Leptin induces secretion of pro‐inflammatory cytokines by human keratinocytes in vitro – a possible reason for increased severity of psoriasis in patients with a high body mass index

Investigations about prevalence of obesity in psoriasis patients are increased nowadays. Higher serum levels of leptin in patients with psoriasis who are overweight or obese suggest that leptin may serve as a molecular link between psoriasis and metabolic comorbidities. However, the pathological functions of leptin in psoriasis are not clearly understood. We investigated the influence of being overweight or obese on the risk of psoriasis, and the relationship between serum leptin levels and the severity of psoriasis in Chinese Han patients. We also investigated biological effects of leptin on the proliferation and secretion of pro‐inflammatory cytokines by human keratinocytes in vitro. Obesity was a significant risk factor for psoriasis in the Chinese Han population; however, we did not observe a significant correlation between Psoriasis Area and Severity Index (PASI) and body mass index (BMI). We observed a positive correlation between the serum leptin level and PASI in overweight and obese male patients with psoriasis. Strong leptin immunoreactivity was detected in the epidermis of psoriatic lesions, particularly in keratinocytes. Leptin significantly increased the proliferation and secretion of pro‐inflammatory cytokines by keratinocytes in vitro. In conclusion, this study suggests leptin as a novel molecular link between psoriasis and obesity, which may help to explain the more server conditions of psoriasis in patients with obesity.     

Delphinidin,a dietary antioxidant,induces human epidermal keratinocyte differentiation but not apoptosis: studies in submerged and three‐dimensional epidermal equivalent models

Delphinidin (Del), [3,5,7,3'‐,4'‐,5'‐hexahydroxyflavylium], an anthocyanidin and a potent antioxidant abundantly found in pigmented fruits and vegetables exhibits proapoptotic effects in many cancer cells. Here, we determined the effect of Del on growth, apoptosis and differentiation of normal human epidermal keratinocytes (NHEKs) in vitro in submerged cultures and examined its effects in a three‐dimensional (3D) epidermal equivalent (EE) model that permits complete differentiation reminiscent of in vivo skin. Treatment of NHEKs with Del (10–40 μm ; 24–48 h) significantly enhanced keratinocyte differentiation. In Del‐treated cells, there was marked increase in human involucrin (hINV) promoter activity with simultaneous increase in the mRNA and protein expressions of involucrin and other epidermal differentiation markers including procaspase‐14 and transglutaminase‐1 (TGM1), but without any effect on TGM2. Del treatment of NHEKs was associated with minimal decrease in cell viability, which was not associated with apoptosis as evident by lack of modulation of caspases, apoptosis‐related proteins including Bcl‐2 family of proteins and poly(ADP‐ribose) polymerase cleavage. To establish the in vivo relevance of our observations in submerged cultures, we then validated these effects in a 3D EE model, where Del was found to significantly enhance cornification and increase the protein expression of cornification markers including caspase‐14 and keratin 1. For the first time, we show that Del induces epidermal differentiation using an experimental system that closely mimics in vivo human skin. These observations suggest that Del could be a useful agent for dermatoses associated with epidermal barrier defects including aberrant keratinization, hyperproliferation or inflammation observed in skin diseases like psoriasis and ichthyoses.     

Clinicopathological differentiation between Pityrosporum folliculitis and acneiform eruption

Distinguishing between Malassezia folliculitis (Pityrosporum folliculitis [P. folliculitis]) and acneiform eruption, based on clinicopathological features, is challenging for clinicians. In the literature, the histopathological differences between P. folliculitis and acneiform eruption lesions have been poorly described. We aimed to determine the clinicopathologic distinctions between P. folliculitis and acneiform eruption by retrospectively analyzing the histology of hematoxylin and eosin stained tissue sections obtained from 52 patients diagnosed with these lesions. The presence of fungal spores in the follicular lumen was most consistent with a P. folliculitis diagnosis (P < 0.001). However, intrafollicular inflammation (P = 0.009), irregular patterns of keratin plugging (P = 0.008), and nuclear dust in the follicular lumen (P < 0.001) favored an acneiform eruption diagnosis. These intrafollicular characteristics and inflammatory differences are believed to be caused by necrotic keratinocytes that lead to vacuolar changes in the follicular wall (P = 0.013). We did not observe any difference between P. folliculitis and acneiform eruption lesions in terms of perifollicular inflammatory cell infiltration. Our study demonstrated that significant differences exist between P. folliculitis and acneiform eruption lesions relative to the presence of necrotic keratinocytes in the follicular wall, intrafollicular characteristics, and inflammatory cell infiltrations. Necrotic keratinocytes are believed to have a key role in these differences. These findings may contribute to an improved understanding of the pathogenesis and differential diagnosis of P. folliculitis and acneiform eruption.     

