Fibroblast growth factor receptors 1 and 2 in keratinocytes control the epidermal barrier and cutaneous homeostasis

Fibroblast growth factors (FGFs) are master regulators of organogenesis and tissue homeostasis. In this study, we used different combinations of FGF receptor (FGFR)-deficient mice to unravel their functions in the skin. Loss of the IIIb splice variants of FGFR1 and FGFR2 in keratinocytes caused progressive loss of skin appendages, cutaneous inflammation, keratinocyte hyperproliferation, and acanthosis. We identified loss of FGF-induced expression of tight junction components with subsequent deficits in epidermal barrier function as the mechanism underlying the progressive inflammatory skin disease. The defective barrier causes activation of keratinocytes and epidermal γδ T cells, which produce interleukin-1 family member 8 and S100A8/A9 proteins. These cytokines initiate an inflammatory response and induce a double paracrine loop through production of keratinocyte mitogens by dermal cells. Our results identify essential roles for FGFs in the regulation of the epidermal barrier and in the prevention of cutaneous inflammation, and highlight the importance of stromal–epithelial interactions in skin homeostasis and disease.     

Fibroblast growth factor receptor 1-IIIb is dispensable for skin morphogenesis and wound healing

Alternative splicing in the extracellular domain is a characteristic feature of members of the fibroblast growth factor receptor (FGFR) family. This splicing event generates receptor variants, which differ in their ligand binding specificities. A poorly characterized splice variant is FGFR1-IIIb, recently found to be a functional FGF receptor predominantly expressed in the skin. Here we show that FGFR1-IIIb is expressed in normal and wounded mouse skin. Reduced expression of this type of receptor was found in wounds of healing-impaired genetically diabetic mice, suggesting that downregulation of FGFR1-IIIb is associated with wound healing defects. To address this possibility, we deleted the IIIb exon of FGFR1 in mice. The lack of FGFR-IIIb did not alter the expression of either FGFR1-IIIc, other FGF receptor genes or of FGFR1-IIIb ligands in normal and wounded skin. Histological analysis of the skin of FGFR1-IIIb knockout animals did not reveal any obvious abnormalities. Furthermore, full-thickness excisional skin wounds in these mice healed normally and no defects could be observed at the macroscopic or histological level. Finally, several genes that encode key players in wound repair were normally expressed in these animals. These data demonstrate that FGFR1-IIIb is dispensable for skin development and wound repair.     

Loss of epidermal MMP-14 expression interferes with angiogenesis but not with re-epithelialization

Synthesis and activation of matrix metalloproteinases during wound healing are important for remodeling the extracellular matrix and modulating various cellular functions. The membrane-type 1 matrix metalloproteinase (MMP-14) has been shown to play a key role during these processes. To analyze the function of epidermal-derived MMP-14 during skin repair we generated mice lacking MMP-14 expression in the epidermis (MMP-14(ep-/-)). These mice displayed overall normal skin morphology and epidermal differentiation patterns. Wound repair in MMP-14(ep-/-) followed the same kinetics as in wild type mice (MMP-14(ep+/+)), and infiltration of neutrophils, leukocytes, and macrophages into the wound site was comparable. Microscopic analysis showed no altered re-epithelialization in the absence of epidermal MMP-14. Furthermore, epidermal differentiation at the end of the repair process and scar formation was normal. However, at day 14 post wounding, sustained angiogenesis was observed in MMP-14(ep-/-) mice in contrast to control mice. Interestingly, decreased levels of endostatin were detected in wound lysates of MMP-14(ep-/-) mice as well as in cultured keratinocytes. Taken together, these data indicate that MMP-14 expression in keratinocytes is dispensable for skin homeostasis and repair, but plays a crucial role in the epidermal-dermal crosstalk leading to modulation of vessel density.     

