Hyaluronan Does Not Regulate Human Epidermal Keratinocyte Proliferation and Differentiation

Abstract

Hyaluronan (HA) is synthesized by three HA synthases (HAS1, HAS2, and HAS3) and secreted in the extracellular matrix. In human skin, large amounts of HA are found in the dermis. HA is also synthesized by keratinocytes in the epidermis, although its epidermal functions are not clearly identified yet. To investigate HA functions, we studied the effects of HA depletion on human keratinocyte physiology within in vitro reconstructed human epidermis. Inhibition of HA synthesis with 4-methylumbelliferone (4MU) did not modify the expression profile of the epidermal differentiation markers involucrin, keratin 10, and filaggrin during tissue reconstruction. In contrast, when keratinocytes were incubated with 4MU, cell proliferation was decreased. In an attempt to rescue the proliferation function, HA samples of various mean molecular masses were added to keratinocyte cultures treated with 4MU. These samples were unable to rescue the initial proliferation rate. Furthermore, treatments with HA-specific hyaluronidase, although removing almost all HA from keratinocyte cultures, did not alter the differentiation or proliferation processes. The differences between 4MU and hyaluronidase effects did not result from differences in intracellular HA, sulfated glycosaminoglycan concentration, apoptosis, or levels of HA receptors, all of which remained unchanged. Similarly, knockdown of UDP-glucose 6-dehydrogenase (UGDH) using lentiviral shRNA effectively decreased HA production but did not affect proliferation rate. Overall, these data suggest that HA levels in the human epidermis are not directly correlated with keratinocyte proliferation and differentiation and that incubation of cells with 4MU cannot equate with HA removal. Hyaluronan (HA),2 a large polysaccharide of the extracellular space, is composed of repetitive D-glucuronic acid and D-Nacetylglucosamine dimer units. Although it belongs to the glycosaminoglycan (GAG) family, HA is not synthesized in the Golgi network; the molecule is assembled at the inner face of the plasma membrane, and the newly formed polymer is extruded into the extracellular matrix as it lengthens by addition of the dimer units. This mechanism allows the formation of huge HA molecules with masses ranging from 10 5 to 10 7 Da and lengths ranging from 2 to 25 m (1).HA synthesis is performed by three different glycosyltransferases called hyaluronan synthases (HAS) located at the plasma membrane. These three enzymes, HAS1, HAS2, and HAS3, differ from each other with respect to temporal expression pattern during development, specific activity, and size of HA polymers generated (2, 3). The degradation of HA is carried out in somatic tissues by HYAL1 and HYAL2, two enzymes belonging to the hyaluronidase family (4).HA has been identified in most tissues of the organism. Half of the total amount of HA is localized in skin (5). The skin is a large organ making up the first barrier against physical, biological, and chemical damages to the body. In the dermis, the main cell type is represented by fibroblasts, which...

HYAL-2–WWOX–SMAD4 Signaling in Cell Death and Anticancer Response

“…HA contributes to the control of cell proliferation, migration and differentiation (Sherman et al, 2015; Turley et al, 2016). A recent study showed that HA does not contribute to the growth and differentiation of human epidermal keratinocyte (Malaisse et al, 2016). Nevertheless, UDP-glucose induces HA synthesis in keratinocytes via P2Y14 receptor, STAT3 signaling and activation of hyaluronan synthase (HAS) promoter (Jokela et al, 2014).…”

Effect of hyaluronic acid in bone formation and its applications in dentistry

“…However, in one study, human keratinocytes were grown in monolayer and treated by HA of various MWs. No difference in proliferation index was observed in cells treated by low‐MW HA when compared with that of cells not treated by HA …”

“…The stimulation effect on the proliferation of periodontal ligament cells was more obvious for synthesized HA of higher concentration . Other researchers reported that the proliferation of cells cultured with the addition of high‐MW HA was not affected when compared with that of cells cultured without HA . However, other studies showed that the cell proliferation was inhibited with the presence of high‐MW HA .…”

“…The effect of high‐MW HA on cell differentiation provoked controversies . On the one hand, researchers reported that cell differentiation was enhanced by high‐MW HA .…”

“…The results showed that the expressions of osteogenesis‐related genes were enhanced in hMSCs cultured with the SiO 2 –PLL–HA system . On the other hand, some studies showed that cell differentiation was not affected by high‐MW HA . Researchers added high‐MW HA to the medium of previously dedifferentiated rabbit chondrocytes.…”