Overfeeding during a critical postnatal period exacerbates hypothalamic-pituitary-adrenal axis responses to immune challenge: a role for adrenal melanocortin 2 receptors.

Early life diet can critically program hypothalamic-pituitary-adrenal (HPA) axis function. We have previously shown rats that are overfed as neonates have exacerbated pro-inflammatory responses to immune challenge with lipopolysaccharide (LPS), in part by altering HPA axis responses, but how this occurs is unknown. Here we examined neonatal overfeeding-induced changes in gene expression in each step of the HPA axis. We saw no differences in glucocorticoid or mineralocorticoid receptor expression in key regions responsible for glucocorticoid negative feedback to the brain and no differences in expression of key HPA axis regulatory genes in the paraventricular nucleus of the hypothalamus or pituitary. On the other hand, expression of the adrenal melanocortin 2 receptor (MC2R) is elevated after LPS in control rats, but significantly less so in the neonatally overfed. The in vitro adrenal response to ACTH is also dampened in these rats, while the in vivo response to ACTH does not resolve as efficiently as it does in controls. These data suggest neonatal diet affects the efficiency of the adrenally-mediated response to LPS, potentially influencing how neonatally overfed rats combat bacterial infection.

Neonatal overfeeding alters hypothalamic microglial profiles and central responses to immune challenge long-term.

The early life period is one of significant vulnerability to programming effects from the environment. Given the sensitivity of microglial cells to early life programming and to adult diet, we hypothesized overfeeding during the neonatal period would acutely alter microglial profiles within the developing brain, predisposing the individual to a lasting central pro-inflammatory profile that contributes to overactive immune responses long-term. We tested this idea by manipulating litter sizes in which Wistar rat pups were raised, so the pups were suckled in litters of 4 (neonatally overfed) or 12 (control). This manipulation induces obesity and susceptibility to lipopolysaccharide (LPS) long-term. We then examined microglial and central pro-inflammatory profiles during development and in adulthood as well as susceptibility to neuroimmune challenge with LPS. Neonatally overfed rats have evidence of microgliosis in the paraventricular nucleus of the hypothalamus (PVN) as early as postnatal day 14. They also show changes in hypothalamic gene expression at this time, with suppressed hypothalamic interleukin 1ß mRNA. These effects persist into adulthood, with basal PVN microgliosis and increased hypothalamic toll-like receptor 4, nuclear factor κB, and interleukin 6 gene expression. These neonatally overfed rats also have dramatically exacerbated microglial activation in the PVN 24h after an adult LPS challenge, coupled with changes in inflammatory gene expression. Thus, it appears neonatal overfeeding sensitizes PVN microglia, contributing to a basal pro-inflammatory profile and an altered response to a neuroimmune challenge throughout life. It remains to be seen if these effects can be reversed with early interventions.

Neonatal overfeeding attenuates acute central pro-inflammatory effects of short-term high fat diet.

Neonatal obesity predisposes individuals to obesity throughout life. In rats, neonatal overfeeding also leads to early accelerated weight gain that persists into adulthood. The phenotype is associated with dysfunction in a number of systems including paraventricular nucleus of the hypothalamus (PVN) responses to psychological and immune stressors. However, in many cases weight gain in neonatally overfed rats stabilizes in early adulthood so the animal does not become more obese as it ages. Here we examined if neonatal overfeeding by suckling rats in small litters predisposes them to exacerbated metabolic and central inflammatory disturbances if they are also given a high fat diet in later life. In adulthood we gave the rats normal chow, 3 days, or 3 weeks high fat diet (45% kcal from fat) and measured peripheral indices of metabolic disturbance. We also investigated hypothalamic microglial changes, as an index of central inflammation, as well as PVN responses to lipopolysaccharide (LPS). Surprisingly, neonatal overfeeding did not predispose rats to the metabolic effects of a high fat diet. Weight changes and glucose metabolism were unaffected by the early life experience. However, short term (3 day) high fat diet was associated with more microglia in the hypothalamus and a markedly exacerbated PVN response to LPS in control rats; effects not seen in the neonatally overfed. Our findings indicate neonatally overfed animals are not more susceptible to the adverse metabolic effects of a short-term high fat diet but may be less able to respond to the central effects.

Ferritin functions as a proinflammatory cytokine via iron-independent protein kinase C zeta/nuclear factor kappaB-regulated signaling in rat hepatic stellate cells.

UNLABELLED: Circulating ferritin levels reflect body iron stores and are elevated with inflammation in chronic liver injury. H-ferritin exhibits a number of extrahepatic immunomodulatory properties, although its role in hepatic inflammation and fibrogenesis is unknown. Hepatic stellate cells respond to liver injury through production of proinflammatory mediators that drive fibrogenesis. A specific receptor for ferritin has been demonstrated on activated hepatic stellate cells, although its identity and its role in stellate cell activation is unclear. We propose that ferritin acts as a cytokine regulating proinflammatory function via nuclear factor kappaB (NF-kappaB)-regulated signaling in hepatic stellate cell biology. Hepatic stellate cells were treated with tissue ferritin and iron-free apoferritin, recombinant H-ferritins and L-ferritins, to assess the role of ferritin versus ferritin-bound iron in the production of proinflammatory mediators of fibrogenesis, and to determine whether signaling pathways act via a proposed H-ferritin endocytosis receptor, T cell immunoglobulin-domain and mucin-domain 2 (Tim-2). This study demonstrated that ferritin activates an iron-independent signaling cascade, involving Tim-2 independent phosphoinositide 3 (PI3)-kinase phosphorylation, protein kinase C zeta (PKCzeta) and p44/p42-mitogen-activated protein kinase, resulting in p50/p65-NF-kappaB activation and markedly enhanced expression of hepatic proinflammatory mediators interleukin-1beta (IL-1beta), inducible nitric oxide synthase (iNOS), regulated on activation normal T cell expressed and secreted (RANTES), inhibitor of kappa Balpha (IkappaBalpha), and intercellular adhesion molecule 1 (ICAM1). CONCLUSIONS: This study has defined the role of ferritin as a proinflammatory mediator of hepatic stellate cell biology acting through the NF-kappaB signaling pathway, and suggests a potential role in the inflammatory processes associated with hepatic fibrogenesis.