A novel form of FGF receptor-3 using an alternative exon in the immunoglobulin domain III

Four distinct FGF receptors were cloned and characterized and it was demonstrated that the ligand binding site of FGF receptors is confined to the extracellular immunoglobulin-like (Ig)-domain 2 and 3. The Ig-domain 3 is encoded by two separate exons: exon IIIa encodes the N-terminal half, and the C-terminal half is encoded by either exon IIIb or IIIc in FGFR1 and FGFR2, whereas FGFR4 is devoid of exon IIIb. Alternative usage of exons IIIb and IIIc determine the ligand binding specificity of the receptor. To analyze the arrangement of these exons in FGFR3 we cloned the genomic sequence between exon IIIa and IIIc of FGFR3 and identified an alternative exon, corresponding to exon IIIb of the FGFR1 and FGFR2. The sequence of this exon shows Ig-domain hallmarks, 44% identity with exon IIIb of other FGF receptors and 36% identity with exon IIIc of FGFR3. Using this exon as a probe for mouse RNA as well as PCR analysis, demonstrated that exon IIIb encodes an authentic form of FGFR3 that is expressed in mouse embryo, mouse skin and mouse epidermal keratinocytes. The results demonstrate that the presence of alternative exons for Ig-domain 3 is a general phenomena in FGFR1, 2 and 3, and represents a novel genetic mechanism for the generation of receptor diversity.     

Fibroblast growth factor (FGF) 18 signals through FGF receptor 3 to promote chondrogenesis

Signaling by fibroblast growth factor (FGF) 18 and FGF receptor 3 (FGFR3) have been shown to regulate proliferation, differentiation, and matrix production of articular and growth plate chondrocytes in vivo and in vitro. Notably, the congenital absence of either FGF18 or FGFR3 resulted in similar expansion of the growth plates of fetal mice and the addition of FGF18 to human articular chondrocytes in culture enhanced proliferation and matrix production. Based on these and other experiments it has been proposed that FGF18 signals through FGFR3 to promote cartilage production by chondrocytes. Its role in chondrogenesis remains to be defined. In the current work we used the limb buds of FGFR3(+/+) and FGFR3(-/-) embryonic mice as a source of mesenchymal cells to determine how FGF18 signaling affects chondrogenesis. Confocal laser-scanning microscopy demonstrated impaired cartilage nodule formation in the FGFR3(-/-) cultures. Potential contributing factors to the phenotype were identified as impaired mitogenic response to FGF18, decreased production of type II collagen and proteoglycan in response to FGF18 stimulation, impaired interactions with the extracellular matrix resulting from altered integrin receptor expression, and altered expression of FGFR1 and FGFR2. The data identified FGF18 as a selective ligand for FGFR3 in limb bud mesenchymal cells, which suppressed proliferation and promoted their differentiation and production of cartilage matrix. This work, thus, identifies FGF18 and FGFR3 as potential molecular targets for intervention in tissue engineering aimed at cartilage repair and regeneration of damaged cartilage.     

Nedd4‐1 binds and ubiquitylates activated FGFR1 to control its endocytosis and function

Fibroblast growth factor receptor 1 (FGFR1) has critical roles in cellular proliferation and differentiation during animal development and adult homeostasis. Here, we show that human Nedd4 (Nedd4‐1), an E3 ubiquitin ligase comprised of a C2 domain, 4 WW domains, and a Hect domain, regulates endocytosis and signalling of FGFR1. Nedd4‐1 binds directly to and ubiquitylates activated FGFR1, by interacting primarily via its WW3 domain with a novel non‐canonical sequence (non‐PY motif) on FGFR1. Deletion of this recognition motif (FGFR1‐Δ6) abolishes Nedd4‐1 binding and receptor ubiquitylation, and impairs endocytosis of activated receptor, as also observed upon Nedd4‐1 knockdown. Accordingly, FGFR1‐Δ6, or Nedd4‐1 knockdown, exhibits sustained FGF‐dependent receptor Tyr phosphorylation and downstream signalling (activation of FRS2α, Akt, Erk1/2, and PLCγ). Expression of FGFR1‐Δ6 in human embryonic neural stem cells strongly promotes FGF2‐dependent neuronal differentiation. Furthermore, expression of this FGFR1‐Δ6 mutant in zebrafish embryos disrupts anterior neuronal patterning (head development), consistent with excessive FGFR1 signalling. These results identify Nedd4‐1 as a key regulator of FGFR1 endocytosis and signalling during neuronal differentiation and embryonic development.     

