled us to study the consequences of plectin deficiency in this particular type of tissues in the context of the whole organism without plectin loss affecting other tissues. Conditional knockout mice died early after birth, showing signs of starvation and growth retardation. Blistering was observed on their extremities and on the oral epithelium after initial nursing, impairing food uptake. Knockout epidermis was very fragile and showed focal epidermal barrier defects caused by the presence of small skin lesions. Stratification, proliferation and differentiation of knockout skin seemed unaffected by epidermis-restricted plectin deficiency. In an additionally generated mouse model, tamoxifen-induced Cre-ERT-mediated recombination led to mice with a mosaic plectin deletion pattern in adult epidermis, combined with microblister formation and epidermal barrier defects. Our study explains the early lethality of plectin-deficient mice and provides a model to ablate plectin in adult animals which could be used for developing gene or pharmacological therapies.

Plectin isoforms as organizers of intermediate filament cytoarchitecture

“…Plectindeficient mice reveal abnormalities reminiscent of minicore myopathies in skeletal muscle and disintegration of intercalated disks in heart, but as they die within 2-3 days after birth due to internal blistering of the oral cavity that disallows food uptake, they are of limited use as animal models for EBS-MD. 20,34 The phenotypic analysis of conditional (MCK-Cre) striated musclerestricted plectin knockout mice was more revealing, showing progressive degenerative alterations including aggregation and partial loss of desmin IFs along with the detachment of the contractile apparatus from the sarcolemma. 35 Overall, desmindeficient and plectin-deficient mice show similar phenotypes, including detachment of the contractile apparatus from the sarcolemma, profound changes in myofiber costameric cytoarchitecture and decreased mitochondrial number and functions ( fig.…”

Plectin Isoform-dependent Regulation of Keratin-Integrin α6β4 Anchorage via Ca2+/Calmodulin

“…11); an autosomal dominant form of the disease (epidermolysis bullosa simplex-Ogna) manifests just in skin (12). Conventional, as well as conditional (K5-Cre-driven) plectin knockouts in prenatal mice led to the death of animals, 2-3 days after birth (13,14), whereas after induced disruption of the plectin gene in the skin of adult mice, keratinocyte fragility and lesional epidermal barrier defects were reported (14).…”

Plectin-related skin diseases

“…This might be explained by the differences in plectin isoforms between humans and mice. Total plectin-null mice and keratinocyte-specific conditional plectin-null mice [29,30] do not have skin phenotypes similar to those of EBS-MD but rather, they have skin phenotypes similar to those of EBS-PA, which will be discussed later.…”

“…2) [22]. Plectin-null mice and plectin conditional null mice under keratin promoter show severe skin detachment and early demise, which correspond to the EBS-PA skin phenotype [29,30]. However, the PA phenotype has not been described in plectin-null mice, although mucosal involvement in the oral cavity was noted.…”

“…It is true that one paper reported mild skin fragility in 60-70% of mice injected with anti-BP230 antibodies [63]; however, another group was unable to reproduce the skin fragility in injected mice [64]. Nevertheless, BP230-null mice do not show an apparent blistering phenotype [65], whereas plectin-null mice reveal severe skin fragility [29,30]. Antibodies directed to intracellular proteins are known to affect the function of the proteins when presented to cultured cells [66,67], so it is still possible that anti-plectin antibodies can induce skin fragility, as patients with autoimmune subepidermal blistering diseases have been reported to harbour antibodies only for plectin [52].…”