Autophagy after Subarachnoid Hemorrhage: Can Cell Death be Good?

Neuritin promotes autophagic flux by inhibiting the cGAS-STING pathway to alleviate brain injury after subarachnoid haemorrhage

BACKGROUND

Early brain injury (EBI) is closely associated with poor prognosis in patients with subarachnoid haemorrhage (SAH), with autophagy playing a pivotal role in EBI. However, research has shown that the stimulator of interferon genes (STING) pathway impacts autophagic flux. While the regulatory impact of neuritin on EBI and autophagic flux has been established previously, the underlying mechanism remains unclear. This study aimed to determine the role of the cGAS-STING pathway in neuritin-mediated regulation of autophagic flux following SAH.

METHODS

A SAH model was established in male Sprague-Dawley rats via intravascular perforation. Neuritin overexpressions using adeno-associated virus, the STING antagonist "C-176," and the activator, "CMA," were determined to investigate the cGAS-STING pathway's influence on autophagic flux and brain injury post-SAH, along with the neuritin's regulatory effect on STING. In this study, SAH grade, neurological score, haematoxylin and eosin (H&E) staining, brain water content (BWC), sandwich enzyme-linked immunosorbent assay, Evans blue staining, immunofluorescence staining, western blot analysis, and transmission electron microscopy (TEM) were examined.

RESULTS

Neuritin overexpression significantly ameliorated neurobehavioural scores, blood-brain barrier injury, brain oedema, and impaired autophagic flux in SAH-induced rats. STING expression remarkably increased post-SAH. C-176 and CMA mitigated and aggravated autophagic flux injury and brain injury, respectively, while inhibiting and enhancing STING, respectively. Particularly, CMA treatment nullified the protective effects of neuritin against autophagic flux and mitigated brain injury.

CONCLUSION

Neuritin alleviated EBI by restoring impaired autophagic flux after SAH through the regulation of the cGAS-STING pathway.

Role of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in autophagy activation following subarachnoid hemorrhage

BACKGROUND

Early brain injury (EBI) refers to a severe brain injury that occurs within hours to days after subarachnoid hemorrhage (SAH). Neuronal damage in EBI is considered a key factor leading to poor prognosis. Currently, our understanding of the mechanisms of neuronal damage, such as neuronal autophagy, is still incomplete. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a key enzyme in metabolism and plays an important role in autophagy. Based on this, this study will further explore the regulation of autophagy by GAPDH after SAH, which may provide a new treatment strategy for improving the prognosis of SAH patients.

METHODS

The rat SAH model was established by endovascular puncturing, and the trend of autophagy in hippocampal neurons at different time points was discussed. Additionally, an in vitro SAH model was created using the oxygenated hemoglobin and hippocampal neuronal HT22 cell line. Through siRNA and overexpression adenovirus techniques, we further investigated the relationship between the key enzyme GAPDH and autophagy in the in vitro SAH model.

RESULTS

We observed significant neuronal damage in the hippocampus 24 h after SAH, and the proteomics showed significant enrichment of autophagy-related pathways at this time point. Further studies showed that the expression of LC3 and Beclin1 peaked at 24 h, and the nuclear translocation of GAPDH occurred simultaneously with SAH-induced neuronal autophagy. Our in vitro SAH model confirmed the role of GAPDH in regulating the level of autophagy in HT22 cells. Knockdown of GAPDH significantly reduced the level of autophagy, while overexpression of GAPDH increased the level of autophagy.

CONCLUSION

This study shows the trend of autophagy in hippocampal neurons after SAH, and reveals the regulatory role of GAPDH in SAH-induced autophagy. However, further studies are needed to reveal the exact mechanism of GAPDH in the nuclear translocation regulation of autophagy and validate in animal models.

Inhibition of CCR1 attenuates neuroinflammation via the JAK2/STAT3 signaling pathway after subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Neuroinflammation is an important mechanism underlying brain injury caused by subarachnoid hemorrhage (SAH). C-C chemokine receptor type 1 (CCR1)-mediated inflammation is involved in the pathology of many central nervous system diseases. Herein, we investigated whether inhibition of CCR1 alleviated neuroinflammation after experimental SAH and aimed to elucidate the mechanisms of its potential protective effects.