An FGF1:FGF2 chimeric growth factor exhibits universal FGF receptor specificity, enhanced stability and augmented activity useful for epithelial proliferation and radioprotection

Structural instability of wild-type fibroblast growth factor (FGF)-1 and its dependence on exogenous heparin for optimal activity diminishes its potential utility as a therapeutic agent. Here we evaluated FGFC, an FGF1:FGF2 chimeric protein, for its receptor affinity, absolute heparin-dependence, stability and potential clinical applicability. Using BaF3 transfectants overexpressing each FGF receptor (FGFR) subtype, we found that, like FGF1, FGFC activates all of the FGFR subtypes (i.e., FGFR1c, FGFR1b, FGFR2c, FGFR2b, FGFR3c, FGFR3b and FGFR4) in the presence of heparin. Moreover, FGFC activates FGFRs even in the absence of heparin. FGFC stimulated keratinocytes proliferation much more strongly than FGF2, as would be expected from its ability to activate FGFR2b. FGFC showed greater structural stability, biological activity and resistance to trypsinization, and less loss in solution than FGF1 or FGF2. When FGFC was intraperitoneally administered to BALB/c mice prior to whole body gamma-irradiation, survival of small intestine crypts was significantly enhanced, as compared to control mice. These results suggest that FGFC could be useful in a variety of clinical applications, including promotion of wound healing and protection against radiation-induced damage.     

Fibroblast growth factor control of cartilage homeostasis

Osteoarthritis (OA) and degenerative disc disease (DDD) are similar diseases involving the breakdown of cartilage tissue, and a better understanding of the underlying biochemical processes involved in cartilage degeneration may allow for the development of novel biologic therapies aimed at slowing the disease process. Three members of the fibroblast growth factor (FGF) family, FGF‐2, FGF‐18, and FGF‐8, have been implicated as contributing factors in cartilage homeostasis. The role of FGF‐2 is controversial in both articular and intervertebral disc (IVD) cartilage as it has been associated with species‐ and age‐dependent anabolic or catabolic events. Recent evidence suggests that FGF‐2 selectively activates FGF receptor 1 (FGFR1) to exert catabolic effects in human articular chondrocytes and IVD tissue via upregulation of matrix‐degrading enzyme production, inhibition of extracellular matrix (ECM) accumulation and proteoglycan synthesis, and clustering of cells characteristic of arthritic states. FGF‐18, on the other hand, most likely exerts anabolic effects in human articular chondrocytes by activating the FGFR3 pathway, inducing ECM formation and chondrogenic cell differentiation, and inhibiting cell proliferation. These changes result in dispersed chondrocytes or disc cells surrounded by abundant matrix. The role of FGF‐8 has recently been identified as a catabolic mediator in rat and rabbit articular cartilage, but its precise biological impact on human adult articular cartilage or IVD tissue remains unknown. The available evidence reveals the promise of FGF‐2/FGFR1 antagonists, FGF‐18/FGFR3 agonists, and FGF‐8 antagonists (i.e., anti‐FGF‐8 antibody) as potential therapies to prevent cartilage degeneration and/or promote cartilage regeneration and repair in the future. J. Cell. Biochem. 114: 735–742, 2013. © 2012 Wiley Periodicals, Inc.     

