Regulation of unfolded protein response modulator XBP1s by acetylation and deacetylation

Pivotal role of the endoplasmic reticulum stress-related XBP1s/miR-22/SIRT1 axis in acute myeloid leukemia apoptosis and response to chemotherapy

Malignant growth relies on rapid protein synthesis frequently leading to endoplasmic reticulum (ER) overload and accumulation of unfolded or misfolded protein in this cellular compartment. In the ER, protein homeostasis is finely regulated by a mechanism called the unfolded protein response (UPR), involving the activation of signalization pathways mediated by three transmembrane proteins, namely PERK, IRE1 and ATF6. IRE1 endoribonuclease activation leads in particular to the splicing of the cytosolic mRNA encoding the key UPR-specific transcription factor XBP1s. Our study shows that sustained activation of XBP1s expression in acute myeloid leukemia (AML) cells induces apoptosis in vitro and in vivo, whereas a moderate XBP1s expression sensitizes cells to chemotherapeutic treatments. ChIP-seq experiments identified specific XBP1s target genes including the MIR22HG lncRNA, the precursor transcript of microRNA-22-3p. miR-22-3p upregulation by XBP1s or forced expression of miR-22 significantly decreases cell's viability and sensitizes leukemic cells to chemotherapy. We found that miR-22-3p intracellular effects result at least partially from the targeting of the mRNA encoding the deacetylase sirtuin-1 (SIRT1), a well-established pro-survival factor. Therefore, this novel XBP1s/miR-22/SIRT1 axis identified could play a pivotal role in the proliferation and chemotherapeutic response of leukemic cells.

Osteogenesis imperfecta type 10 and the cellular scaffolds underlying common immunological diseases

Osteogenesis imperfecta type 10 (OI10) is caused by loss of function codon variants in the gene SERPINH1 that encodes heat shock protein 47 (HSP47), rather than in a gene specifying bone formation. The HSP47 variants disrupt the folding of both collagen and the endonuclease IRE1α (inositol-requiring enzyme 1α) that splices X-Box Binding Protein 1 (XBP1) mRNA. Besides impairing bone development, variants likely affect osteoclast differentiation. Three distinct biochemical scaffold play key roles in the differentiation and regulated cell death of osteoclasts. These scaffolds consist of non-templated protein modifications, ordered lipid arrays, and protein filaments. The scaffold components are specified genetically, but assemble in response to extracellular perturbagens, pathogens, and left-handed Z-RNA helices encoded genomically by flipons. The outcomes depend on interactions between RIPK1, RIPK3, TRIF, and ZBP1 through short interaction motifs called RHIMs. The causal HSP47 nonsynonymous substitutions occur in a novel variant leucine repeat region (vLRR) that are distantly related to RHIMs. Other vLRR protein variants are causal for a variety of different mendelian diseases. The same scaffolds that drive mendelian pathology are associated with many other complex disease outcomes. Their assembly is triggered dynamically by flipons and other context-specific switches rather than by causal, mendelian, codon variants.

Melatonin attenuates scopolamine-induced cognitive dysfunction through SIRT1/IRE1α/XBP1 pathway

BACKGROUND

The prevalence of dementia around the world is increasing, and these patients are more likely to have cognitive impairments, mood and anxiety disorders (depression, anxiety, and panic disorder), and attention deficit disorders over their lifetime. Previous studies have proven that melatonin could improve memory loss, but its specific mechanism is still confused.

METHODS

In this study, we used in vivo and in vitro models to examine the neuroprotective effect of melatonin on scopolamine (SCOP)-induced cognitive dysfunction. The behavioral tests were performed. 18F-FDG PET imaging was used to assess the metabolism of the brain. Protein expressions were determined through kit detection, Western blot, and immunofluorescence. Nissl staining was conducted to reflect neurodegeneration. MTT assay and RNAi transfection were applied to perform the in vitro experiments.

RESULTS

We found that melatonin could ameliorate SCOP-induced cognitive dysfunction and relieve anxious-like behaviors or HT22 cell damage. 18F-FDG PET-CT results showed that melatonin could improve cerebral glucose uptake in SCOP-treated mice. Melatonin restored the cholinergic function, increased the expressions of neurotrophic factors, and ameliorated oxidative stress in the brain of SCOP-treated mice. In addition, melatonin upregulated the expression of silent information regulator 1 (SIRT1), which further relieved endoplasmic reticulum (ER) stress by decreasing the expression of phosphorylate inositol-requiring enzyme (p-IRE1α) and its downstream, X-box binding protein 1 (XBP1).

CONCLUSIONS

These results indicated that melatonin could ameliorate SCOP-induced cognitive dysfunction through the SIRT1/IRE1α/XBP1 pathway. SIRT1 might be the critical target of melatonin in the treatment of dementia.

Lycium barbarum polysaccharide ameliorates the accumulation of lipid droplets in adipose tissue via an ATF6/SIRT1-dependent mechanism

Lipid droplets (LDs) are dynamic organelles that store neutral lipids and are closely linked to obesity. Previous studies have suggested that Lycium barbarum polysaccharide (LBP) supplements can ameliorate obesity, but the underlying mechanisms remain unclear. In this study, we hypothesize that LBP alleviates LD accumulation in adipose tissue (AT) by inhibiting fat-specific protein 27 (Fsp27) through an activating transcription factor-6 (ATF6)/small-molecule sirtuin 1 (SIRT1)-dependent mechanism. LD accumulation in AT is induced in high-fat diet (HFD)-fed mice, and differentiation of 3T3-L1 preadipocytes (PAs) is induced. The ability of LBP to alleviate LD accumulation and the possible underlying mechanism are then investigated both in vivo and in vitro. The influences of LBP on the expressions of LD-associated genes ( ATF6 and Fsp27) are also detected. The results show that HFD and PA differentiation markedly increase LD accumulation in ATs and adipocytes, respectively, and these effects are markedly suppressed by LBP supplementation. Furthermore, LBP significantly activates SIRT1 and decreases ATF6 and Fsp27 expressions. Interestingly, the inhibitory effects of LBP are either abolished or exacerbated when ATF6 is overexpressed or silenced, respectively. Furthermore, SIRT1 level is transcriptionally regulated by LBP through opposite actions mediated by ATF6. Collectively, our findings suggest that LBP supplementation alleviates obesity by ameliorating LD accumulation, which might be partially mediated by an ATF6/SIRT1-dependent mechanism.

SIRT1 exerts protective effects by inhibiting endoplasmic reticulum stress and NF-κB signaling pathways

Silent information regulator two homolog 1 (SIRT1), an NAD + -dependent histone deacetylase, plays a pivotal regulatory role in a myriad of physiological processes. A growing body of evidence suggests that SIRT1 can exert protective effects in metabolic disorders and neurodegenerative diseases by inhibiting endoplasmic reticulum (ER) stress and the nuclear factor-κB (NF-κB) inflammatory signaling pathway. This review systematically elucidates the molecular mechanisms and biological significance of SIRT1 in regulating ER stress and the NF-κB pathway. On one hand, SIRT1 can deacetylate key molecules in the ER stress pathway, such as glucose-regulated protein 78 (GRP78), X-box binding protein 1 (XBP1), PKR-like ER kinase (PERK), inositol-requiring enzyme 1α (IRE1α), and activating transcription factor 6 (ATF6), thereby alleviating ER stress. On the other hand, SIRT1 can directly or indirectly remove the acetylation modification of the NF-κB p65 subunit, inhibiting its transcriptional activity and thus attenuating inflammatory responses. Through these mechanisms, SIRT1 can ameliorate insulin resistance in metabolic diseases, exert cardioprotective effects in ischemia-reperfusion injury, and reduce neuronal damage in neurodegenerative diseases. However, it is important to note that while these findings are promising, the complex nature of the biological systems involved warrants further investigation to fully unravel the intricacies of SIRT1's regulatory mechanisms. Nevertheless, understanding the regulatory mechanisms of SIRT1 on ER stress and the NF-κB pathway is of great significance for expanding our knowledge of the pathogenesis of related diseases and exploring new preventive and therapeutic strategies targeting SIRT1.

Lack of the Histone Deacetylase SIRT1 Leads to Protection against Endoplasmic Reticulum Stress through the Upregulation of Heat Shock Proteins

Histone deacetylase SIRT1 represses gene expression through the deacetylation of histones and transcription factors and is involved in the protective cell response to stress and aging. However, upon endoplasmic reticulum (ER) stress, SIRT1 impairs the IRE1α branch of the unfolded protein response (UPR) through the inhibition of the transcriptional activity of XBP-1 and SIRT1 deficiency is beneficial under these conditions. We hypothesized that SIRT1 deficiency may unlock the blockade of transcription factors unrelated to the UPR promoting the synthesis of chaperones and improving the stability of immature proteins or triggering the clearance of unfolded proteins. SIRT1+/+ and SIRT1-/- fibroblasts were exposed to the ER stress inducer tunicamycin and cell survival and expression of heat shock proteins were analyzed 24 h after the treatment. We observed that SIRT1 loss significantly reduced cell sensitivity to ER stress and showed that SIRT1-/- but not SIRT1+/+ cells constitutively expressed high levels of phospho-STAT3 and heat shock proteins. Hsp70 silencing in SIRT1-/- cells abolished the resistance to ER stress. Furthermore, accumulation of ubiquitinated proteins was lower in SIRT1-/- than in SIRT1+/+ cells. Our data showed that SIRT1 deficiency enabled chaperones upregulation and boosted the proteasome activity, two processes that are beneficial for coping with ER stress.

