Type V Collagen in Hepatic Fibrosis and as Fibrosis Biomarker

Research Article

Austin Biomark Diagn. 2016; 3(1): 1025.

Type V Collagen in Hepatic Fibrosis and as Fibrosis Biomarker

Mak KM*

Department of Medical Education and Center for Anatomy and Functional Morphology, Icahn School of Medicine at Mount Sinai, USA

*Corresponding author: Ki Mark Mak, Department of Medical Education and Center for Anatomy and Functional Morphology, Icahn School of Medicine at Mount Sinai, New York, USA

Received: April 25, 2016; Accepted: May 16, 2016; Published: May 17, 2016


Type V collagen (COLV) is a regulatory fibril-forming collagen. It is multifunctional in health, disease and fibrosis. In normal human liver, COLV constitutes 10-16% of total hepatic collagen. COLV expression is upregulated in early stages of hepatic fibrosis and its expression continues to rise as fibrosis progresses to end-stage cirrhosis with a 4-7-fold increase. COLV is ubiquitous in the liver extracellular matrix with COLV immunostaining regularly observed in the space of Disse, stroma of portal tracts, wall of central veins, and cytoplasm of hepatic stellate cells. Enhanced COLV immunostaining occurs in perisinusoidal fibrosis, portal fibrosis, central vein fibrosis, and fibrous septa of septal fibrosis and cirrhosis, coincident with increased presence of COLI, III and VI. Elastin is present in the portal stroma, fibrotic central veins and fibrous septa. In normal rat, COLV constitutes 5.5 % of total hepatic collagen; in experimental cirrhosis, COLV increases 4.6-fold. Collagen fibrils of fibrotic liver are haphazardly arranged and thinner, attributable to COLV’s ability to limit the diameter growth of fibrils resulting from heterotypic fibril formation with COLI. COLV binds TGF-β1, matrix metalloproteinase (MMP)-2, and tissue inhibitor of metalloproteinase-1, regulating their availability for fibrogenesis and fibrolysis. Degradation of COLV by MMP-2 and MMP-9 contributes to extracellular matrix remodeling in fibrosis. Protein fingerprint technique has been applied in the measurement of neoepitopes that serve as fibrosis biomarkers. COLV neo-epitope P5CP-1230 is a useful noninvasive biomarker of liver fibrosis progression and resolution in experimental fibrogenesis and a promising indicator of portal hypertension in alcoholic patients with cirrhosis.

Keywords: Type V collagen; Hepatic fibrosis; Protein fingerprints; Neoepitopes; Liver fibrosis biomarkers


COLV: Type V Collagen; MMP: Matrix Metalloproteinase; ECM: Extracellular Matrix; HSC: Hepatic Stellate Cell; TGF-β: Transforming Growth Factor-β; CCL4: Carbon Tetrachloride; TIMP- 1: Tissue Inhibitor of Metalloproteinase-1; ELISA: Enzyme-Linked Immunosorbent Assay


Type V collagen (COLV) is multifunctional in health, disease and fibrosis. Deficiency of COLV is associated with loss of corneal transparency and classic Ehlers-Danlos syndrome. Increased expression of COLV is found in cancer, inflammation, atherosclerosis, and fibrosis of the lung, skin, kidney, adipose tissue, and liver. These aspects of COLV have recently been reviewed [1]. As a major focus, this article updates COLV’s involvement in hepatic fibrosis of humans and experimental animal models. We will discuss the application of protein fingerprint technology in the measurement of neo-epitope peptides that serve as noninvasive biomarkers for diagnosing and monitoring liver fibrogenesis and fibrosis. Finally, this review summarizes the recent achievements in the use neo-epitope P5CP- 1230, which is a COLV formation marker, as a biochemical marker for the assessment of liver fibrosis progression and resolution in experimental fibrosis as well as an indicator of portal hypertension in patients with alcoholic cirrhosis.


COLV is a regulatory fibril-forming collagen regulating the fibrillogenesis of interstitial fibrillar COLI and III [2], although it has structural and biological properties different from COLI and III. COLV was first isolated from human placentas and organs rich in basement membranes [3,4], and then in human liver [5]. It was later found to be a ubiquitous component of connective tissue matrices. There are at least three different molecular isoforms of COLV: a1(V)2 a2(V), a1(V)3, and a1(V) a2(V) a3(V). These are formed by combinations of three different polypeptide a chains, namely a1(V), a2(V), and a3(V), providing each isoform with a unique chain composition with different functions and tissue distribution [2, 6-8]. The COLV isoform containing the heterotrimeric a1(V)2a 2(V) chains primarily forms heterotypic fibrils with other fibrilforming collagens and is broadly distributed in tissues and is most often referred to as COLV. COLV is also found to a lesser extent in the form of a 1(V)3, referred to as a1(V) homotrimer, which was first observed in cultured Chinese hamster lung cells [9,10]. Uniquely, the a1(V) homotrimer occurs as microfilaments of 5-10 nm in diameter in the skin dermis [11]. The functionally distinct a1(V)a2(V)a3(V) heterotrimer, referred to as COLV isoform containing the a3(V) chain, has been described in the placenta and other tissues: skin, synovial membrane and uterus [12,13].