Delayed cutaneous wound healing and aberrant expression of hair follicle stem cell markers in mice selectively lacking Ctip2 in epidermis

Background

COUP-TF interacting protein 2 [(Ctip2), also known as Bcl11b] is an important regulator of skin homeostasis, and is overexpressed in head and neck cancer. Ctip2^ep−/− mice, selectively ablated for Ctip2 in epidermal keratinocytes, exhibited impaired terminal differentiation and delayed epidermal permeability barrier (EPB) establishment during development, similar to what was observed in Ctip2 null (Ctip2^−/−) mice. Considering that as an important role of Ctip2, and the fact that molecular networks which underlie cancer progression partially overlap with those responsible for tissue remodeling, we sought to determine the role of Ctip2 during cutaneous wound healing.

Methodology/Principal Findings

Full thickness excisional wound healing experiments were performed on Ctip2^L2/L2 and Ctip2^ep−/− animals per time point and used for harvesting samples for histology, immunohistochemistry (IHC) and immunoblotting. Results demonstrated inherent defects in proliferation and migration of Ctip2 lacking keratinocytes during re-epithelialization. Mutant mice exhibited reduced epidermal proliferation, delayed keratinocyte activation, altered cell-cell adhesion and impaired ECM development. Post wounding, Ctip2^ep−/− mice wounds displayed lack of E-Cadherin suppression in the migratory tongue, insufficient expression of alpha smooth muscle actin (alpha SMA) in the dermis, and robust induction of K8. Importantly, dysregulated expression of several hair follicle (HF) stem cell markers such as K15, NFATc1, CD133, CD34 and Lrig1 was observed in mutant skin during wound repair.

Conclusions/Significance

Results confirm a cell autonomous role of keratinocytic Ctip2 to modulate cell migration, proliferation and/or differentiation, and to maintain HF stem cells during cutaneous wounding. Furthermore, Ctip2 in a non-cell autonomous manner regulated granulation tissue formation and tissue contraction during wound closure.     

FGF/FGFR signaling: From lung development to respiratory diseases

The fibroblast growth factor/fibroblast growth factor receptor (FGF/FGFR) signaling system regulates a variety of biological processes, including embryogenesis, angiogenesis, wound repair, tissue homeostasis, and cancer. It exerts these regulatory functions by controlling proliferation, differentiation, migration, survival, and metabolism of target cells. The morphological structure of the lung is a complex tree-like network for effective oxygen exchange, and the airway terminates in the middle and distal ends of many alveoli. FGF/FGFR signaling plays an important role in the pathophysiology of lung development and pathogenesis of various human respiratory diseases. Here, we mainly review recent advances in FGF/FGFR signaling during human lung development and respiratory diseases, including lung cancer, acute lung injury (ALI), pulmonary arterial hypertension (PAH), chronic obstructive pulmonary disease (COPD), asthma, and pulmonary fibrosis.     

Targeted expression of a dominant-negative FGF receptor mutant in the epidermis of transgenic mice reveals a role of FGF in keratinocyte organization and differentiation.

In this study we used a dominant-negative FGF receptor mutant to block FGF function in a specific tissue of transgenic mice. The mutant receptor, which is known to block signal transduction in cells when co-expressed with wild-type receptors, was targeted to suprabasal keratinocytes using a keratin 10 promoter. The transgene was expressed specifically in the skin and highest expression levels were found in the tail. Expression of the mutant receptor disrupted the organization of epidermal keratinocytes, induced epidermal hyperthickening and resulted in an aberrant expression of keratin 6. This suggests that FGF is essential for the morphogenesis of suprabasal keratinocytes and for the establishment of the normal program of keratinocyte differentiation. Our study demonstrates that dominant-negative growth factor receptors can be used to block selectively the action of a growth factor in specific tissues of transgenic mice.     