METHODS

To analyze SAH transcriptome data R studio was used, and a mouse model of SAH was established using endovascular perforations. In this model, the selective CCR1 antagonist Met-RANTES (Met-R) and the CCR1 agonist recombinant CCL5 (rCCL5) were administered 1 h after SAH induction. To investigate the possible downstream mechanisms of CCR1, the JAK2 inhibitor AG490 and the JAK2 activator coumermycin A1 (C-A1) were administered 1 h after SAH induction. Furthermore, post-SAH evaluation, including SAH grading, neurological function tests, Western blot, the terminal deoxynucleotidyl transferase dUTP nick end labeling assay, and Fluoro-Jade B and fluorescent immunohistochemical staining were performed. Cerebrospinal fluid (CSF) samples were detected by ELISA.

RESULTS

CCL5 and CCR1 expression levels increased significantly following SAH. Met-R significantly improved neurological deficits in mice, decreased apoptosis and degeneration of ipsilateral cerebral cortex neurons, reduced infiltrating neutrophils, and promoted microglial activation after SAH induction. Furthermore, Met-R inhibited the expression of p-JAK2, p-STAT3, interleukin-1β, and tumor necrosis factor-α. However, the protective effects of Met-R were abolished by C-A1 treatment. Furthermore, rCCL5 injection aggravated neurological dysfunction and increased the expression of p-JAK2, p-STAT3, interleukin-1β, and tumor necrosis factor-α in SAH mice, all of which were reversed by the administration of AG490. Finally, the levels of CCL5 and CCR1 were elevate in the CSF of SAH patient and high level of CCL5 and CCR1 levels were associated with poor outcome.

CONCLUSION

The present results suggested that inhibition of CCR1 attenuates neuroinflammation after SAH via the JAK2/STAT3 signaling pathway, which may provide a new target for the treatment of SAH.

Molecular mechanisms of neuronal death in brain injury after subarachnoid hemorrhage

Subarachnoid haemorrhage (SAH) is a common cerebrovascular disease with high disability and mortality rates worldwide. The pathophysiological mechanisms involved in an aneurysm rupture in SAH are complex and can be divided into early brain injury and delayed brain injury. The initial mechanical insult results in brain tissue and vascular disruption with hemorrhages and neuronal necrosis. Following this, the secondary injury results in diffused cerebral damage in the peri-core area. However, the molecular mechanisms of neuronal death following an aneurysmal SAH are complex and currently unclear. Furthermore, multiple cell death pathways are stimulated during the pathogenesis of brain damage. Notably, particular attention should be devoted to necrosis, apoptosis, autophagy, necroptosis, pyroptosis and ferroptosis. Thus, this review discussed the mechanism of neuronal death and its influence on brain injury after SAH.

S100A8 regulates autophagy-dependent ferroptosis in microglia after experimental subarachnoid hemorrhage

Targeting microglial activation has been shown to ameliorate early brain injury (EBI) after subarachnoid hemorrhage (SAH). Ferroptosis is a new form of programmed cell death after SAH, but these molecular features were not recognized as evidence of microglial function so far. In this study, we constructed microglial S100A8-specific knockdown and established the SAH model in vivo and in vitro. Multi-technology strategies, including high throughput sequencing, adeno-associated virus gene gene-editing and several molecular biotechnologies to validate the effects of S100A8 on microglial autophagy and ferroptosis after SAH. Our results revealed that the expression of S100A8 was significantly increased in brain tissue after SAH. Targeted microglial S100A8 inhibition improved neural function and neuronal apoptosis in mice after SAH. Further mechanism exploration found that favourable effects of S100A8 depletion in EBI may be through the inhibition of microglia autophagy-dependent ferroptosis. In conclusion, S100A8 may be a potential intervention target for microglial ferroptosis in EBI after SAH.

