USP25 inhibition ameliorates Alzheimer's pathology through the regulation of APP processing and Aβ generation

Down syndrome (DS), or trisomy 21, is one of the critical risk factors for early-onset Alzheimer’s disease (AD), implicating key roles for chromosome 21–encoded genes in the pathogenesis of AD. We previously identified a role for the deubiquitinase USP25, encoded on chromosome 21, in regulating microglial homeostasis in the AD brain; however, whether USP25 affects amyloid pathology remains unknown. Here, by crossing 5×FAD AD and Dp16 DS mice, we observed that trisomy 21 exacerbated amyloid pathology in the 5×FAD brain. Moreover, bacterial artificial chromosome (BAC) transgene–mediated USP25 overexpression increased amyloid deposition in the 5×FAD mouse brain, whereas genetic deletion of Usp25 reduced amyloid deposition. Furthermore, our results demonstrate that USP25 promoted β cleavage of APP and Aβ generation by reducing the ubiquitination and lysosomal degradation of both APP and BACE1. Importantly, pharmacological inhibition of USP25 ameliorated amyloid pathology in the 5×FAD mouse brain. In summary, we identified the DS-related gene USP25 as a critical regulator of AD pathology, and our data suggest that USP25 serves as a potential pharmacological target for AD drug development.

Vitamin D3 combined with antibody agents suppresses alloreactive memory T-cell responses to induce heart allograft long-term survival

BACKGROUND

The pre-stored memory T cells in organ transplant patient carry a high risk of allograft rejection. The current study aimed to determine whether the allogenic response of adoptively transferred memory T cells in mice was suppressed by vitamin D3 monotherapy alone or in combination with monoclonal antibody treatment.

METHODS

Prior to vascularized heterotopic heart transplantation, naïve C57BL/6 mice were primed with memory T cells. Recipient mice were administered vitamin D3 alone or in combination with monoclonal antibodies (anti-CD40L/ anti-LFA-1). Memory T cells and CD4⁺ forkhead box P3⁺ T cells in recipient spleens were measured using flow cytometry. Additionally, the expression of cytokines was measured by ELISA and quantitative PCR. Inflammatory factors in the grafts were identified by hematoxylin and eosin staining.

RESULTS

Vitamin D3 in conjunction with anti-CD40L/ anti-LFA-1 antibodies were administered according to the median survival time from 6.5 to 80 days. The results revealed that grafts were protected through the prevention of inflammatory cell infiltration. Combined treatment decreased the mRNA levels of IL-2, IFN-γ and IL-10 and increased the mRNA levels of IL-4, Foxp3 and TGF-β in the allograft. Rejection was suppressed by a reduction of CD4⁺CD44^high CD62L⁺ and CD8⁺ CD44^high CD62L⁺ memory T cells, the induction of regulatory T cells in the recipient spleen and a reduction of serum IL-2, IFN-γ and IL-10 levels.

CONCLUSION

Vitamin D3 efficiently protected allografts from memory T-cell allo-responses when combined with anti-CD40L/anti-LFA-1 antibodies therapy.

Trisomy 21-induced dysregulation of microglial homeostasis in Alzheimer's brains is mediated by USP25

Down syndrome (DS), caused by trisomy of chromosome 21, is the most significant risk factor for early-onset Alzheimer's disease (AD); however, underlying mechanisms linking DS and AD remain unclear. Here, we show that triplication of homologous chromosome 21 genes aggravates neuroinflammation in combined murine DS-AD models. Overexpression of USP25, a deubiquitinating enzyme encoded by chromosome 21, results in microglial activation and induces synaptic and cognitive deficits, whereas genetic ablation of Usp25 reduces neuroinflammation and rescues synaptic and cognitive function in 5×FAD mice. Mechanistically, USP25 deficiency attenuates microglia-mediated proinflammatory cytokine overproduction and synapse elimination. Inhibition of USP25 reestablishes homeostatic microglial signatures and restores synaptic and cognitive function in 5×FAD mice. In summary, we demonstrate an unprecedented role for trisomy 21 and pathogenic effects associated with microgliosis as a result of the increased USP25 dosage, implicating USP25 as a therapeutic target for neuroinflammation in DS and AD.

Combined treatment with vitamin D3 and antibody agents suppresses secondary heart transplant rejection in the early postoperative period

BACKGROUND

Accelerated transplant rejection mediated by donor reactive memory T cells is another barrier to the induction of graft tolerance. The aim of this study was to investigate the immunosuppressing effects of vitamin D (1,25(OH)2D3), administered alone or in combination with a costimulatory blockade treatment, on rejection of secondary heart allografts in a mouse model.