Activating FGFR3 mutations cause mild hyperplasia in human skin,but are insufficient to drive benign or malignant skin tumors

Fibroblast growth factor receptor 3 (FGFR3) activating mutations are drivers of malignancy in several human tissues, including bladder, lung, cervix, and blood. However, in skin, these mutations are associated predominantly with benign, common epidermal growths called seborrheic keratoses (SKs). How epidermis resists FGFR3 mediated transformation is unclear, but previous studies have suggested that FGFR3 activation in skin keratinocytes may serve a tumor-suppressive role by driving differentiation and antagonizing Ras signaling. To define the role of FGFR3 in human normal and neoplastic epidermis, and to directly test the hypothesis that FGFR3 antagonizes Ras, we engineered human skin grafts in vivo with mutant active FGFR3 or shRNA FGFR3 knockdown. We show that FGFR3 active mutants drive mild hyperproliferation, but are insufficient to support benign or malignant tumorigenesis, either alone, or in combination with G₁–S checkpoint release. This suggests that additional cell-intrinsic or stromal cues are required for formation of benign SKs with FGFR3 mutations. Further, FGFR3 activation does not alter the growth kinetics or differentiation status of engineered human epidermal SCCs driven by Ras, and FGFR3 protein itself is dispensable for Ras-driven SCC. To extend these findings to patients, we examined a uniquely informative human tumor in which SCC developed in continuity with a SK, raising the hypothesis that one of the tumors evolved from the other. However, mutational analysis from each tumor indicates that the overlapping SK and SCC evolved independently and supports our conclusion that FGFR3 activation is insufficient to drive SCC.     

Fibroblast growth factor‐2 and interleukin‐4 synergistically induce eotaxin‐1 expression in adipose tissue‐derived stromal cells

The relationships between eosinophils and adipose tissues are involved in metabolic homeostasis. Eotaxin is a chemokine with potent effects on eosinophil migration. To clarify the mechanisms of eotaxin expression in adipose tissues, we examined the effects of fibroblast growth factor‐2 (FGF‐2) and interleukin‐4 (IL‐4) stimulation on eotaxin expression in adipose tissue‐derived stromal cells (ASCs), a type of adipocyte progenitor, in vitro. ASCs expressed eotaxin‐1 and did not express eotaxin‐2 or ‐3. Eotaxin‐1 expression was increased in a concentration‐dependent manner following FGF‐2 treatment. Additionally, ASCs expressed FGF receptor‐1 (FGFR‐1) and did not express FGFR‐2, ‐3, or ‐4. Eotaxin‐1 expression was inhibited in cells treated with the FGFR tyrosine kinase inhibitor and extracellular signal‐regulated kinase (ERK) inhibitor U0126, even in the presence of FGF‐2. Moreover, eotaxin‐1 expression was synergistically enhanced by combined treatment with FGF‐2 and IL‐4 and inhibited in the presence of U0126. Eotaxin‐1 expression induced by FGF‐2 and IL‐4 was involved in ERK activation via FGFR‐1 in ASCs. Upregulation of eotaxin expression in adipose tissues could increase eosinophil migration, thereby inducing IL‐4 secretion and activation of alternative macrophages and improving glucose homeostasis. These findings provide insights into the mechanisms through which eotaxin mediates metabolic homeostasis in adipose tissues and eosinophils.     

Independent repression of bile acid synthesis and activation of c-Jun N-terminal kinase (JNK) by activated hepatocyte fibroblast growth factor receptor 4 (FGFR4) and bile acids

