fc00Peroxisomes in Dermatology

Peroxisomes & Peroxisome Proliferator-Activated Receptors in Dermatology : 

1 Peroxisomes & Peroxisome Proliferator-Activated Receptors in Dermatology M.Y.ABDEL_MAWLA,MD Zagazig Faculty of Medicine,Zagzig,EGYPT

Peroxisomes in Cells : 

2 Peroxisomes in Cells The trouble with simple things is that one must understand them very well !!!

The Peroxisome : 

3 The Peroxisome Single membrane Roughly spherical 0.2 - 1.7?m Composition varies

Peroxisomes : 

4 Peroxisomes Peroxisomes : intracellular organelles with important roles defined in many metabolic processes. Peroxisomes:in all mamalian cells,including kertatinocytes They derive their name from their ability to produce H2O2 through a group of oxidizing enzymes which use molecular oxygen to transform their substrates, releasing H2O2 and OH

Peroxisomes : 

5 Peroxisomes The oxidative stress resulting from H2O2 is known to stimulate phospholipase D, associated with the production of phosphatidic acid and diacylglycerol. These in turn affect adenylyl cyclase and protein kinase C, respectively, which can modulate a wide array of target proteins including plasma membrane receptors, contractile proteins and regulatory enzymes.

Peroxisomes : 

6 Peroxisomes Peroxisomes are similar physically to lysosomes, but they are different in two important ways First, they are believed to be formed by self-replication (or perhaps by budding off from the smooth endoplasmic reticulum) rather than from the Golgi apparatus. Second, they contain oxidases rather than hydrolases.

Peroxisomes Biogenesis : 

7 Peroxisomes Biogenesis The development of peroxisomes involves a series of events including the recruitment of (phospho)lipids, synthesis, sorting and assembly/activation of matrix &membrane proteins. The peroxisomal membrane mainly consists of phosphatidylcholine &phosphatidylethanolamine and largely resembles that of the endoplasmic reticulum (ER)

Peroxisome Biogenesis : 

8 Peroxisome Biogenesis

Peroxisomes Biogenesis : 

9 Peroxisomes Biogenesis Membrane proteins are synthesized on free polysomes in the cytosol. The model discriminates between membrane proteins essential for the biogenesis of organelles (PMBs) and those involved in the organellar function (PMFs, e.g. transporters). PMBs (e.g. Pex2p, Pex3p, Pex15p and Pex16p) may initially be transported to the ER and, eventually vesicle-mediated, be sorted to the growing peroxisome; PMFs may be transported directly to the organelle

Peroxisomes Functions : 

10 Peroxisomes Functions Peroxisomes play only a minor role in cellular functions. Peroxisomes play an important role in regulating cellular proliferation and differentiation as well as in the modulation of inflammatory mediators. Peroxisomes have broad effects on the metabolism of lipids, hormones. Peroxisomes also affect cellular membranes and adipocyte formation, as well as insulin sensitivity. Peroxisomes play a role in aging and tumorigenesis through their effects on oxidative stress.

Peroxisomes Functions : 

11 Peroxisomes Functions Peroxisomes may be either catabolic or anabolic. Some functions are exclusively peroxisomal Others : shared with other cellular compartments (microsomes endoplasmic reticulum, and mitochondria).

Peroxisomes Functions in Cell signaling : 

12 Peroxisomes Functions in Cell signaling N =nucleus, MIT = mitochondria, MIC = microsomes, Per = peroxisome, PKO = phosphatidyl choline, PC = phosphosphatidyl choline, AA = arachidonic acid, OX = peroxisomal oxidases, LCFA = long-chain fatty acids, MCFA = medium-chain fatty acids, DG = diacylglycerol, PA = phosphatidic acid, CAT = catalase, OFR = oxygen free radicals. Peroxisome functions involved n cell signaling would potentiate differentiation, while reactive oxygen species would potentiate tumorigenesis and aging and catalase and other peroxisomal scavengers would moderate the effects of reactive oxygen species

Peroxisomes &Free Radicles : 

13 Peroxisomes &Free Radicles

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Peroxisomal Enzymes : 

15 Peroxisomal Enzymes

Key peroxisomal enzymes : 

16 Key peroxisomal enzymes

How Peroxisomes to Function? : 

17 How Peroxisomes to Function? Peroxisomes, contribute to key metabolic pathways of the cell function. These organelles are able to proliferate abundantly upon exposure to so-called peroxisome proliferators. Peroxisome-located enzymes are also regulated by many molecules including nutrients (fatty acids, steroids), hormones (T3, retinoids), PPARs and other nuclear signaling factors.

How Peroxisomes to Function? : 

18 How Peroxisomes to Function? Peroxisomal proliferator activator receptors (PPARs) and ligands for these receptors modulate different peroxisomal functions.

