Downregulation of aquaporin 3 in bullous pemphigoid patients

Downregulation of aquaporin 3 in patients with pemphigus vulgaris

BACKGROUND

Pemphigus vulgaris (PV) is an autoimmune bullous skin disease. Aquaporin 3 (AQP3) is a glycerol/ water channel involved in several physiological functions.

OBJECTIVES

Evaluation of the tissue expression and localization of AQP3 in the skin of PV patients.

METHODS

Twenty-seven PV patients and 30 controls were included. The patients were subjected to history taking, clinical evaluation, Autoimmune Bullous Skin Disorder Intensity Score (ABSIS) and four-millimeter punch biopsy. The biopsies were stained using anti-human AQP3 antibody and the immunofluorescence pattern and intensity were evaluated using a scoring system and image J software analysis.

RESULTS

AQP3 was expressed in the basal epidermis in 27 (100%) and in the suprabasal epidermis in 19 PV patients (70.4%). It was expressed in all controls in basal and suprabasal layers. Intensity of AQP3 immunofluorescence was strong in 2 (7.4%), moderate in 19 (70.4%) and weak in 6 patients (22.2%) while it was strong in 18 (60%), and moderate in 12 controls (40%). AQP3 expression was significantly lower in patients than controls in the suprabasal epidermis (p=0.001). Patients with extensive disease had significantly weaker AQP3 intensity than those with marked disease (p=0.005) CONCLUSION: Downregulation of AQP3 in patients with PV, especially in the suprabasal layers and in extensive clinical disease, suggests a potential role of AQP3 in the pathogenesis of PV.

Human Aquaporins: Functional Diversity and Potential Roles in Infectious and Non-infectious Diseases

Aquaporins (AQPs) are integral membrane proteins and found in all living organisms from bacteria to human. AQPs mainly involved in the transmembrane diffusion of water as well as various small solutes in a bidirectional manner are widely distributed in various human tissues. Human contains 13 AQPs (AQP0-AQP12) which are divided into three sub-classes namely orthodox aquaporin (AQP0, 1, 2, 4, 5, 6, and 8), aquaglyceroporin (AQP3, 7, 9, and 10) and super or unorthodox aquaporin (AQP11 and 12) based on their pore selectivity. Human AQPs are functionally diverse, which are involved in wide variety of non-infectious diseases including cancer, renal dysfunction, neurological disorder, epilepsy, skin disease, metabolic syndrome, and even cardiac diseases. However, the association of AQPs with infectious diseases has not been fully evaluated. Several studies have unveiled that AQPs can be regulated by microbial and parasitic infections that suggest their involvement in microbial pathogenesis, inflammation-associated responses and AQP-mediated cell water homeostasis. This review mainly aims to shed light on the involvement of AQPs in infectious and non-infectious diseases and potential AQPs-target modulators. Furthermore, AQP structures, tissue-specific distributions and their physiological relevance, functional diversity and regulations have been discussed. Altogether, this review would be useful for further investigation of AQPs as a potential therapeutic target for treatment of infectious as well as non-infectious diseases.

Aquaporins and diseases pathogenesis: From trivial to undeniable involvements, a disease-based point of view

Aquaporins (AQPs), as transmembrane proteins, were primarily identified as water channels with the ability of regulating the transmission of water, glycerol, urea, and other small-sized molecules. The classic view of AQPs involvement in therapeutic plan restricted them and their regulators into managing only a narrow spectrum of the diseases such as diabetes insipidus and the syndrome of inappropriate ADH secretion. However, further investigations performed, especially in the third millennium, has found that their cooperation in water transmission control can be manipulated to handle other burden-imposing diseases such as cirrhosis, heart failure, Meniere's disease, cancer, bullous pemphigoid, eczema, and Sjögren's syndrome.

Aquaporin-3 in the epidermis: more than skin deep

The skin is essential for terrestrial life. It is responsible for regulating water permeability and functions as a mechanical barrier that protects against environmental insults such as microbial infection, ultraviolet light, injury, and heat and cold, which could damage the cells of the body and compromise survival of the organism. This barrier is provided by the outer layer, the epidermis, which is composed predominantly of keratinocytes; keratinocytes undergo a program of differentiation to form the stratum corneum comprising the cornified squame "bricks" and lipid "mortar." Dysregulation of this differentiation program can result in skin diseases, including psoriasis and nonmelanoma skin cancers, among others. Accumulating evidence in the literature indicates that the water-, glycerol-, and hydrogen peroxide-transporting channel aquaporin-3 (AQP3) plays a key role in various processes involved in keratinocyte function, and abnormalities in this channel have been observed in several human skin diseases. Here, we discuss the data linking AQP3 to keratinocyte proliferation, migration, differentiation, and survival as well as its role in skin properties and functions like hydration, water retention, wound healing, and barrier repair. We also discuss the mechanisms regulating AQP3 levels, localization, and function and the anomalies in AQP3 that are associated with various skin diseases.