Endoplasmic reticulum-associated SARS-CoV-2 ORF3a elicits heightened cytopathic effects despite robust ER-associated degradation

IMPORTANCE

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has tragically claimed millions of lives through coronavirus disease 2019 (COVID-19), and there remains a critical gap in our understanding of the precise molecular mechanisms responsible for the associated fatality. One key viral factor of interest is the SARS-CoV-2 ORF3a protein, which has been identified as a potent inducer of host cellular proinflammatory responses capable of triggering the catastrophic cytokine storm, a primary contributor to COVID-19-related deaths. Moreover, ORF3a, much like the spike protein, exhibits a propensity for frequent mutations, with certain variants linked to the severity of COVID-19. Our previous research unveiled two distinct types of ORF3a mutant proteins, categorized by their subcellular localizations, setting the stage for a comparative investigation into the functional and mechanistic disparities between these two types of ORF3a variants. Given the clinical significance and functional implications of the natural ORF3a mutations, the findings of this study promise to provide invaluable insights into the potential roles undertaken by these mutant ORF3a proteins in the pathogenesis of COVID-19.

Constitutive expression of spliced X-box binding protein 1 inhibits dentin formation in mice

Upon endoplasmic reticulum (ER) stress, inositol-requiring enzyme 1 (IRE1) is activated, which subsequently converts an unspliced X-box binding protein 1 (XBP1U) mRNA to a spliced mRNA that encodes a potent XBP1S transcription factor. XBP1S is essential for relieving ER stress and secretory cell differentiation. We previously established Twist2-Cre;Xbp1 CS/+ mice that constitutively expressed XBP1S in the Twist2-expressing cells as well as in the cells derived from the Twist2-expressing cells. In this study, we analyzed the dental phenotype of Twist2-Cre;Xbp1 CS/+ mice. We first generated a mutant Xbp1s minigene that corresponds to the recombinant Xbp1 Δ26 allele (the Xbp1 CS allele that has undergone Cre-mediated recombination) and confirmed that the Xbp1s minigene expressed XBP1S that does not require IRE1α activation in vitro. Consistently, immunohistochemistry showed that XBP1S was constitutively expressed in the odontoblasts and other dental pulp cells in Twist2-Cre;Xbp1 CS/+ mice. Plain X-ray radiography and µCT analysis revealed that constitutive expression of XBP1S altered the dental pulp chamber roof- and floor-dentin formation, resulting in a significant reduction in dentin/cementum formation in Twist2-Cre;Xbp1 CS/+ mice, compared to age-matched Xbp1 CS/+ control mice. However, there is no significant difference in the density of dentin/cementum between these two groups of mice. Histologically, persistent expression of XBP1S caused a morphological change in odontoblasts in Twist2-Cre;Xbp1 CS/+ mice. Nevertheless, in situ hybridization and immunohistochemistry analyses showed that continuous expression of XBP1S had no apparent effects on the expression of the Dspp and Dmp1 genes. In conclusion, these results support that sustained production of XBP1S adversely affected odontoblast function and dentin formation.

Characterizing genetic variation in the regulation of the ER stress response through computational and cis-eQTL analyses

Misfolded proteins in the endoplasmic reticulum (ER) elicit the ER stress response, a large transcriptional response driven by 3 well-characterized transcription factors (TFs). This transcriptional response is variable across different genetic backgrounds. One mechanism in which genetic variation can lead to transcriptional variability in the ER stress response is through altered binding and activity of the 3 main TFs: XBP1, ATF6, and ATF4. This work attempts to better understand this mechanism by first creating a computational pipeline to identify potential binding sites throughout the human genome. We utilized GTEx data sets to identify cis-eQTLs that fall within predicted TF binding sites (TFBSs). We also utilized the ClinVar database to compare the number of pathogenic vs benign variants at different positions of the binding motifs. Finally, we performed a cis-eQTL analysis on human cell lines experiencing ER stress to identify cis-eQTLs that regulate the variable ER stress response. The majority of these cis-eQTLs are unique to a given condition: control or ER stress. Some of these stress-specific cis-eQTLs fall within putative binding sites of the 3 main ER stress response TFs, providing a potential mechanism by which these cis-eQTLs might be impacting gene expression under ER stress conditions through altered TF binding. This study represents the first cis-eQTL analysis on human samples experiencing ER stress and is a vital step toward identifying the genetic components responsible for the variable ER stress response.

SIRT-1 is required for release of enveloped enteroviruses

Enterovirus D68 (EV-D68) is a re-emerging enterovirus that causes acute respiratory illness in infants and has recently been linked to Acute Flaccid Myelitis. Here, we show that the histone deacetylase, SIRT-1, is essential for autophagy and EV-D68 infection. Knockdown of SIRT-1 inhibits autophagy and reduces EV-D68 extracellular titers. The proviral activity of SIRT-1 does not require its deacetylase activity or functional autophagy. SIRT-1's proviral activity is, we demonstrate, mediated through the repression of endoplasmic reticulum stress (ER stress). Inducing ER stress through thapsigargin treatment or SERCA2A knockdown in SIRT-1 knockdown cells had no additional effect on EV-D68 extracellular titers. Knockdown of SIRT-1 also decreases poliovirus and SARS-CoV-2 titers but not coxsackievirus B3. In non-lytic conditions, EV-D68 is primarily released in an enveloped form, and SIRT-1 is required for this process. Our data show that SIRT-1, through its translocation to the cytosol, is critical to promote the release of enveloped EV-D68 viral particles.

The Aspergillus fumigatus UPR is variably activated across nutrient and host environments and is critical for the establishment of corneal infection

The Aspergillus fumigatus unfolded protein response (UPR) is a two-component relay consisting of the ER-bound IreA protein, which splices and activates the mRNA of the transcription factor HacA. Spliced hacA accumulates under conditions of acute ER stress in vitro, and UPR null mutants are hypovirulent in a murine model of invasive pulmonary infection. In this report, we demonstrate that a hacA deletion mutant (ΔhacA) is furthermore avirulent in a model of fungal keratitis, a corneal infection, and an important cause of ocular morbidity and unilateral blindness worldwide. Interestingly, we demonstrate that A. fumigatus hacA is spliced in infected lung samples, but not in the cornea, suggesting the amount of ER stress experienced by the fungus varies upon the host niche. To better understand how the UPR contributes to fungal cell biology across a spectrum of ER-stress levels, we employed transcriptomics on the wild-type and ΔhacA strains in glucose minimal media (low stress), glucose minimal media with dithiothreitol (high stress), and gelatin minimal media as a proxy for the nutrient stress encountered in the cornea (mid-level stress). These data altogether reveal a unique HacA-dependent transcriptome under each condition, suggesting that HacA activity is finely-tuned and required for proper fungal adaptation in each environment. Taken together, our results indicate that the fungal UPR could serve as an important antifungal target in the setting of both invasive pulmonary and corneal infections.

SIRT3 alleviates imiquimod-induced psoriatic dermatitis through deacetylation of XBP1s and modulation of TLR7/8 inducing IL-23 production in macrophages

Current evidence suggests that IL-23, IL-6, and TNF-α play pivotal roles in the pathogenesis of psoriasis. Although it has been established that Sirtuin 3 (SIRT3) mediates the inflammatory process, the underlying mechanisms remain largely unclear. Herein, we substantiated that the inhibition or deletion of SIRT3 increased the acetylation level of spliced form of X-box binding protein 1 (XPB1s), enhancing its transcriptional activity and IL-23a production. Pharmacologically inhibition of XBP1s with MKC8866 downregulated the expression of inflammatory cytokines in SIRT3-inhibited or Sirt3-KO BMDMs stimulated by IMQ. Inhibition or knockdown of SIRT3 could exacerbate psoriasis-like skin inflammation in an imiquimod-induced psoriasis-like mouse model. Besides, a decrease in SIRT3 expression was observed in the macrophages of psoriasis patients, which increased the expression and acetylation level of XBP1s. Overall, we provide compelling evidence of the crucial role of SIRT3 in the IL-23 axis in psoriatic inflammation and novel molecular insights into the anti-inflammatory effects of SIRT3.

SIRT7 orchestrates melanoma progression by simultaneously promoting cell survival and immune evasion via UPR activation

Melanoma is the most lethal type of skin cancer, originating from the malignant transformation of melanocyte. While the development of targeted therapy and immunotherapy has gained revolutionary advances in potentiating the therapeutic effect, the prognosis of patients with melanoma is still suboptimal. During tumor progression, melanoma frequently encounters stress from both endogenous and exogenous sources in tumor microenvironment. SIRT7 is a nuclear-localized deacetylase of which the activity is highly dependent on intracellular nicotinamide adenine dinucleotide (NAD⁺), with versatile biological functions in maintaining cell homeostasis. Nevertheless, whether SIRT7 regulates tumor cell biology and tumor immunology in melanoma under stressful tumor microenvironment remains elusive. Herein, we reported that SIRT7 orchestrates melanoma progression by simultaneously promoting tumor cell survival and immune evasion via the activation of unfolded protein response. We first identified that SIRT7 expression was the most significantly increased one in sirtuins family upon stress. Then, we proved that the deficiency of SIRT7 potentiated tumor cell death under stress in vitro and suppressed melanoma growth in vivo. Mechanistically, SIRT7 selectively activated the IRE1α-XBP1 axis to potentiate the pro-survival ERK signal pathway and the secretion of tumor-promoting cytokines. SIRT7 directly de-acetylated SMAD4 to antagonize the TGF-β-SMAD4 signal, which relieved the transcriptional repression on IRE1α and induced the activation of the IRE1α-XBP1 axis. Moreover, SIRT7 up-regulation eradicated anti-tumor immunity by promoting PD-L1 expression via the IRE1α-XBP1 axis. Additionally, the synergized therapeutic effect of SIRT7 suppression and anti-PD-1 immune checkpoint blockade was also investigated. Taken together, SIRT7 can be employed as a promising target to restrain tumor growth and increase the effect of melanoma immunotherapy.

