The Preventive Effects of Salubrinal against Pyrethroid-Induced Disruption of Adult Hippocampal Neurogenesis in Mice.

Environmental factors, including pesticide exposure, have been identified as substantial contributors to neurodegeneration and cognitive impairments. Previously, we demonstrated that repeated exposure to deltamethrin induces endoplasmic reticulum (ER) stress, reduces hippocampal neurogenesis, and impairs cognition in adult mice. Here, we investigated the potential relationship between ER stress and hippocampal neurogenesis following exposure to deltamethrin, utilizing both pharmacological and genetic approaches. To investigate whether ER stress is associated with inhibition of neurogenesis, mice were given two intraperitoneal injections of eIf2α inhibitor salubrinal (1 mg/kg) at 24 h and 30 min prior to the oral administration of deltamethrin (3 mg/kg). Salubrinal prevented hippocampal ER stress, as indicated by decreased levels of C/EBP-homologous protein (CHOP) and transcription factor 4 (ATF4) and attenuated deltamethrin-induced reductions in BrdU-, Ki-67-, and DCX-positive cells in the dentate gyrus (DG) of the hippocampus. To further explore the relationship between ER stress and adult neurogenesis, we used caspase-12 knockout (KO) mice. The caspase-12 KO mice exhibited significant protection against deltamethrin-induced reduction of BrdU-, Ki-67-, and DCX-positive cells in the hippocampus. In addition, deltamethrin exposure led to a notable upregulation of CHOP and caspase-12 expression in a significant portion of BrdU- and Ki-67-positive cells in WT mice. Conversely, both salubrinal-treated mice and caspase-12 KO mice exhibited a considerably lower number of CHOP-positive cells in the hippocampus. Together, these findings suggest that exposure to the insecticide deltamethrin triggers ER stress-mediated suppression of adult hippocampal neurogenesis, which may subsequently contribute to learning and memory deficits in mice.

Exposure to deltamethrin at the NOAEL causes ER stress and disruption of hippocampal neurogenesis in adult mice.

In addition to age and traumatic brain injury, environmental exposure to pesticides is a potential risk factor for neurodegenerative diseases and cognitive impairments in humans. Deltamethrin is a type II pyrethroid insecticide widely used in agriculture and homes for pest control. Previously, we reported that repeated exposure of mice to 3 mg/kg deltamethrin for 30 or 60 days caused a marked increase in the endoplasmic reticulum (ER) stress and reduced adult hippocampal neurogenesis that was accompanied by impaired learning and memory. However, it is unknown whether an acute exposure to low doses of deltamethrin elicits similar effects. Here, we sought to characterize the dose-related effects of deltamethrin on ER stress and hippocampal neurogenesis at different time points following acute exposure. Following oral administration of 0, 0.3, 1, or 3 mg/kg deltamethrin, doses below, at, and above the acute NOAEL, mice were euthanized at 24 h, 48 h, 7 d, or 14 d to assess the acute and intermediate-term effects of deltamethrin on neural progenitor cells (NPCs). Deltamethrin at both 1 and 3 mg/kg elicited ER stress response and activation of apoptotic signaling. Data revealed that a dose as low as 1 mg/kg of deltamethrin, considered the acute NOAEL, produced a significant reduction in BrdU+ and Ki-67+ neural stem cells in the subgranular zone of the dentate gyrus of the hippocampus as early as 48 h after exposure. Furthermore, mice treated with 1 and 3 mg/kg deltamethrin exhibited a decreased number of immature neurons, determined by counting DCX-positive cells 7 days after exposure. These data establish that 0.3 mg/kg should be considered a NOAEL and that the previously established acute NOAEL of 1 mg/kg shows significant effects on ER stress and apoptotic pathways accompanied by deficits in aspects of adult hippocampal neurogenesis.

Deltamethrin Exposure Inhibits Adult Hippocampal Neurogenesis and Causes Deficits in Learning and Memory in Mice.

