Synopsis
Melanins, the main pigments of the skin and hair in mammals, are synthesized within membrane-bound organelles of melanocytes called melanosomes. Melanosome structure and function are ...determined by a cohort of resident transmembrane proteins, many of which are expressed only in pigment cells and localize specifically to melanosomes. Defects in the genes that encode melanosome-specific proteins or components of the machinery required for their transport in and out of melanosomes underlie various forms of ocular or oculocutaneous albinism, characterized by hypopigmentation of the hair, skin, and eyes and by visual impairment. We review major components of melanosomes, including the enzymes that catalyze steps in melanin synthesis from tyrosine precursors, solute transporters that allow these enzymes to function, and structural proteins that underlie melanosome shape and melanin deposition. We then review the molecular mechanisms by which these components are biosynthetically delivered to newly forming melanosomes—many of which are shared by other cell types that generate cell type-specific lysosome-related organelles. We also highlight unanswered questions that need to be addressed by future investigation.
Resumen Este trabajo es un comentario del artículo: Singh S, McGuinness MB, Anderson AJ, Downie LE. Interventions for the Management of Computer Vision Syndrome: A Systematic Review and ...Meta-analysis. Ophthalmology. 2022 Oct;129(10):1192-1215. doi: 10.1016/j.ophtha. 2022.05.009
Tissue homeostasis requires regulation of cell-cell communication, which relies on signaling molecules and cell contacts. In skin epidermis, keratinocytes secrete factors transduced by melanocytes ...into signaling cues promoting their pigmentation and dendrite outgrowth, while melanocytes transfer melanin pigments to keratinocytes to convey skin photoprotection. How epidermal cells integrate these functions remains poorly characterized. Here, we show that caveolae are asymmetrically distributed in melanocytes and particularly abundant at the melanocyte-keratinocyte interface in epidermis. Caveolae in melanocytes are modulated by ultraviolet radiations and keratinocytes-released factors, like miRNAs. Preventing caveolae formation in melanocytes increases melanin pigment synthesis through upregulation of cAMP signaling and decreases cell protrusions, cell-cell contacts, pigment transfer and epidermis pigmentation. Altogether, we identify that caveolae serve as molecular hubs that couple signaling outputs from keratinocytes to mechanical plasticity of pigment cells. The coordination of intercellular communication and contacts by caveolae is thus crucial to skin pigmentation and tissue homeostasis.
Mahogunin Ring Finger 1 (MGRN1) is an E3-ubiquitin ligase absent in dark-furred
mahoganoid
mice. We investigated the mechanisms of hyperpigmentation in
Mgrn1
-null melan-md1 melanocytes,
Mgrn1
-KO ...cells obtained by CRISPR-Cas9-mediated knockdown of
Mgrn1
in melan-a6 melanocytes, and melan-a6 cells depleted of MGRN1 by siRNA treatment.
Mgrn1
-deficient melanocytes showed higher melanin content associated with increased melanosome abundance and higher fraction of melanosomes in highly melanized maturation stages III–IV. Expression, post-translational processing and enzymatic activity of the rate-limiting melanogenic enzyme tyrosinase measured in cell-free extracts were comparable in control and MGRN1-depleted cells. However, tyrosinase activity measured in situ in live cells and expression of genes associated with regulation of pH increased upon MGRN1 repression. Using pH-sensitive fluorescent probes, we found that downregulation of MGRN1 expression in melanocytes and melanoma cells increased the pH of acidic organelles, including melanosomes, strongly suggesting a previously unknown role of MGRN1 in the regulation of melanosomal pH. Among the pH regulatory genes upregulated by
Mgrn1
knockdown, we identified those encoding several subunits of the vacuolar adenosine triphosphatase V-ATPase (mostly
Atp6v0d2
) and a calcium channel of the transient receptor potential channel family, Mucolipin 3 (
Mcoln3
). Manipulation of expression of the
Mcoln3
gene showed that overexpression of
Mcoln3
played a significant role in neutralization of the pH of acidic organelles and activation of tyrosinase in MGRN1-depleted cells. Therefore, lack of MGRN1 led to cell-autonomous stimulation of pigment production in melanocytes mostly by increasing tyrosinase specific activity through neutralization of the melanosomal pH in a MCOLN3-dependent manner.