P300 Interacted With N-Myc and Regulated Its Protein Stability via Altering Its Post-Translational Modifications in Neuroblastoma

MYCN amplification is an independent risk factor for poor prognosis in neuroblastoma (NB), but its protein product cannot be directly targeted because of protein structure. Thus, this study aimed to explore novel ways to indirectly target N-Myc by regulating its post-translational modifications (PTMs) and therefore protein stability. N-Myc coimmunoprecipitation combined with HPLC-MS/MS identified 16 PTM residues and 114 potential N-Myc-interacting proteins. Notably, both acetylation and ubiquitination were identified on lysine 199 of N-Myc. We then discovered that p300, which can interact with N-Myc, modulated the protein stability of N-Myc in MYCN-amplified NB cell lines and simultaneously regulated the acetylation level and ubiquitination level on lysine-199 of N-Myc protein in vitro. Furthermore, p300 correlated with poor prognosis in NB patients. Taken together, p300 can be considered as a potential therapeutic target to treat MYCN-amplified NB patients, and other identified PTMs and interacting proteins also provide potential targets for further study.

The Dialogue Between Neuroinflammation and Adult Neurogenesis: Mechanisms Involved and Alterations in Neurological Diseases

Adult neurogenesis occurs mainly in the subgranular zone of the hippocampal dentate gyrus and the subventricular zone of the lateral ventricles. Evidence supports the critical role of adult neurogenesis in various conditions, including cognitive dysfunction, Alzheimer's disease (AD), and Parkinson's disease (PD). Several factors can alter adult neurogenesis, including genetic, epigenetic, age, physical activity, diet, sleep status, sex hormones, and central nervous system (CNS) disorders, exerting either pro-neurogenic or anti-neurogenic effects. Compelling evidence suggests that any insult or injury to the CNS, such as traumatic brain injury (TBI), infectious diseases, or neurodegenerative disorders, can provoke an inflammatory response in the CNS. This inflammation could either promote or inhibit neurogenesis, depending on various factors, such as chronicity and severity of the inflammation and underlying neurological disorders. Notably, neuroinflammation, driven by different immune components such as activated glia, cytokines, chemokines, and reactive oxygen species, can regulate every step of adult neurogenesis, including cell proliferation, differentiation, migration, survival of newborn neurons, maturation, synaptogenesis, and neuritogenesis. Therefore, this review aims to present recent findings regarding the effects of various components of the immune system on adult neurogenesis and to provide a better understanding of the role of neuroinflammation and neurogenesis in the context of neurological disorders, including AD, PD, ischemic stroke (IS), seizure/epilepsy, TBI, sleep deprivation, cognitive impairment, and anxiety- and depressive-like behaviors. For each disorder, some of the most recent therapeutic candidates, such as curcumin, ginseng, astragaloside, boswellic acids, andrographolide, caffeine, royal jelly, estrogen, metformin, and minocycline, have been discussed based on the available preclinical and clinical evidence.

Ebola Virus Activates IRE1α-Dependent XBP1u Splicing

Ebola (EBOV) and Marburg virus (MARV) are highly pathogenic filoviruses that influence cellular signaling according to their own needs. MARV has been shown to regulate the IRE1α-dependent unfolded protein response (UPR) to ensure optimal virus replication. It was not known whether EBOV affects this signaling cascade, which can be beneficial or detrimental for viruses. Activation of IRE1α leads to the expression of the transcription factor XBP1s, which binds to cis-acting UPR elements (UPRE), resulting in the expression of genes aimed at restoring homeostasis in the endoplasmic reticulum. We observed that EBOV infection, in contrast to MARV infection, led to UPR activation by IRE1α-dependent but not ATF6-dependent signaling. We showed an activation of IRE1α, XBP1s and UPRE target genes upon EBOV infection. ATF6, another UPRE transcription factor, was not activated. UPRE activation was mainly attributed to the EBOV nucleoprotein NP and the soluble glycoprotein sGP. Finally, activation of UPR by thapsigargin, a potent ER-stress inducer, in parallel to infection as well as knock-out of XBP1 had no effect on EBOV growth, while MARV proliferation was affected by thapsigargin-dependent UPR activation. Taken together EBOV and MARV differ in their strategy of balancing IRE1α-dependent signaling for their own needs.

Combined inhibition of BCR-ABL1 and the proteasome as a potential novel therapeutic approach in BCR-ABL positive acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is a disease of lymphoid progenitor cells with an often aggressive course and is commonly caused by the BCR-ABL fusion gene t(9;22) in adults. This fusion gene encodes a constitutively active tyrosine kinase that can be effectively inhibited by tyrosine kinase inhibitors (TKIs), with imatinib being the paradigmatic agent of this class. However, BCR-ABL+ ALL cells rapidly develop mutations against many of the available TKIs, and consecutive disease relapse still results in an overall unfavorable prognosis for patients with this disease. To date, allogeneic stem cell transplantation is the only known curative therapeutic option for the mostly elderly patients with BCR-ABL+ ALL. The discrepancy between the limited therapeutic armamentarium and the growing therapeutic need in an aging population is therefore a reason to test drug combinations against BCR-ABL+ ALL. In this study, we demonstrate that the combination of TKIs with proteasome inhibitors efficiently and under certain conditions synergistically exerts cytotoxic effects in BCR-ABL+ ALL cells in vitro with respect to the induction of apoptosis. Both sole and combined treatment of BCR-ABL+ ALL with the proteasome inhibitors bortezomib and ixazomib, respectively, and TKI causes a significantly greater reduction in cell viability than TKI treatment alone in both BCR-ABL+ cell lines TOM-1 and BV-173. In BV-173 cells, we observed a significant reduction in cell viability to only 1.26%±0.46% with bortezomib treatment and 1.57±0.7% with combination treatment, whereas cells treated with dasatinib alone still had a viable percentage of 40.58±2.6%. Similar results were obtained when ixazomib was applied to both cell lines, and apoptosis was induced in both cases (93.36%±2.7% apoptotic BV-173 cells when treated with ixazomib and TKI). The combination of TKI and proteasome inhibitor is efficient in vitro, potentially expanding the spectrum of therapeutic options for patients with BCR-ABL+ ALL.

4-PBA rescues hyperoxaluria induced nephrolithiasis by modulating urinary glycoproteins: Cross talk between endoplasmic reticulum, calcium homeostasis and mitochondria

AIM

Urinary glycoproteins such as Tamm Horsfall Protein (THP) and Osteopontin (OPN) are well established key regulators of renal stone formation. Additionally, recent revelations have highlighted the influence of Endoplasmic Reticulum (ER) and mitochondria of crucial importance in nephrolithiasis. However, till date conclusive approach highlighting the influence of ER stress on urinary glycoproteins and chaperone in nephrolithiasis remains elusive. Therefore, the present study was focussed on deciphering the possible effect of 4-PBA mitigating ER stress on urinary glycoproteins and calnexin (chaperone) with emphasis on interlinking calcium homeostasis in hyperoxaluric rats.

MATERIAL AND METHODS

Post 9 days of treatment, animals were sacrificed, and renal tissues were investigated for urinary glycoproteins, calnexin, calcium homeostasis, ER environment, redox status, and mitochondrial linkage.

KEY FINDINGS

4-PBA appreciably reversed the altered levels of THP, OPN, and calnexin observed along with curtailing the disrupted calcium homeostasis when assessed for SERCA activity and intra-cellular calcium levels. Additionally, significant improvement in the perturbed ER environment as verified by escalated ER stress markers, disturbed protein folding-aggregation-degradation (congo red assay) pathway, and redox status was found post 4-PBA intervention. Interestingly, linkage of ER stress and mitochondria was established under hyperoxaluric conditions when assessed for protein levels of VDAC1 and GRP75.

SIGNIFICANCE

4-PBA treatment resulted in rectifying the repercussions of ER-mitochondrial caused distress when assessed for protein folding/aggregation/degradation events along with disturbed calcium homeostasis. The present study advocates the necessity to adopt a holistic vision towards hyperoxaluria with emphasis on glycoproteins and ER environment.

Impact of Calcium Influx on Endoplasmic Reticulum in Excitotoxic Neurons: Role of Chemical Chaperone 4-PBA

Excessive activation of α-amino-3-hydroxy-5-methyl-4-isoxazole propoinic acid (AMPA) receptors instigates excitotoxicity via enhanced calcium influx in the neurons thus inciting deleterious consequences. Additionally, Endoplasmic Reticulum (ER) is pivotal in maintaining the intracellular calcium balance. Considering this, studying the aftermath of enhanced calcium uptake by neurons and its effect on ER environment can assist in delineating the pathophysiological events incurred by excitotoxicty. The current study was premeditated to decipher the role of ER pertaining to calcium homeostasis in AMPA-induced excitotoxicity. The findings showed, increased intracellular calcium levels (measured by flowcytometry and spectroflourimeter using Fura 2AM) in AMPA excitotoxic animals (male Sprague dawely rats) (intra-hippocampal injection of 10 mM AMPA). Further, ER resident proteins like calnexin, PDI and ERp72 were found to be upregulated, which further modulated the functioning of ER membrane calcium channels viz. IP3R, RyR, and SERCA pump. Altered calcium homeostasis further led to ER stress and deranged the protein folding capacity of ER post AMPA toxicity, which was ascertained by unfolded protein response (UPR) pathway markers such as IRE1α, eIF2α, and ATF6α. Chemical chaperone, 4-phenybutric acid (4-PBA), ameliorated the protein folding capacity and subsequent UPR markers. In addition, modulation of calcium channels and calcium regulating machinery of ER post 4-PBA administration restored the calcium homeostasis. Therefore the study reinforces the significance of ER stress, a debilitating outcome of impaired calcium homeostasis, under AMPA-induced excitotoxicity. Also, employing chaperone-based therapeutic approach to curb ER stress can restore the calcium imbalance in the neuropathological diseases.