COLV in Disease and Fibrosis

Deficiency of COLV associated with mutations in the a1(V) or a2(V) genes–COL5A1 and COL5A2— in humans is a cause of classic Ehlers-Danlos syndrome [14,15]. Loss of corneal transparency has been described in COLV-knockout mice [16]. COLV overexpression is found in the timorous skin of mice, cancer of the colon and mammary glands, hepatocellular carcinoma, granulation tissue, inflammation, atherosclerosis and fibrosis of the lung, skin, kidney, adipose tissue, and liver—reviewed in [1]. The present discussion will focus on fibrosis of the liver, updating COLV’s role in the histogenesis of hepatic fibrosis and its value as a noninvasive biochemical marker of hepatic fibrogenesis and fibrosis.

Hepatic Fibrosis

Hepatic COLV content

COLV is a regular component of the extracellular matrix (ECM) proteins of liver tissue. It comprises 16.3% [17] or 10.6% [18] of the total hepatic collagen of the normal human liver. The amount of COLV is about 45% relative to that of COLI or COLIII (0.9 mg/g of liver tissue vs. 2.0 mg/g of liver tissue), the most abundant collagens in the liver. The level of COLV rises about 7-fold in cirrhosis [17,19] and about 4-fold in alcoholic cirrhosis [18], coincident with increases in COLI, III, and IV and a disproportional elevation of COLI. In the human liver, COLV has been reported as being present in the heterotrimeric a1(V)2 a2(V) isoform [18,20]. Interestingly, expression of pro- a2(V) collagen mRNA occurs in human liver at 15 and 17 weeks of gestation [21].

COLV immunohistochemistry of human liver

Immunofluorescent localization of COLV expression in human liver was first reported in the eighties [17,22,23]. In normal liver, COLV was seen as fine interwoven fibrillar materials in the interstitium of portal tracts. Portal vasculatures showed staining for COLV, predominately in the intima, while portal basement membranes were not stained. A weak but uniform COLV immunofluorescence was detected in the sinusoidal lining of the lobules. In liver fibrosis, enhanced COLV immunofluorescence was noted in foci of parenchymal fibrosis with a fine fibrillar network enmeshing the hepatocytes. The thickened wall of central veins (terminal hepatic venules) was strongly stained for COLV. The fibrotic bands of cirrhotic livers showed intense COLV immunofluorescence. No assessment was made of COLV staining of liver cells.

COLV in progressive stages of liver fibrosis

Little work, however, has characterized the lobular distribution of COLV in progressive stages of liver fibrosis and its codistribution with COLI, III and VI, the latter being filamentous [2,24,25]. Because fibrosis of the liver is prevalent in elderly cadavers, even when liver disease is not indicated as the cause of death [26], we have examined the lobular distribution of COLV in elderly cadaveric livers with progressive stages of fibrosis by the immunoperoxidase method [1,27]. In the liver showing nearly normal histology with minimal fibrotic changes, COLV immunostaining is generally uniform along the sinusoidal borders of the lobules—from periportal to pericentral— in most of the specimens. In the lobules, there are perisinusoidal located hepatic stellate cells (HSCs) that contain COLV immunedeposits, which could be a source of COLV deposition in the space of Disse. Figure 1 illustrates the localization of COLV immunostained fibrils to the collagenous matrix of the perisnusiodal space of Disse. COLV is a regular component of the stroma of portal tracts. In portal tract fibrosis, the fibrotic stroma displays prominent COLV staining (Figure 2A and B). Normal central veins are surrounded by a thin rim, which is vividly stained for COLV (Figure 3A). Central vein fibrosis is characterized by a thickening of the vein wall, > 9 μm in thickness [26], which is conspicuously stained for COLV (Figure 3B). COLV immune-deposits are greatly increased in foci of severe perisinusoidal/pericellular fibrosis, and significantly, the fibrotic lesions also show increased staining for COLI, III and VI (Figure 4), demonstrating codistribution of these collagen types, as previously described [1,27]. The fibrous matrices of developing septa and bridging septa of septal fibrosis and the fibrotic bands of cirrhosis revealed an abundant COLV staining, in coincidence with COLI, III and VI (Figure 5). Moreover, as shown in (Figure 6), elastin— detected by resorcin fuchsin stain—is rich in the fibrous septa. Elastin has also been found in the stroma of normal and fibrotic portal tracts and the wall of fibrotic central veins, but it is not detectable in the space of Disse [28]. These immunohistological data point to a role for COLV in integrating fibrillar COL1/III and filamentous COLVI (as well as elastin when present) in the histogenesis of fibrotic lesions and promotion of hepatic fibrosis progression. (Figure 7) schematizes the distribution of COLV fibrils along with other protein fibers in the ECM, forming an elaborate tissue scaffolds, reminiscent of the matrices of fibrous septa.