Extra-enzymatic roles of DPIV and FAP in cell adhesion and migration on collagen and fibronectin

Dipeptidyl Peptidase 4 (DPP4) as A Novel Adipokine: Role in Metabolism and Fat Homeostasis

Dipeptidyl peptidase 4 (DPP4) is a molecule implicated in the regulation of metabolic homeostasis and inflammatory processes, and it exerts its main action through its enzymatic activity. DPP4 represents the enzyme most involved in the catabolism of incretin hormones; thus, its activity impacts appetite, energy balance, and the fine regulation of glucose homeostasis. Indeed, DPP4 inhibitors represent a class of antidiabetic agents widely used for the treatment of Type 2 diabetes mellitus (T2DM). DPP4 also acts as an adipokine and is mainly secreted by the adipose tissue, mostly from mature adipocytes of the visceral compartment, where it exerts autocrine and paracrine activities. DPP4 can disrupt insulin signaling within the adipocyte and in other target cells and tissues, where it also favors the development of a proinflammatory environment. This is likely at the basis of the presence of elevated circulating DPP4 levels in several metabolic diseases. In this review, we summarize the most recent evidence of the role of the DPP4 as an adipokine-regulating glucose/insulin metabolism and fat homeostasis, with a particular focus on clinical outcomes associated with its increased secretion in the presence of adipose tissue accumulation and dysfunction.

Mechanism of Fibronectin Binding to Human Trabecular Meshwork Exosomes and Its Modulation by Dexamethasone

Exosomes are emerging as important mediators of cell-matrix interactions by means of specific adhesion proteins. Changes in the tissue-specific exosomal protein expression may underlie pathological conditions whereby extracellular matrix turnover and homeostasis is disrupted. Ocular hypertension due to extracellular matrix accumulation in the trabecular meshwork is a hallmark of glucocorticoid-induced glaucoma. In the trabecular meshwork, exosomal fibronectin mediates cell matrix interactions at cellular structures called “invadosomes”. Trabecular meshwork cells use invadosomes to turn over their surrounding matrix and maintain passageways for flow of aqueous humor. In this study, we observed that human trabecular meshwork explants treated with dexamethasone released exosomes with significantly reduced amounts of fibronectin bound per exosome. Further, we found that exosome-fibronectin binding is heparan sulfate-dependent, consistent with our observation that trabecular meshwork exosomes are enriched in the heparin/heparan sulfate binding annexins A2 and A6. In this way, dexamethasone-treated explants released exosomes with a significant reduction in annexin A2 and A6 per exosome. Interestingly, we did not detect exosomal matrix metalloproteinases, but we identified abundant dipeptidyl peptidase 4, a serine protease whose activity was reduced on exosomes isolated from dexamethasone-treated explants. Together, our findings demonstrate mechanistically how corticosteroid-induced alterations in exosomal adhesion cargo and properties can account for the pathological matrix accumulation seen in many glaucoma patients.

Metabolic role of dipeptidyl peptidase 4 (DPP4) in primary human (pre)adipocytes

Dipeptidyl peptidase 4 (DPP4) is the target of the gliptins, a recent class of oral antidiabetics. DPP4 (also called CD26) was previously characterized in immune cells but also has important metabolic functions which are not yet fully understood. Thus, we investigated the function of DPP4 in human white preadipocytes and adipocytes. We found that both cell types express DPP4 in high amounts; DPP4 release markedly increased during differentiation. In preadipocytes, lentiviral DPP4 knockdown caused significant changes in gene expression as determined by whole-genome DNA-array analysis. Metabolic genes were increased, e.g. PDK4 18-fold and PPARγC1α (=PGC1α) 6-fold, and proliferation-related genes were decreased (e.g. FGF7 5-fold). These effects, contributing to differentiation, were not inhibited by the PPARγ antagonist T0070907. Vice versa, the PPARγ agonist pioglitazone induced a different set of genes (mainly FABP4). DPP4 knockdown also affected growth factor signaling and, accordingly, retarded preadipocyte proliferation. In particular, basal and insulin-induced ERK activation (but not Akt activation) was markedly diminished (by around 60%). This indicates that DPP4 knockdown contributes to adipocyte maturation by mimicking growth factor withdrawal, an early step in fat cell differentiation. In mature adipocytes, DPP4 becomes liberated so that adipose tissue may constitute a relevant source of circulating DPP4.

Characterization of dedifferentiating human mature adipocytes from the visceral and subcutaneous fat compartments: fibroblast-activation protein alpha and dipeptidyl peptidase 4 as major components of matrix remodeling

Mature adipocytes can reverse their phenotype to become fibroblast-like cells. This is achieved by ceiling culture and the resulting cells, called dedifferentiated fat (DFAT) cells, are multipotent. Beyond the potential value of these cells for regenerative medicine, the dedifferentiation process itself raises many questions about cellular plasticity and the pathways implicated in cell behavior. This work has been performed with the objective of obtaining new information on adipocyte dedifferentiation, especially pertaining to new targets that may be involved in cellular fate changes. To do so, omental and subcutaneous mature adipocytes sampled from severely obese subjects have been dedifferentiated by ceiling culture. An experimental design with various time points along the dedifferentiation process has been utilized to better understand this process. Cell size, gene and protein expression as well as cytokine secretion were investigated. Il-6, IL-8, SerpinE1 and VEGF secretion were increased during dedifferentiation, whereas MIF-1 secretion was transiently increased. A marked decrease in expression of mature adipocyte transcripts (PPARγ2, C/EBPα, LPL and Adiponectin) was detected early in the process. In addition, some matrix remodeling transcripts (FAP, DPP4, MMP1 and TGFβ1) were rapidly and strongly up-regulated. FAP and DPP4 proteins were simultaneously induced in dedifferentiating mature adipocytes supporting a potential role for these enzymes in adipose tissue remodeling and cell plasticity.