Melatonin promotes sirtuin 1 expression and inhibits IRE1α–XBP1S–CHOP to reduce endoplasmic reticulum stress–mediated apoptosis in chondrocytes

Osteoarthritis (OA) is the most common chronic disease characterized by a loss of chondrocytes and the degeneration of cartilage. Inflammation plays an important role in the pathogenesis and progression of OA via the activation of the endoplasmic reticulum (ER) stress signaling pathway. In this study, we stimulated human primary chondrocytes with lipopolysaccharide (LPS) to reduce cell viability and induce chondrocyte apoptosis. LPS–stimulated human primary chondrocytes induced ER stress and significantly upregulated the ER chaperone glucose–regulated protein 78 (GRP78) and increased the expression level of C/EBP–homologous protein (CHOP), a key mediator of ER stress––induced apoptosis. Interestingly, melatonin treatment attenuated ER stress–mediated chondrocyte apoptosis. Melatonin inhibited the expression of cleaved caspase-3, cleaved caspase-10, Bax, CHOP, GRP78, cleaved caspase-4, phospho–inositol–requiring enzyme 1α (P-IRE1α), and spliced X-box-binding protein 1 (XBP1S). In an anterior cruciate ligament transection mouse model of OA, melatonin (50 and 150 mg/kg) dose–dependently relieved joint cartilage degeneration and inhibitied of chondrocyte apoptosis. Immunohistochemical analysis indicated that melatonin could promote SIRT1 the expression and inhibit CHOP and cleaved caspase-3 expression in OA mice. In conclusion, our findings demonstrate for the first time that melatonin inhibits the IRE1α-XBP1S-CHOP signaling pathway by promoting the expression of SIRT1 in LPS-treated human chondrocytes and delaying OA progression in vivo.

Notch-activated mesenchymal stromal/stem cells enhance the protective effect against acetaminophen-induced acute liver injury by activating AMPK/SIRT1 pathway

Background

Notch signaling plays important roles in regulating innate immunity. However, little is known about the role of Notch in mesenchymal stromal/stem cell (MSC)-mediated immunomodulation during liver inflammatory response.

Methods

Notch activation in human umbilical cord-derived MSCs was performed by a tissue culture plate coated with Notch ligand, recombinant human Jagged1 (JAG1). Mice were given intravenous injection of Notch-activated MSCs after acetaminophen (APAP)-induced acute liver injury. Liver tissues were collected and analyzed by histology and immunohistochemistry.

Results

MSC administration reduced APAP-induced hepatocellular damage, as manifested by decreased serum ALT levels, intrahepatic macrophage/neutrophil infiltration, hepatocellular apoptosis and proinflammatory mediators. The anti-inflammatory activity and therapeutic effects of MSCs were greatly enhanced by Notch activation via its ligand JAG1. However, Notch2 disruption in MSCs markedly diminished the protective effect of MSCs against APAP-induced acute liver injury, even in the presence of JAG1 pretreatment. Strikingly, Notch-activated MSCs promoted AMP-activated protein kinase (AMPKα) phosphorylation, increased the sirtuins 1 (SIRT1) deacetylase expression, but downregulated spliced X-box-binding protein 1 (XBP1s) expression and consequently reduced NLR family pyrin domain-containing 3 (NLRP3) inflammasome activation. Furthermore, SIRT1 disruption or XBP1s overexpression in macrophages exacerbated APAP-triggered liver inflammation and augmented NLRP3/caspase-1 activity in MSC-administrated mice. Mechanistic studies further demonstrated that JAG1-pretreated MSCs activated Notch2/COX2/PGE2 signaling, which in turn induced macrophage AMPK/SIRT1 activation, leading to XBP1s deacetylation and inhibition of NLRP3 activity.

Conclusions

Activation of Notch2 is required for the ability of MSCs to reduce the severity of APAP-induced liver damage in mice. Our findings underscore a novel molecular insights into MSCs-mediated immunomodulation by activating Notch2/COX2/AMPK/SIRT1 pathway and thus provide a new strategy for the treatment of liver inflammatory diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02999-6.

Effects of Epigenetic Modification of PGC-1α by a Chemical Chaperon on Mitochondria Biogenesis and Visual Function in Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a hereditary blinding disease characterized by gradual photoreceptor death, which lacks a definitive treatment. Here, we demonstrated the effect of 4-phenylbutyric acid (PBA), a chemical chaperon that can suppress endoplasmic reticulum (ER) stress, in P23H mutant rhodopsin knock-in RP models. In the RP models, constant PBA treatment led to the retention of a greater number of photoreceptors, preserving the inner segment (IS), a mitochondrial- and ER-rich part of the photoreceptors. Electroretinography showed that PBA treatment preserved photoreceptor function. At the early point, ER-associated degradation markers, xbp1s, vcp, and derl1, mitochondrial kinetic-related markers, fis1, lc3, and mfn1 and mfn2, as well as key mitochondrial regulators, pgc-1α and tfam, were upregulated in the retina of the models treated with PBA. In vitro analyses showed that PBA upregulated pgc-1α and tfam transcription, leading to an increase in the mitochondrial membrane potential, cytochrome c oxidase activity, and ATP levels. Histone acetylation of the PGC-1α promoter was increased by PBA, indicating that PBA affected the mitochondrial condition through epigenetic changes. Our findings constituted proof of concept for the treatment of ER stress-related RP using PBA and revealed PBA’s neuroprotective effects, paving the way for its future clinical application.

Regulation of the Homeostatic Unfolded Protein Response in Diabetic Nephropathy

A growing body of scientific evidence indicates that protein homeostasis, also designated as proteostasis, is causatively linked to chronic diabetic nephropathy (DN). Experimental studies have demonstrated that the insulin signaling in podocytes maintain the homeostatic unfolded protein response (UPR). Insulin signaling via the insulin receptor non-canonically activates the spliced X-box binding protein-1 (sXBP1), a highly conserved endoplasmic reticulum (ER) transcription factor, which regulates the expression of genes that control proteostasis. Defective insulin signaling in mouse models of diabetes or the genetic disruption of the insulin signaling pathway in podocytes propagates hyperglycemia induced maladaptive UPR and DN. Insulin resistance in podocytes specifically promotes activating transcription factor 6 (ATF6) dependent pathogenic UPR. Akin to insulin, recent studies have identified that the cytoprotective effect of anticoagulant serine protease-activated protein C (aPC) in DN is mediated by sXBP1. In mouse models of DN, treatment with chemical chaperones that improve protein folding provides an additional benefit on top of currently used ACE inhibitors. Understanding the molecular mechanisms that transmute renal cell specific adaptive responses and that deteriorate renal function in diabetes will enable researchers to develop new therapeutic regimens for DN. Within this review, we focus on the current understanding of homeostatic mechanisms by which UPR is regulated in DN.

Integrated omics analysis reveals sirtuin signaling is central to hepatic response to a high fructose diet

BACKGROUND

Dietary high fructose (HFr) is a known metabolic disruptor contributing to development of obesity and diabetes in Western societies. Initial molecular changes from exposure to HFr on liver metabolism may be essential to understand the perturbations leading to insulin resistance and abnormalities in lipid and carbohydrate metabolism. We studied vervet monkeys (Clorocebus aethiops sabaeus) fed a HFr (n=5) or chow diet (n=5) for 6 weeks, and obtained clinical measures of liver function, blood insulin, cholesterol and triglycerides. In addition, we performed untargeted global transcriptomics, proteomics, and metabolomics analyses on liver biopsies to determine the molecular impact of a HFr diet on coordinated pathways and networks that differed by diet.

RESULTS

We show that integration of omics data sets improved statistical significance for some pathways and networks, and decreased significance for others, suggesting that multiple omics datasets enhance confidence in relevant pathway and network identification. Specifically, we found that sirtuin signaling and a peroxisome proliferator activated receptor alpha (PPARA) regulatory network were significantly altered in hepatic response to HFr. Integration of metabolomics and miRNAs data further strengthened our findings.

CONCLUSIONS

Our integrated analysis of three types of omics data with pathway and regulatory network analysis demonstrates the usefulness of this approach for discovery of molecular networks central to a biological response. In addition, metabolites aspartic acid and docosahexaenoic acid (DHA), protein ATG3, and genes ATG7, and HMGCS2 link sirtuin signaling and the PPARA network suggesting molecular mechanisms for altered hepatic gluconeogenesis from consumption of a HFr diet.

Inhibition of histone deacetylation with vorinostat does not prevent tunicamycin-mediated acute kidney injury

Endoplasmic reticulum (ER) stress is associated with acute kidney injury (AKI) caused by various mechanisms, including antibiotics, non-steroidal anti-inflammatory drugs, cisplatin, and radiocontrast. Tunicamycin (TM) is a nucleoside antibiotic that induces ER stress and is a commonly used model of AKI. 4-phenylbutyrate (4-PBA) is a chemical chaperone and histone deacetylase (HDAC) inhibitor and has been shown to protect the kidney from ER stress, apoptosis, and structural damage in a tunicamycin model of AKI. The renal protection provided by 4-PBA is attributed to its ability to prevent misfolded protein aggregation and inhibit ER stress; however, the HDAC inhibitor effects of 4-PBA have not been examined in the TM-induced model of AKI. As such, the main objective of this study was to determine if histone hyperacetylation provides any protective effects against TM-mediated AKI. The FDA-approved HDAC inhibitor vorinostat was used, as it has no ER stress inhibitory effects and therefore the histone hyperacetylation properties alone could be investigated. In vitro work demonstrated that vorinostat inhibited histone deacetylation in cultured proximal tubular cells but did not prevent ER stress or protein aggregation induced by TM. Vorinostat induced a significant increase in cell death, and exacerbated TM-mediated total cell death and apoptotic cell death. Wild type male mice were treated with TM (0.5 mg/kg, intraperitoneal injection), with or without vorinostat (50 mg/kg/day) or 4-PBA (1 g/kg/day). Mice treated with 4-PBA or vorinostat exhibited similar levels of histone hyperacetylation. Expression of the pro-apoptotic protein CHOP was induced with TM, and not inhibited by vorinostat. Further, vorinostat did not prevent any renal damage or decline in renal function caused by tunicamycin. These data suggest that the protective mechanisms found by 4-PBA are primarily due to its molecular chaperone properties, and the HDAC inhibitors used did not provide any protection against renal injury caused by ER stress.