PPARs Distribution : 

19 PPARs Distribution PPARs are found mainly in tissues associated with high fatty acid metabolism. Thus are expressed mainly in liver, They are also found in kidney, muscle, heart, fat, B and T lymphocytes , vascular smooth muscle and keratinocytes

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21 Peroxisome Proliferator-Activated Receptors (PPARs) Nuclear hormone receptor superfamily Multiple isoforms (?, ? (d), ?) Unique tissue distribution

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22 PPAR:RXR? Co-repressors Co-activators Modulation of gene transcription ? ? ? Biological effect Mechanism of PPAR action

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23 Mechanism of PPAR action

PPARs FUNCTIONS : 

24 PPARs FUNCTIONS PPARs play a significant role in many in skin homeostasis. On binding of ligand, PPARs undergo a conformational change enabling them to form a heterodimer with the 9-cis retinoic acid receptor (RXR). PPAR/RXR complex forms a transcription factor able to bind to DNA at PPREs, which are DNA sequences specifically capable of ‘recognition’ and binding by the DNA-binding component of this transcription factor.

PPAR FUNCTIONS : 

25 PPAR FUNCTIONS A large number of PPAR target genes have been identified with wide-ranging effects on cell proliferation differentiation, inflammatory responses and angiogenesis, as well as lipid and glucose metabolism.

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26 Peroxisome proliferator-activated receptors (PPARs) function as heterodimers with retinoid X receptors (RXRs) and are activated by specific ligands; they then modulate DNA transcription by binding to defined nucleotide sequences (peroxisome proliferator response element, PPRE) in the promoter region of target genes. Several cofactors (coactivators or corepressors) mediate the ability of nuclear receptors to stimulate or repress the transcription process. (b) The N-terminus A/B domain contains a ligand-independent transcriptional activation domain (AF-1), which can be regulated by mitogen-activated protein kinase (MAPK) phosphorylation in a and ? isotypes. The C domain contains two zinc-finger-like motifs that specifically bind the PPRE in the regulatory region of PPAR-responsive genes. The D domain or hinge region allows conformational changes in the molecule. The E/F domain consists of the ligand-binding domain and the ligand-dependent transcriptional activation domain (AF-2). The ligand-binding pocket appears to be quite large in comparison with other nuclear receptors, allowing the PPARs to interact with a broad range of natural and synthetic ligands

ACTIVATION OF PPARs : 

27 ACTIVATION OF PPARs Most nuclear hormone receptors exist in an inactive form complexed with heats hock proteins PPAR activation and regulation may occur either following interaction with specific ligands or by kinase-mediated phosphorylation, following a variety of extracellular signals. Following binding of ligand, the PPAR undergoes a conformational change and becomes able to interact through the E/F domain with RXR to form heterodimers. These dimers will then interact with the cognate recognition motif (PPREs) in the promoter region of relevant genes to activate transcription of target genes.

ACTIVATION OF PPARs : 

28 ACTIVATION OF PPARs PPARs are held in inactive complex associated with heat shock proteins (HsP). Following binding with ligand or other activation signals . HsP is replaced with retinoic acid receptor (RXR) forming active transcription factor. The active PPAR/RXR heterodimer binds to PPAR response element AGGTCA X AGGTCA to initiate transcription of relevant genes.

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29 Biological roles of PPARa PPARa mediates the induction of multiple enzymes required to mobilize and transport fatty acids from adipose stores to liver for catabolism. Basis for therapeutic use in humans to lower serum lipids.

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30 Biological roles of PPARb/d Ligand activation of PPARb/d leads to terminal differentiation of keratinocytes as shown by four independent laboratories. Activation of PPARb/d in skeletal muscle leads to increased catabolism of fatty acids and improved insulin sensitivity.

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31 Biological roles of PPARg The role of PPARg in carcinogenesis is also controversial. There is evidence that activation of PPARg can either potentiate or attenuate cancer, but current consensus favors attenuation.

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32 Orchestration of Immune Responses TISSUES Thymus Spleen Lymph nodes Blood CELLS Lymphocytes Monocytes/Macs Neutrophils Eosinophils Basophils Dendritic cells MOLECULES Complement Lysozyme Inflammatory mediators Chemokines Cytokines Innate immunity Adaptive Immunity PPARs are found in a number of immune cell types and there is evidence that they could modulate a number of different immune responses

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33 Role of PPARa in Immune Function Expressed in monocytes/macrophages, increased after treatment with phorbol ester PPARa ligands induce apoptosis in activated macrophages PPARa ligands decrease secretion of MMPs in LPS-treated monocytes PPARa ligands decrease NOS activity in macrophages BUT… Natural PPARa ligands increase NOS activity in macrophages

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34 Role of PPARa in Immune Function Inflammatory response induced by LTB4 is enhanced in PPARa-null mice PPARa ligands can inhibit inflammatory cytokine production BUT… PPARa ligands cause increase in serum TNFa after LPS

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35 Role of PPARa in Immune Function Reports suggest that PPARa ligands are anti-inflammatory but there are also some reports suggesting that PPARa ligands are pro-inflammatory

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Peroxisomes &Inflammation : 

37 Peroxisomes &Inflammation PPAR-a activation: transcription factor for peroxisomal metabolism for arachidonic-derived proinflammatory eicosanoids. ligands for this activation are the w-3 fatty acids, which may explain their antiinflammatory effects.

