Keratinocyte differentiation promotes ER stress-dependent lysosome biogenesis

Abstract

Keratinocytes maintain epidermal integrity through cellular differentiation. This process enhances intraorganelle digestion in keratinocytes to sustain nutritional and calcium-ionic stresses observed in upper skin layers. However, the molecular mechanisms governing keratinocyte differentiation and concomitant increase in lysosomal function is poorly understood. Here, by using primary neonatal human epidermal keratinocytes, we identified the molecular link between signaling pathways and cellular differentiation/lysosome biogenesis. Incubation of keratinocytes with CaCl2 induces differentiation with increased cell size and early differentiation markers. Further, differentiated keratinocytes display enhanced lysosome biogenesis generated through ATF6-dependent ER stress signaling, but independent of mTOR-MiT/TFE pathway. In contrast, chemical inhibition of mTORC1 accelerates calcium-induced keratinocyte differentiation, suggesting that activation of autophagy promotes the differentiation process. Moreover, differentiation of keratinocytes results in lysosome dispersion and Golgi fragmentation, and the peripheral lysosomes showed colocalization with Golgi-tethering proteins, suggesting that these organelles possibly derived from Golgi. In line, inhibition of Golgi function, but not the depletion of Golgi-tethers or altered lysosomal acidity, abolishes keratinocyte differentiation and lysosome biogenesis. Thus, ER stress regulates lysosome biogenesis and keratinocyte differentiation to maintain epidermal homeostasis.

Diurnal Control of Sensory Axon Growth and Shedding in the Mouse Cornea

“…Although corneal basal epithelial cells also have lysosomes, lysosomal biogenesis is increased in differentiating cells of the epithelium where lysosomes function in autophagy to degrade organelles in cells before the cells are sloughed off. 28 The large dynamic range of expression in LAMP1 made it difficult to quantify changes in LAMP1 expression over time. By analyzing LAMP1 in n = 5 male and n = 5 female corneas, we could confirm that LAMP1 is expressed at significantly higher levels at ZT 22.5 than at any other time point ( Fig.…”

Live imaging of alterations in cellular morphology and organelles during cornification using an epidermal equivalent model

“…Factors that influence mitochondrial conditions, such as ROS and ER stress, may participate in preparing for cornification. Indeed, several previous studies showed the importance of ROS and ER stress in keratinocyte differentiation [61][62][63][64] .…”

“…This finding supports the notion that mitochondria are partly degraded by autophagy in granular cells before the start of morphological change. It is debatable, however, whether autophagy itself is essential for cornification in the physiological epidermis 10,[55][56][57][58][59][60][61] . Factors that influence mitochondrial conditions, such as ROS and ER stress, may participate in preparing for cornification.…”

Epidermal Lamellar Body Biogenesis: Insight Into the Roles of Golgi and Lysosomes

“…Several studies have shown that the gradient of calcium that spans the epidermis regulates gradual differentiation across epidermal sublayers (Figure 1; Hennings et al, 1989; also reviewed in Bikle et al, 2012). Based on this fact, many in vitro studies utilizing human primary keratinocytes use calcium to trigger the differentiation process (Hennings et al, 1989;Tu et al, 2007Tu et al, , 2012Toufighi et al, 2015;Mahanty et al, 2019;reviewed in Bikle et al, 2012;Elsholz et al, 2014). Note that the epidermal sublayers having eLBs are only observed in vivo or in three-dimensional (3D) skin models (Pillai et al, 1988;Boyce and Williams, 1993;Fartasch and Ponec, 1994).…”