Synapses between engram cells are believed to be substrates for memory storage, and the weakening or loss of these synapses leads to the forgetting of related memories. We found engulfment of synaptic components by microglia in the hippocampi of healthy adult mice. Depletion of microglia or inhibition of microglial phagocytosis prevented forgetting and the dissociation of engram cells. By introducing CD55 to inhibit complement pathways, specifically in engram cells, we further demonstrated that microglia regulated forgetting in a complement- and activity-dependent manner. Additionally, microglia were involved in both neurogenesis-related and neurogenesis-unrelated memory degradation. Together, our findings revealed complement-dependent synapse elimination by microglia as a mechanism underlying the forgetting of remote memories.

Under natural conditions, injured cells can be repaired rapidly through inherent biological processes. However, in the case of diabetes, cardiovascular disease, muscular dystrophy, and other degenerative conditions, the natural repair process is impaired. Repair of injury to the cell membrane is an important aspect of physiology. Inadequate membrane repair function is implicated in the pathophysiology of many human disorders. Recent studies show that Mitsugumin 53 (MG53), a TRIM family protein, plays a key role in repairing cell membrane damage and facilitating tissue regeneration. Clarifying the role of MG53 and its molecular mechanism are important for the application of MG53 in regenerative medicine. In this review, we analyze current research dissecting MG53′s function in cell membrane repair and tissue regeneration, and highlight the development of recombinant human MG53 protein as a potential therapeutic agent to repair multiple-organ injuries.

The neovascularization of ischemic tissue is a crucial initial step for the functional rehabilitation and wound healing. However, the short of seed cell candidate for the foundation of vascular network is still a big issue. Human adipose tissue derived mesenchymal stem cells (hADSCs), which possess multilineage potential, are capable of adipogenic, osteogenic, and chondrogenic differentiation. We examined whether this kind of stem cells could differentiate into endothelial-like cells and participate in blood vessel formation, and whether they could be used as an ideal cell source for therapeutic angiogenesis in ischemic diseases or vascularization of tissue constructs. The results showed that hADSCs, grown under appropriately induced conditions, displayed characteristics similar to those of vessel endothelium. The differentiated cells expressed endothelial cell markers CD34 and vWF, and had high metabolism of acetylated low-density lipoprotein and prostacyclin. In addition, the induced cells were able to form tube-like structures when cultured on matrigel. Our data indicated that induced hADSCs could exhibit characteristics of endothelial cells. Therefore, these cells, as a source of human endothelial cells, may find many applications in such realms as engineering blood vessels, endothelial cell transplantation for myocardial regeneration, and induction of angiogenesis for treatment of regional ischemia.

The functional realization is the most important problem in vascular tissue engineering. The small-caliber blood vessel substitutes are prone to thrombi, which results in functional loss of blood vessels. However, this is probably due to the imperfection of endothelial layer in the substitutes. In this study, MSCs were seeded on a series of porous PLGA films with various porosity and pore size made by sodium chloride (NaCl) particulate leaching, and cell proliferation on each film was inspected. The film made of the 75% (w/w) particulate proportion and 30-50 μm pore size maximized the proliferation rate and was chosen as the scaffolds for the differentiation of MSCs into endothelial cells. The induced cells expressed endothelial cells specific Flk-1, Ⅷ factor and CD34, possessed endothelial cells specific Weible-palade (W-P) body, and had the abilities of ingesting low density lipoprotein and secreting prostacyclin (PGI 2 ). The results show that MSCs not only have the ideal biological compatibility with the porous PLGA films, but also have the potency of differentiating into functional endothelial cells, which should facilitate the endothelialization in vascular tissue engineering.

