Archives

  • 2018-07
  • 2018-10
  • 2018-11
  • 2019-04
  • 2019-05
  • 2019-06
  • 2019-07
  • 2019-08
  • 2019-09
  • 2019-10
  • 2019-11
  • 2019-12
  • 2020-01
  • 2020-02
  • 2020-03
  • 2020-04
  • 2020-05
  • 2020-06
  • 2020-07
  • 2020-08
  • 2020-09
  • 2020-10
  • 2020-11
  • 2020-12
  • 2021-01
  • 2021-02
  • 2021-03
  • 2021-04
  • 2021-05
  • 2021-06
  • 2021-07
  • 2021-08
  • 2021-09
  • 2021-10
  • 2021-11
  • 2021-12
  • 2022-01
  • 2022-02
  • 2022-03
  • 2022-04
  • 2022-05
  • 2022-06
  • 2022-07
  • 2022-08
  • 2022-09
  • 2022-10
  • 2022-11
  • 2022-12
  • 2023-01
  • 2023-02
  • 2023-03
  • 2023-04
  • 2023-05
  • 2023-06
  • 2023-07
  • 2023-08
  • 2023-09
  • 2023-10
  • 2023-11
  • 2023-12
  • 2024-01
  • 2024-02
  • 2024-03
  • Introduction The hippocampus is a critical brain

    2019-04-25

    Introduction The hippocampus is a critical brain region for episodic memory formation in rodents and humans [1]. Hippocampal neurons, especially CA1 neurons, are highly vulnerable to ischemic injury [2], and failure of hippocampal function causes memory impairment and reduced cognitive ability [3,4]. Ischemic attack impairs glucose and oxygen utilization via reduced Radicicol blood flow [5,6], and subsequent events promote ischemic injury, such as the elevation of extracellular concentration of glutamate [7], activation of glutamate receptors [8], and intracellular calcium accumulation [9]. By using primary neuronal cultures or brain slices prepared from embryonic or postnatal hippocampus, many agents have been investigated to protect against hippocampal injury. These agents include basic fibroblast growth factor (FGF) [10], nerve growth factor [11], brain-derived neurotrophic factor [12], insulin and insulin-like growth factors [13,14], tumor necrosis factor [15], estrogen [16], platelet-derived growth factor [17], and retinoic Radicicol [18]. Mitogen-activated protein (MAP) kinase is part of a potent intracellular mechanism for transducing external stimuli, including protective molecules, to internal cellular responses such as cell survival and cell death [19]. The MAP kinase family is composed of three kinases: extracellular signal-regulated kinases 1 and 2 (ERK1/2), c-Jun NH2-terminal kinase (JNK), and p38 MAP kinase (p38, also known as stress-activated protein kinase 2 [SAPK2]). Activation of ERK1/2 or JNK promotes hippocampal neuronal cell death in experiments with postnatal brain slices [[20], [21], [22], [23], [24]], whereas activation of ERK1/2 leads to cell survival of other types of neurons, such as cortical neurons, sympathetic neurons, and cerebellar neurons [22]. Studies using p38-specific chemical inhibitors have demonstrated that the activation of p38 induces cell death of hippocampal neurons rather than cell survival in hippocampal slice cultures [18,[25], [26], [27], [28]], adult mice with intracerebroventrical administration of the inhibitor [29,30], or embryonic or perinatal hippocampal cultures [31,32]. Given the low specificity of p38 inhibitors at high concentrations (i.e., above 5 μM) [42], the use of chemical inhibitors does not preclude the possibility that a molecule other than p38 participates in hippocampal neuronal cell death. As such, the direct action of p38 on the survival of adult hippocampal neurons is still unclear. In this study, a cell permeable p38 protein, in which the HIV PTD was fused to the N-terminus of p38 [33,34], and cultured adult hippocampal neurons, which had differentiated from cultured adult hippocampal neural stem/progenitor cells (NPCs), were used to evaluate the direct function of p38 on adult hippocampal neurons. Our immunocytochemical experiments demonstrated that the wild-type cell-permeable p38 protein prevents cell death of adult hippocampal neurons at levels comparable to cells treated with FGF, suggesting that the cell-permeable p38 protein is a direct modulator of intracellular p38’s regulation of hippocampal function.
    Material and methods
    Results
    Discussion In this study, we demonstrated the expression of endogenous p38 protein in adult hippocampal NPCs. Our previous study showed that endogenous p38 enhanced cell migration of cortical NPCs without affecting cell survival or differentiation [34]; thus, endogenous p38 protein may participate in cell migration of adult hippocampal NPCs. Our current results demonstrated that the p38 protein directly prevents cell death of adult hippocampal neurons induced by a low glucose culture condition using both cell-permeable p38 protein and hippocampal neurons that differentiated from adult hippocampal NPCs. Traditionally, primary neuronal cultures or brain slices have been used to elucidate the mechanism of protective agents for hippocampal cells. However, brain slices and primary cultures, especially those obtained from postnatal animals, contain non-negligible amounts of supporting cells; i.e., astrocyte and microglia, that support neuronal survival by producing growth factors [41]. Thus, a sophisticated experimental design is required to elucidate the neuroprotective effects of various agents [5]. Under the differentiated culture condition, the hippocampal neuronal cells used in this report did not contain GFAP-positive astrocytes or amoeboid and/or rod-shape microglia (data not shown). These results suggest that our hippocampal neuronal culture should be suitable for hippocampal neuronal assays, and also that the neuroprotective effect of cell-permeable p38 protein could act directly on hippocampal neurons rather than indirectly through the trophic action of glial cells.