Hyaluronan Does Not Regulate Human Epidermal Keratinocyte Proliferation and Differentiation

Area of Science:

• Dermatology
• Biochemistry
• Cell Biology

Background:

• Hyaluronan (HA) is crucial in the extracellular matrix, with significant presence in dermal and epidermal layers of human skin.
• While HA's dermal roles are established, its specific functions within the epidermis, particularly concerning keratinocyte physiology, remain unclear.

Purpose of the Study:

• To investigate the functional role of hyaluronan (HA) in human keratinocyte physiology within reconstructed epidermis.
• To determine if inhibiting HA synthesis or removing existing HA impacts keratinocyte proliferation and differentiation.

Main Methods:

• Utilized in vitro reconstructed human epidermis models.
• Inhibited HA synthesis using 4-methylumbelliferone (4MU) and removed HA using HA-specific hyaluronidase.
• Assessed epidermal differentiation markers (involucrin, keratin 10, filaggrin), cell proliferation, intracellular HA, and HA receptor levels.
• Investigated the role of UDP-glucose 6-dehydrogenase (UGDH) via lentiviral shRNA knockdown.

Main Results:

• 4MU treatment decreased keratinocyte proliferation but did not alter epidermal differentiation marker expression.
• Neither HA addition nor HA removal by hyaluronidase rescued or affected proliferation and differentiation.
• Knockdown of UGDH reduced HA production without impacting proliferation.
• Intracellular HA, sulfated glycosaminoglycan concentration, apoptosis, and HA receptor levels remained unchanged across treatments.

Conclusions:

• Epidermal hyaluronan levels do not appear to be directly correlated with keratinocyte proliferation or differentiation.
• 4MU treatment's effects on keratinocytes cannot be solely attributed to HA depletion, indicating other mechanisms may be involved.
• The study highlights a discrepancy between inhibiting HA synthesis and actual HA removal in cellular models.