Peroxisomes &Inflammation : 

38 Peroxisomes &Inflammation PPARa repress NFkB transcription, signal transducer and activator of transcriptions (STATs) and AP-1 (Jun/ Fos) transcription and the downstream signaling mechanism. These effects result in the decreased production of inflammatory cytokines, protease production, and some mechanisms for proliferation and apoptotic signaling.

Peroxisomes &Inflammation : 

39 Peroxisomes &Inflammation Activation of PPARs also modulates endothelial cell adhesion molecules, and endothelial cells express both PPARa and PPAR gamma

Peroxisomes &INFLAMMATION : 

40 Peroxisomes &INFLAMMATION The peroxisome proliferator-activated receptors (PPARs) a, ß/d, and ? are ligand-activated transcription factors belonging to the nuclear receptor superfamily. In addition to their regulatory role on lipid and glucose metabolism, they exert anti-inflammatory properties. In skin both PPAR-a and PPAR-ß/d regulate keratinocyte proliferation/differentiation and contribute to wound healing. The 3 PPAR isoforms are expressed by several cell types recruited into the dermis during inflammation.

Effects on angiogenesis : 

41 Effects on angiogenesis Vascular endothelial cell growth factor(VEGF) is a potent endothelial cell-specific mitogen. PPAR agonists have diverse effects on the expression of VEGF . PPAR gamma ligands increase the generation of VEGF , which might be expected to have pro-angiogenic effects.

Peroxisomes and Sterol Metabolism : 

42 Peroxisomes and Sterol Metabolism The levels of 17b-hydroxy forms of sex steroids are regulated by the 17b-hydroxysteroid dehydrogenase (17b- HSD) family of proteins. The type IV enzyme, found primarily in peroxisomes, possesses a number of unique features

Peroxisomes and Sterol Metabolism : 

43 Peroxisomes and Sterol Metabolism 17b-HSD IV is involved in degradation of branched-chain fatty acids and the side chain of cholesterol. Its expression is stimulated by PPARa ligands

Peroxisomes in Epidermal Differentiation & Proliferation : 

44 Peroxisomes in Epidermal Differentiation & Proliferation A well documented effects of PPARs on gene transcription associated with lipid metabolism & energy homeostasis. Roles in epidermal maturation, repair and angiogenesis are highlighted.

Peroxisomes in Epidermal Differentiation & Proliferation : 

45 Peroxisomes in Epidermal Differentiation & Proliferation PPARa has a role in barrier development. Activators of PPARa, such as clofibrate, oleic acid and linoleic acid, accelerate the barrier development. as evidenced by: decreased transepidermal water loss (TEWL); increased epidermal stratification; the appearance of mature lamellae in the extracellular spaces of a multilayered stratum corneum. the induction of b-galactosidase and steroid sulphatase, accelerated the expression of profilaggrin, and its processing to filaggrin, and the expression of loricrin, a

Peroxisomes & Atopic Dermatitis : 

46 Peroxisomes & Atopic Dermatitis Changes in immunoglobulin-associated transcription in atopic dermatitis may favour IgE over secretory immunoglobulin (multimeric IgM and IgA) expression in AD skin. Decreased PPAR activity appears common to both AD and psoriasis, and reduced cutaneous IFNa2 transcription also appears characteristic of AD

Peroxisomes in Epidermal Differentiation & Proliferation : 

47 Peroxisomes in Epidermal Differentiation & Proliferation PPARa ligands : to promote epidermal differentiation,to restore epidermal homeostasis in hyperproliferative mouse epidermis and regulate apoptosis. PPARb / gamma:induced expression of involucrin and transglutaminase( markers of keratinocyte differentiation)

Wound healing : 

48 Wound healing PPARa and PPARb / gamma:expression is upregulated in the keratinocytes at the wound edge of the damaged skin. PPARa is re-expressed transiently in this area during the early inflammatory phase of the healing. Delays in wound healing parallel the pattern of PPAR expression of the respective PPAR isotypes PPARb upregulation : linked to proinflammatory cytokines, such as interferon, tumour necrosis factor (TNF)-a.

Wound healing : 

49 Wound healing PPARb : a key mediator ofepidermal effects in wound healing by converting the extracellular inflammatory signal into an organized pattern of gene expression leading to survival, migration and differentiation of keratinocytes.