Exosomes are endosome-derived extracellular vesicles involved in intercellular communication. They are generated as intraluminal vesicles within endosomal compartments that fuse with the plasma ...membrane (PM). The molecular events that generate secretory endosomes and lead to the release of exosomes are not well understood. We identified a subclass of non-proteolytic endosomes at prelysosomal stage as the compartment of origin of CD63 positive exosomes. These compartments undergo a Rab7a/Arl8b/Rab27a GTPase cascade to fuse with the PM. Dynamic endoplasmic reticulum (ER)-late endosome (LE) membrane contact sites (MCS) through ORP1L have the distinct capacity to modulate this process by affecting LE motility, maturation state, and small GTPase association. Thus, exosome secretion is a multi-step process regulated by GTPase switching and MCS, highlighting the ER as a new player in exosome-mediated intercellular communication.
Food-derived bioactive peptides are essential in the regulation of the nutritional homeostasis. Water-soluble peptides (WSP) from fresh buffalo cheese were evaluated for their antioxidant properties ...and the percentage scavenging of the cation radical 2,2′-azino-bis-(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS) ranged from 33.39 ± 0.06% to 63.27 ± 0.18%, while that of the radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) reached about 42 ± 0.3%. ACE (angiotensin-converting enzyme)-inhibitory activity of WSP extracts showed activity levels in the range of 26.17 ± 2.02% to 58.79 ± 0.34%, for concentrations between 2.5 and 20 mg/mL, respectively, which confirmed their antihypertensive activity. All WSP extracts showed antimicrobial activity against Enterococcus faecalis and Bacillus subtilis, with an inhibitory concentration of 12.5 and 25 mg/mL, respectively. The cheeses evaluated here are discussed as sources of bioactive peptides with potential antioxidant, antihypertensive and antimicrobial properties which potentially can be applied in the food and pharmaceutical sectors.
•Water soluble peptides from fresh buffalo cheese present bioactivities.•Peptides from fresh buffalo cheese show anti-hypertensive activity.•Peptides from fresh buffalo cheese present antioxidant activity.•Two peptides might be used as markers to fresh buffalo cheese.•Peptide extract from buffalo cheese has properties for applications in food sectors.
Ergothioneine (ET) is a natural compound that humans and other vertebrates must absorb from dietary sources. In general, ET is considered an intracellular antioxidant. However, the precise ...physiological purpose of ET and the consequences of ET deficiency are still unclear. The ergothioneine transporter ETT (human gene symbol SLC22A4) is a highly specific transporter for the uptake of ET. Here, we sought to identify and knock out ETT from zebrafish (Danio rerio) to determine the function of ET. We cloned and assayed three related proteins from zebrafish, only one of which catalyzed the uptake of ET. RT-PCR analysis revealed that the protein is strongly expressed in the skin, brain, kidney, intestine, and eye. In ETT-knockout animals generated by retroviral insertion into exon 1, ET content was reduced by more than 1000-fold compared to the wild type. Thus, ETT is the sole transporter responsible for uptake of ET into zebrafish. ETT-knockout fish did not exhibit obvious differences in morphology or behavior. In whole-fish homogenates, an increase in 4-hydroxy-2,3-trans-nonenal and malondialdehyde was observed, but only after stress caused by incubation with Pb2+ or Cu2+. Comparison of unstressed fish at the level of small molecules by LC–MS difference shading revealed a 3.8-fold increase in 8-oxoguanine (8-oxo-7,8-dihydroguanine) in the skin of ETT-knockout animals. Our knockout represents a new model for examining the consequences of complete absence of ET. Based on the phenotype observed here, we hypothesize that the specific purpose of ET could be to eliminate singlet oxygen.
