Collagen Formation Assessed by N-Terminal Propeptide of Type 3 Procollagen Is a Heritable Trait and Is Associated With Liver Fibrosis Assessed by Magnetic Resonance Elastography

Abstract

N-terminal propeptide of type 3 procollagen (PRO-C3) is a biomarker of liver fibrosis in nonalcoholic fatty liver disease (NAFLD). This study examines the association between PRO-C3 concentration and liver fibrosis assessed by magnetic resonance elastography (MRE)-measured stiffness (MRE-stiffness) and the heritability of PRO-C3 concentration in a cohort of twins and families with and without NAFLD. We performed a cross-sectional analysis of a well-characterized prospective cohort of 306 participants, including 44 probands with NAFLD-cirrhosis and their 72 first-degree relatives, 24 probands with NAFLD without advanced fibrosis and their 24 first-degree relatives, and 72 controls without NAFLD and their 72 first-degree relatives. Liver steatosis was assessed by magnetic resonance imaging proton density fat fraction, and liver fibrosis was assessed by MRE-stiffness. Serum PRO-C3 was assessed by competitive, enzyme-linked immunosorbent assay. We assessed the familial correlation of PRO-C3 concentration, the shared gene effects between PRO-C3 concentration and liver steatosis and fibrosis, and the association between PRO-C3 concentration and genetic variants in the patatin-like phospholipase domain-containing 3 (PNPLA3), transmembrane 6 superfamily member 2 (TM6SF2), membrane-bound O-acyltransferase domain-containing (MBOAT), and glucokinase regulator (CGKR) genes. In multivariable-adjusted models including age, sex, body mass index, and ethnicity, serum PRO-C3 correlated strongly with liver fibrosis (r² = 0.50, P < 0.001) and demonstrated robust heritability (h² , 0.36; 95% confidence interval [CI], 0.07, 0.59; P = 0.016). PRO-C3 concentration and steatosis had a strong genetic correlation (shared genetic determination: 0.62; 95% CI, 0.236, 1.001; P = 0.002), whereas PRO-C3 concentration and fibrosis had a strong environmental correlation (shared environmental determination: 0.55; 95% CI, 0.317, 0.717; P < 0.001). PRO-C3 concentrations were higher in carriers of the TM6SF2 rs58542926-T allele compared with noncarriers: 15.7 (± 10.5) versus 10.8 (± 5.7) ng/L (P = 0.047). Conclusion: Serum PRO-C3 correlates with MRE-assessed fibrosis, is heritable, shares genetic correlation with liver steatosis and shares environmental correlation with liver fibrosis. PRO-C3 concentration appears to be linked to both fibrosis and steatosis and increased in carriers of the TM6SF2 rs58542926 risk allele.

Figure 1.. Correlation between PRO-C3 and other ECM remodeling biomarkers and liver fibrosis assessed by MRE

*rank coefficient an p-value determined using partial correlation adjusted for age, sex, BMI, and Hispanic ethnicity are shown for PRO-C3, C3M, C4M2 and P4NP7S.

Figure 2.. Serum PRO-C3 levels are significantly increased in NAFLD-cirrhosis

Median and 95% confidence interval of PRO-C3 levels across 3 independent group: non-NAFLD control (blue), proband with NAFLD without advanced fibrosis (green), and NAFLD-cirrhosis (pink) are shown. P-value were determined using nonparametric Mann-Whitney test

Figure 3.. Familial and Twinship correlation of PRO-C3 levels

Twinship correlations; A. The monozygotic twin-pairs showed a robust correlation in PRO-C3 (r2=0.58; p <0.001) but not B. the dizygotic twin-pairs (r= 0.30; p=0.15), showing that PRO-C3 concentration is a heritable trait. C. Familial correlation shown as Spearman correlation coefficient and 95% confidence interval within random unrelated pairs (white dots, n=135 pairs) and within related pairs (black squares, n=115 pairs) as a significant association was found between PRO-C3 and NAFLD-cirrhosis, individuals with cirrhosis were excluded from the analysis. Spearman coefficient values are indicated in the in Y axis legend (unrelated/related pairs), *p<0.05, **p<0.01, ***p<0.001.

Figure 4.. Shared genetic and environmental determination of PRO-C3 and higher PRO-C3 levels in TM6SF2 risk allele

A. AE Model for genetic correlation between PRO-C3 and hepatic steatosis assessed by MRI-PDFF and environmental correlation between PRO-C3 and liver fibrosis assessed by MRE. B. Mean and standard deviation of PRO-C3 concentration in TM6SF2 rs5854296 rare allele T carriers compared to non-carriers. *P-value derived from Generalized Estimating Equations to account for correlation within twinship adjusted for age and sex.