| Synthesis and release | In rodents, α-MSH release is under strong inhibitorycontrol by direct innervation from hypothalamic neurons. Dopamine plays a role as a physiological melanotropin release-inhibiting hormone (MRIH). In contrastto ACTH release from corticotropes in the pars distalisof the pituitary, there is no apparent negative feedbackcontrol on α-MSH release from melanotropes. Similarmechanisms of regulation have also been demonstratedin amphibians. In humans, the pars intermedia is functional in the fetus and neonate, whereas adults lack thepars intermedia. |
| Receptors | α-MSH and other MSH peptides interact with four ofthe five subtypes of melanocortin receptors (MC1R,MC3R, MC4R, and MC5R, excluding the ACTH-specificreceptor MC2R), which are members of the GPCR family.Among them, MC1R is a classical α-MSH receptor. ACTHinteracts with all five MC receptors. α-MSH activates the AC/PKA pathway viaG proteins. |
| Agonists and Antagonists | NDP-MSH and MT-II are agonists for human MC1R,MC3R, MC4R, and MC5R. Kd for [125I]NDP-MSH:0.33 nM (MC1R), 0.2 nM (MC3R), 4–1.2 nM (MC4R),2.8 nM (MC5R). HS024 is an antagonist for human MC1R, MC3R,MC4R, and MC5R. |
| Clinical implications | The antiinflammatory activity of α-MSH includesimmunomodulatory effects on several resident skin cellsand antifibrogenic effects mediated via MC1R that areexpressed by dermal fibroblasts. In human mast cells,α-MSH appears to be proinflammatory due to histaminerelease. α-MSH exhibits cytoprotective activity againstultraviolet B-induced apoptosis and DNA damage,which is associated with the increased risk of cutaneousmelanoma in individuals with the loss of functionMC1R mutation. The congenital deficiency of POMCresults in a syndrome of hypoadrenalism, severe obesity,and altered skin and hair pigmentation. In one case froma Turkish family, a child who was homozygous for aframeshift mutation in the N-terminal region of POMC,and was thus predicted to have a loss of all POMC-derived peptides, showed typical symptoms of POMCdeficiency. However, this child did not have red hair,unlike cases of Northern European origin. |
| Biological functions | α-MSH and other MSH peptidesare associated with a wide spectrum of biological functions through MC receptors that distribute in many tissues. MC1R is expressed in melanocytes, keratinocytes,macrophages, leukocytes, and adipose tissue; MC3R isexpressed in the central nervous system (CNS), kidney,testis, ovary, skeletal muscle, placenta, and mammarygland; MC4R is expressed in the CNS and associated withfood intake; and MC5R is expressed in exocrine glands,muscle, and the CNS. The representative physiologicalfunctions of MSH peptides mediated by MC receptorsare stimulation of melanocytes in the skin to synthesizemelanin, including regulation of the eumelaninpheomelanin switch via MC1R; energy homeostasisand natriuresis via MC3R; energy homeostasis and erectile function via MC4R; and synthesis and secretion ofexocrine gland products via MC5R. |
| Description | A pituitary hormone secreted from the pars intermedia,MSH was one of the first adenohypophysial hormonesdemonstrated to be present in vertebrates, from jawless fishto mammals, together with adrenocorticotropic hormone(ACTH). The fact that MSH is derived from a precursor proteincalled proopiomelanocortin (POMC) was demonstratedin 1979, using the pars intermedia from the bovinepituitary. |
| Uses | alpha-Melanocyte Stimulating Hormone amide is an endogenous melanocortin receptor agonist (Ki values are 0.12, 31, 660 and 5700 nM for MC1, MC3, MC4 and MC5 receptors respectively). Anti-inflammatory peptide; antagonizes proinflammatory mediators, including TNF-α, IL-6 and NO and induces anti-inflammatory cytokine IL-10. Inhibits food intake and induces penile erections following i.c.v. administration. |
| General Description | α-Melanocyte-stimulating hormone (α-MSH) is a tridecapeptide, mostly produced by the cells in the brain, pituitary and circulation. Pro-inflammatory cytokines or UV light induced epidermal cells such as keratinocytes and melanocytes synthesize and discharge α–MSH. Poopiomelanocortin (POMC) acts as a precursor for α-Melanocyte-stimulating hormone (α-MSH) production. |
| Biochem/physiol Actions | α-Melanocyte-stimulating hormone (α-MSH) acts as an anti-inflammatory agent via down regulating the production and activity of the pro-inflammatory cytokines interleukin-1 (IL-1), tumor necrosis factor (TNF)-α and IL-6 expressed in various cells of the immune system. It also controls the nitric oxide production associated with inflammation. α?MSH inhibits nuclear factor-κB (NF-κB)-dependent gene transcription and NF-κB pathway induced by TNF and other inflammatory agents. This activity of α-MSH is mediated through the production of cyclic adenosine monophosphate (cAMP) and activation of protein kinase A (PKA) enzyme. α–MSH functions as a potent therapeutics for various conditions resulted through NF-κB activation including, inflammatory diseases, human immunodeficiency virus (HIV) replication in AIDS (acquired immunodeficiency syndrome), and septic shock. α-MSH has an essential role to play in melanin production in animals. α-MSH regulates development of several skin diseases, including cutaneous inflammation and hyper-proliferative skin diseases. |
| Clinical Use | The measurement of the blood concentration of MSHhas not been validated for routine clinical use. MSH analogs have recently been developed for antiobesity medication, treatment of skin diseases, and prevention ofactinic keratoses in organ transplant recipients. Thepotential use of radiolabeled α-MSH peptides in melanoma imaging and the treatment of disseminated diseasehas also been reported. |
| storage | Store at -20°C |
| Purification Methods | Its solubility in H2O is 1mg/mL. It is separated from the extract by ion-exchange on carboxymethyl cellulose, desalted, evaporated and lyophilised, then chromatographed on Sephadex G-25. [Lande et al. Biochemical Preparations 13 45 1971.] |
| Structure and conformation | Three types of MSH molecules, with different aminoacid sequences, are contained in the common precursorPOMC in mammals. α-Melanocyte-stimulating hormone(α-MSH) is composed of 13 aa residues. This peptide is generated from the N-terminal region of the adrenocorticotropic hormone (ACTH), and corresponds to acetylACTH(1–13)-amide. In MSH, the N-terminal Ser residueis free, monoacetylated at the N position, or diacetylatedat the N and O positions, whereas the carboxyl terminalis consistently in the amide form. These variations ofMSH are called desacetyl-α-MSH, α-MSH, and diacetyl-α-MSH, respectively. Of these peptides, α-MSH is a classicalα-MSH. β-MSH, which is generated from POMC viaβ-lipotropin (β-LPH), is composed of 18 aa residues. Unlikeα-MSH, in β-MSH both termini are free. γ-MSH is producedfrom POMC via pro-γ-MSH or N-POMC, which consists ofγ-MSH together with a joining peptide. γ-MSH (also knownas γ1-MSH) is composed of 12 aa residues in which theN-terminus and the C-terminus are free and amide, respectively. γ3-MSH is composed of 25 aa residues in which theN-terminal region corresponds to γ1-MSH. Each MSH segment is flanked by basic amino acid residues. Cartilaginousfish such as sharks, rays, and ratfish possess δ-MSH in addition to the three other MSH peptides. Comparison with theamino acid sequence and topology of POMC suggests thatδ-MSH might have evolved from β-MSH. Accordingly,α-MSH and γ-MSH are suggested to share an antecedent.Teleost POMC lacks γ-MSH.
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