Leptin has not evolved as a therapeutic modality for the treatment of obesity due to the prevalence of leptin resistance in a majority of the obese population. Nevertheless, the molecular mechanisms of leptin resistance remain poorly understood. Here, we show that increased endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR) in the hypothalamus of obese mice inhibits leptin receptor signaling. The genetic imposition of reduced ER capacity in mice results in severe leptin resistance and leads to a significant augmentation of obesity on a high-fat diet. Moreover, we show that chemical chaperones, 4-phenyl butyric acid (PBA), and tauroursodeoxycholic acid (TUDCA), which have the ability to decrease ER stress, act as leptin-sensitizing agents. Taken together, our results may provide the basis for a novel treatment of obesity.

To determine whether the type 2 iodothyronine deiodinase (D2), the principal central nervous system enzyme converting T(4) to biologically active T(3), is regulated in tanycytes by immune activation, D2 activity was measured in the mediobasal hypothalamus (MBH) 4, 12, and 24 h after administration of bacterial lipopolysaccharide (LPS) and compared with D2 levels in the cortex and anterior pituitary of rats. In contrast to D2 activity in the cortex and anterior pituitary that showed a steady linear increase over 24 h, which was coincident with a decline in thyroid hormone and TSH levels, D2 activity peaked in the MBH 12 h after LPS administration. By in situ hybridization, the increased D2 mRNA synthesis induced by LPS was specifically localized to tanycytes lining the third ventricle. In vitro assays in HC11 and HEK-293 cells demonstrated that the p65 subunit of nuclear factor-kappaB markedly increased both rat and human D2 genes (dio2) as analyzed by promoter assays. No activation of human dio2 was observed when an 83-bp minimal promoter was used. We propose that LPS or LPS-induced cytokines directly induce D2 mRNA in tanycytes. The ensuing MBH-specific D2-mediated local thyrotoxicosis may suppress the hypothalamus-pituitary-thyroid axis by local feedback inhibition of hypophysiotropic TRH and/or TSH and contribute to the mechanism of central hypothyroidism associated with infection.

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Parkinsonism is a progressive motor disease that affects 1.5 million Americans and is the second most common neurodegenerative disease after Alzheimer’s. Typical neuropathological features of Parkinson’s disease (PD) include degeneration of dopaminergic neurons located in the pars compacta of the substantia nigra that project to the striatum (nigro-striatal pathway) and depositions of cytoplasmic fibrillary inclusions (Lewy bodies) which contain ubiquitin and α-synuclein. The cardinal motor signs of PD are tremors, rigidity, slow movement (bradykinesia), poor balance, and difficulty in walking (Parkinsonian gait). In addition to motor symptoms, non-motor symptoms that include autonomic and psychiatric as well as cognitive impairments are pressing issues that need to be addressed. Several different mechanisms play an important role in generation of Lewy bodies; endoplasmic reticulum (ER) stress induced unfolded proteins, neuroinflammation and eventual loss of dopaminergic neurons in the substantia nigra of mid brain in PD. Moreover, these diverse processes that result in PD make modeling of the disease and evaluation of therapeutics against this devastating disease difficult. Here, we will discuss diverse mechanisms that are involved in PD, neuroprotective and therapeutic strategies currently in clinical trial or in preclinical stages, and impart views about strategies that are promising to mitigate PD pathology.

Because alpha-MSH has a potent stimulatory action on hypophysiotropic TRH synthesizing neurons in the hypothalamic paraventricular nucleus (PVN), preventing the effects of fasting on the gene expression of the TRH prohormone (proTRH), we hypothesized that agouti-related protein (AGRP), a melanocortin receptor antagonist, may exert a central inhibitory action on these neurons. To test the hypothesis, the effects of intracerebroventricularly administered AGRP on circulating thyroid hormone levels and proTRH mRNA in the hypothalamic paraventricular nucleus (PVN) were compared with the effects of the recently described central inhibitor of the HPT axis, neuropeptide Y (NPY). AGRP administration increased food consumption and weight gain, suppressed circulating levels of thyroid hormones (T(3) and T(4)), and resulted in an inappropriately normal TSH. These alterations were associated with a significant suppression of proTRH mRNA in the PVN, indicating that AGRP infusion resulted in a state of central hypothyroidism. While similar observations were made in the NPY-infused animals, AGRP-treated animals had higher feeding efficiency, higher T(4) levels, and lower type 2 iodothyronine deiodinase levels in brown adipose tissue than NPY-infused animals. These data demonstrate that AGRP and NPY have a similarly potent inhibitory action on the proTRH gene expression of hypophysiotropic neurons, indicating that both AGRP and NPY may play a major role in the inhibition of the HPT axis during fasting.

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Various iron-oxide nanoparticles have been in use for a long time as therapeutic and imaging agents and for supplemental delivery in cases of iron-deficiency. While all of these products have a specified size range of ∼ 40 nm and above, efforts are underway to produce smaller particles, down to ∼ 1 nm. Here, we show that after a 24-h exposure of SHSY-5Y human neuroblastoma cells to 10 μg/ml of 10 and 30 nm ferric oxide nanoparticles (Fe-NPs), cellular dopamine content was depleted by 68 and 52 %, respectively. Increases in activated tyrosine kinase c-Abl, a molecular switch induced by oxidative stress, and neuronal α-synuclein expression, a protein marker associated with neuronal injury, were also observed (55 and 38 % percent increases, respectively). Inhibition of cell-proliferation, significant reductions in the number of active mitochondria, and a dose-dependent increase in reactive oxygen species (ROS) were observed in neuronal cells. Additionally, using a rat in vitro blood-brain barrier (BBB) model, a dose-dependent increase in ROS accompanied by increased fluorescein efflux demonstrated compromised BBB integrity. To assess translational implications, in vivo Fe-NP-induced neurotoxicity was determined using in vivo MRI and post-mortem neurochemical and neuropathological correlates in adult male rats after exposure to 50 mg/kg of 10 nm Fe-NPs. Significant decrease in T 2 values was observed. Dynamic observations suggested transfer and retention of Fe-NPs from brain vasculature into brain ventricles. A significant decrease in striatal dopamine and its metabolites was also observed, and neuropathological correlates provided additional evidence of significant nerve cell body and dopaminergic terminal damage as well as damage to neuronal vasculature after exposure to 10 nm Fe-NPs. These data demonstrate a neurotoxic potential of very small size iron nanoparticles and suggest that use of these ferric oxide nanoparticles may result in neurotoxicity, thereby limiting their clinical application.