Acetyl CoA synthase 2 potentiates ATG5-induced autophagy against neuronal apoptosis after subarachnoid hemorrhage

ATG5-induced autophagy is triggered in the early stages after SAH, which plays a vital role in subarachnoid hemorrhage (SAH). Acyl-CoA synthetase short-chain family 2 (ACSS2) is not just involved in energy metabolism but also binds to TEFB to form a complex translocated to related autophagy genes to regulate the expression of autophagy-related genes. However, the contribution of ACSS2 to the activation of autophagy in early brain injury (EBI) after SAH has barely been discussed. The purpose of this study was to investigate the alterations of ACSS2 and its neuroprotective effects following SAH. We first evaluated the expression of ACSS2 at different time points (6, 12, 24, and 72 h after SAH) in vivo and primary cortical neurons stimulated by oxyhemoglobin (OxyHb). Subsequently, adeno-associated virus and lentivirus were used to regulate ACSS2 expression to investigate the effect of ACSS2 after SAH. The results showed that the ACSS2 level decreased significantly in the early stages of SAH and was minimized at 24 h post-SAH. After artificial intervention to overexpress ACSS2, ATG5-induced autophagy was further enhanced in EBI after SAH, and neuronal apoptosis was alleviated to protect brain injury. In addition, brain edema and neurological function scores were improved. These results suggest that ACSS2 plays an important role in the neuroprotection against EBI after SAH by increasing ATG5-induce autophagy and inhibiting apoptosis.

Reverse relationship between autophagy and apoptosis in an in vitro model of cortical neuronal injury

Autophagy and apoptosis are intertwined, and their relationship involves complex cross-talk. Whether the activation and inhibition of autophagy protect or damage neurons in the central nervous system has been a matter of longstanding controversy. We investigated the effect of autophagy on the apoptosis of cortical neurons after oxygen- and glucose-deprivation/reoxygenation (OGD/R) injury in vitro and found that protective mechanism activation was the predominant response to enhanced autophagy activation and increased autophagic flux. After successful establishment of an OGD/R model with cortical neurons, the autophagy activator rapamycin (Rap) or the late-autophagy inhibitor bafilomycin A1 (BafA1) was added to cell groups according to the experimental design. Cell viability was determined by Cell Counting Kit-8 (CCK-8) and lactate dehydrogenase (LDH) assays, and the apoptosis rate was measured by analysing Annexin V-FITC/PI-stained cells. The protein and mRNA expression levels of the apoptosis factors Caspase8 and Caspase3 and autophagy-associated proteins LC3 and p62 were measured by Western blotting and RT-qPCR. The extent of autophagic flux was determined by measuring the intensity of double immunofluorescence labelled protein after cells were transfected with RFP-GFP-LC3-expressing virus, and the ultrastructures of autophagosomes were observed by transmission electron microscopy (TEM). The results showed that cell viability decreased and that cells underwent autophagy and apoptosis after OGD/R. After the addition of Rap, cell viability was increased, and the apoptosis rate was decreased significantly. In addition, the level of the autophagic flux protein LC3II was increased, and the level of p62 was decreased. The number of autophagosomes and the ratio of autophagosomes to lysosomes were increased significantly. After BafA1 intervention, however, these results were reversed, with decreased cell viability, a significantly increased apoptosis rate, and disrupted autophagic flux. In conclusion, enhanced autophagy activation or autophagic flux exerted a significant protective effect on neurons after OGD/R injury in vitro.

Bioinformatics Analysis of Autophagy and Mitophagy Markers Associated with Delayed Cerebral Ischemia Following Subarachnoid Hemorrhage

Objective

To evaluate the interactions among differentially expressed autophagy and mitophagy markers in subarachnoid hemorrhage (SAH) patients with delayed cerebral ischemia (DCI).

Methods

The expression data of autophagy and mitophagy-related makers in the cerebrospinal fluid (CSF) cells was analyzed by real-time reverse transcription-polymerase chain reaction and Western blotting. The markers included death-associated protein kinase (DAPK)-1, BCL2 interacting protein 3 like (BNIP3L), Bcl-1 antagonist X, PINK, Unc-51 like autophagy activating kinase 1, nuclear dot protein 52, and p62. In silico functional analyses including gene ontology enrichment and the protein-protein interaction network were performed.