METHODS

Circular full-thickness skin grafts from BALB/c mice were cut and grafted onto the lumbar regions of C57BL/6 mice as allo-primed recipients. Four weeks after skin grafting, the vascularized hearts from the BALB/c mice were transplanted heterotopically into the allo-primed recipients using a non-suture cuff technique. The recipients were then randomly divided into four groups and given either intraperitoneal injection of isotype, Ab, 1,25(OH)2D3, or a combination of Ab and 1,25(OH)2D3. Allograft incidence was determined by hematoxylin-eosin staining, and cytokine expression was assessed by the quantitative real-time polymerase chain reaction, enzyme-linked immunosorbent assays, and cytometric bead arrays. Spleen cells from the recipient were used to assess mixed lymphocyte reactions. Memory T cells and regulatory T cells (Tregs) in spleen cells were measured by flow cytometry.

RESULTS

The median allograft survival time was longer with the combined treatment with Ab and 1,25(OH)2D3 than with no treatment or with treatment with Ab or 1,25(OH)2D3 alone. The grafts were protected from infiltration by inflammatory cells and by inhibition of interleukin 2 and interferon gamma expression. Rejection was initially suppressed in the early postoperative period by a reduction in the number of memory T cells and induction of Foxp3⁺ Tregs, but this effect disappeared by day 15 after transplantation upon withdrawal of the treatment.

CONCLUSION

Vitamin D3 administered as an immunosuppressive agent, when combined with monoclonal antibody treatment, may protect heart grafts from memory T cell responses in a secondary heart transplant model.

Calcium-G protein interactions in the regulation of macrophage secretion

The interplay between activated G proteins and intracellular calcium ([Ca(2+)](i)) in the regulation of secretion was studied in the macrophage, coupling membrane capacitance with calcium-sensitive microfluorimetry. Intracellular elevation of either the nonhydrolyzable analogue of GTP, guanosine-5'-O-(3-thiotriphosphate) (GTP gamma S), or [Ca(2+)](i) enhanced the amplitude and shortened the time course of stimulus-induced secretion in a dose-dependent manner. Both the ionophore- and the stimulus-induced secretory response were abolished in the presence of guanosine-5'-O-(2-thiodiphosphate) (GDP beta S). The K(d) of Ca(2+)-driven secretion was independent of GTP gamma S concentration, whereas the K(d) of the GTP gamma S-driven response decreased from 63 to 31 microM in the presence of saturating concentrations of [Ca(2+)](i). The time course of stimulus-induced secretion was dependent upon the concentration of [Ca(2+)](i). The time course of GTP gamma S-driven secretion was concentration-independent at high levels of [Ca(2+)](i), suggesting that a calcium-dependent translocation/binding step was rate-limiting. Our data strongly support a model in which [Ca(2+)](i) and activated G proteins act independently of one another in the sequential regulation of macrophage secretion. [Ca(2+)](i) appears to play a role in the recruitment and priming of vesicles from reserve intracellular pools at a step that is upstream of G protein activation. While activated, G proteins appear to play a key role in fusion of docked vesicles. Thus, secretion can result either from activating more G proteins or from elevating [Ca(2+)](i) at basal levels of G protein activation.

Regulation of human CLC-3 channels by multifunctional Ca2+/calmodulin-dependent protein kinase

The multifunctional calcium/calmodulin-dependent protein kinase II, CaMKII, has been shown to regulate chloride movement and cellular function in both excitable and non-excitable cells. We show that the plasma membrane expression of a member of the ClC family of Cl(-) channels, human CLC-3 (hCLC-3), a 90-kDa protein, is regulated by CaMKII. We cloned the full-length hCLC-3 gene from the human colonic tumor cell line T84, previously shown to express a CaMKII-activated Cl(-) conductance (I(Cl,CaMKII)), and transfected this gene into the mammalian epithelial cell line tsA, which lacks endogenous expression of I(Cl,CaMKII). Biotinylation experiments demonstrated plasma membrane expression of hCLC-3 in the stably transfected cells. In whole cell patch clamp experiments, autonomously active CaMKII was introduced into tsA cells stably transfected with hCLC-3 via the patch pipette. Cells transfected with the hCLC-3 gene showed a 22-fold increase in current density over cells expressing the vector alone. Kinase-dependent current expression was abolished in the presence of the autocamtide-2-related inhibitory peptide, a specific inhibitor of CaMKII. A mutation of glycine 280 to glutamic acid in the conserved motif in the putative pore region of the channel changed anion selectivity from I(-) > Cl(-) to Cl(-) > I(-). These results indicate that hCLC-3 encodes a Cl(-) channel that is regulated by CaMKII-dependent phosphorylation.