Therapeutic Role of Sirtuins Targeting Unfolded Protein Response, Coagulation, and Inflammation in Hypoxia-Induced Thrombosis

Thrombosis remains one of the leading causes of morbidity and mortality across the world. Many pathological milieus in the body resulting from multiple risk factors escort thrombosis. Hypoxic condition is one such risk factor that disturbs the integrity of endothelial cells to cause an imbalance between anticoagulant and procoagulant proteins. Hypoxia generates reactive oxygen species (ROS) and triggers inflammatory pathways to augment the coagulation cascade. Hypoxia in cells also activates unfolded protein response (UPR) signaling pathways in the endoplasmic reticulum (ER), which tries to restore ER homeostasis and function. But the sustained UPR linked with inflammation, generation of ROS and apoptosis stimulates the severity of thrombosis in the body. Sirtuins, a group of seven proteins, play a vast role in bringing down inflammation, oxidative and ER stress and apoptosis. As a result, sirtuins might provide a therapeutic approach towards the treatment or prevention of hypoxia-induced thrombosis. Sirtuins modulate hypoxia-inducible factors (HIFs) and counteract ER stress-induced apoptosis by attenuating protein kinase RNA-like endoplasmic reticulum kinase (PERK)/Eukaryotic translation initiation factor 2α (eIF2α) pathway activation. It prevents ER-stress mediated inflammation by targeting X-Box Binding Protein 1 (XBP1) and inhibiting nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κβ) signaling through deacetylation. Sirtuins also obstruct nucleotide-binding domain, leucine-rich-containing family, pyrin domain containing 3 (NLRP3) inflammasome activation to reduce the expression of several pro-inflammatory molecules. It protects cells against oxidative stress by targeting nuclear factor erythroid 2-related factor 2 (Nrf2), glutathione (GSH), forkhead box O3 (FOXO3), superoxide dismutase (SOD), catalase (CAT), peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α), glucose-6-phosphate dehydrogenase (G6PD), phosphoglucomutase-2 (PGAM2), and NF-κB, to name few. This review, thus, discusses the potential role of sirtuins as a new treatment for hypoxia-induced thrombosis that involves an intersection of UPR and inflammatory pathways in its pathological manifestation.

Genome-wide mRNA profiling identifies X-box-binding protein 1 (XBP1) as an IRE1 and PUMA repressor

Accumulation of misfolded proteins in ER activates the unfolded protein response (UPR), a multifunctional signaling pathway that is important for cell survival. The UPR is regulated by three ER transmembrane sensors, one of which is inositol-requiring protein 1 (IRE1). IRE1 activates a transcription factor, X-box-binding protein 1 (XBP1), by removing a 26-base intron from XBP1 mRNA that generates spliced XBP1 mRNA (XBP1s). To search for XBP1 transcriptional targets, we utilized an XBP1s-inducible human cell line to limit XBP1 expression in a controlled manner. We also verified the identified XBP1-dependent genes with specific silencing of this transcription factor during pharmacological ER stress induction with both an N-linked glycosylation inhibitor (tunicamycin) and a non-competitive inhibitor of the sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA) (thapsigargin). We then compared those results to the XBP1s-induced cell line without pharmacological ER stress induction. Using next‐generation sequencing followed by bioinformatic analysis of XBP1-binding motifs, we defined an XBP1 regulatory network and identified XBP1 as a repressor of PUMA (a proapoptotic gene) and IRE1 mRNA expression during the UPR. Our results indicate impairing IRE1 activity during ER stress conditions accelerates cell death in ER-stressed cells, whereas elevating XBP1 expression during ER stress using an inducible cell line correlated with a clear prosurvival effect and reduced PUMA protein expression. Although further studies will be required to test the underlying molecular mechanisms involved in the relationship between these genes with XBP1, these studies identify a novel repressive role of XBP1 during the UPR.

Roles of XBP1s in Transcriptional Regulation of Target Genes

The spliced form of X-box binding protein 1 (XBP1s) is an active transcription factor that plays a vital role in the unfolded protein response (UPR). Under endoplasmic reticulum (ER) stress, unspliced Xbp1 mRNA is cleaved by the activated stress sensor IRE1α and converted to the mature form encoding spliced XBP1 (XBP1s). Translated XBP1s migrates to the nucleus and regulates the transcriptional programs of UPR target genes encoding ER molecular chaperones, folding enzymes, and ER-associated protein degradation (ERAD) components to decrease ER stress. Moreover, studies have shown that XBP1s regulates the transcription of diverse genes that are involved in lipid and glucose metabolism and immune responses. Therefore, XBP1s has been considered an important therapeutic target in studying various diseases, including cancer, diabetes, and autoimmune and inflammatory diseases. XBP1s is involved in several unique mechanisms to regulate the transcription of different target genes by interacting with other proteins to modulate their activity. Although recent studies discovered numerous target genes of XBP1s via genome-wide analyses, how XBP1s regulates their transcription remains unclear. This review discusses the roles of XBP1s in target genes transcriptional regulation. More in-depth knowledge of XBP1s target genes and transcriptional regulatory mechanisms in the future will help develop new therapeutic targets for each disease.

The P300/XBP1s/Herpud1 axis promotes macrophage M2 polarization and the development of choroidal neovascularization

Neovascular age‐related macular degeneration (AMD), which is characterized by choroidal neovascularization (CNV), leads to vision loss. M2 macrophages produce vascular endothelial growth factor (VEGF), which aggravates CNV formation. The histone acetyltransferase p300 enhances the stability of spliced X‐box binding protein 1 (XBP1s) and promotes the transcriptional activity of the XBP1s target gene homocysteine inducible endoplasmic reticulum protein with ubiquitin‐like domain 1 (Herpud1). Herpud1 promotes the M2 polarization of macrophages. This study aimed to explore the roles of the p300/XBP1s/Herpud1 axis in the polarization of macrophages and the pathogenesis of CNV. Hypoxia‐induced p300 interacted with XBP1s to acetylate XBP1s in RAW264.7 cells. Additionally, hypoxia‐induced p300 enhanced the XBP‐1s‐mediated unfolded protein response (UPR), alleviated the proteasome‐dependent degradation of XBP1s and enhanced the transcriptional activity of XBP1s for Herpud1. The hypoxia‐induced p300/XBP1s/Herpud1 axis facilitated RAW264.7 cell M2 polarization. Knockdown of the p300/XBP1s/Herpud1 axis in RAW264.7 cells inhibited the proliferation, migration and tube formation of mouse choroidal endothelial cells (MCECs). The p300/XBP1s/Herpud1 axis increased in infiltrating M2‐type macrophages in mouse laser‐induced CNV lesions. Blockade of the p300/XBP1s/Herpud1 axis inhibited macrophage M2 polarization and alleviated CNV lesions. Our study demonstrated that the p300/XBP1s/Herpud1 axis in infiltrating macrophages increased the M2 polarization of macrophages and the development of CNV.

Constitutive expression of spliced XBP1 causes perinatal lethality in mice

Upon endoplasmic reticulum (ER) stress, inositol-requiring enzyme 1 (IRE1) is activated and catalyzes nonconventional splicing of an unspliced X-box binding protein 1 (XBP1U) mRNA to yield a spliced XBP1 (XBP1S) mRNA that encodes a potent XBP1S transcription factor. XBP1S is a key mediator of the IRE1 branch that is essential for alleviating ER stress. We generated a novel mouse strain (referred to as "Xbp1^CS/+ " mice) that constitutively expressed XBP1S after Cre recombinase-mediated recombination. Further breeding of these mice with Twist2 Cre recombinase (Twist2-Cre) knock-in mice generated Twist2-Cre;Xbp1^CS/+ mice. Most Twist2-Cre;Xbp1^CS/+ mice died shortly after birth. Reverse-transcription polymerase chain reaction (RT-PCR) showed that constitutive expression of XBP1S occurred in various mouse tissues examined, but not in the brain. Immunohistochemistry confirmed that although the immunostaining signals for total XBP1 (XBP1U and XBP1S) were found in the calvarial bones in both Twist2-Cre;Xbp1^CS/+ and control mice, the signals for XBP1S were only detected in the Twist2-Cre;Xbp1^CS/+ mice, but not in the control mice. These results suggest that a precise control of XBP1S production is essential for normal mouse development.

Sirtuins: To Be or Not To Be in Diabetic Cardiomyopathy

Diabetic cardiomyopathy is the leading cause of death among people with diabetes. Despite its severity and poor prognosis, there are currently no approved specific drugs to prevent or even treat diabetic cardiomyopathy. There is a need to understand the pathogenic mechanisms underlying the development of diabetic cardiomyopathy to design new therapeutic strategies. These mechanisms are complex and intricate and include metabolic dysregulation, inflammation, oxidative stress, fibrosis, and apoptosis. Sirtuins, a group of deacetylase enzymes, play an important role in all these processes and are, therefore, potential molecular targets for treating this disease. In this review, we discuss the role of sirtuins in the heart, focusing on their contribution to the pathogenesis of diabetic cardiomyopathy and how their modulation could be therapeutically useful.

