Idiopathic pulmonary fibrosis (IPF) is etiologically complex, with well-documented genetic and nongenetic origins. In this Review, we speculate that the development of IPF requires two hits: the first establishes a vulnerable bronchoalveolar epithelium, and the second triggers mechanisms that reprogram distal epithelia to initiate and perpetuate a profibrotic phenotype. While vulnerability of the bronchoalveolar epithelia is most often driven by common or rare genetic variants, subsequent injury of the bronchoalveolar epithelia results in persistent changes in cell biology that disrupt tissue homeostasis and activate fibroblasts. The dynamic biology of IPF can best be contextualized etiologically and temporally, including stages of vulnerability, early disease, and persistent and progressive lung fibrosis. These dimensions of IPF highlight critical mechanisms that adversely disrupt epithelial function, activate fibroblasts, and lead to lung remodeling. Together with better recognition of early disease, this conceptual approach should lead to the development of novel therapeutics directed at the etiologic and temporal drivers of lung fibrosis that will ultimately transform the care of patients with IPF from palliative to curative.

Maternal obesity and consumption of a high-fat diet significantly elevate risk for pediatric nonalcoholic fatty liver disease (NAFLD), affecting 10% of children in the US. Almost half of these children are diagnosed with nonalcoholic steatohepatitis (NASH), a leading etiology for liver transplant. Animal models show that signs of liver injury and perturbed lipid metabolism associated with NAFLD begin in utero; however, safe dietary therapeutics to blunt developmental programming of NAFLD are unavailable. Using a mouse model of maternal Western-style diet (WD), we previously showed that pyrroloquinoline quinone (PQQ), a potent dietary antioxidant, protected offspring of WD-fed dams from development of NAFLD and NASH. Here, we used untargeted mass spectrometry-based lipidomics to delineate lipotoxic effects of WD on offspring liver and identify lipid targets of PQQ. PQQ exposure during pregnancy altered hepatic lipid profiles of WD-exposed offspring, upregulating peroxisome proliferator-activated receptor (PPAR) α signaling and mitochondrial fatty acid oxidation to markedly attenuate triglyceride accumulation beginning in utero. Surprisingly, the abundance of very long-chain ceramides, important in promoting gut barrier and hepatic function, was significantly elevated in PQQ-treated offspring. PQQ exposure reduced the hepatic phosphatidylcholine/phosphatidylethanolamine (PC/PE) ratio in WD-fed offspring and improved glucose tolerance. Notably, levels of protective n − 3 polyunsaturated fatty acids (PUFAs) were elevated in offspring exposed to PQQ, beginning in utero, and the increase in n − 3 PUFAs persisted into adulthood. Our findings suggest that PQQ supplementation during gestation and lactation augments pathways involved in the biosynthesis of long-chain fatty acids and plays a unique role in modifying specific bioactive lipid species critical for protection against NAFLD risk in later life.

The autonomic regulation of hepatic metabolism offers a novel target for the treatment of non-alcoholic fatty liver disease (NAFLD). However, the molecular characteristics of neurons that regulate the brain-liver axis remain unclear. Since mice lacking neuronal lipoprotein lipase (LPL) develop perturbations in neuronal lipid-sensing and systemic energy balance, we reasoned that LPL might be a component of pre-autonomic neurons involved in the regulation of hepatic metabolism. Here, we show that, despite obesity, mice with reduced neuronal LPL (NEXCreLPL^flox (LPL KD)) show improved glucose tolerance and reduced hepatic lipid accumulation with aging compared to wilt type (WT) controls (LPL^flox). To determine the effect of LPL deficiency on neuronal physiology, liver-related neurons were identified in the paraventricular nucleus (PVN) of the hypothalamus using the transsynaptic retrograde tracer PRV-152. Patch-clamp studies revealed reduced inhibitory post-synaptic currents in liver-related neurons of LPL KD mice. Fluorescence lifetime imaging microscopy (FLIM) was used to visualize metabolic changes in LPL-depleted neurons. Quantification of free vs. bound nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) revealed increased glucose utilization and TCA cycle flux in LPL-depleted neurons compared to controls. Global metabolomics from hypothalamic cell lines either deficient in or over-expressing LPL recapitulated these findings. Our data suggest that LPL is a novel feature of liver-related preautonomic neurons in the PVN. Moreover, LPL loss is sufficient to cause changes in neuronal substrate utilization and function, which may precede changes in hepatic metabolism.