Sebocyte glands : 

50 Sebocyte glands Activation of PPAR gamma &a by their respective specific ligands, stimulates lipid droplet accumulation in sebocytes. Because increased sebum production is an important element in the pathogenesis of acne vulgaris, development PPAR antagonists interfering selectively with sebum formation may have implications for the treatment of acne.

Psoriasis : 

51 Psoriasis The hallmarks of psoriasis are abnormal differentiation & hyperproliferation of keratinocytes with inflammatory cell infiltration. These cellular changes are likely to find their explanation in activated T lymphocytes infiltrating the skin.

Psoriasis : 

52 Psoriasis PPARs : a critical regulator of cutaneous homeostasis in psoriasis. In view of their prodifferentiating, antiproliferative & immunomodulating effects, PPAR ligands may be interesting compounds for the treatment of epidermal disorders showing inflammation,hyperproliferation& aberrant differentiation, such as psoriasis.

Psoriasis : 

53 Psoriasis PPAR gamma and some of its ligands, including two lipoxygenase metabolites, are induced by the T helper (TH)2 cytokine IL-4 in macrophages. PPAR gamma activation may also be an integral part of the effecter mechanism for downregulation TH1 dominate inflammatory reaction such as psoriasis and rheumatoid arthritis

Psoriasis : 

54 Psoriasis The expression of both PPARa & gamma is decreased in epidermis , whereas the exact opposite happens with PPAR dela. Treatment by troglitazone, a specific PPAR gamma activator, inhibited the proliferation of both normal and psoriatic human keratinocytes

Psoriasis : 

55 Psoriasis There may be an association between psoriasis and the genes encoding PPARa or PPAR gamma

Effects on angiogenesis : 

56 Effects on angiogenesis Vascular endothelial cell growth factor(VEGF) is a potent endothelial cell-specific mitogen. PPAR agonists have diverse effects on the expression of VEGF . PPAR gamma ligands increase the generation of VEGF , which might be expected to have pro-angiogenic effects.

Human immunodeficiencyvirus-1-protease inhibitor associatedlipodystrophy : 

57 Human immunodeficiencyvirus-1-protease inhibitor associatedlipodystrophy HIV-1-protease inhibitor-associated lipodystrophy : the result of impaired cellular retinoic acid binding protein type I (CRABP-1)-mediated 9-cis retinoic stimulation of PPARc:RXR. Altered differentiation status of peripheral adipocytes in HIV-1-infected patients with protease inhibitor lipodystrophy is associated with greatly reduced sterol-regulatory element-binding protein 1c (SREBP1c) mRNA expression Reduced SREBP1 expression consequently alters the PPAR gamma activity, which may lead to lipodystrophy and to metabolic alterations.

Peroxisome defects : 

58 Peroxisome defects There are now many inherited disorders known to relate to peroxisome defects, frequently with significant cutaneous manifestations such as ichthyosis Recurrent ulceration, alopecia, follicular atrophoderma And photosensitivity, Thus ,it is suggested that modification of their activity may be of therapeutic benefit in the field of dermatology

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PEROXISOMAL DISORDERS : 

61 PEROXISOMAL DISORDERS

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Summary : 

63 Summary Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that regulate the expression of target genes involved in many cellular functions including cell proliferation, differentiation and immune/inflammation response. The PPAR subfamily consists of three isotypes: PPARa, PPARß/d and PPAR?, which have all been identified in keratinocytes.

Summary : 

64 Summary PPARß/d is the predominant subtype in human keratinocytes, whereas PPARa and PPAR? are expressed at much lower levels and increase significantly upon keratinocyte differentiation. PPARß/d is significantly upregulated upon various conditions that result in keratinocyte proliferation, and during skin wound healing.

Summary : 

65 Summary PPARs appear to play an important role in skin barrier permeability, inhibiting epidermal cell growth, promoting epidermal terminal differentiation and regulating skin inflammatory response by diverse mechanisms. These proprieties are pointing in the direction of PPARs being key regulators of skin conditions characterized by hyperproliferation, inflammatory infiltrates and aberrant differentiation such as psoriasis, They may also have clinical implications in other inflammatory skin disease (e.g. atopic dermatitis), proliferative skin disease, wound healing, acne and protease inhibitor associated lipodystrophia.

A Message Home : 

66 A Message Home Peroxisomes are small cellular organelles that were almost ignored for years because they were believed to play only a minor role in cellular functions. Peroxisomes play an important role in regulating cellular proliferation and differentiation as well as in the modulation of inflammatory mediators. Peroxisomes have broad effects on the metabolism of lipids, hormones,. Through their effects on lipid metabolism, peroxisomes also affect cellular membranes and adipocyte formation, as well as insulin sensitivity Peroxisomes play a role in aging and tumorigenesis through their effects on oxidative stress.

THANK YOU : 

67 THANK YOU