Background: In the past 30 years, incidences of non-alcoholic fatty liver disease (NAFLD) has risen by 30%. However, there is still no clear mechanism or accurate method of anticipating liver failure. Here we reveal the phase transitions of liquid crystalline qualities in hepatic lipid droplets (HLDs) as a novel method of anticipating prognosis. Methods: NAFLD was induced by feeding C57BL/6J mice on a high-fat (HiF) diet. These NAFLD livers were then evaluated under polarized microscopy, X-ray diffraction and small-angle scattering, lipid component chromatography analysis and protein expression analysis. Optically active HLDs from mouse model and patient samples were both then confirmed to have liquid crystal characteristics. Liver MAP1LC3A expression was then evaluated to determine the role of autophagy in liquid crystal HLD (LC-HLD) formation. Results: Unlike the normal diet cohort, HiF diet mice developed NAFLD livers containing HLDs exhibiting Maltese cross birefringence, phase transition, and fluidity signature to liquid crystals. These LC-HLDs transitioned to anisotropic crystal at 0 °C and remain crystalline. Temperature increase to 42 °C causes both liquid crystal and crystal HLDs to convert to isotropic droplet form. These isotropic HLDs successfully transition to anisotropic LC with fast temperature decrease and anisotropic crystal with slow temperature decrease. These findings were duplicated in patient liver. Patient LC-HLDs with no inner optical activity were discovered, hinting at lipid saturation as the mechanism through which HLD acquire LC characteristics. Downregulation of MAP1LC3A in conjunction with increased LC-HLD also implicated autophagy in NAFLD LC-HLD formation. Conclusions: Increasing concentrations of amphiphilic lipids in HLDs favors organization into alternating hydrophilic and hydrophobic layers, which present as LC-HLDs. Thus, evaluating the extent of liquid crystallization with phase transition in HLDs of NAFLD patients may reveal disease severity and predict impending liver damage.

Hippocampal neurogenesis declines with aging. Wnt ligands and antagonists within the hippocampal neurogenic niche regulate the proliferation of neural progenitor cells and the development of new neurons, and the changes of their levels in the niche mediate aging-associated decline of neurogenesis. We found that RNA-binding protein Lin28a remained existent in neural progenitor cells and granule neurons in the adult hippocampus, and decreased with aging. Loss of Lin28a inhibited the responsiveness of neural progenitor cells to niche Wnt agonist and reduced neurogenesis, thus impairing pattern separation. Overexpression of Lin28a increased the proliferation of neural progenitor cells, promoted the functional integration of newborn neurons, restored neurogenesis in Wnt-deficient dentate gyrus, and rescued the impaired pattern separation in aging mice. Our data suggest that Lin28a regulates adult hippocampal neurogenesis as an intracellular mechanism by responding to niche Wnt signals, and its decrease is involved in aging-associated decline of hippocampal neurogenesis as well as related cognitive functions.

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Metabotropic glutamate receptor 2 (GRM2) is highly expressed in hippocampal dentate granule cells (DGCs), regulating synaptic transmission and hippocampal functions. Newborn DGCs are continuously generated throughout life, and express GRM2 when they are mature. However, it remained unclear whether and how GRM2 regulates the development and integration of these newborn neurons. We discovered that the expression of GRM2 in adult-born DGCs increased with neuronal development in mice of both sexes. Lack of GRM2 caused developmental defects of DGCs and impaired hippocampus-dependent cognitive functions. Intriguingly, our data showed that knockdown ofGrm2resulted in decreased b/c-Raf kinases, and paradoxically led to an excessive activation of MEK/ERK1/2 pathway. Inhibition of MEK ameliorated the developmental defects caused byGrm2knockdown. Together, our results indicate that GRM2 is necessary for the development and functional integration of newborn DGCs in the adult hippocampus through regulating the phosphorylation and activation state of MEK/ERK1/2 pathway.SIGNIFICANCE STATEMENT:Metabotropic glutamate receptor 2 (GRM2) is highly expressed in mature dentate granule cells (DGCs) in the hippocampus. It remains unclear whether GRM2 is required for the development and integration of adult-born DGCs. We provided a series ofin vivoandin vitroevidence to show GRM2 regulates the development of adult-born DGCs and their integration into existing hippocampal circuits. Lack of GRM2 in a cohort of newborn DGCs impaired object-to-location memory in mice. Moreover, we revealed that GRM2 knockdown paradoxically upregulated MEK/ERK1/2 pathway by suppressing b/c-Raf in developing neurons, which is likely a common mechanism underlying the regulation of the development of neurons expressing GRM2. Thus, Raf/MEK/ERK1/2 pathway could be a potential target for brain diseases related to GRM2 abnormality.