Leucine-rich repeat kinase 2 (LRRK2), a large protein kinase containing multi-functional domains, has been identified as the causal molecule for autosomal-dominant Parkinson's disease (PD). In the present study, we demonstrated for the first time that (i) LRRK2 interacts with tau in a tubulin-dependent manner; (ii) LRRK2 directly phosphorylates tubulin-associated tau, but not free tau; (iii) LRRK2 phosphorylates tau at Thr181 as one of the target sites; and (iv) The PD-associated LRRK2 mutations, G2019S and I2020T, elevated the degree of tau-phosphorylation. These results provide direct proof that tau is a physiological substrate for LRRK2. Furthermore, we revealed that LRRK2-mediated phosphorylation of tau reduces its tubulin-binding ability. Our results suggest that LRRK2 plays an important role as a physiological regulator for phosphorylation-mediated dissociation of tau from microtubules, which is an integral aspect of microtubule dynamics essential for neurite outgrowth and axonal transport.

Questions about which reactive oxygen species (ROS) or reactive nitrogen species (RNS) can escape from the mitochondria and activate signals must be addressed. In this study, two parameters, the calculated dipole moment (debye, D) and permeability coefficient (Pm) (cm s⁻¹), are listed for hydrogen peroxide (H₂O₂), hydroxyl radical (•OH), superoxide (O₂^•−), hydroperoxyl radical (HO₂•), nitric oxide (•NO), nitrogen dioxide (•NO₂), peroxynitrite (ONOO⁻), and peroxynitrous acid (ONOOH) in comparison to those for water (H₂O). O₂^•− is generated from the mitochondrial electron transport chain (ETC), and several other ROS and RNS can be generated subsequently. The candidates which pass through the mitochondrial membrane include ROS with a small number of dipoles, i.e., H₂O₂, HO₂•, ONOOH, •OH, and •NO. The results show that the dipole moment of •NO₂ is 0.35 D, indicating permeability; however, •NO₂ can be eliminated quickly. The dipole moments of •OH (1.67 D) and ONOOH (1.77 D) indicate that they might be permeable. This study also suggests that the mitochondria play a central role in protecting against further oxidative stress in cells. The amounts, the long half-life, the diffusion distance, the Pm, the one-electron reduction potential, the pK_a, and the rate constants for the reaction with ascorbate and glutathione are listed for various ROS/RNS, •OH, singlet oxygen (¹O₂), H₂O₂, O₂^•−, HO₂•, •NO, •NO₂, ONOO⁻, and ONOOH, and compared with those for H₂O and oxygen (O₂). Molecules with negative electrical charges cannot directly diffuse through the phospholipid bilayer of the mitochondrial membranes. Short-lived molecules, such as •OH, would be difficult to contribute to intracellular signaling. Finally, HO₂• and ONOOH were selected as candidates for the ROS/RNS that pass through the mitochondrial membrane.

Dysbiosis, an imbalance of intestinal flora, can cause serious conditions such as obesity, cancer, and psychoneurological disorders. One cause of dysbiosis is inflammation. Ulcerative enteritis is a side effect of non-steroidal anti-inflammatory drugs (NSAIDs). To counteract this side effect, we proposed the concurrent use of histamine H₂ receptor antagonists (H₂RA), and we examined the effect on the intestinal flora. We generated a murine model of NSAID-induced intestinal mucosal injury, and we administered oral H₂RA to the mice. We collected stool samples, compared the composition of intestinal flora using terminal restriction fragment length polymorphism, and performed organic acid analysis using high-performance liquid chromatography. The intestinal flora analysis revealed that NSAID [indomethacin (IDM)] administration increased Erysipelotrichaceae and decreased Clostridiales but that both had improved with the concurrent administration of H₂RA. Fecal levels of acetic, propionic, and n-butyric acids increased with IDM administration and decreased with the concurrent administration of H₂RA. Although in NSAID-induced gastroenteritis the proportion of intestinal microorganisms changes, leading to the deterioration of the intestinal environment, concurrent administration of H₂RA can normalize the intestinal flora.

Tris (2-butoxyethyl) phosphate (TBEP) is an organophosphate flame retardant and used as a plasticizer in various household products such as plastics, floor polish, varnish, textiles, furniture, and electronic equipment. However, little is known about the effects of TBEP on the brain and behavior. We aimed to examine the effects of dietary exposure of TBEP on memory functions, their-related genes, and inflammatory molecular markers in the brain of allergic asthmatic mouse models. C3H/HeJSlc male mice were given diet containing TBEP (0.02 (TBEP-L), 0.2 (TBEP-M), or 2 (TBEP-H) μg/kg/day) and ovalbumin (OVA) intratracheally every other week from 5 to 11 weeks old. A novel object recognition test was conducted in each mouse at 11 weeks old. The hippocampi were collected to detect neurological, glia, and immunological molecular markers using the real-time RT-PCR method and immunohistochemical analyses. Mast cells and microglia were examined by toluidine blue staining and ionized calcium-binding adapter molecule (Iba)-1 immunoreactivity, respectively. Impaired discrimination ability was observed in TBEP-H-exposed mice with or without allergen. The mRNA expression levels of N-methyl-D aspartate receptor subunits Nr1 and Nr2b, inflammatory molecular markers tumor necrosis factor-α oxidative stress marker heme oxygenase 1, microglia marker Iba1, and astrocyte marker glial fibrillary acidic protein were significantly increased in TBEP-H-exposed mice with or without allergen. Microglia and mast cells activation were remarkable in TBEP-H-exposed allergic asthmatic mice. Our results indicate that chronic exposure to TBEP with or without allergen impaired object recognition ability accompanied with alteration of molecular expression of neuronal and glial markers and inflammatory markers in the hippocampus of mice. Neuron-glia-mast cells interaction may play a role in TBEP-induced neurobehavioral toxicity.