Cellular senescence and tumor promotion: Role of the Unfolded Protein Response

Senescence is a cellular state which can be viewed as a stress response phenotype implicated in various physiological and pathological processes, including cancer. Therefore, it is of fundamental importance to understand why and how a cell acquires and maintains a senescent phenotype. Direct evidence has pointed to the homeostasis of the endoplasmic reticulum whose control appears strikingly affected during senescence. The endoplasmic reticulum is one of the sensing organelles that transduce signals between different pathways in order to adapt a functional proteome upon intrinsic or extrinsic challenges. One of these signaling pathways is the Unfolded Protein Response (UPR), which has been shown to be activated during senescence. Its exact contribution to senescence onset, maintenance, and escape, however, is still poorly understood. In this article, we review the mechanisms through which the UPR contributes to the appearance and maintenance of characteristic senescent features. We also discuss whether the perturbation of the endoplasmic reticulum proteostasis or accumulation of misfolded proteins could be possible causes of senescence, and-as a consequence-to what extent the UPR components could be considered as therapeutic targets allowing for the elimination of senescent cells or altering their secretome to prevent neoplastic transformation.

Protective effects of pterostilbene against hepatic damage, redox imbalance, mitochondrial dysfunction, and endoplasmic reticulum stress in weanling piglets

This investigation evaluated the potential of natural antioxidants, pterostilbene (PT) and its parent compound resveratrol (RSV), to alleviate hepatic damage, redox imbalance, mitochondrial dysfunction, and endoplasmic reticulum (ER) stress in early-weaned piglets. A total of 144 suckling piglets were randomly assigned to four treatments (six replicates per group, n = 6): 1) sow reared, 2) early weaned and fed a basal diet, 3) early weaned and fed the basal diet supplemented with 300 mg/kg PT, or with 4) 300 mg/kg RSV. Early weaning increased plasma alanine aminotransferase (P = 0.004) and aspartate aminotransferase (P = 0.009) activities and hepatic apoptotic rate (P = 0.001) in piglets compared with the sow-reared piglets. Early weaning decreased hepatic adenosine triphosphate (ATP; P = 0.006) content and mitochondrial complexes III (P = 0.019) and IV activities (P = 0.038), but it increased superoxide anion accumulation (P = 0.026) and the expression levels of ER stress markers, such as glucose-regulated protein 78 (P < 0.001), CCAAT/enhancer-binding protein-homologous protein (P = 0.001), and activating transcription factor (ATF) 4 (P = 0.006). PT was superior to RSV at mitigating liver injury and oxidative stress after early weaning, as indicated by decreases in the number of apoptotic cells (P = 0.036) and the levels of superoxide anion (P = 0.002) and 8-hydroxy-2 deoxyguanosine (P < 0.001). PT increased mitochondrial deoxyribonucleic acid content (P = 0.031) and the activities of citrate synthase (P = 0.005), complexes I (P = 0.004) and III (P = 0.011), and ATP synthase (P = 0.041), which may contribute to the mitigation of hepatic ATP deficit (P = 0.017) in the PT-treated weaned piglets. PT also prevented increases in the ER stress marker and ATF 6 expression levels and in the phosphorylation of inositol-requiring enzyme 1 alpha caused by early weaning (P < 0.05). PT increased sirtuin 1 activity (P = 0.031) in the liver of early-weaned piglets than those in the early-weaned piglets fed a basal diet. In conclusion, PT supplementation alleviates liver injury in weanling piglets probably by inhibiting mitochondrial dysfunction and ER stress.

Build-UPS and break-downs: metabolism impacts on proteostasis and aging

Perturbation of metabolism elicits cellular stress which profoundly modulates the cellular proteome and thus protein homeostasis (proteostasis). Consequently, changes in the cellular proteome due to metabolic shift require adaptive mechanisms by molecular protein quality control. The mechanisms vitally controlling proteostasis embrace the entire life cycle of a protein involving translational control at the ribosome, chaperone-assisted native folding, and subcellular sorting as well as proteolysis by the proteasome or autophagy. While metabolic imbalance and proteostasis decline have been recognized as hallmarks of aging and age-associated diseases, both processes are largely considered independently. Here, we delineate how proteome stability is governed by insulin/IGF1 signaling (IIS), mechanistic target of Rapamycin (TOR), 5′ adenosine monophosphate-activated protein kinase (AMPK), and NAD-dependent deacetylases (Sir2-like proteins known as sirtuins). This comprehensive overview is emphasizing the regulatory interconnection between central metabolic pathways and proteostasis, indicating the relevance of shared signaling nodes as targets for future therapeutic interventions.

Temperature Down-Shift Modifies Expression of UPR-/ERAD-Related Genes and Enhances Production of a Chimeric Fusion Protein in CHO Cells

Low culture temperature enhances the cell-specific productivity of Chinese hamster ovary (CHO) cells expressing varied recombinant (r-) proteins, but the mechanisms remain unclear. Regulation of unfolded protein response (UPR) pathway genes, such as transcriptional regulatory factors and endoplasmic reticulum (ER)-resident proteins, appear to be involved in the improvements of r-protein production under low temperature conditions. The transcriptional regulation of UPR-specific targets is studied in response to decreased culture temperature in relation to production of a difficult-to-express protein. A clonally-derived CHO cell line expressing a chimeric fusion protein (human erythropoietin [hEPO] linked to a murine Fc region, hEPO-Fc) is evaluated in terms of growth, metabolism, r-protein production and UPR-/ER associated degradation (ERAD)-specific gene expression at standard (37 °C) and low (32 °C) temperature in batch and fed-batch systems. Low temperature decreased peak cell density, improved viability, generated cell cycle arrest in the G1 phase and enhanced hEPO-Fc expression in both batch and fed-batch cultures. A low culture temperature significantly upregulated genes encoding UPR-specific transcriptional activators (xbp1s, ddit3, and atf5) and ER-resident proteins (grp78, grp94, trib3, and ero1α), that are associated with folding and processing of proteins within the ER. Further, low culture temperature decreased expression of genes involved in ERAD (edem3, sels, herpud1, and syvn1) indicating a decreased potential for protein degradation.

Expression of XBP1s in B lymphocytes is critical for pristane-induced lupus nephritis in mice

B lymphocyte hyperactivity plays a pathogenic role in systemic lupus erythematosus (SLE), and spliced X box-binding protein 1 (XBP1s) has been implicated in B cell maturation and differentiation. We hypothesized that blockade of the XBP1s pathway inhibits the B cell hyperactivity underlying SLE and lupus nephritis (LN) development. In the present study, we systematically evaluated the changes in B cell activation induced by the Xbp1 splicing inhibitor STF083010 in a pristane-induced lupus mouse model. The lupus mouse model was successfully established, as indicated by the presence of LN with markedly increased urine protein levels, renal deposition of Ig, and mesangial cell proliferation. In lupus mice, B cell hyperactivity was confirmed by increased CD40 and B cell-activating factor levels. B cell activation and plasma cell overproduction were determined by increases in CD40-positive and CD138-positive cells in the spleens of lupus mice by flow cytometry and further confirmed by CD45R and Ig light chain staining in the splenic tissues of lupus mice. mRNA and protein expression of XBP1s in B cells was assessed by real-time PCR, Western blot analysis, and immunofluorescence analysis and was increased in lupus mice. In addition, almost all changes were reversed by STF083010 treatment. However, the expression of XBP1s in the kidneys did not change when mice were exposed to pristane and STF083010. Taken together, these findings suggest that expression of XBP1s in B cells plays key roles in SLE and LN development. Blockade of the XBP1s pathway may be a potential strategy for SLE and LN treatment.

Inhibition of XBP1s ubiquitination enhances its protein stability and improves glucose homeostasis

BACKGROUND

Hepatic ER stress is a risk factor of insulin resistance and type 2 diabetes. X-box binding protein 1 spliced (XBP1s), a transcription factor, plays a key role in ameliorating insulin resistance and maintaining glucose homeostasis. Unfortunately, the short half-life of the protein dampens its clinical application, and the specific site of lysine residue that could be ubiquitinated and involved in the degradation of XBP1s remains elusive.

METHODS AND RESULTS

Here, we identified K60 and K77 on XBP1s as two pivotal ubiquitin sites required for its proteasome-dependent degradation. We also constructed a double mutant form of XBP1s (K60/77R) and found that it showed higher capacity in resisting against ubiquitin-mediated protein degradation, increasing nuclear translocation, enhancing transcriptional activity, suppressing ER stress and promoting Foxo1 degradation, compared to that of wild type XBP1s (WT). Consistently, overexpression of the K60/77R XBP1s mutant in DIO mice increased the ability to reduce ER stress and decrease Foxo1 levels, thus contributed to maintaining glucose homeostasis.

CONCLUSION

Our results suggest that delaying the degradation of XBP1s by preventing ubiquitination might provide a strategic approach for reducing ER stress as an anti-diabetes therapy.