Oxidants potentiate Ca(2+)- and cAMP-stimulated Cl(-) secretion in intestinal epithelial T84 cells

BACKGROUND & AIMS

Diarrhea is one of the major complications of inflammatory bowel disease. The role of oxidants in promoting net intestinal secretion is important, but the cellular mechanisms underlying their effects are unclear. We examined the effects and defined the cellular actions of the oxidant monochloramine (NH(2)Cl) on anion secretion in human colonic T84 cells.

METHODS

Effects of NH(2)Cl on basal and agonist-stimulated short-circuit current (Isc) of T84 monolayers were determined. Apical Cl(-) and basolateral K(+) conductances were measured by efflux of (125)I(-) and (86)Rb(+), respectively.

RESULTS

NH(2)Cl alone had little effect on Isc and (125)I(-) efflux. However, pretreatment with NH(2)Cl led to a concentration-dependent potentiation of the Ca(2+)-mediated Isc and of submaximal cAMP-mediated responses. These effects were associated with increased basolateral K(+) channel conductance and were blocked by increasing cellular Ca(2+) buffering capacity with Quin-2. Whole-cell voltage clamp experiments showed that NH(2)Cl potentiated Ca(2+) activation of basolateral K(+) channel conductance.

CONCLUSIONS

Oxidants potentiate both Ca(2+)- and cAMP-stimulated Cl(-) secretion by a direct effect on calcium-activated basolateral K(+) channel conductance, lowering its Ca(2+) activation threshold. This effect may play an important role in amplifying and prolonging the secretory response of inflamed intestinal mucosa and enhancing the severity of diarrhea.

Impermeability of the GIRK2 weaver channel to divalent cations

A single amino acid mutation (G156S) in the putative pore-forming region of the G protein-sensitive, inwardly rectifying K(+) channel subunit, GIRK2, renders the conductance constitutively active and nonselective for monovalent cations. The mutant channel subunit (GIRK2wv) causes the pleiotropic weaver disease in mice, which is characterized by the selective vulnerability of cerebellar granule cells and Purkinje cells, as well as dopaminergic neurons in the mesencephalon, to cell death. It has been proposed that divalent cation permeability through constitutively active GIRK2wv channels contributes to a rise in internal calcium in the GIRK2wv-expressing neurons, eventually leading to cell death. We carried out comparative studies of recombinant GIRK2wv channels expressed in Xenopus oocytes and COS-7 cells to determine the magnitude and relative permeability of the GIRK2wv conductance to Ca(2+). Data from these studies demonstrate that the properties of the expressed current differ in the two systems and that when recombinant GIRK2wv is expressed in mammalian cells it is impermeable to Ca(2+).

Syntaxin 1A is expressed in airway epithelial cells, where it modulates CFTR Cl(-) currents

The CFTR Cl(-) channel controls salt and water transport across epithelial tissues. Previously, we showed that CFTR-mediated Cl(-) currents in the Xenopus oocyte expression system are inhibited by syntaxin 1A, a component of the membrane trafficking machinery. This negative modulation of CFTR function can be reversed by soluble syntaxin 1A peptides and by the syntaxin 1A binding protein, Munc-18. In the present study, we determined whether syntaxin 1A is expressed in native epithelial tissues that normally express CFTR and whether it modulates CFTR currents in these tissues. Using immunoblotting and immunofluorescence, we observed syntaxin 1A in native gut and airway epithelial tissues and showed that epithelial cells from these tissues express syntaxin 1A at >10-fold molar excess over CFTR. Syntaxin 1A is seen near the apical cell surfaces of human bronchial airway epithelium. Reagents that disrupt the CFTR-syntaxin 1A interaction, including soluble syntaxin 1A cytosolic domain and recombinant Munc-18, augmented cAMP-dependent CFTR Cl(-) currents by more than 2- to 4-fold in mouse tracheal epithelial cells and cells derived from human nasal polyps, but these reagents did not affect CaMK II-activated Cl(-) currents in these cells.

[Effects of growth factors and estrogen on the proliferation and prolactin gene expression in anterior pituitary cells of rats]

OBJECTIVE

Detect the effects of exogenous 17 beta-estradiol (E2), epidermal growth factor (EGF), and transforming growth factor beta 1 (TGF beta 1) on the proliferation and prolactin (PRL) gene expression in primary serum-free cultured anterior pituitary cells in vitro.