The fibroblast growth factor (FGF) receptor complex is a regulator of adult organ homeostasis in addition to its central role in embryonic development and wound healing. FGF receptor 4 (FGFR4) is the sole FGFR receptor kinase that is significantly expressed in mature hepatocytes. Previously, we showed that mice lacking mouse FGFR4 (mR4(-/-)) exhibited elevated fecal bile acids, bile acid pool size, and expression of liver cholesterol 7alpha-hydroxylase (CYP7A1), the rate-limiting enzyme for canonical neutral bile acid synthesis. To prove that hepatocyte FGFR4 was a negative regulator of cholesterol metabolism and bile acid synthesis independent of background, we generated transgenic mice overexpressing a constitutively active human FGFR4 (CahR4) in hepatocytes and crossed them with the FGFR4-deficient mice to generate CahR4/mR4(-/-) mice. In mice expressing active FGFR4 in liver, fecal bile acid excretion was 64%, bile acid pool size was 47%, and Cyp7a1 expression was 10-30% of wild-type mice. The repressed level of Cyp7a1 expression was resistant to induction by a high cholesterol diet relative to wild-type mice. Expression of CahR4 in mR4(-/-) mouse livers depressed bile acid synthesis below wild-type levels from the elevated levels observed in mR4(-/-). Levels of phosphorylated c-Jun N-terminal kinase (JNK), which is part of a pathway implicated in bile acid-mediated repression of synthesis, was 30% of wild-type levels in mR4(-/-) livers, whereas CahR4 livers exhibited an average 2-fold increase. However, cholate still strongly induced phospho-JNK in mR4(-/-) livers. These results confirm that hepatocyte FGFR4 regulates bile acid synthesis by repression of Cyp7a1 expression. Hepatocyte FGFR4 may contribute to the repression of bile acid synthesis through JNK signaling but is not required for activation of JNK signaling by bile acids.     

Generation of an Frs2alpha conditional null allele

The fibroblast growth factor (FGF) signaling family controls a broad spectrum of cellular processes in development and adult tissue homeostasis and function, which is expressed in almost all tissues at all stages. FGF receptor substrate 2 alpha (FRS2alpha) is an adaptor protein that recruits downstream substrates to the FGF receptor (FGFR) tyrosine kinase. Disruption of Frs2alpha gene in mice abrogates activation of the mitogen-activated protein kinase pathway by the FGFR and leads to embryonic lethality at day E7.5 post copulation. To circumvent the embryonic lethality resulting from disruption of the Frs2alpha gene, which hinders further characterization of the role of FRS2alpha in adult tissue function and homeostasis, we generated an Frs2alpha conditional null allele for temporally- and tissue-specific disruption of the Frs2alpha gene. Using gene targeting in mouse embryonic stem cells, we introduced two loxP sites flanking the largest coding exon, exon 5, in the Frs2alpha allele. Our results indicate that the floxed Frs2alpha (Frs2alpha(flox)) allele is a true conditional null allele that encodes wildtype activity and is converted to a null allele after Cre recombinase mediated recombination.     

FGF19-induced Hepatocyte Proliferation Is Mediated through FGFR4 Activation

FGF19 and FGF21, unique members of the fibroblast growth factor (FGF) family, are hormones that regulate glucose, lipid, and energy homeostasis. Increased hepatocyte proliferation and liver tumor formation have also been observed in FGF19 transgenic mice. Here, we report that, in contrast to FGF19, FGF21 does not induce hepatocyte proliferation in vivo. To identify the mechanism for FGF19-induced hepatocyte proliferation, we explored similarities and differences in receptor specificity between FGF19 and FGF21. We find that although both are able to activate FGF receptors (FGFRs) 1c, 2c, and 3c, only FGF19 activates FGFR4, the predominant receptor in the liver. Using a C-terminal truncation mutant of FGF19 and a series of FGF19/FGF21 chimeric molecules, we determined that amino acids residues 38–42 of FGF19 are sufficient to confer both FGFR4 activation and increased hepatocyte proliferation in vivo to FGF21. These data suggest that activation of FGFR4 is the mechanism whereby FGF19 can increase hepatocyte proliferation and induce hepatocellular carcinoma formation.     

Fibroblast growth factor 22 is not essential for skin development and repair but plays a role in tumorigenesis

Fibroblast Growth Factors play critical roles during development, tissue homeostasis and repair by controlling cell proliferation, survival, migration and differentiation. Of the 22 mammalian FGFs, FGF22, a member of the FGF7/10/22 subfamily, has been shown to have a clear role in synaptogenesis, but its roles in other tissues have not been studied. We have investigated the in vivo functions of FGF22 in mice. Fgf22 null animals were viable, fertile and did not display any obvious abnormalities. Despite the known expression profile of FGF22 in the skin, no differences in either skin or pelage were observed, demonstrating that FGF22 is dispensable during embryogenesis and in unchallenged adult skin. Mice lacking FGF22 were able to heal acute wounds just as efficiently as wild type mice. However, classical two-step skin carcinogenesis challenge revealed that FGF22 null mice developed fewer papillomas than wild type controls, suggesting a potential pro-oncogenic role for FGF22 in the skin.     

