Liver injury instigates a proinflammatory response in tissue-resident macrophages, called Kupffer cells (KCs), resulting in the recruitment of monocytes and neutrophils. The high energy demand required for a rapid proinflammatory response in macrophages like KCs is achieved through metabolic reprogramming. This is supported by increased glycolysis. On the other hand, injury resolution requires hepatic macrophages to undergo an anti-inflammatory polarization, which relies on oxidative phosphorylation (OXPHOS). In addition to shifts in mechanisms of adenosine triphosphate (ATP) production, lipid metabolic reprogramming supplies metabolic intermediates and lipids for membrane remodeling and the production of inflammatory mediators. AMP-activated protein kinase (AMPK) is a master metabolic regulator that influences the metabolic reprogramming of macrophages. While AMPK activation promotes an anti-inflammatory polarization, disruption of activity exacerbates proinflammatory signaling. For this thesis work, we addressed whether macrophage AMPK is protective against liver injury by altering immunometabolism. Specifically, we investigated this question in the context of chronic (nonalcoholic steatohepatitis (NASH)) and acute (acetaminophen (APAP) overdose) liver injury.
While APAP overdose is a robust and directly translational model of acute injury, models of NASH-induced hepatic fibrosis rely on nutrient-deficient diets like the choline-deficient high-fat
diet (CDAHFD) or genetic manipulation. Despite the utility of these models, they seldom mirror
the pathogenesis of human NASH, with diets like CDAHFD being completely dissociated from metabolic syndrome. Moreover, models are required to address the divergence between male and
female mice. Recently, there has been a shift towards addressing other variables that drive inflammation and metabolism. At room temperature (RT) (22 °C), mice experience cold stress that alters various biological functions. Cold stress drives brown adipose tissue (BAT) activation and upregulates corticosterone production and immunosuppression, all processes that blunt NASH progression. Giles et al. (2016) demonstrated that housing mice at thermoneutrality (TN) (30 °C) exacerbated metabolic-dysfunction associated fatty liver disease (MAFLD) progression toward NASH in both male and female mice. Since then, we and others have implemented TN housing with different dietary interventions and mice strains. We determined that 16-week Western diet (WD) feeding of male and female mice at 29 °C was insufficient to drive hepatic fibrosis, however alterations in glucose tolerance and elevated liver injury enzymes as well as profibrotic gene expression in male mice may indicate that a longer timeline is necessary (24 weeks).
Given that our TN NASH model did not produce hepatic fibrosis, we implemented the CDAHFD
to investigate macrophage AMPK in chronic liver injury. Male and female AMPK Flox (Prkaa1 fl/fl/Prkaa2 fl/fl) and MacKO (Flox-LysM-Cre+) mice were fed CDAHFD for 8 weeks. In this time frame, CDAHFD produces a lean euglycemic phenotype with hepatic steatosis, inflammation, and fibrosis, to which AMPK MacKO had no influence. Moreover, intervention with a low dose of metformin had no effect, contrary to the reduction in hepatic steatosis observed in HFD-fed mice. Although macrophage AMPK is dispensable in the CDAHFD model of chronic liver injury, acute liver injury needed to be addressed. We found that priming with systemic activation of a direct AMPK activator MK-8722 did not influence hepatic injury and necrosis in our model of APAP-induced liver injury (AILI). Moreover, deletion of hepatocellular AMPK (Flox-Alb-Cre+) or AMPK MacKO did not influence injury at 24 hours post overdose. Despite the lack of effect of systemic AMPK activation, we were interested in a nanoparticle-based targeting of direct AMPK activator MK-8722 (NP-MK8722) delivery. We determined that PLGA-PEG nanoparticles (NPs) accumulated in hepatic macrophages as early as 2 hours post-injection, but NP-MK8722 did not alter hepatic necrosis, injury, or immune infiltration.
Overall, my thesis work has advanced our knowledge of the effects of housing temperatures on NASH pathogenesis. Moreover, we are the first to address the effects of macrophage AMPK signaling in NASH and AILI. This is especially true for assessing how AMPK deficiency and targeted activation influences KC immunometabolism during injury.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/45798 |
| Date | 05 January 2024 |
| Creators | Rolim Cavalcanti Nunes, Julia |
| Contributors | Fullerton, Morgan |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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