Deacetylation of XBP1s by sirtuin 6 confers resistance to ER stress-induced hepatic steatosis

The active spliced form of X-box-binding protein 1 (XBP1s) is a key modulator of ER stress, but the functional role of its post-translational modification remains unclear. Here, we demonstrate that XBP1s is a deacetylation target of Sirt6 and that its deacetylation protects against ER stress-induced hepatic steatosis. Specifically, the abundance of acetylated XBP1s and concordant hepatic steatosis were increased in hepatocyte-specific Sirt6 knockout and obese mice but were decreased by genetic overexpression and pharmacological activation of Sirt6. Mechanistically, we identified that Sirt6 deacetylated a transactivation domain of XBP1s at Lys257 and Lys297 and promoted XBP1s protein degradation through the ubiquitin-proteasome system. Overexpression of XBP1s, but not its deacetylation mutant 2KR (K257/297R), in mice increased lipid accumulation in the liver. Importantly, in liver tissues obtained from patients with nonalcoholic fatty liver disease (NAFLD), the extent of XBP1s acetylation correlated positively with the NAFLD activity score but negatively with the Sirt6 level. Collectively, we present direct evidence supporting the importance of XBP1 acetylation in ER stress-induced hepatic steatosis.

Activating a protein that regulates cellular health could protect against fat accumulation during the onset of non-alcoholic fatty liver disease (NAFLD). A high-fat diet disrupts the endoplasmic reticulum (ER), a cellular membrane network responsible for synthesizing and processing proteins and fats, and can lead to NAFLD development. Previous studies found that a protein called XBP1s activates fat-related genes during NAFLD. Byung-Hyun Park and Eun Ju Bae at Chonbuk National University in Jeonbuk, South Korea, and co-workers, recently demonstrated that high levels of a regulatory protein called Sirt6 limits liver inflammation and ER stress during high-fat diets. Now, in experiments on mouse models and human liver cells, Park’s team have shown that Sirt6 reduces liver ER stress by modifying XBP1s. Encouraging Sirt6 activation may help protect against NAFLD progression.

miR-34c-5p modulates X-box-binding protein 1 (XBP1) expression during the adaptive phase of the unfolded protein response

During endoplasmic reticulum (ER) stress conditions, an adaptive signaling network termed the unfolded protein response (UPR) is activated. The UPR's function is to increase ER protein-folding capacity in order to attenuate ER stress, restore ER homeostasis, and, most importantly, promote cell survival. X-box-binding protein 1 (XBP1) is one component of the UPR and is a proadaptive transcription factor that is subject to transcriptional, post-transcriptional, and post-translational control. In the present study, we identified a post-transcriptional mechanism mediated by miR-34c-5p that governs the expression of both the spliced (active) and unspliced (latent) forms of XBP1 mRNAs. We showed that miR-34c-5p directly attenuates spliced XBP1 (XBP1s) mRNA levels during ER stress and thus regulates the proadaptive component of the UPR that is mediated by XBP1s without interfering with the induction of apoptotic responses.-Bartoszewska, S., Cabaj, A., Dąbrowski, M., Collawn, J. F., Bartoszewski, R. miR-34c-5p modulates X-box-binding protein 1 (XBP1) expression during the adaptive phase of the unfolded protein response.

The orphan nuclear receptor SHP regulates ER stress response by inhibiting XBP1s degradation

In this study, Sun et al. investigated the role of the orphan nuclear receptor SHP, a well-known transcriptional corepressor of bile acid and lipid metabolism in the liver, in other tissues. They report that SHP functions as a regulator of ER stress in the exocrine pancreas, specifically via the regulation of XBP1s stability.

The orphan nuclear receptor SHP (small heterodimer partner) is a well-known transcriptional corepressor of bile acid and lipid metabolism in the liver; however, its function in other tissues is poorly understood. Here, we report an unexpected role for SHP in the exocrine pancreas as a modulator of the endoplasmic reticulum (ER) stress response. SHP expression is induced in acinar cells in response to ER stress and regulates the protein stability of the spliced form of X-box-binding protein 1 (XBP1s), a key mediator of ER stress response. Loss of SHP reduces XBP1s protein level and transcriptional activity, which in turn attenuates the ER stress response during the fasting–feeding cycle. Consequently, SHP-deficient mice also are more susceptible to cerulein-induced pancreatitis. Mechanistically, we show that SHP physically interacts with the transactivation domain of XBP1s, thereby inhibiting the polyubiquitination and degradation of XBP1s by the Cullin3–SPOP (speckle-type POZ protein) E3 ligase complex. Together, our data implicate SHP in governing ER homeostasis and identify a novel posttranslational regulatory mechanism for the key ER stress response effector XBP1.

Influence of Resveratrol on the Immune Response

Resveratrol is the most well-known polyphenolic stilbenoid, present in grapes, mulberries, peanuts, rhubarb, and in several other plants. Resveratrol can play a beneficial role in the prevention and in the progression of chronic diseases related to inflammation such as diabetes, obesity, cardiovascular diseases, neurodegeneration, and cancers among other conditions. Moreover, resveratrol regulates immunity by interfering with immune cell regulation, proinflammatory cytokines’ synthesis, and gene expression. At the molecular level, it targets sirtuin, adenosine monophosphate kinase, nuclear factor-κB, inflammatory cytokines, anti-oxidant enzymes along with cellular processes such as gluconeogenesis, lipid metabolism, mitochondrial biogenesis, angiogenesis, and apoptosis. Resveratrol can suppress the toll-like receptor (TLR) and pro-inflammatory genes’ expression. The antioxidant activity of resveratrol and the ability to inhibit enzymes involved in the production of eicosanoids contribute to its anti-inflammation properties. The effects of this biologically active compound on the immune system are associated with widespread health benefits for different autoimmune and chronic inflammatory diseases. This review offers a systematic understanding of how resveratrol targets multiple inflammatory components and exerts immune-regulatory effects on immune cells.

Transforming growth factor β (TGFβ) cross-talk with the unfolded protein response is critical for hepatic stellate cell activation

Transforming growth factor β (TGFβ) potently activates hepatic stellate cells (HSCs), which promotes production and secretion of extracellular matrix (ECM) proteins and hepatic fibrogenesis. Increased ECM synthesis and secretion in response to TGFβ is associated with endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). TGFβ and UPR signaling pathways are tightly intertwined during HSC activation, but the regulatory mechanism that connects these two pathways is poorly understood. Here, we found that TGFβ treatment of immortalized HSCs (i.e. LX-2 cells) induces phosphorylation of the UPR sensor inositol-requiring enzyme 1α (IRE1α) in a SMAD2/3-procollagen I-dependent manner. We further show that IRE1α mediates HSC activation downstream of TGFβ and that its role depends on activation of a signaling cascade involving apoptosis signaling kinase 1 (ASK1) and c-Jun N-terminal kinase (JNK). ASK1-JNK signaling promoted phosphorylation of the UPR-associated transcription factor CCAAT/enhancer binding protein β (C/EBPβ), which is crucial for TGFβ- or IRE1α-mediated LX-2 activation. Pharmacological inhibition of C/EBPβ expression with the antiviral drug adefovir dipivoxil attenuated TGFβ-mediated activation of LX-2 or primary rat HSCs in vitro and hepatic fibrogenesis in vivo Finally, we identified a critical relationship between C/EBPβ and the transcriptional regulator p300 during HSC activation. p300 knockdown disrupted TGFβ- or UPR-induced HSC activation, and pharmacological inhibition of the C/EBPβ-p300 complex decreased TGFβ-induced HSC activation. These results indicate that TGFβ-induced IRE1α signaling is critical for HSC activation through a C/EBPβ-p300-dependent mechanism and suggest C/EBPβ as a druggable target for managing fibrosis.

Sirtuin-1 ameliorates cadmium-induced endoplasmic reticulum stress and pyroptosis through XBP-1s deacetylation in human renal tubular epithelial cells

Cadmium (Cd), an occupational and environmental pollutant, induces nephrotoxicity by primarily damaging renal proximal tubular cells. In this study, we hypothesized that pyroptosis, a caspase-1-dependent inflammatory programmed cell death mechanism, mediates Cd-induced nephrotoxicity. Human proximal tubular epithelial HK-2 cells were treated with 0-10 µM CdCl₂ for 48 h. We found that Cd dose-dependently caused cytotoxicity, which correlated with activation of the NLRP3 inflammasome, increases in the expression and secretion of pro-inflammatory cytokines and upregulation of pyroptosis-related genes in HK-2 cells or/and in kidneys of Cd-treated mice. These effects were significantly abrogated by inhibiting caspase-1 activity with inhibitor YVAD or silencing NLRP3 with siRNA in vitro, suggesting that Cd induces caspase-1- and NLRP3-inflammasome-dependent pyroptosis. Moreover, Cd treatment also activated three branches (ATF6, PERK and IRE-1α) of endoplasmic reticulum stress. Selective inhibition of the IRE-1α/XBP-1s branch by a pharmacological inhibitor STF-083010 or by genetic silencing of XBP-1 significantly attenuated Cd-induced NLRP3 inflammasome activation and pyroptosis. Mechanistically, Cd suppressed deacetylase Sirtuin-1 (SIRT-1) protein expression and activity leading to decrease in physical binding with XBP-1s protein, and thus the accumulation of acetylated XBP-1s levels. Activation of SIRT1 using a pharmacological agonist resveratrol or genetic SIRT1 overexpression significantly abolished Cd-induced activation of the IRE-1α/XBP-1s pathway and the NRLP3 inflammasome as well as pyroptosis, which were counteracted by co-overexpression of both SIRT1 and XBP-1s. Collectively, our findings indicate that SIRT1 activity protects against Cd-induced pyroptosis through deacetylating XBP-1s, and thus inhibiting the IRE-1α/XBP-1s pathway in HK-2 cells. These results provide a novel mechanism for Cd-induced nephrotoxicity.