Deficits in learning and memory are often associated with disruption of hippocampal neurogenesis, which is regulated by numerous processes, including precursor cell proliferation, survival, migration, and differentiation to mature neurons. Recent studies demonstrate that adult born neurons in the dentate gyrus (DG) in the hippocampus can functionally integrate into the existing neuronal circuitry and contribute to hippocampal-dependent learning and memory. Here, we demonstrate that relatively short-term deltamethrin exposure (3 mg/kg every 3 days for 1 month) inhibits adult hippocampal neurogenesis and causes deficits in learning and memory in mice. Hippocampal-dependent cognitive functions were evaluated using 2 independent hippocampal-dependent behavioral tests, the novel object recognition task and Morris water maze. We found that deltamethrin-treated mice exhibited profound deficits in novel object recognition and learning and memory in water maze. Deltamethrin exposure significantly decreased bromodeoxyuridine (BrdU)-positive cells (39%) and Ki67+ cells (47%) in the DG of the hippocampus, indicating decreased cellular proliferation. In addition, deltamethrin-treated mice exhibited a 44% decrease in nestin-expressing neural progenitor cells and a 38% reduction in the expression of doublecortin (DCX), an early neuronal differentiation marker. Furthermore, deltamethrin-exposed mice exhibited a 25% reduction in total number of granule cells in the DG. These findings indicate that relatively short-term exposure to deltamethrin causes significant deficits in hippocampal neurogenesis that is associated with impaired learning and memory.

Basal cell carcinoma preferentially arises from stem cells within hair follicle and mechanosensory niches.

Basal cell carcinoma (BCC) is characterized by frequent loss of PTCH1, leading to constitutive activation of the Hedgehog pathway. Although the requirement for Hedgehog in BCC is well established, the identity of disease-initiating cells and the compartments in which they reside remain controversial. By using several inducible Cre drivers to delete Ptch1 in different cell compartments in mice, we show here that multiple hair follicle stem cell populations readily develop BCC-like tumors. In contrast, stem cells within the interfollicular epidermis do not efficiently form tumors. Notably, we observed that innervated Gli1-expressing progenitors within mechanosensory touch dome epithelia are highly tumorigenic. Sensory nerves activate Hedgehog signaling in normal touch domes, while denervation attenuates touch dome-derived tumors. Together, our studies identify varying tumor susceptibilities among different stem cell populations in the skin, highlight touch dome epithelia as "hot spots" for tumor formation, and implicate cutaneous nerves as mediators of tumorigenesis.

Lung inflammation induces IL-1ß expression in hypoglossal neurons in rat brainstem.

Perinatal inflammation is associated with respiratory morbidity. Immune modulation of brainstem respiratory control centers may provide a link for this pathobiology. We exposed 11-day old rats to intratracheal lipopolysaccharide (LPS, 0.5 µg/g) to test the hypothesis that intrapulmonary inflammation increases expression of the proinflammatory cytokine IL-1ß within respiratory-related brainstem regions. Intratracheal LPS resulted in a 32% increase in IL-1ß protein expression in the medulla oblongata. In situ hybridization showed increased intensity of IL-1ß mRNA but no change in neuronal numbers. Co-localization experiments showed that hypoglossal neurons express IL-1ß mRNA and immunostaining showed a 43% increase in IL-1ß protein-expressing cells after LPS exposure. LPS treatment also significantly increased microglial cell numbers though they did not express IL-1ß mRNA. LPS-induced brainstem expression of neuronal IL-1ß mRNA and protein may have implications for our understanding of the vulnerability of neonatal respiratory control in response to a peripheral proinflammatory stimulus.

Intrapulmonary lipopolysaccharide exposure upregulates cytokine expression in the neonatal brainstem.

UNLABELLED: Perinatal inflammation and neonatal sepsis trigger lung and brain injury. We hypothesized that endotoxin exposure in the immature lung upregulates proinflammatory cytokine expression in the brainstem and impairs respiratory control. Lipopolysaccharide (LPS) or saline was administered intratracheally to vagal intact or denervated rat pups. LPS increased brainstem IL-1ß and vagotomy blunted this response. There was an attenuated ventilatory response to hypoxia and increased brainstem IL-1ß expression after LPS. CONCLUSION: Intratracheal endotoxin exposure in rat pups is associated with upregulation of IL-1ß in the brainstem that is vagally mediated and associated with an impaired hypoxic ventilatory response.

Cutaneous denervation of psoriasiform mouse skin improves acanthosis and inflammation in a sensory neuropeptide-dependent manner.

