Activation and upregulation of keratinocyte and epidermal transglutaminases are associated with depletion of their substrates in psoriatic lesions.

OBJECTIVE: Psoriasis is a chronic skin disorder caused by abnormal interactions between epidermal and immune cells. Thus, the interplay between the proliferation and differentiation of epidermal components should be tightly regulated to protect against psoriasis. The differentiation process is primarily controlled by transglutaminases (TGs). However, studies on TG enzymes and their molecular alterations in psoriatic skin lesions are limited. Therefore, this study aimed to investigate TG activity and gene and protein expression in human psoriatic and normal skin tissues. MATERIALS AND METHODS: Keratinocyte TG (TG1), and epidermal TG (TG3) activity, localization, protein levels, and gene expression in human psoriatic skin were determined by immunohistochemistry and RT-qPCR. The expression of TG substrates (loricin and involucrin - IVL) was also investigated using RT-qPCR. RESULTS: TG1 and TG3 enzymatic activities and gene expression were significantly higher in psoriatic skin tissue than in normal skin tissue. However, both TGs were present in the same location and were equally highly expressed. Moreover, the expression of two TG substrates (loricin and involucrin) was significantly decreased compared to that in psoriatic and healthy skin samples. CONCLUSIONS: The activation and upregulation of TG1 and TG3 result from the depletion of their substrates (loricin and involucrin), both of which play a major role in the pathogenicity of psoriatic skin tissue and are necessary for proper skin development.

Elucidating the mechanism underlying cognitive dysfunction by investigating the effects of CMF and MET treatment on hippocampal neurons.

OBJECTIVE: Chemotherapy causes long-term cognitive impairment in cancer survivors. A combination of cyclophosphamide (CYP), methotrexate (MTX), and 5-fluorouracil (5-FU) (i.e., CMF) is widely used for cancer treatment. Metformin (MET), an oral antidiabetic drug, confers protection against the adverse effects of chemotherapeutic agents, such as CYP. To elucidate the potential mechanism underlying cognitive dysfunction, we investigated the impact of CMF and MET treatment on the activities of mitochondrial respiratory chain complexes I and IV, as well as lipid peroxidation, in hippocampal neurons. MATERIALS AND METHODS: Hippocampal neurons (H19-7) cells were treated for 24 h with MET (0.5 mM) alone; CYP (1 µM), MTX (0.5 µM), and 5-FU (1 µM); and MET (0.5 mM) + CYP (1 µM), MTX (0.5 mM), and 5-FU (1 µM). A 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyl tetrazolium bromide assay was performed to evaluate cell survival. Neurons were collected and homogenized in a neuronal lysis buffer to assess mitochondrial complexes (I and IV) activity and lipid peroxidation. RESULTS: Compared to the control, MET-treated cells showed no significant difference in survival rate; however, CMF- and CMF + MET-treated cells showed a significant reduction in survival rate. In addition, relative to the control, CMF- and CMF + MET-treated cells showed a reduction in mitochondrial complex I activity, whereas no significant changes were observed in mitochondrial complex IV activity. MET-treated cells showed no significant differences in lipid peroxidation, but CMF- and CMF + MET-treated cells showed a slight increase in lipid peroxidation. CONCLUSIONS: The reduction in the activity of mitochondrial complex I and a slight increase in lipid peroxidation levels may explain the cognitive impairment following CMF and MET treatments.

Organophosphates modulate tissue transglutaminase activity in differentiated C6 neural cells.

OBJECTIVE: The organophosphate compounds chlorpyrifos (O, O-diethyl O-[3,5,6-trichloro-2-pyridinyl] phosphorothioate, CPF) and phenyl saligenin phosphate (PSP) have been widely implicated in developmental neurotoxicity and neurodegeneration. However, the underlying mechanism remains unclear. Transglutaminase (TG)2 is a calcium ion (Ca2+)-dependent enzyme with an important role in neuronal cell outgrowth and differentiation and in neurotoxin activity and is modulated by organophosphates. MATERIALS AND METHODS: We studied TG2 activity modulation by CPO and PSP during differentiation in C6 glioma cells. We studied the effects of CPO or PSP treatment with or without the TG2 inhibitor Z-DON and identified potential TG2 protein substrates via mass spectrometry. RESULTS: PSP and CPO did not affect cell viability but affected TG2 activity in differentiating cells. Our results indicate that the organophosphate-induced amine incorporation activity of TG2 may have a direct effect on neuronal outgrowth, differentiation, and cell survival by modifying several essential microtubule proteins, including tubulin. Inhibiting TG2 reduced neurite length but not cell survival. CONCLUSIONS: TG2 inhibitors can protect against organophosphate-induced neuropathy and could be used for developing novel therapeutic strategies for treating brain cancer and neurodegenerative disorders.