Editor’s Note: Metabolic dysfunction-associated steatohepatitis (MASH) represents a severe subtype of metabolic dysfunction-associated fatty liver disease (MAFLD), a global public health issue affecting over 25% of the global population. MASH is characterized by typical pathological features, including steatosis, ballooning degeneration, and lobular inflammation. MASH patients can develop liver fibrosis, and progression of fibrosis significantly increases liver-related mortality. Recently, a study led by Dr. Hong You and Dr. Jidong Jia from Beijing Friendship Hospital, Capital Medical University, published in Hepatology International, explored the morphological characteristics associated with fibrosis regression in MASH patients with advanced fibrosis.Previous studies have demonstrated that liver fibrosis can be reversible if the underlying cause is controlled. Wanless and colleagues described the pathological changes associated with cirrhosis regression in chronic hepatitis B (CHB) patients who successfully suppressed or eliminated the virus. They found that delicate fibrous septa were a hallmark of the “hepatic repair complex” (HRC). Building on this theory, Dr. You’s team explored the role of dynamic morphological changes in fibrous septa in assessing fibrosis regression in CHB patients and proposed the “Beijing Classification” (R-I-P classification), where “R” indicates regressive, “P” indicates progressive, and “I” indicates indeterminate.
Based on previous research and the “HRC” theory, the researchers hypothesized that the morphological characteristics of fibrous septa observed in a single liver biopsy could reflect the dynamic changes of fibrosis in MASH. The appearance of regressive (R) septa might suggest a trend towards fibrosis regression in MASH patients, but this requires further validation. Additionally, perisinusoidal (PS) fibrosis, a characteristic of MASH, is difficult to distinguish from thin R-septa. Therefore, a quantitative method is needed to differentiate perisinusoidal fibrosis from R-septa. Furthermore, the mechanisms behind the formation of R-septa remain unclear.
The researchers collected clinical and histological data from 79 patients with biopsy-confirmed advanced liver fibrosis (F3~F4) diagnosed with MAFLD (≥5% steatosis) at the Liver Disease Center of Beijing Friendship Hospital between January 2008 and December 2022.
Using second harmonic generation/two-photon excited fluorescence (SHG/TPEF) technology, the researchers quantitatively identified regressive (R) septa, progressive (P) septa, and perisinusoidal fibrosis. They compared fibrosis levels between patients with and without R-septa using non-invasive methods and explored the key genes involved in the formation of R-septa through transcriptomic analysis.
R-Septa Have Denser Collagen Fibers Compared to Perisinusoidal Fibrosis
SHG/TPEF quantitative collagen analysis revealed significant differences between R-septa, P-septa, and perisinusoidal fibrosis. Morphologically, R-septa had smaller septal areas (10,951 μm² vs. 61,238 μm²), shorter septal lengths (461 μm vs. 623 μm), narrower average septal widths (15 μm vs. 56 μm), and smaller maximum septal widths (37 μm vs. 113 μm) compared to P-septa.
Additionally, R-septa differed morphologically from perisinusoidal fibrosis. The percentage of collagen area (0.42 vs. 0.05), the number of fibers per unit area (14,375 vs. 1,832), the percentage of aggregated collagen (0.38 vs. 0.03), and the percentage of scattered collagen (0.03 vs. 0.02) were all higher in R-septa than in perisinusoidal fibrosis, while the percentage of cellular area (0.07 vs. 0.66) was lower (P < 0.05).
The researchers also found that the collagen fibers in R-septa were denser than in perisinusoidal fibrosis, with the average minimum distance between collagen fibers in R-septa being significantly smaller than in perisinusoidal fibrosis (8.9 vs. 13, P < 0.001, AUROC = 0.838).
Dynamic Changes in Fibrous Septa Observed in MASH Patients with Fibrosis Regression
The researchers observed 22 cases with two biopsies. Nine cases exhibited fibrosis regression, including six patients with baseline fibrosis levels greater than F3. Among these six patients, three achieved fibrosis regression through lifestyle changes (from F4 to F3). After a median follow-up of 27 months, their weight had decreased by 15.7%, 10.4%, and 12.9% compared to their initial weight.
As fibrosis regressed, the shape of the fibrous septa changed from wide and loose to thin and dense. According to the “Beijing Classification” proposed by the researchers, these thin regressive (R) septa are a hallmark of fibrosis regression. In the two liver biopsies, R-septa appeared in all three patients with fibrosis regression, while no R-septa were observed in the three patients without fibrosis regression.
Comparison of Non-Invasive Fibrosis Markers in Patients With and Without R-Septa
The researchers divided the patients into two groups based on septal morphology: the R-septa group (n=10, 12.7%) and the non-R-septa group (n=69, 87.3%). Patients with R-septa had lower scores in most non-invasive fibrosis markers, particularly the LSM-TE value (12.3 kPa vs. 19.4 kPa, P=0.010) and FAST score (0.43 vs. 0.70, P=0.003).
To account for the effect of different fibrosis stages, the researchers compared patients with F3 fibrosis in both groups and found that the FAST score was significantly lower in the R-septa group than in the non-R-septa group. No significant differences were found between the FAST scores of F3 and F4 patients in the non-R-septa group.
Additionally, transcriptomic analysis showed that the expression of five fibrotic hub genes, Col3A1, BGN, Col4A1/THBS2, and Col4A2, was significantly reduced in the R-septa group.
The researchers concluded that quantitative SHG/TPEF technology could distinguish R-septa from P-septa and perisinusoidal fibrosis. The appearance of R-septa may indicate a tendency for fibrosis regression in MASH patients.