Nervous system involvement in psoriasis pathogenesis is supported by increases in nerve fiber numbers and neuropeptides in psoriatic skin and by reports detailing spontaneous plaque remission following nerve injury. Using the KC-Tie2 psoriasiform mouse model, we investigated the mechanisms by which nerve injury leads to inflammatory skin disease remission. Cutaneous nerves innervating dorsal skin of KC-Tie2 animals were surgically axotomized and beginning 1 day after denervation, CD11c(+) cell numbers decreased by 40% followed by a 30% improvement in acanthosis at 7 days and a 30% decrease in CD4(+) T-cell numbers by 10 days. Restoration of substance P (SP) signaling in denervated KC-Tie2 skin prevented decreases in CD11c(+) and CD4(+) cells, but had no effect on acanthosis; restoration of calcitonin gene-related peptide (CGRP) signaling reversed the improvement in acanthosis and prevented denervated-mediated decreases in CD4(+) cells. Under innervated conditions, small-molecule inhibition of SP in KC-Tie2 animals resulted in similar decreases to those observed following surgical denervation for cutaneous CD11c(+) and CD4(+) cell numbers; whereas small-molecule inhibition of CGRP resulted in significant reductions in CD4(+) cell numbers and acanthosis. These data demonstrate that sensory nerve-derived peptides mediate psoriasiform dendritic cell and T-cell infiltration and acanthosis and introduce targeting nerve-immunocyte/KC interactions as potential psoriasis therapeutic treatment strategies.

Triterpenoid modulation of IL-17 and Nrf-2 expression ameliorates neuroinflammation and promotes remyelination in autoimmune encephalomyelitis.

Inflammatory cytokines and endogenous anti-oxidants are variables affecting disease progression in multiple sclerosis (MS). Here we demonstrate the dual capacity of triterpenoids to simultaneously repress production of IL-17 and other pro-inflammatory mediators while exerting neuroprotective effects directly through Nrf2-dependent induction of anti-oxidant genes. Derivatives of the natural triterpene oleanolic acid, namely CDDO-trifluoroethyl-amide (CDDO-TFEA), completely suppressed disease in a murine model of MS, experimental autoimmune encephalomyelitis (EAE), by inhibiting Th1 and Th17 mRNA and cytokine production. Encephalitogenic T cells recovered from treated mice were hypo-responsive to myelin antigen and failed to adoptively transfer the disease. Microarray analyses showed significant suppression of pro-inflammatory transcripts with concomitant induction of anti-inflammatory genes including Ptgds and Hsd11b1. Finally, triterpenoids induced oligodendrocyte maturation in vitro and enhanced myelin repair in an LPC-induced non-inflammatory model of demyelination in vivo. These results demonstrate the unique potential of triterpenoid derivatives for the treatment of neuroinflammatory disorders such as MS.

CXCR2-positive neutrophils are essential for cuprizone-induced demyelination: relevance to multiple sclerosis.

Multiple sclerosis is an inflammatory demyelinating disorder of the CNS. Recent studies have suggested diverse mechanisms as underlying demyelination, including a subset of lesions induced by an interaction between metabolic insult to oligodendrocytes and inflammatory mediators. For mice of susceptible strains, cuprizone feeding results in oligodendrocyte cell loss and demyelination of the corpus callosum. Remyelination ensues and has been extensively studied. Cuprizone-induced demyelination remains incompletely characterized. We found that mice lacking the type 2 CXC chemokine receptor (CXCR2) were relatively resistant to cuprizone-induced demyelination and that circulating CXCR2-positive neutrophils were important for cuprizone-induced demyelination. Our findings support a two-hit process of cuprizone-induced demyelination, supporting the idea that multiple sclerosis pathogenesis features extensive oligodendrocyte cell loss. These data suggest that cuprizone-induced demyelination is useful for modeling certain aspects of multiple sclerosis pathogenesis.

Truncated Tau with the Fyn-binding domain and without the microtubule-binding domain hinders the myelinating capacity of an oligodendrocyte cell line.

The mechanisms underlying developmental myelination have therapeutic potential following CNS injury and degeneration. We report that transplanted central glial (CG)-4 cells had a diminished myelinating capacity in myelin-deficient (md) rats when cells express a mutated form of Tau (Tau [688]), which binds Fyn but not the microtubules. In the brain of the md rats, Tau [688]-transfected CG-4 cells displayed a decrease in cellular process outgrowth and myelination; in the spinal cord the extent of myelination rostral and caudal to the injection site was decreased. In contrast, control Tau [605]-transfected CG-4 cells formed long cellular processes and substantial areas of myelin both in the brain and spinal cord. In culture, Tau [688]-transfected CG-4 cells displayed a decrease in cellular process outgrowth, and Fyn localized largely in the cell body, not the processes. Thus, Tau in oligodendrocytes plays a key role in myelination, and a functional Tau-Fyn interaction might have therapeutic potential during demyelination and myelin repair following CNS injury and degeneration.