4-Phenylbutyric Acid Protects Against Ethanol-Induced Damage in the Developing Mouse Brain

BACKGROUND

Ethanol (EtOH) exposure during pregnancy may result in fetal alcohol spectrum disorders (FASD). One of the most deleterious consequences of EtOH exposure is neuronal loss in the developing brain. Previously, we showed that EtOH exposure induced neuroapoptosis in the brain of postnatal day 4 (PD4) mice but not PD12 mice. This differential susceptibility may result from an insufficient cellular stress response system such as unfolded protein response (also known as endoplasmic reticulum [ER] stress) in PD4 mice. In this study, we compared the effect of EtOH on ER stress in PD4 and PD12 mice and determined whether the inhibition of ER stress could protect the developing brain against EtOH damage.

METHODS

We used a third-trimester equivalent mouse model of FASD. PD4 and PD12 C57BL/6 mice were subcutaneously injected with saline (control), EtOH, EtOH plus 4-phenylbutyric acid (4-PBA), a chemical chaperone known as ER stress inhibitor, and 4-PBA alone. The expression of apoptosis marker, ER stress markers, and markers for glial cell activation was examined in the cerebral cortex.

RESULTS

EtOH induced neuroapoptosis and increased the expression of ER stress markers, such as activating transcription factor 6, 78-kDa glucose-regulated protein, inositol-requiring enzyme 1α, mesencephalic astrocyte-derived neurotrophic factor, and caspase-12 in PD4 but not PD12 mice. EtOH exposure also activated microglia and astrocytes. Interestingly, treatment with 4-PBA attenuated EtOH-induced neuroapoptosis. Moreover, 4-PBA inhibited the expression of the aforementioned ER stress markers and EtOH-induced glial activation in PD4 mice.

CONCLUSIONS

ER stress plays an important role in EtOH-induced damage to the developing brain. Inhibition of ER stress is neuroprotective and may provide a new therapeutic strategy for treating FASD.

Protective effect of 4-Phenylbutyrate against proteolipid protein mutation-induced endoplasmic reticulum stress and oligodendroglial cell death

Proteolipid protein (PLP) mutation causes oligodendrocyte degeneration and myelin disorders including Pelizaeus-Merzbacher Disease (PMD). As the pathophysiological mechanisms involved in PMD are poorly known, the development of therapies remains difficult. To elucidate the pathogenic pathways, an immortalized oligodendroglial cell line (158JP) expressing PLP mutation has been generated. Previous investigations revealed that 158JP oligodendrocytes exhibit several abnormalities including aberrant PLP insertion into the plasma membrane, cAMP, plasmalogen and cell cycle deficits. However, further clarifications of abnormal PLP-induced oligodendrocyte degeneration are required in order to identify relevant mechanisms to target for efficient protection against oligodendrocyte death. Because PLP overexpression may lead to its accumulation inside the endoplasmic reticulum (ER) and cause ER-stress, we explored whether ER-stress may pivotally determine 158JP cell survival/death. Viability assays, RT-qPCR, western blot and flow cytometry were combined to compare cell survival, ER-stress and apoptotic markers in 158JP and control (158N) oligodendrocytes. We observed a significant decreased viability/survival of 158JP compared to 158N cells. Consistently, ER-stress markers (BiP, caspase-12) increased in 158JP (+30%) compared to the controls. mRNA and protein ratios of apoptotic modulators (Bax/Bcl2) are higher in 158JP oligodendrocytes which are also more vulnerable than 158N cells to tunicamycin-induced ER-stress. Interestingly, 4-Phenylbutyrate (ER-stress inhibitor), which decreased ER-stress and apoptotic markers in 158JP cells, significantly increased their survival. Our results, which show a direct link between the viability and endogenous levels of ER-stress and apoptotic markers in 158JP cells, also suggest that 4-Phenylbutyrate-based strategy may contribute to develop effective strategies against oligodendrocyte dysfunctions/death and myelin disorders.

Foie gras and liver regeneration: a fat dilemma

The liver has a unique ability of regenerating after injuries or partial loss of its mass. The mechanisms responsible for liver regeneration - mostly occurring when the hepatic tissue is damaged or functionally compromised by metabolic stress - have been studied in considerable detail over the last few decades, because this phenomenon has both basic-biology and clinical relevance. More specifically, recent interest has been focusing on the widespread occurrence of abnormal nutritional habits in the Western world that result in an increased prevalence of non-alcoholic fatty liver disease (NAFLD). NAFLD is closely associated with insulin resistance and dyslipidemia, and it represents a major clinical challenge. The disease may progress to steatohepatitis with persistent inflammation and progressive liver damage, both of which will compromise regeneration under conditions of partial hepatectomy in surgical oncology or in liver transplantation procedures. Here, we analyze the impact of ER stress and SIRT1 in lipid metabolism and in fatty liver pathology, and their consequences on liver regeneration. Moreover, we discuss the fine interplay between ER stress and SIRT1 functioning when contextualized to liver regeneration. An improved understanding of the cellular and molecular intricacies contributing to liver regeneration could be of great clinical relevance in areas as diverse as obesity, metabolic syndrome and type 2 diabetes, as well as oncology and transplantation.

CTRP3 attenuates high-fat diet-induced male reproductive dysfunction in mice

Recent studies have suggested a role for abdominal obesity in male infertility. Previous studies have found that cell apoptosis exerts an important role in obesity-related male infertility. C1q/TNF-related protein 3 (CTRP3), a paralog of adiponectin, has been proposed to exert anti-apoptotic effects and to attenuate diabetes-related cardiac injuries. However, the role of CTRP3 in high-fat diet (HFD)-induced spermatogenic impairment remains unclear. In the present study, we fed male mice an HFD for 24 weeks to induce obesity. The expression of CTRP3 was decreased by HFD feeding. Supplementation with the recombinant human globular domain of CTRP3 (0.25 μg/g/day) for 4 weeks beginning at 20 weeks of the HFD improved spermatogenic function in the HFD-fed mice, which were characterized by improved testis morphology, increased testis weight/body weight ratio, and increased sperm count, sperm viability, and sperm motility. We also found that CTRP3 infusion resulted in the attenuation of endoplasmic reticulum (ER) stress and the activation of silence information regulator 1 (SIRT1) in the testes of obese mice. Our in vitro study also suggested that CTRP3 attenuated the palmitic acid (PA)-induced reductions in sperm viability and motility via the inhibition of ER stress. Moreover, germ cell-specific Sirtuin1 knockout abolished the protective effects of CTRP3 in vivo and in vitro. In vitro studies of human sperm showed that the protective effects of CTRP3 on sperm viability and motility were abrogated by a specific inhibitor of SIRT1. Thus, our results demonstrated that CTRP3 expression protected against HFD-induced spermatogenic deficiency through the SIRT1/ER stress pathway.

Sirtuin-1 (SIRT1) stimulates growth-plate chondrogenesis by attenuating the PERK-eIF-2α-CHOP pathway in the unfolded protein response

The NAD⁺-dependent deacetylase sirtuin-1 (SIRT1) has emerged as an important regulator of chondrogenesis and cartilage homeostasis, processes that are important for physiological skeletal growth and that are dysregulated in osteoarthritis. However, the functional role and underlying mechanism by which SIRT1 regulates chondrogenesis remain unclear. Using cultured rat metatarsal bones and chondrocytes isolated from rat metatarsal rudiments, here we studied the effects of the SIRT1 inhibitor EX527 or of SIRT1 siRNA on chondrocyte proliferation, hypertrophy, and apoptosis. We show that EX527 or SIRT1 siRNA inhibits chondrocyte proliferation and hypertrophy and induces apoptosis. We also observed that SIRT1 inhibition mainly induces the PERK-eIF-2α-CHOP axis of the endoplasmic reticulum (ER) stress response in growth-plate chondrocytes. Of note, EX527- or SIRT1 siRNA-mediated inhibition of metatarsal growth and growth-plate chondrogenesis were partly neutralized by phenylbutyric acid, a chemical chaperone that attenuates ER stress. Moreover, EX527-mediated impairment of chondrocyte function (i.e. of chondrocyte proliferation, hypertrophy, and apoptosis) was partly reversed in CHOP^-/- cells. We also present evidence that SIRT1 physically interacts with and deacetylates PERK. Collectively, our findings indicate that SIRT1 deacetylates PERK and attenuates the PERK-eIF-2α-CHOP axis of the unfolded protein response pathway and thereby promotes growth-plate chondrogenesis and longitudinal bone growth.

Microbial-Host Co-metabolites Are Prodromal Markers Predicting Phenotypic Heterogeneity in Behavior, Obesity, and Impaired Glucose Tolerance

The influence of the gut microbiome on metabolic and behavioral traits is widely accepted, though the microbiome-derived metabolites involved remain unclear. We carried out untargeted urine ¹H-NMR spectroscopy-based metabolic phenotyping in an isogenic C57BL/6J mouse population (n = 50) and show that microbial-host co-metabolites are prodromal (i.e., early) markers predicting future divergence in metabolic (obesity and glucose homeostasis) and behavioral (anxiety and activity) outcomes with 94%–100% accuracy. Some of these metabolites also modulate disease phenotypes, best illustrated by trimethylamine-N-oxide (TMAO), a product of microbial-host co-metabolism predicting future obesity, impaired glucose tolerance (IGT), and behavior while reducing endoplasmic reticulum stress and lipogenesis in 3T3-L1 adipocytes. Chronic in vivo TMAO treatment limits IGT in HFD-fed mice and isolated pancreatic islets by increasing insulin secretion. We highlight the prodromal potential of microbial metabolites to predict disease outcomes and their potential in shaping mammalian phenotypic heterogeneity.

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High-fat diet drives phenotypic heterogeneity in metabolism and behavior

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Microbial metabolites, including methylamines, predict phenotypic heterogeneity

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TMAO attenuates ER stress and reduces lipogenesis in adipocytes

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TMAO improves insulin secretion and restores glucose tolerance in vivo