SOX9 promotes hepatocyte proliferation via upregulating TGF-α expression during liver regeneration

The liver possesses a remarkable capacity for regeneration. Previous studies have shown that SOX9/HNF4α double-positive hepatocytes play a role in chronic liver injury. Furthermore, the deletion of HNF4α results in prolonged hepatocyte proliferation following partial hepatectomy. However, the precise role of SOX9 in liver regeneration remains poorly understood.

We established acute liver injury models using standard partial hepatectomy (sHx), extended partial hepatectomy (eHx), and intraperitoneal injection of carbon tetrachloride (CCl₄). To investigate the interplay between HNF4α and SOX9, we employed hepatocyte-specific Hnf4α knockout (Hnf4α^HKO) and Sox9 knockout (Sox9^HKO) mice. We assessed how SOX9 influenced liver regeneration in Sox9^HKO and SOX9-overexpressing (Sox9^HOE) mice.

Our study found that SOX9 expression was increased, while HNF4α expression decreased in the priming phase of acute liver injury. HNF4α suppressed SOX9 expression by upregulating miR-124/381 in hepatocytes. Deletion of SOX9 in hepatocytes resulted in a reduced liver-to-body weight ratio and impaired hepatocyte proliferation in both sHx- and CCl₄-treated mice. Conversely, hepatocyte-specific SOX9 overexpression improved survival rates in eHx-treated mice. Single-nucleus RNA sequencing of liver tissue and bulk RNA sequencing of hepatocytes from sHx-treated Sox9^HKO mice revealed that SOX9 upregulated TGF-α expression in hepatocytes. Co-culture experiments further indicated that SOX9 overexpression enhanced the hepatocyte proliferation by promoting TGF-α secretion. Importantly, inhibiting TGF-α-induced EGFR activation partially reduced the pro-proliferative effects of SOX9 on hepatocytes and the survival rates by SOX9 overexpression in eHx-treated mice.

Our findings revealed that HNF4α negatively regulates SOX9 and demonstrated that SOX9 promotes hepatocyte proliferation by upregulating TGF-α levels, ultimately enhancing liver regeneration.