Serpins

Metabolic dysfunction-associated steatohepatitis (MASH) is associated with the activation of Kupffer cells (KCs) and hepatic stellate cells, at which point a metabolically stressed hepatocyte becomes integral to the progression of the disease. We observed a significant reduction in the level of alpha-1-antitrypsin (A1AT), a hepatocyte-derived secreted factor, in both patients with MASH and mice fed a fast-food diet (FFD). KC-mediated hepatic inflammation, most notably IL-1β, led to the transcriptional inhibition of A1AT by HNF4α. In quintuple Serpina1a-e knockout mice, ablation of A1AT worsened MASH through increased activity of proteinase 3 (PR3), a proinflammatory protease produced by F4/80hi/CD11blow/TIM4-/CCR2+ monocyte-derived KCs (MoKCs). Conversely, A1AT restoration or PR3 inhibition mitigated MASH progression. A PR3-bound cytokine array identified IL-32 as a key factor associated with MASH. Combining IL-32 with SERPINA1, the gene encoding A1AT, synergistically predicted patients at risk of MASH through univariate logistic regression analysis. Furthermore, in vivo overexpression of IL-32γ alleviated MASH induced by FFD. However, additional knockout of A1AT increased PR3 activity, consequently abolishing the anti-MASH effects of IL-32γ. Blocking PR3-mediated IL-32γ cleavage via the V104A mutation sustained its protective actions, while the PR3-cleaved C-terminal fragment activated KCs. Additionally, after cleavage, the antifibrogenic effect of IL-32γ is lost, resulting in a failure to prevent the activation of hepatic stellate cells. This study highlights the critical role of hepatocyte-derived A1AT in the PR3/IL-32γ axis during MASH development. Strategies to correct A1AT dysregulation, such as A1AT supplementation or PR3 inhibition with sivelestat, may offer protection against the development and progression of MASH and fibrosis. Elevated hepatic IL-1β levels in MASH lead to the downregulation of A1AT via the transcription factor HNF4α, resulting in increased recruitment of proinflammatory MoKCs and heightened PR3 activity. PR3 cleaves IL-32γ, transforming it from an anti-inflammatory and antifibrogenic cytokine into a potent activator of KCs and failing to prevent HSC activation. This cascade amplifies liver inflammation and fibrosis, suggesting that targeting the A1AT/PR3/IL-32γ axis could be a strategy for treating MASH.

How cellular metabolism facilitates tissue-resident macrophage maintenance remains elusive. Here we show that visceral adipose tissue (VAT)-resident macrophages, unlike monocyte-derived macrophages, are enriched with mitochondrial-specific antioxidant enzymes restraining inflammation and promoting VAT homeostasis and insulin sensitivity. Additionally, VAT resident macrophages express high levels of plasminogen activator inhibitor type 2, encoded by SerpinB2, which is involved in the blood coagulation cascade. SerpinB2 promotes adipose resident macrophage survival by regulating mitochondrial oxidative phosphorylation and preventing the release of pro-apoptotic cytochrome c from the mitochondria into the cytoplasm via antioxidant glutathione production. Chronic inflammation, such as obesity, diminishes SerpinB2 expression in VAT macrophages in patients and mice, leading to the decline of this macrophage subset. Mechanistically, interferon-γ elevation in diabetes induces Ikaros, a transcriptional suppressor, which binds to the SerpinB2 promoter and decreases SerpinB2 expression. Congruently, selective depletion of the IFN-γ receptor in myeloid cells or supplementation of macrophage-specific SerpinB2 deficient mice with N-acetylcysteine, a glutathione precursor, restores VAT resident macrophage survival, decreases adipocyte size, and improves glucose tolerance and insulin sensitivity. Our data thus reveal an unexpected function of SerpinB2 in the regulation of mitochondrial function and survival of tissue-resident macrophages.

Alpha-1 antitrypsin deficiency (AATD) constitutes an inborn disorder arising due to mutations in alpha-1 antitrypsin (AAT), a secreted protease inhibitor produced primarily in hepatocytes. It leads to diminished serum AAT levels, and this loss-of-function predisposes to chronic obstructive pulmonary disease and lung emphysema. The characteristic Pi*Z mutation results in hepatic Z-AAT accumulation. In its homozygous form (Pi*ZZ genotype), it is responsible for the majority of severe AATD cases and can cause both pediatric and adult liver disease, while the heterozygous form (Pi*MZ) is considered a disease modifier that becomes apparent primarily in the presence of other comorbidities or risk factors. In the current review, we collate conditions associated with AATD, introduce typical AAT variants, and discuss our understanding of disease pathogenesis. We present both cross-sectional and longitudinal data informing about the natural disease history and noninvasive tools that can be used for disease stratification as well as a basis for disease monitoring. Given that AATD-associated liver disease is highly heterogeneous, we discuss the risk factors affecting disease progression. While the loss-of-function lung disease is treated by weekly intravenous administration of purified AAT, recombinant modified AAT and oral protease inhibitors are currently in clinical trials. Among the liver candidates, small interfering RNA fazirsiran efficiently suppresses AAT production and is currently in phase 3 clinical trial, while several other genetic approaches, such as RNA editing, are at earlier stages. In summary, AATD represents a systemic disorder increasingly seen in the hepatologic routine and requiring thorough interdisciplinary care, since the currently ongoing clinical trials often address only one of the organs it affects.