Thursday, November 21, 2024
11/21/2024
Project Summary Chronic, low-grade inflammation (inflammaging) is a hallmark of aging and is one of the ‘seven pillars of aging’ associated with age-related diseases. Liver aging is characterized by an increase in chronic inflammation that is associated with chronic liver diseases (CLD), a leading cause of liver transplantation and mortality in the elderly. Liver inflammation and CLD are proposed to promote neuroinflammation and cognitive impairment in humans, supporting a role of liver in cognitive dysfunction. Despite the link between the liver-brain inflammation axis, pathway(s) promoting liver inflammation or how liver aging contributes to neuroinflammation or cognitive deficit is not known. Necroptosis is a cell death pathway that releases damage associated molecular patterns (DAMPs such as HMGB1) and promote inflammation through the activation innate immune cells. We found that necroptosis increases with age in the liver of mice, and inhibiting necroptosis (using Ripk3-/- or Mlkl-/- mice or pharmacological inhibitor) reduced HMGB1, proinflammatory M1 macrophages, proinflammatory cytokines, and liver pathology (steatosis and fibrosis) in the liver of old mice. Necroptosis inhibition improved autophagy and reduced cellular senescence, key pathways associated with inflammaging and liver pathology. Importantly, activating necroptosis specifically in hepatocytes of adult mice (7-month-old) impaired autophagy and increased cellular senescence, macrophage numbers, and proinflammatory cytokines in the liver. Together, these data support the conclusion that necroptosis is a key factor in liver inflammation and pathology through activation of macrophages and senescence in the liver. Our data show that hepatocyte-specific necroptosis increases neuroinflammation (proinflammatory cytokines and glial cell activation) and levels of circulating HMGB1, a known mediator of neuroinflammation. Neuroinflammation is a significant contributor to cognitive decline, and we found that hepatocyte necroptosis reduced nest building capacity, an early indicator of behavioral deficits in mice. Given that hepatocytes undergo age-related necroptosis and are the primary source to circulating HMGB1 in liver diseases, the central hypothesis of the proposal is that necroptosis activation specifically in hepatocytes will increase HMGB1 release from hepatocytes that will increase liver inflammation by activating macrophages, and liver pathology by increasing cellular senescence. Circulating HMGB1, in turn, will promote neuroinflammation and cognitive impairment through systemic effects. We will test this hypothesis using novel mouse models that allow us to either inhibit or activate necroptosis specifically in hepatocytes. Aim 1. Determine the role of hepatocyte specific necroptosis on macrophage activation and liver inflammation; Aim 2. Determine the role of hepatocyte specific necroptosis on cellular senescence and liver pathology; Aim 3. Determine the effects of hepatocyte specific necroptosis on neuroinflammation and brain function.
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