METHODS

Laser scanning confocal microscopy (LSCM) and in situ hybridization in primary serum-free cultures of rat anterior pituitary cells were employed.

RESULTS

After 36 hours incubation of the monolayer with E2(10(-8) mol/L) and EGF(10(-8) mol/L), DNA and PRL mRNA contents in the cells were increased significantly (P < 0.001); and when cells were co-incubated with E2 and EGF at the same time, the levels of DNA and PRL mRNA were higher than those treated with E2 or EGF alone (P < 0.01), respectively. TGF beta 1(2 ng/ml) treatment decreased the DNA and PRL mRNA contents significantly (P < 0.001). Its inhibitory effect was reduced at the presence of E2, the DNA and PRL mRNA levels in the cells were higher than those treated with TGF beta 1 alone (P < 0.001), but still lower than E2 alone treatment (P < 0.001).

CONCLUSIONS

The results indicate that EGF and TGF beta 1 exerte stimulatory inhibitory effects, on cell proliferation and PRL gene expression in anterior pituitary cells of rats in both basal and E2-induced conditions. EGF and TGF beta 1 may be involoved in the regulation of proliferation and PRL gene expression in anterior pituitary cells in vivo; and also may be correlated with prolactin-secreting tumors formation induced by E2.

[E2-induced prolactin-secreting tumor of heteroplasty pituitary in renal capsule of the rats]

OBJECTIVE

A prolactin-producing tumor induced by 17-beta-estradiol (E2) in isotransplanted pituitaries under renal capsules of SD rats were studied.

METHODS

Male SD rats (30 days old) were transplanted with an isologaus pituitary under renal capsule and treated with subcutaneous implantation of an empty or E2-laden silastic capsule.

RESULTS

After treated with E2 for 60 days and 120 days, both the eutopic and ectopic pituitaries were more than three times heavier than those from control rats, accompanied by hyperprolactinemia, and the body weight of rats decreased significantly. The effects of E2 on the weight of eutopic pituitary and the concentration of plasma PRL were time-dependent. In situ hybridization was employed to measure the levels of PRL mRNA expression in cells from the eutopic and ectopic pituitaries 120 days after treatment of E2. The PRL mRNA contents in both the eutopic and ectopic pituitary cells were much greater than those in untreated pituitary cells. But PRL mRNA levels showed no significant difference between the eutopic and ectopic pituitary cells.

CONCLUSIONS

Our previous data has shown that prolactinomas can be induced by chronic treatment of E2 in eutopic pituitaries of SD rats. In present study it appeared that E2 exerted similar effect on the ectopic pituitaries which were distant from the hypothalamus. Our results also demonstrated that E2 could promote the PRL gene expression in both the eutopic and ectopic pituitary cells, and there was no significant difference between them. Our data suggested the possibility of PRL-producing pituitary tumors could originate from anterior pituitary.

[Melatonin inhibits TRH-stimulating prolactin gene expression of anterior pituitary cells in newborn rat in vitro]

OBJECTIVE AND METHODS

This work was to investigate whether melatonin (MEL) plays a role in the gene expression of prolactin (PRL), by the Method of in situ hybridyzation.

RESULTS

Our results indicated that, at a higher concentration, MEL not only inhibits TRH (thyrotropin releasing hormone) stimulating PRL gene expression of anterior pituitary cell in newborn rat, but also exerts a direct inhibitory effect on PRL gene expression in vitro.

CONCLUSION

These results suggest that MEL may be a regulator of PRL synthesis and secreting in vivo.

[The effects of E2 and it's metabolites on the proliferation of rat anterior pituitary cells in vitro]

OBJECTIVE AND METHODS

The present work is determined to observe the effects of E2 (estradiol), 2-OHE1 (2-hydroxyestrone), 2-OHE2 (2-hydroxyestrodiol) on the proliferation of rat anterior pituitary cells (APC) in vitro by laser scanning confocal microscopy.

RESULTS

10(-6) mol/L E2 stimulated the growth of APC. After 2 days of incubation with E2, the DNA content of APC increased to 1.3 times of the control group (P < 0.01). 10(-6) mol/L 2-OHE2 (other than 2-OHE1) stimulated proliferative activity of APC and inhibited the inhibitory effect of peribidil (10(-5) mol/L), a dopamine receptor agonist, on the poliferative activity of rat APC.