The human CILP gene: exon/intron organization and chromosomal mapping

Cartilage intermediate layer protein affects the progression of intervertebral disc degeneration by regulating the extracellular microenvironment (Review)

Intervertebral disc degeneration (IDD), which is caused by multiple factors, affects the health of individuals and contributes to low back pain. The pathology of IDD is complicated, and changes in the extracellular microenvironment play an important role in promoting the process of degeneration. Cartilage intermediate layer protein (CILP) is a matrix protein that resides in the middle of human articular cartilage and is involved in numerous diseases that affect cartilage. However, there is no detailed review of the relationship between CILP and degenerative disc disease. Growing evidence has revealed the presence of CILP in the extracellular microenvironment of intervertebral discs (IVDs) and has suggested that there is a gradual increase in CILP in degenerative discs. Specifically, CILP plays an important role in regulating the metabolism of the extracellular matrix (ECM), an important component of the extracellular microenvironment. CILP can combine with transforming growth factor-β or insulin-like growth factor-1 to regulate the ECM synthesis of IVDs and influence the balance of ECM metabolism, which leads to changes in the extracellular microenvironment to promote the process of IDD. It may be possible to show the correlation of CILP with IDD and to target CILP to interfere with IDD. For this purpose, in the present study, the current knowledge on CILP was summarized and a detailed description of CILP in discs was provided.

Cartilage intermediate layer protein 1 (CILP1): A novel mediator of cardiac extracellular matrix remodelling

Heart failure is accompanied by extracellular matrix (ECM) remodelling, often leading to cardiac fibrosis. In the present study we explored the significance of cartilage intermediate layer protein 1 (CILP1) as a novel mediator of cardiac ECM remodelling. Whole genome transcriptional analysis of human cardiac tissue samples revealed a strong association of CILP1 with many structural (e.g. COL1A2 r² = 0.83) and non-structural (e.g. TGFB3 r² = 0.75) ECM proteins. Gene enrichment analysis further underscored the involvement of CILP1 in human cardiac ECM remodelling and TGFβ signalling. Myocardial CILP1 protein levels were significantly elevated in human infarct tissue and in aortic valve stenosis patients. CILP1 mRNA levels markedly increased in mouse heart after myocardial infarction, transverse aortic constriction, and angiotensin II treatment. Cardiac fibroblasts were found to be the primary source of cardiac CILP1 expression. Recombinant CILP1 inhibited TGFβ-induced αSMA gene and protein expression in cardiac fibroblasts. In addition, CILP1 overexpression in HEK293 cells strongly (5-fold p < 0.05) inhibited TGFβ signalling activity. In conclusion, our study identifies CILP1 as a new cardiac matricellular protein interfering with pro-fibrotic TGFβ signalling, and as a novel sensitive marker for cardiac fibrosis.

Cartilage intermediate layer protein (CILP) regulation in intervertebral discs. The effect of age, degeneration, and bone morphogenetic protein-2

STUDY DESIGN

An in vitro study using rabbit intervertebral disc tissue and disc cells.

OBJECTIVE

To evaluate the effects of disc degeneration, age, and bone morphogenetic proteins-2 (BMP-2) on cartilage intermediate layer protein (CILP) expression and elucidate the molecular mechanism by which BMP-2 regulates CILP expression.

SUMMARY OF BACKGROUND DATA

CILP is implicated in several diseases that affect cartilage. The CILP polymorphism acts as a modulator of lumbar disc disease susceptibility. However, regulation of the CILP gene in disc tissue remains poorly understood.

METHODS

Intact discs from young rabbits were punctured to induce disc degeneration. These young rabbits and other older rabbits were used to measure the expression of CILP, proteoglycan, and collagen II using Western blot and real-time PCR. Primary disc cells from the rabbits were treated with rhBMP-2, or siRNAs, and the gene expression was analyzed by Western blot and real-time PCR. The activity of the CILP promoter was measured by using the Dual Luciferase Reporter Assay System.

RESULTS

Our study demonstrates that the intervertebral disc expresses significant levels of CILP and that the expression of CILP increases substantially with increasing age and disc degeneration. In contrast, the expression of proteoglycan and collagen II decrease with increasing age and disc degeneration. BMP-2 induces the expression of CILP protein and stimulates the activity of the CILP promoter in rabbit primary disc cells. The induction of CILP by BMP-2 can be augmented with age. Knockdown of Smad1 by siRNA abolishes the stimulatory effects of BMP-2 on CILP expression in the primary disc cells.