Cutaneous nociception: Role of keratinocytes

Recent years have brought an enhanced understanding of keratinocyte contribution to cutaneous nociception. While intra‐epidermal nerve endings were classically considered as the exclusive transducers of cutaneous noxious stimuli, it has now been demonstrated that epidermal keratinocytes can initiate nociceptive responses, like Merkel cells do for the innocuous mechanotransduction. In the light of recent in vivo findings, this article outlines this paradigm shift that points to a not yet considered population of sensory epidermal cells.     

TWEAK/Fn14 activation induces keratinocyte proliferation under psoriatic inflammation

Tumor necrosis factor (TNF)‐like weak inducer of apoptosis (TWEAK) has been reported to induce keratinocyte apoptosis in vitro by engaging its sole receptor of fibroblast growth factor‐inducible 14 (Fn14). In this study, we explored the role of TWEAK/Fn14 pathway in the growth of psoriatic keratinocytes that is, however, characterized by suppressed apoptotic cell death. Skin tissues from the patients with psoriasis or healthy donors were determined for TWEAK and Fn14 expression, and primary keratinocytes were evaluated under the stimulation of psoriatic proinflammatory cytokines or plus TWEAK. The results showed that both TWEAK and Fn14 were highly expressed in psoriatic skins. Moreover, the stimulation of psoriatic cytokines enhanced Fn14 expression by keratinocytes in vitro, which expressed TNF receptor 2 predominantly and proliferated increasingly with the addition of TWEAK. Furthermore, TWEAK stimulation enhanced the synthesis of survivin, inhibitor of apoptosis protein 2 and cellular FLICE‐inhibitory protein in lesional keratinocytes. Therefore, TWEAK/Fn14 interaction prefers to enhance proliferation but not apoptosis of keratinocytes under psoriatic inflammation. The activation of nuclear factor‐κB signalling‐dependent anti‐apoptotic proteins and biased expression of TNF receptors may be responsible for such a novel principle in keratinocytes under psoriatic inflammation.     

Baicalein increases keratin 1 and 10 expression in HaCaT keratinocytes via TRPV4 receptor activation

In this study, we characterized the effect of baicalein on the regulation of keratinocyte differentiation and proliferation, which are abnormal in atopic dermatitis or psoriasis. Treatment of HaCaT keratinocytes with 10 μm baicalein slightly inhibited cell growth, caused morphological differentiation and increased expression of keratins 1 and 10 (K1/K10) without affecting ROS generation, cytochrome c release or apoptosis. Baicalein treatment caused growth arrest in G₀/G₁ phase and also induced Ca²⁺ influx via TRPV4 receptor activation. Phosphorylation of ERK, Akt and p38 MAPK, but not JNK, was increased by baicalein, and inhibition of phosphorylation of ERK, but not that of Akt or p38 MAPK, blocked the baicalein‐induced increase in K1/K10 expression, suggesting that ERK activation is involved in this increase. Removal of extracellular Ca²⁺ or blockade of Ca²⁺ influx by pharmacological inhibition or silencing of the TRPV4 receptor did not affect growth arrest, ROS generation or apoptosis, but inhibited baicalein‐induced ERK phosphorylation and K1/K10 expression. Thus, baicalein treatment increases differentiation, and decreases proliferation, of keratinocytes. The mechanism of differentiation of keratinocytes is distinct from that of proliferation, the former being Ca²⁺ dependent and the latter Ca²⁺ independent.