Results

A total of 56 SAH patients were included and 22 (38.6%) of them experienced DCI. The DCI patients had significantly increased mRNA levels of DAPK1, BNIP3L, and PINK1, and increased expression of BECN1 compared to the non-DCI patients. The most enriched biological process was the positive regulation of autophagy, followed by the response to mitochondrial depolarization. The molecular functions ubiquitin-like protein ligase binding and ubiquitin-protein ligase binding were enriched. In the cluster of cellular components, Lewy bodies and the phagophore assembly site were enriched. BECN1 was the most connected gene among the differentially expressed markers related to autophagy and mitophagy in the development of DCI.

Conclusion

Our study may provide novel insight into mitochondrial dysfunction in DCI pathogenesis.

Ferritinophagy is Involved in Experimental Subarachnoid Hemorrhage-Induced Neuronal Ferroptosis

Ferroptosis is a novel form of regulated cell death involved in the pathophysiological process of experimental subarachnoid hemorrhage (SAH), but how neuronal ferroptosis occurs remains unknown. In this study, we report that SAH-induced ferroptosis is macroautophagy/autophagy dependent because the inhibition of autophagy by knocking out autophagy-related gene 5 (ATG5) apparently mitigated SAH-induced ferroptosis. We created an experimental SAH model in Sprague-Dawley rats to determine the possible mechanism. We found that SAH can trigger neuronal ferroptosis, as evidenced by the disruption of iron homeostasis, elevation of intracellular lipid peroxidation (LPO) and decreased expression of ferroptosis-protective proteins. Then, we inhibited autophagy by ATG5 gene knockout, showing that autophagy inhibition can reduce the intracellular iron level and LPO, improve the expression of ferroptosis-protective proteins, and subsequently alleviate SAH-induced cell death. Additionally, autophagy inhibition also attenuated SAH prognostic indicators, such as brain edema, blood-brain barrier permeability, and neurological deficits. These findings not only present an opinion that SAH triggers neuronal ferroptosis via activation of ferritinophagy but also indicate that regulating ferritinophagy and maintaining iron homeostasis could provide clues for the prevention of early brain injury.

Neuritin attenuates oxygen-glucose deprivation/reoxygenation (OGD/R)-induced neuronal injury by promoting autophagic flux

The autophagy/apoptosis interaction has always been a focus of study in pathogenicity models. Neuritin is a neurotrophic factor that is highly expressed primarily in the central nervous system. Our previous study revealed that it protects against apoptosis in cortical neurons subjected to oxygen-glucose deprivation (OGD)/reoxygenation (OGD/R), and later animal experiments revealed that it can increase the expression of the autophagy-related protein LC3. Whether this neuroprotective effect is closely related to autophagy is still unclear. In this study, we hypothesized that neuritin can promote autophagic flux to protect nerve cells after OGD/R. To verify this hypothesis, we induced OGD/R in primary cortical neurons and assessed cell viability by the CCK8 and LDH assays. Cell apoptosis was assessed by Annexin V-FITC/PI, staining, and the contents and mRNA abundances of the autophagy-related proteins LC3 and p62, the apoptotic protein Caspase3 were quantified by Western blotting and RT-PCR. Autophagic flux was assessed by immunofluorescence after RFP-GFP-LC3 virus transfection, and ultrastructural changes in autophagosomes were observed by transmission electron microscopy (TEM). The results showed that cell viability was decreased, apoptosis was increased and autophagy was enhanced after OGD/R. Neuritin significantly increased cell viability, decreased apoptosis, further increased the expression of the autophagic flux-related protein LC3, further decreased p62 expression, and significantly increased the autophagosome number and autophagosome to lysosome ratio. Bafilomycin A1 (BafA1) is a late autophagy inhibitor, aggravated cell damage and apoptosis and counteracted the enhancement of autophagy activation and protective effects of neuritin. In conclusion, neuritin may promote the completion of autophagic flux by ameliorating neuronal damage after OGD/R.