CONCLUSION

Our data demonstrate that disc degeneration, age, and BMP-2 are regulators of the CILP gene. BMP-2 induces CILP expression by activating the Smad1 signal pathway.

Identification and validation of novel adipokines released from primary human adipocytes

Adipose tissue is a major endocrine organ, releasing signaling and mediator proteins, termed adipokines, via which adipose tissue communicates with other organs. Expansion of adipose tissue in obesity alters adipokine secretion, which may contribute to the development of metabolic diseases. Although recent profiling studies have identified numerous adipokines, the amount of overlap from these studies indicates that the adipokinome is still incompletely characterized. Therefore, we conducted a complementary protein profiling on concentrated conditioned medium derived from primary human adipocytes. SDS-PAGE/liquid chromatography-electrospray ionization tandem MS and two-dimensional SDS-PAGE/matrix-assisted laser desorption ionization/time of flight MS identified 347 proteins, 263 of which were predicted to be secreted. Fourty-four proteins were identified as novel adipokines. Furthermore, we validated the regulation and release of selected adipokines in primary human adipocytes and in serum and adipose tissue biopsies from morbidly obese patients and normal-weight controls. Validation experiments conducted for complement factor H, αB-crystallin, cartilage intermediate-layer protein, and heme oxygenase-1 show that the release and expression of these factors in adipocytes is regulated by differentiation and stimuli, which affect insulin sensitivity, as well as by obesity. Heme oxygenase-1 especially reveals to be a novel adipokine of interest. In vivo, circulating levels and adipose tissue expression of heme oxygenase-1 are significantly increased in obese subjects compared with lean controls. Collectively, our profiling study of the human adipokinome expands the list of adipokines and further highlights the pivotal role of adipokines in the regulation of multiple biological processes within adipose tissue and their potential dysregulation in obesity.

One of two chondrocyte-expressed isoforms of cartilage intermediate-layer protein functions as an insulin-like growth factor 1 antagonist

OBJECTIVE

Aging and osteoarthritic (OA) cartilage commonly demonstrate enhanced expression of the large, transforming growth factor beta (TGFbeta)-inducible glycoprotein cartilage intermediate-layer protein (CILP) as well as enhanced extracellular inorganic pyrophosphate (PPi) that promotes the deposition of calcium pyrophosphate dihydrate crystals. In normal chondrocytes, TGFbeta induces elevated chondrocyte extracellular PPi. Insulin-like growth factor 1 (IGF-1) normally blocks this response and reduces extracellular PPi. However, chondrocyte resistance to IGF-1 is observed in OA and aging. Because CILP was reported to chromatographically fractionate with PPi-generating nucleotide pyrophosphatase phosphodiesterase (NPP) activity, it has been broadly assumed that CILP itself has NPP activity. Our objective was to directly define CILP functions and their relationship to IGF-1 in chondrocytes.

METHODS

Using primary cultures of articular chondrocytes from the knee, we defined the function of the previously described CILP (CILP-1) and of a recently described 50.6% identical protein that we designated the CILP-2 isoform.

RESULTS

Both CILP isoforms were constitutively expressed by primary cultured articular chondrocytes, but only CILP-1 expression was detectable in cultured knee meniscal cartilage cells. Neither CILP isoform had intrinsic NPP activity. But CILP-1 blocked the ability of IGF-1 to decrease extracellular PPi, an activity specific for the CILP-1 N-terminal domain. The CILP-1 N-terminal domain also suppressed IGF-1-induced (but not TGFbeta-induced) proliferation and sulfated proteoglycan synthesis, and it inhibited ligand-induced IGF-1 receptor autophosphorylation.

CONCLUSION

Two CILP isoforms are differentially expressed by chondrocytes. Neither CILP isoform exhibits PPi-generating NPP activity. But, increased expression of CILP-1, via N-terminal domain-mediated inhibitory effects of CILP-1 on chondrocyte IGF-1 responsiveness, could impair chondrocyte growth and matrix repair and indirectly promote PPi supersaturation in aging and OA cartilage.

