Biochemistry

What are the implications of your new How did it feel to answer some of the understanding of ionic signalling in key questions that arose from your ? previous research? Beginning to understand ionic signalling The TPC2 study was developed almost in melanosomes is an important step in parallel with the first OCA2 study that towards understanding the complex we published. Once we were able to mechanisms that regulate pigment measure ionic fluxes across melanosomal generation and storage in the eye, skin membranes, we found the anionic and . Because melanosomes are the conductance mediated by OCA2 and the best-studied model for lysosomal-related cationic one mediated by TPC2. There organelles, understanding are certainly many more ion channels -regulating function will be highly relevant for and/or transporters in melanosomes, other organelles, such as platelet dense but these were the first two that we granules and lung alveolar type II lamellar could measure under our experimental ion channels discovery bodies. conditions. Could you speculate what new What direction do you think your future treatments for pigmentation disorders research will take? A new study by and her laboratory at Brown University Dr Elena Oancea and skin cancers may arise from your We would first like to understand how reveals the mechanism that regulates pigmentation. The discovery could research? the currents mediated by these two aid development of future treatments for skin, eye and hair disorders It is too early to think about treatments, channels are regulated by different caused by defective melanin production. as we are only starting to understand cellular signals, from the cytosolic side how these molecules work. If I were or from the melanosomal lumen side. In to speculate based on our data, at other words, are these channels always least for some forms of , open or are there specific molecules decreasing melanosomal acidity could that, when produced or activated in the restore pigmentation levels. Altering cell, bind to the channels and allow them melanosomal pH, however, without to open? We would also like to get a changing the acidity of other cellular more complete picture of melanosomal organelles (like lysosomes or endosomes) physiology: What other channels are is not a trivial task. We discovered present in melanosomes and how do they that TPC2 is a negative regulator for function? How do the proteins encoded pigmentation and thus blocking its ion by genes mutated in other forms of channel activity could lead to more oculocutaneous albinism contribute to pigment being produced. This would also pigmentation? What allows proteins like be very difficult, as TPC2 functions in the TPC2 to function only in melanosomes in lysosomes of most cells in our body and and in lysosomes in all the is important for their function. other cells?

elanin is our body’s natural affects the development and function of the pigment, responsible for visual system and reduces an individual’s the colour of our hair, eyes protection against ultraviolet radiation. Ion channels that regulate melanin were and skin. Skin disorders Worryingly, individuals who underproduce discovered using patch clamp recordings of such as albinism, melanin are at increased risk of skin and eye melanosomes, the cellular organelles that produce and store melanin. A glass patch and , occur when our cancers as their DNA is more exposed to pipette (shown in blue) was used to cut a Mcells abnormally synthesise or over/under harmful ultraviolet radiation. On the opposite small slit into the plasma membrane of a skin produce melanin. As in the commonly side of the spectrum, the overproduction of in order to expose and patch a melanosome (small circle filled with blue) known albino symptoms of pale skin, eyes melanin is usually a benign condition; with that is 1-3 microns in size. and hair, the underproduction of melanin many choosing to embrace their unique

