peroxisomes in dermatology

Peroxisomes in Peroxisomes in DermatologyDermatology

M.Y.ABDEL_MAWLA,MDM.Y.ABDEL_MAWLA,MD

Zagazig Faculty of Zagazig Faculty of Medicine,Zagzig,EGYPTMedicine,Zagzig,EGYPT

M.Y.Abdel-Mawla M.Y.Abdel-Mawla Zagazig,Egypt Zagazig,Egypt

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Peroxisomes

Peroxisomes : intracellular organelles with important roles defined in many metabolic processes.

Peroxisomes:in all mamalian cells except erythrocytes ,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


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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.


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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.


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How Peroxisomes to How Peroxisomes to Function?Function? Peroxisomal proliferator activator

receptors (PPARs) and ligands for these receptors modulate different peroxisomal functions.


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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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Peroxisome Proliferator-Activated Receptors (PPARs)

•Nuclear hormone receptor superfamily

•Multiple isoforms ()

•Unique tissue distribution


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PPAR:RXR

Co-repressors Co-activators

Modulation of gene transcription

RXR Ligands

PPAR Ligand

??

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Biological effect

Mechanism of PPAR action


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Mechanism of PPAR action


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


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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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Biological roles of PPAR

PPAR 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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Biological roles of PPAR/

Ligand activation of PPAR/ leads to terminal differentiation of keratinocytes as shown by four independent laboratories.

Activation of PPAR/ in skeletal muscle leads to increased catabolism of fatty acids and improved insulin sensitivity.


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Biological roles of PPAR

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


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Orchestration of Immune Responses

TISSUESThymusSpleen

Lymph nodesBlood

CELLSLymphocytes

Monocytes/MacsNeutrophilsEosinophilsBasophils

Dendritic cells

MOLECULESComplement

LysozymeInflammatory mediators

ChemokinesCytokines

Innate immunityAdaptive 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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Role of PPAR in Immune Function

•Expressed in monocytes/macrophages, increased after treatment with phorbol ester

•PPAR ligands induce apoptosis in activated macrophages

•PPAR ligands decrease secretion of MMPs in LPS-treated monocytes

•PPAR ligands decrease NOS activity in macrophages

BUT…

•Natural PPAR ligands increase NOS activity in macrophages


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•Inflammatory response induced by LTB4 is enhanced in PPAR-null mice

•PPAR ligands can inhibit inflammatory cytokine production

BUT…

•PPAR ligands cause increase in serum TNF after LPS


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•Reports suggest that PPAR ligands are anti-inflammatory but there are also some reports suggesting that PPAR ligands are pro-inflammatory


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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.


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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.


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


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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.


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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


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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


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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.


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PPARα has a role in barrier development.PPARα has a role in barrier development. Activators of PPARα, such as clofibrate, Activators of PPARα, such as clofibrate,

oleic acid and linoleic acid, accelerate the oleic acid and linoleic acid, accelerate the barrier development. barrier development. as evidenced by:

1. decreased transepidermal water loss (TEWL);2. increased epidermal stratification; 3. the appearance of mature lamellae in the

extracellular spaces of a multilayered stratum corneum.

4. the induction of b-galactosidase and steroid sulphatase,

5. accelerated the expression of profilaggrin, and its processing to filaggrin, and the expression of loricrin, a


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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)


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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.


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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.


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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.


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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.


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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.


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PsoriasisPsoriasis

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


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PsoriasisPsoriasis

There may be an association between

psoriasis and the genes encoding PPARa or PPAR gamma


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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.


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Peroxisome defects

There are now many inherited disorders known to relate to peroxisome defects, frequently with significant cutaneous manifestations such as

1. ichthyosis2. Recurrent ulceration,3. alopecia, 4. follicular atrophoderma 5. 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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SummarySummary

Peroxisome proliferator-activated Peroxisome proliferator-activated receptors (PPARs) are ligand-activated receptors (PPARs) are ligand-activated transcription factors that regulate the transcription factors that regulate the expression of target genes involved in many expression of target genes involved in many cellular functions including cell proliferation, cellular functions including cell proliferation, differentiation and immune/inflammation differentiation and immune/inflammation response.response.

The PPAR subfamily consists of three The PPAR subfamily consists of three isotypes: PPARα, PPARβ/δ and PPARγ, which isotypes: PPARα, PPARβ/δ and PPARγ, which have all been identified in keratinocytes.have all been identified in keratinocytes.


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SummarySummary

PPARβ/δ is the predominant PPARβ/δ is the predominant subtype in human keratinocytes, subtype in human keratinocytes, whereas PPARα and PPARγ are whereas PPARα and PPARγ are expressed at much lower levels and expressed at much lower levels and increase significantly upon increase significantly upon keratinocyte differentiation.keratinocyte differentiation.

PPARβ/δ is significantly PPARβ/δ is significantly upregulated upon various upregulated upon various conditions that result in conditions that result in keratinocyte proliferation, and keratinocyte proliferation, and during skin wound healing.during skin wound healing.


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SummarySummary

PPARs appear to play an important role in skin PPARs appear to play an important role in skin barrier permeability, inhibiting epidermal cell barrier permeability, inhibiting epidermal cell growth, promoting epidermal terminal growth, promoting epidermal terminal differentiation and regulating skin inflammatory differentiation and regulating skin inflammatory response by diverse mechanisms. response by diverse mechanisms.

These proprieties are pointing in the direction These proprieties are pointing in the direction of PPARs being key regulators of skin conditions of PPARs being key regulators of skin conditions characterized by hyperproliferation, characterized by hyperproliferation, inflammatory infiltrates and aberrant inflammatory infiltrates and aberrant differentiation such as psoriasis,differentiation such as psoriasis,

They may also have clinical implications in They may also have clinical implications in other inflammatory skin disease (e.g. atopic other inflammatory skin disease (e.g. atopic dermatitis), proliferative skin disease, wound dermatitis), proliferative skin disease, wound healing, acne and protease inhibitor associated healing, acne and protease inhibitor associated lipodystrophia.lipodystrophia.


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A Message HomeA 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.


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peroxisomes in dermatology

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