Differential specificity of endocrine FGF19 and FGF21 to FGFR1 and FGFR4 in complex with KLB

Background

Recent studies suggest that betaKlotho (KLB) and endocrine FGF19 and FGF21 redirect FGFR signaling to regulation of metabolic homeostasis and suppression of obesity and diabetes. However, the identity of the predominant metabolic tissue in which a major FGFR-KLB resides that critically mediates the differential actions and metabolism effects of FGF19 and FGF21 remain unclear.

Methodology/Principal Findings

We determined the receptor and tissue specificity of FGF21 in comparison to FGF19 by using direct, sensitive and quantitative binding kinetics, and downstream signal transduction and expression of early response gene upon administration of FGF19 and FGF21 in mice. We found that FGF21 binds FGFR1 with much higher affinity than FGFR4 in presence of KLB; while FGF19 binds both FGFR1 and FGFR4 in presence of KLB with comparable affinity. The interaction of FGF21 with FGFR4-KLB is very weak even at high concentration and could be negligible at physiological concentration. Both FGF19 and FGF21 but not FGF1 exhibit binding affinity to KLB. The binding of FGF1 is dependent on where FGFRs are present. Both FGF19 and FGF21 are unable to displace the FGF1 binding, and conversely FGF1 cannot displace FGF19 and FGF21 binding. These results indicate that KLB is an indispensable mediator for the binding of FGF19 and FGF21 to FGFRs that is not required for FGF1. Although FGF19 can predominantly activate the responses of the liver and to a less extent the adipose tissue, FGF21 can do so significantly only in the adipose tissue and adipocytes. Among several metabolic and endocrine tissues, the response of adipose tissue to FGF21 is predominant, and can be blunted by the ablation of KLB or FGFR1.

Conclusions

Our results indicate that unlike FGF19, FGF21 is unable to bind FGFR4-KLB complex with affinity comparable to FGFR1-KLB, and therefore, at physiological concentration less likely to directly and significantly target the liver where FGFR4-KLB predominantly resides. However, both FGF21 and FGF19 have the potential to activate responses of primarily the adipose tissue where FGFR1-KLB resides.     

Responsiveness to androgens and effectiveness of antisense oligonucleotides against the androgen receptor on human epidermal keratinocytes is dependent on the age of the donor and the location of cell origin.

Local androgen excess has been associated with attenuation of wound healing in elderly individuals and with a decline in permeability barrier homeostasis in adult human skin. In this study we have applied specific antisense oligonucleotides, whose activity has already been investigated in SZ95 sebocytes, to inactivate transiently the androgen receptor in a reconstituted epidermis model and in primary human epidermal keratinocytes of different origin (breast, abdomen, foreskin) and donor age (females, 30- and 60-year-old). Further a possible interaction between blockage of androgen receptor and the expression of tissue inhibitors of matrix metalloproteinases was investigated. Androgen receptor levels were similar in pooled keratinocytes of the two age groups. Cell transfection with antisense oligonucleotides against the androgen receptor resulted in decreasing protein levels detected in all epidermal keratinocytes tested, whereas cells of aged donors (60-year-old) exhibited a stronger response than cells of young individuals (30-year-old). Keratinocytes from aged donors also responded to androgens with a stronger regulation of proliferation than keratinocytes of young individuals. The pattern of the androgen-induced response was dependent on the skin region of keratinocyte origin. The expression levels of tissue inhibitor of matrix metalloproteinase-1 were not age-related. Our results demonstrate an enhanced androgen sensitivity of keratinocytes from aged individuals associated with an origin-specific type of response.