Melanin 6/22/2009. Group of compounds that serves predominantly as pigment.

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1 Tessa Sinnige Liliana Joachín-Rodríguez Directed by: David Egan Melanin Group of compounds that serves predominantly as pigment. Pheomelanin (red/yellow) * Eumelanin (brown/black) * Neuromelanin (dark brown/black) Mixed melanin 1

2 Functions of melanin Melanin localization Skin Eye Hair Neural cells Inner ear Function Protection against UV radiation Protection against UV and high-frequency visible light. Function in the development of optic nervous system and regulate retinal function. Antioxidant defence for the skin Capability to trap and/or bind chemicals, toxins, and heavy metals to prevent their access to living tissues Protection against toxic compounds Sound conduction Melanin deficiency Skin disorders (melasma, vitiligo) Neurologic disorders (Parkinson s disease) Hearing impairment Oftalmologic l disorders d (Waardenburg s syndrome) 2

3 What do we know about melanin production? Melanocytes Specialized cell that are responsible for producing melanin Melanosome Lysosome-related organelle within which h melanin pigments are synthesized and stored. Mature melanosomes are transferred to keratinocytes Melanogenesis : Melanin production 3

4 Melanin synthesis Journal of Investigative Dermatology (2005) 124, Phenylalanin Melanin synthesis Tyrosin DOPA Dihidroxyphenylalanina Tyrosinase Dopachrome Journal of Investigative Dermatology (2005) 124,

5 Microphtalmia-associated transcription factor Tyrosinase -127 genes involved in coat color in mouse - 68/127 have human homologues -29/68 of these homologues impact pigmentation in humans But Pharmacologic modulation of melanin production primarily focused on identifying inhibitors of tyrosinase Key molecular regulators of melanogenesis not well defined 5

6 Tessa Sinnige Liliana Joachín-Rodríguez Directed by: David Egan Aim To identify novel regulators of melanogenesis in human cells Better understanding of the molecular network governing pigment production to aid design of agents thatt inhibit or stimulate t pigmentation ti in humans 6

7 Identifying novel regulators in melanogenesis Methodology SiRNA library against 21,127 human genes MNT-1 cell culture Spectrophotometric melanin quantitation essay + Cell viability essay Small interfering RNA (interferes with the expression of a specific gene) MNT-1 highly pigmented melanoma cells Viability essay: to eliminate sirna that decreases melanin production by impacting cell proliferation or survival Identifying novel regulators in melanogenesis Results of the screening SiRNA library against 21,127 human genes MNT-1 cell culture Spectrophotometric melanin quantitation essay + Cell viability essay 98 genes identified as regulators of melanogenesis. 2 / 98 recently eliminated from the RefSeq database. 96 genes to evaluate!!!! 7

8 Identifying novel regulators in melanogenesis Validation of the data Retest t of 35/96 RT-PCR (data not shown) Off-target effect evaluation Identifying novel regulators in melanogenesis Conclusion of the screening Identification of novel regulators Accurate genome wide sirna screening platform lll 8

9 Central role for Tyr and MITF Many novel regulators affect Tyr and/or MITF on mrna and/or protein levels Complex interplay between regulators Regulation depends on genetic background Different genes regulate melanogenesis in MNT-1, moderately and darkly pigmented cells Tyr, Wipi1 and ALDH1A1 common regulators 9

10 Melanogenesis inhibited via ALDH ALDH drugs inhibit tyrosinase accumulation u at Melanogenesis also inhibited Melanogenesis linked to autophagy 10

11 Intermezzo: autophagy Starvation Aging Elimination of abberant structures Cell differentiation and development UMDNJ research, Spring 2007 Lysosomes and autophagy linked to melanogenesis Inhibition of lysosomal acidification rescues Zdhhc9 and Rab4a knock-downs Autophagy factors Autophagy factors inhibit melanogenesis 11

12 Coat color defect by deletion autophagy gene Heterozygous deletion Beclin1 causes hypopimented hair follicles Beclin1 influences melanin levels Autophagy and melanosome markers colocalize 12

13 Conclusions 92 novel genes found to influence melanogenesis Tyrosinase plays a central role Different regulation in different melanocytes Melanogenesis linked to autophagy Discussion Cross-talk MITF and tyrosinase Complex regulatory network Different depending on genetic background 13

14 Link with autophagy Discussion Model 1: Melanosomes derived from autophagosomes melanosome - Model 2: autophagosome formed when docking to melanosome is blocked ER Vesicles with melanosome cargo autophagosome melanosome Model based on Smith et al., Pigment Cell Res