[Dipeptidyl peptidase IV in inflammatory bowel diseases (DPP IV/CD26)]

Inflammatory bowel diseases (Crohn's disease, ulcerative colitis, undetermined colitis) are a group of chronic autoimmune inflammatory diseases distinguished by recurrent inflammation of various parts of the gastrointestinal (GI) system and presenting a significant public health problem. Despite large basic and clinical research, the aetiology of these diseases and the pathogenesis of inflammation itself remain elusive. Previous studies have confirmed a causal relationship between mediators of inflammatory response and molecules involved in the regulation of their biological activity, especially proteases. The aim of this review is to summarise earlier findings on different aspects of inflammatory bowel diseases, paying particular attention to the involvement of dipeptidyl peptidase IV (CD26 molecule, DPP IV/CD26) in the etiopathogenesis of inflammatory processes in the GI tract. Animal studies of colitis have significantly contributed to the understanding and treatment of these diseases, investigations of ulcerative colitis (DSS-colitis) and Crohn's disease (TNBS-colitis) on the murine model in particular.

Leukemia inhibitory factor signaling is required for lung protection during pneumonia

Lung infections represent a tremendous disease burden and a leading cause of acute lung injury. STAT3 signaling is essential for controlling lung injury during pneumonia. We previously identified LIF as a prominent STAT3-activating cytokine expressed in the airspaces of pneumonic lungs, but its physiological significance in this setting has never been explored. To do so, Escherichia coli was intratracheally instilled into C57BL/6 mice in the presence of neutralizing anti-LIF IgG or control IgG. Anti-LIF completely eliminated lung LIF detection and markedly exacerbated lung injury compared with control mice as evidenced by airspace albumin content, lung liquid accumulation, and histological analysis. Although lung bacteriology was equivalent between groups, bacteremia was more prevalent with anti-LIF treatment, suggestive of compromised barrier function rather than impaired antibacterial defense as the cause of dissemination. Inflammatory cytokine expression was also exaggerated in anti-LIF-treated lungs, albeit after injury had ensued. Interestingly, alveolar neutrophil recruitment was modestly but significantly reduced compared with control mice despite elevated cytokine levels, indicating that inflammatory injury was not a consequence of excessive neutrophilic alveolitis. Lastly, the lung transcriptome was dramatically remodeled during pneumonia, but far more so following LIF neutralization, with gene changes implicating cell death and epithelial homeostasis among other processes relevant to tissue injury. From these findings, we conclude that endogenous LIF facilitates tissue protection during pneumonia. The LIF-STAT3 axis is identified in this study as a critical determinant of lung injury with clinical implications for pneumonia patients.

Stromal expression of CD34, α-smooth muscle actin and CD26/DPPIV in squamous cell carcinoma of the skin: a comparative immunohistochemical study

Invasion pathogenesis is one of the most complicated issues in the literature. There are numerous studies concerning the tumor markers implicated in the preinvasive-invasive tumor sequence. Despite ample studies on the invasion pathogenesis of cutaneous melanomas, there is limited and dispersed work presently available on non-melanoma skin cancer. The vast knowledge in the literature concerning this issue in squamous cell carcinoma comes mostly from the studies of the oral cavity, esophagus, larynx, and cervix. In this study, we investigated tumor-free neighboring stroma and tumor stroma in squamous cell carcinomas (SCCs) of the skin as well as keratoacanthomas (KAs) with respect to the presence of stromal CD34-positive (CD34+) fibrocytes and α-smooth muscle actin-positive (α-SMA+) myofibroblasts using seborrheic keratosis (SKs) and non-tumoral skin samples as controls. We also evaluated the stromal expression pattern of CD26/DPPIV (CD26), a tumor suppressor gene product that also has immunoregulatory properties. Immunohistochemistry was performed on samples of 31 SCC, 8 KA, 15 SK and 10 non-tumoral skin samples. Peri-tumoral stroma from resection margins was also evaluated. We found that CD34 and α-SMA demonstrated significantly different staining between benign and malignant squamous skin lesions consisting of a loss of CD34+ fibrocytes paralleled by a gain of α-SMA+ myofibroblasts in malignant tumor stroma. Additionally, it was shown that CD26 expression was lower in tumor stroma when compared to that of tumor neighboring stroma. However, we concluded that this finding may be attributable to the solar elastosis areas in the peritumoral tissue, which shows diffuse strong positivity for this marker.

The Role of Neuropeptide Endopeptidases in Cutaneous Immunity

Proteolytic processing and degradation plays an important role in modulating the generation and bioactivity of neuroendocrine peptide mediators, a class of key molecules in cutaneous biology.

Accordingly, the cellular localization and expression, and the molecular biology and structural properties of selected intracellular prohormone convertases and ectopically expressed zinc-binding metalloendoproteases are discussed.

A special reference will be made to the physiologic and pathophysiologic significance of these endopeptidases in cutaneous immunobiology.

Because of the number of pathologically relevant changes in inflammation and tumor progression that can be directly attributed to neprilysin and angiotensin-converting enzyme, a particular focus will be on the role of these enzymes in modulating innate and adaptive immune responses in the skin.