•An ergothioneine (ET) transporter (ETT) from zebrafish was identified.•High levels of ETT mRNA were detected in skin, brain, kidney, intestine, and eye.•Knockout of ETT reduced ET content in whole-fish lysates by more than 1000-fold.•In the skin of ETT-knockout animals, 8-oxoguanine was increased 3.8-fold.•Hypothesis: the specific purpose of ET could be to eliminate singlet oxygen.
Natural additives with antioxidant properties can be used as biodegradable and sustainable alternatives to synthetic products, because they can inhibit the biodiesel oxidation reaction, increasing ...oxidative stability and extending its storage period. This research evaluated the efficiency of jabuticaba peels, gabiroba leaves, and hibiscus flowers in ethanolic extracts, analyzing through the simplex-centroid design, the induction periods (IP) and rate constants (k) of the biodiesel oxidation reaction at 110 °C. Antioxidant activity was observed in all extracts, either decreasing k or increasing the IP. The mathematical models obtained showed coefficients of determination greater than 0.9400, a non-significant lack of fit at the 5% level, and low dispersion between predicted and experimental data, indicating that the 1st order reaction fit was appropriate and can be used for predictive purposes. In this work, the optimization was performed with maximization of IP and minimization of k showing that the mixture containing 25% of jabuticaba peels extract and 75% of gabiroba leaves extract was the most suitable, because proportionally increased the IP and decreased k of the biodiesel oxidation reaction. It is possible to suggest the use of jabuticaba peels extract or gabiroba leaves extract as well as various combinations between them as antioxidant additives.
Myosin VI (Myo6) is the only minus-end directed nanomotor on actin, allowing it to uniquely contribute to numerous cellular functions. As for other nanomotors, the proper functioning of Myo6 relies ...on precise spatiotemporal control of motor activity via a poorly defined off-state and interactions with partners. Our structural, functional, and cellular studies reveal key features of myosin regulation and indicate that not all partners can activate Myo6. TOM1 and Dab2 cannot bind the off-state, while GIPC1 binds Myo6, releases its auto-inhibition and triggers proximal dimerization. Myo6 partners thus differentially recruit Myo6. We solved a crystal structure of the proximal dimerization domain, and show that its disruption compromises endocytosis in HeLa cells, emphasizing the importance of Myo6 dimerization. Finally, we show that the L926Q deafness mutation disrupts Myo6 auto-inhibition and indirectly impairs proximal dimerization. Our study thus demonstrates the importance of partners in the control of Myo6 auto-inhibition, localization, and activation.
Caffeic acid derivatives represent promising lead compounds in the search for tyrosinase inhibitors to be used in the treatment of skin local hyperpigmentation associated to an overproduction or ...accumulation of melanin. We recently reported the marked inhibitory activity of a conjugate of caffeic acid with dihydrolipoic acid, 2-
-lipoylcaffeic acid (LCA), on the tyrosine hydroxylase (TH) and dopa oxidase (DO) activities of mushroom tyrosinase. In the present study, we evaluated a more lipophilic derivative, 2-
-lipoyl caffeic acid methyl ester (LCAME), as an inhibitor of tyrosinase from human melanoma cells. Preliminary analysis of the effects of LCAME on mushroom tyrosinase indicated more potent inhibitory effects on either enzyme activities (IC
= 0.05 ± 0.01 μM for DO and 0.83 ± 0.09 μM for TH) compared with LCA and the reference compound kojic acid. The inhibition of DO of human tyrosinase was effective (Ki = 34.7 ± 1.1 μM) as well, while the action on TH was weaker. Lineweaver⁻Burk analyses indicated a competitive inhibitor mechanism. LCAME was not substrate of tyrosinase and proved nontoxic at concentrations up to 50 μM. No alteration of basal tyrosinase expression was observed after 24 h treatment of human melanoma cells with the inhibitor, but preliminary evidence suggested LCAME might impair the induction of tyrosinase expression in cells stimulated with α-melanocyte-stimulating hormone. All these data point to this compound as a valuable candidate for further trials toward its use as a skin depigmenting agent. They also highlight the differential effects of tyrosinase inhibitors on the human and mushroom enzymes.
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