Inorganic pyrophosphate generation and disposition in pathophysiology

Inorganic pyrophosphate (PP(i)) regulates certain intracellular functions and extracellular crystal deposition. PP(i) is produced, degraded, and transported by specialized mechanisms. Moreover, dysregulated cellular PP(i) production, degradation, and transport all have been associated with disease, and PP(i) appears to directly mediate specific disease manifestations. In addition, natural and synthetic analogs of PP(i) are in use or currently under evaluation as prophylactic agents or therapies for disease. This review summarizes recent developments in the understanding of how PP(i) is made and disposed of by cells and assesses the body of evidence for potentially significant physiological functions of intracellular PP(i) in higher organisms. Major topics addressed are recent lines of molecular evidence that directly link decreased and increased extracellular PP(i) levels with diseases in which connective tissue matrix calcification is disordered. To illustrate in depth the effects of disordered PP(i) metabolism, this review weighs the roles in matrix calcification of the transmembrane protein ANK, which regulates intracellular to extracellular movement of PP(i), and the PP(i)-generating phosphodiesterase nucleotide pyrophosphatase family isoenzyme plasma cell membrane glycoprotein-1 (PC-1).

Up-regulated expression of the phosphodiesterase nucleotide pyrophosphatase family member PC-1 is a marker and pathogenic factor for knee meniscal cartilage matrix calcification

OBJECTIVE

Elevated cartilage inorganic pyrophosphate (PPi) production and PPi-generating nucleoside triphosphate pyrophosphohydrolase (NTPPPH) activity are strongly linked with aging-related cartilage calcification in meniscal and articular cartilages. We hypothesized that there were divergent relationships of 3 NTPPPH isozymes with cartilage matrix calcification and sought to identify them.

METHODS

We studied knee medial meniscal expression in situ of 3 NTPPPH isozymes of the phosphodiesterase nucleotide pyrophosphatase (PDNP) family: plasma cell membrane glycoprotein 1 (PC-1, or PDNP1), autotaxin (ATX, or PDNP2), and B10/PDNP3. We also used complementary DNA transfection to assess differential functions in matrix calcification of each NTPPPH isozyme in vitro in meniscal cells.

RESULTS

We observed diffuse cell-associated ATX and B10/PDNP3 expression in central (chondrocytic) and, to a lesser degree, peripheral (fibroblastic) regions of normal, degenerative uncalcified, and degenerative calcified menisci. In contrast, PC-1 expression was only robust at sites of apoptotic cells and calcification in central regions of degenerative menisci. Only PC-1 was abundant at the perimeter of meniscal cells and in association with meniscal cell-derived matrix vesicles (MVs). Because each PDNP-family isozyme was expressed by cells near calcifications, we transfected the isozymes in nonadherent knee meniscal cells cultured with ascorbic acid, beta-glycerophosphate, and dexamethasone supplementation to stimulate them to calcify the matrix. PC-1, but not ATX or B10/PDNP3, consistently promoted increased MV NTPPPH, MV-associated PPi, and extracellular PPi. PC-1 also increased matrix calcification (with hydroxyapatite crystals) by meniscal cells. ATX uniquely induced alkaline phosphatase activity, but promoted only moderately increased matrix calcification.

CONCLUSION

We identified divergent effects of 3 PDNP-family NTPPPH isozymes on meniscal cell matrix calcification. Increased expression of PC-1 is both a marker and a potential pathogenic factor for knee meniscal cartilage matrix calcification.

09/15: Comparative genomics of a conserved chromosomal region associated with a complex human phenotype

Three genes that encode related immunoglobulin superfamily molecules have recently been mapped to human chromosome 15 in the region q22.3-q23 and to the syntenic region on mouse chromosome 9. These genes presumably derived from gene duplications, and they are highly similar to Deleted in Colorectal Cancer (DCC), which functions as an axon guidance molecule during development of the nervous system. To find out whether additional genes of this class were present in a chromosomal cluster, we produced a comparative physical map within the region of synteny between mouse chromosome 9 and human chromosome 15. This interval overlaps the critical region for the fourth genetic locus for Bardet-Biedl syndrome (BBS4) in humans. Bardet-Biedl syndrome (OMIM 600374) is characterized by poly/syn/brachydactyly, retinal degeneration, hypogonadism, mental retardation, obesity, diabetes, and kidney abnormalities. A detailed map of this locus will help to identify candidate genes for this disorder.