75 Biochemistry hyperpigmentation. However, in some cases, Providing vital the appearance of blotchy, asymmetrical dark Detail patches can have a negative psychological knowledge required impact. To avoid defective melanin synthesis, RESEARCH OBJECTIVES a delicate balance of pigment production is to construct a The focus of Dr. Oancea’s laboratory required. is understanding signal transduction comprehensive events primarily in pigment cells. Her FINDING THE BALANCE research team investigates the molecular Melanosomes are specialised organelles model of ionic mechanisms mediating pigmentation in within skin melanocytes and ocular pigment skin melanocytes and retinal pigmented cells that regulate the production and storage signalling in epithelium, as well as the physiological and of melanin. Melanosomes are surrounded by pathological effects of ultraviolet radiation a membrane that contains transmembrane melanosomes, on . proteins that regulate the flux of ions into or the researchers out of the melanosomes, a process critical for FUNDING pigment production in these organelles. have provided a National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) Dr Elena Oancea and her team at Brown significant step branch of the National Institutes of University, have been studying ionic signalling Health (NIH) in melanosomes, or how exactly ion channels towards a better regulate melanin synthesis, storage, and COLLABORATORS transfer. In 2014, the team made their first understanding of Nick Bellono was a PhD student in Dr breakthrough, identifying an ion channel Oancea's laboratory, who did all the patch- called OCA2 that is defective in people with human pigmentation clamp recordings from melanosomes oculocutaneous albinism type 2 (OCA2) and after learning how to patch lysosomes in that functions to increase the production Dr Dejian Ren’s laboratory at University of melanin. More recently, the team found of Pennsylvania. Bellono then adapted the counterpart to OCA2 - an ion channel the technique to melanosomes. A key with the reverse effect on cellular pigment collaborator on the OCA2 paper, adviser, production. and friend of Dr Oancea is Dr Michael Marks from University of Pennsylvania. In their new study, Dr Oancea’s team have discovered a new regulatory protein for the BIO pigmentation process: two-pore channel 2 out of the melanosomes. The new current of both TPC channels. This stopped the from melanosomes is indeed mediated by the research will provide other scientists with the Associate Professor Elena Oancea earned (TPC2). The team had a clue that TPC2 relates was consistent with a typical two-pore electrical current, as they had expected, and TPC2 ion channel. What’s more, they could basis for uncovering “novel therapeutic her PhD at Duke University with Dr to pigmentation as two in the gene channel and appeared to depend on a further experiments identified that the ion reestablish the flow of current by adding the targets” for pigmentation disorders, as Tobias Meyer then worked with encoding the ion channel were linked to lipid (fat) named PI(3,5)P2 that exists in the channels are of the TPC2 variety, not TPC1. TPC2 gene back into the cells. During this well as skin and eye cancers. Perhaps Dr David Clapham at Harvard light hair colour and fair skin in a 2008 study membrane around the melanosome and process, they observed that the melanosomes as a result of the study, future research University / Boston Children’s of northern Europeans. Using direct patch- other cellular organelles. Investigating further, The team deleted the TPC2 gene using of cells with fewer TPC2 channels are less will be able to find a way to treat Hospital. In 2008 Dr Oancea clamp recordings, a laboratory technique that the researchers added verapamil to the cell a gene editing tool called CRISPR-Cas9, acidic and produce more melanin, suggesting albinism and hyperpigmentation. moved to Brown University allows the study of ion channels, of skin and culture, a chemical that blocks the activity confirming that the outflow of positive charges TPC2 is a negative regulator of pigmentation. Should that prediction prove correct, to start her own lab and also eye melanosomes from mouse melanocytes They discovered that TPC2 counterbalances a significant proportion of skin and eye shifted the focus of her research to and frog retinal pigment cells, the researchers Defective Melanin Albinism OCA2, a positive regulator of pigmentation, cancer could be pro-actively prevented, and pigment cells, how these cells respond were able to identify the first reported Synthesis Disorder by increasing the melanosomal membrane much psychological distress eliminated. to different physiological stimuli and the melanosomal cation conductance mediated potential and acidity to decrease melanin complex mechanisms that govern pigment Type Underproduction and Overproduction and by TPC2. Mouse skin cells and frog eye cells storage of melanin storage of melanin content. In simple terms, if TCP2 lets too many However, there is much research still to do, production in melanosomes. have the same proteins and mechanisms as positive ions escape the melanosome, the particularly due to the existence of TPC2 Prevalence Affects 1 in 17,000 people Global prevalence unknown - in humans. However, the melanosomes are production of melanin is turned off. channels in other cells. Dr Oancea explains: CONTACT worldwide relatively understudied area of larger making the experiments possible. “Unfortunately, this is not simple. TPC2 Department of Molecular Pharmacology, Male and females equally PROGRESS FOR PIGMENT TREATMENT channels also have important functions in the Physiology and Biotechnology affected, except for sub-type Between 75-90% affected are In the laboratory, Dr Oancea and the co- that occurs more female “We now know how TPC2 functions in lysosomes of non-pigment cells. Blocking Brown University Box G-B3 lead authors Nicholas Bellono and Illiana melanosomes and can use this information to TPC2 would not only increase pigmentation, Providence, RI 02912, USA often in males More common in people with Escobar, measured the flux of ions across the Can affect individuals of all naturally darker skin, or who tan understand how melanosomes function under but interfere with other functions mediated membranes that surround the melanosomes ethnicities easily normal conditions, and how their function by the ion channels. Local delivery of specific E: [email protected] found inside melanocytes. They found can be perturbed by mutations,” says Dr TPC2 blockers to melanocytes might be a way T: +1 401 863-6116 Characteristic Very pale skin, eyes Symmetrical, blotchy, brownish an electrical current that corresponds to Oancea. Providing vital knowledge required to circumvent this problem.” vivo.brown.edu/display/eoancea Appearance and hair facial pigmentation W: positive ions flowing out of the organelles, to construct a comprehensive model of ionic ElenaOancea into the cytoplasm. Notably, this current Prognosis Causes problems with eyesight Benign condition, but can cause signalling in melanosomes, the researchers • Find out more about Dr Oancea’s research: was found to be independent of the already Increased risk of skin and eye significant psychological distress have provided a significant step towards a www.nature.com/articles/srep26570 and embarrassment known OCA2 ion channel, which the same cancers better understanding of human pigmentation. elifesciences.org/interviews/early-career- group showed transports negative ions The research team are hopeful that their researchers/elena-oancea

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