Despite Alzheimer’s disease (AD) disproportionately affecting women, the mechanisms remain elusive. In AD, microglia undergo ‘metabolic reprogramming’, which contributes to microglial dysfunction and AD pathology. However, how sex and age contribute to metabolic reprogramming in microglia is understudied. Here, we use metabolic imaging, transcriptomics, and metabolic assays to probe age-and sex-associated changes in brain and microglial metabolism. Glycolytic and oxidative metabolism in the whole brain was determined using Fluorescence Lifetime Imaging Microscopy (FLIM). Young female brains appeared less glycolytic than male brains, but with aging, the female brain became ‘male-like.’ Transcriptomic analysis revealed increased expression of disease-associated microglia (DAM) genes (e.g., ApoE , Trem2 , LPL ), and genes involved in glycolysis and oxidative metabolism in microglia from aged females compared to males. To determine whether estrogen can alter the expression of these genes, BV-2 microglia-like cell lines, which abundantly express DAM genes, were supplemented with 17β-estradiol (E2). E2 supplementation resulted in reduced expression of DAM genes, reduced lipid and cholesterol transport, and substrate-dependent changes in glycolysis and oxidative metabolism. Consistent with the notion that E2 may suppress DAM-associated factors, LPL activity was elevated in the brains of aged female mice. Similarly, DAM gene and protein expression was higher in monocyte-derived microglia-like (MDMi) cells derived from middle-aged females compared to age-matched males and was responsive to E2 supplementation. FLIM analysis of MDMi from young and middle-aged females revealed reduced oxidative metabolism and FAD+ with age. Overall, our findings show that altered metabolism defines age-associated changes in female microglia and suggest that estrogen may inhibit the expression and activity of DAM-associated factors, which may contribute to increased AD risk, especially in post-menopausal women.

Background: Biliary atresia (BA) is a neonatal fibroinflammatory cholangiopathy of infancy and the most common indication for pediatric liver transplantation. We aimed to define the molecular mechanisms responsible for differences in the rate of disease progression among children with BA. Methods: We performed spatial transcriptomics (ST) analysis on frozen liver tissue at transplant from 14 children: BA with survival with native liver (SNL) 2 years (BA2, n=4), non-BA cholestasis (n=4), and non-diseased donors (n=3). Transcriptional signatures were compared between patient groups by tissue region (scar, hepatocyte, cholangiocyte). Findings were validated in larger patient cohorts that included BA samples at diagnosis. Results: ST analysis of patients with BA1 showed the most aggressive disease phenotype, characterized by reduced hepatocyte zonation, low expression of homeostatic metabolic signatures, and increased scar heterogeneity enriched for pathways including extracellular matrix remodeling, interferon response, and leukocyte activation. Notably, genes involved in SOX4 hepatocyte-to-cholangiocyte reprogramming were most enriched in patients with BA1. Liver immunohistochemistry with in situ mRNA hybridization showed that patients with BA at diagnosis had increased SOX4 quantification as compared with patients with BA at transplant. Lastly, previously published liver bulk RNA-sequencing data demonstrated higher SOX4 gene-set expression in patients with BA at diagnosis with SNL <2 years. Conclusions: Children with BA and worse outcomes exhibit increased SOX4 gene-set expression at diagnosis with greater loss of hepatocyte zonation and immune-driven scar heterogeneity at transplant. Further mechanistic studies are needed to determine whether SOX4-associated biliary reprogramming contributes to maladaptive reparative processes in BA.

Postnatally, glucagon acutely lowers plasma amino acid (AA) concentrations by stimulating hepatic AA catabolism, but its fetal actions remain unclear. This study tested whether a 2 h fetal glucagon infusion would stimulate hepatic AA catabolism and inhibit placental AA transfer. Late-gestation pregnant sheep (0.9 gestation) underwent surgical, vascular catheterization and received fetal glucagon (n = 8) or vehicle infusions (n = 8) in a crossover design with a 48 h washout period. Nutrient uptake and utilization were assessed during each infusion, and fetal liver and placental tissue were collected post-infusion under hyperglucagonemic (n = 4) or vehicle (n = 4) conditions. Glucagon receptor was identified in fetal hepatocyte and trophoblast cells. Glucagon reduced fetal plasma AA concentrations by 20% (p = 0.0103) and increased plasma glucose by 47% (p = 0.0152), leading to a three-fold rise in fetal plasma insulin (p = 0.0459). Hepatic gene expression associated with AA catabolism and gluconeogenesis increased (p < 0.0500) following glucagon infusion, and hepatic metabolomic analysis showed enrichment in AA metabolism pathways. However, placental AA transfer was unaffected by 2 h fetal glucagon infusions. In conclusion, a 2 h glucagon infusion stimulates hepatic glucose production and enhances AA catabolism in the fetal liver, lowering plasma AA concentrations. The primary acute effects of fetal glucagon are hepatic, as placental AA transfer is unchanged.