Morphine-Induced Modulation of Endolysosomal Iron Mediates Upregulation of Ferritin Heavy Chain in Cortical Neurons

Abstract

HIV-associated neurocognitive disorders (HAND) remain prevalent and are aggravated by µ-opioid use. We have previously shown that morphine and other µ-opioids may contribute to HAND by inhibiting the homeostatic and neuroprotective chemokine receptor CXCR4 in cortical neurons, and this novel mechanism depends on upregulation of the protein ferritin heavy chain (FHC). Here, we examined the cellular events and potential mechanisms involved in morphine-mediated FHC upregulation using rat cortical neurons of either sex in vitro and in vivo. Morphine dose dependently increased FHC protein levels in primary neurons through µ-opioid receptor (µOR) and Gαi-protein signaling. Cytoplasmic FHC levels were significantly elevated, but nuclear FHC levels and FHC gene expression were unchanged. Morphine-treated rats also displayed increased FHC levels in layer 2/3 neurons of the prefrontal cortex. Importantly, both in vitro and in vivo FHC upregulation was accompanied by loss of mature dendritic spines, which was also dependent on µOR and Gαi-protein signaling. Moreover, morphine upregulated ferritin light chain (FLC), a component of the ferritin iron storage complex, suggesting that morphine altered neuronal iron metabolism. Indeed, prior to FHC upregulation, morphine increased cytoplasmic labile iron levels as a function of decreased endolysosomal iron. In line with this, chelation of endolysosomal iron (but not extracellular iron) blocked morphine-induced FHC upregulation and dendritic spine reduction, whereas iron overloading mimicked the effect of morphine on FHC and dendritic spines. Overall, these data demonstrate that iron mediates morphine-induced FHC upregulation and consequent dendritic spine deficits and implicate endolysosomal iron efflux to the cytoplasm in these effects.

Deletion of ferritin H in neurons counteracts the protective effect of melatonin against traumatic brain injury‐induced ferroptosis

“…The present results extend these studies to the brain under physiological and pathological conditions. In the CNS, Fth is mainly in neurons, whereas Ftl is enriched in microglia cells 17,18 . To characterize the functional role of ferritin H (Fth) in the brain, we generated neuron‐specific Fth conditional knockout mice ( Fth‐ KO) in the present study.…”

“…Global loss of Fth in mice causes early embryonic lethality, 15 but Ftl deletion is not embryonically lethal in mice, 16 suggesting that the latter is not a functionally redundant gene. In brain tissue, microglia cells are rich in Ftl‐chains, whereas Fth is expressed predominantly in the neurons 17,18 . Notably, we and others previously tried to generate conditional Fth knockout mice, which develop tissue damage in solid organs, including the liver, 19 kidneys, 20 and heart 21 .…”

Mechanisms of neuronal dysfunction in HIV-associated neurocognitive disorders

“…Ferritin heavy chain was also upregulated by the inflammatory mediators TNFα and IL-1β [ 90 ]. Interestingly, morphine-mediated ferritin heavy chain upregulation and subsequent dendritic spine deficits occurred via a pathway that modulates endolysosomal iron stores [ 186 ]. These studies indicate that morphine and potentially other µ-opioid agonists produce synaptodendritic damage by dysregulating neuronal iron metabolism.…”

Cerebrospinal Fluid Iron Status Predicts Neurocognitive Performance Over Time in Adults with HIV

“…Either H-ferritin-deficient or H-ferritin-overexpressing mice may show evidence of iron deficiency in the brain, and the former also exhibit increased oxidative stress [29, 39, 40]. The beneficial effects of H-ferritin that we found in people with HIV may, however, be outweighed by iron-mediated oxidative stress in the setting of opioid drug abuse, which may increase endolysosomal iron (accompanied by neuronal H-ferritin upregulation) and dendritic spine loss [41]. Since the effect of transferrin was primarily in individuals with viremia, it is possible that this protein protects against oxidative stress by reducing NTBI entry into the brain during inflammation and preserving the iron supply to neurons and immature or differentiating oligodendrocytes, which depend upon transferrin-bound iron.…”