Mitochondrial dysfunction associated with autophagy and mitophagy in cerebrospinal fluid cells of patients with delayed cerebral ischemia following subarachnoid hemorrhage

Decreased mitochondrial membrane potential in cerebrospinal fluid (CSF) was observed in patients with subarachnoid hemorrhage (SAH) accompanied by delayed cerebral ischemia (DCI). However, whether abnormal mechanisms of mitochondria are associated with the development of DCI has not been reported yet. Under cerebral ischemia, mitochondria can transfer into the extracellular space. Mitochondrial dysfunction can aggravate neurologic complications. The objective of this study was to evaluate whether mitochondrial dysfunction might be associated with autophagy and mitophagy in CSF cells to provide possible insight into DCI pathogenesis. CSF samples were collected from 56 SAH patients (DCI, n = 21; and non-DCI, n = 35). We analyzed CSF cells using autophagy and mitophagy markers (DAPK1, BNIP3L, BAX, PINK1, ULK1, and NDP52) via qRT-PCR and western blotting of proteins (BECN1, LC3, and p62). Confocal microscopy and immunogold staining were performed to demonstrate the differentially expression of markers within dysfunctional mitochondria. Significant induction of autophagic flux with accumulation of autophagic vacuoles, increased expression of BECN1, LC3-II, and p62 degradation were observed during DCI. Compared to non-DCI patients, DCI patients showed significantly increased mRNA expression levels (2^-ΔCt) of DAPK1, BNIP3L, and PINK1, but not BAX, ULK1, or NDP52. Multivariable logistic regression analysis revealed that Hunt and Hess grade ≥ IV (p = 0.023), DAPK1 (p = 0.003), and BNIP3L (p = 0.039) were related to DCI. Increased mitochondrial dysfunction associated with autophagy and mitophagy could play an important role in DCI pathogenesis.

Pseudo-ginsenoside Rh2 Induces Protective Autophagy in Hepatocellular Carcinoma HepG2 Cells

BACKGROUND

Pseudo-ginsenoside-Rh2 (pseudo-G-Rh2), a novel derivative of ginsenoside Rh2, is reported to exert a pro-apoptotic effect on various malignancies. However, whether this anti-cancer action of pseudo-G-Rh2 involves autophagy remains to be determined and explored.

OBJECTIVES

Investigation of pseudo-G-Rh2-induced apoptosis and autophagy and the underlying mechanism.

METHODS

In the present study, the MTT assay was used for evaluating cell viability and the lactate dehydrogenase (LDH) assay was performed to assess cell toxicity. Autophagy evaluation was performed using monodansylcadaverine (MDC) staining and transmission electron microscopy (TEM). The levels of autophagy-associated and apoptosis-associated proteins were determined using Western blotting. The Annexin V FITC/propidium iodide (PI) assay was used to assess apoptosis.

RESULTS

The Annexin V FITC/PI assay revealed that the percentage of apoptotic cells in HepG2 cells at concentrations 0, 20, 40, and 60 μM was 3.75%±1.37%, 5.70%±1.04%, 12.30%±2.10%, and 34.26%±4.73%, respectively. Pseudo-G-Rh2 was observed to significantly increase the expressions of BAX, cleaved-caspase-3, and cleaved-caspase-9, while it decreased the Bcl-2 expression. MDC and TEM analyses revealed that pseudo-G-Rh2 at concentrations 20, 40, and 60 μM significantly facilitated the accumulation of autophagosomes and autolysosomes within the HepG2 cells. Moreover, pseudo-G-Rh2 significantly increased the expressions of LC3 Ⅱ/LC3 Ⅰ, and Beclin-1 and decreased the expression of p62. The Annexin V FITC/PI assay also revealed that in comparison to the pseudo-G-Rh2 group, the concurrent treatment with pseudo-G-Rh2 and an autophagy inhibitor (CQ or 3-MA) significantly induced distinct apoptosis. In addition, pseudo-G-Rh2 activated AMPK and inhibited the PI3K/Akt/mTOR pathway in a concentration-dependent manner. Pseudo-G-Rh2 is similar to the current patents, which enhanced its anti-cancer activity by combining with autophagy inhibitors.

CONCLUSION

Pseudo-G-Rh2 could induce protective autophagy in HepG2 cells, at least in part, via AMPK and the PI3K/Akt/mTOR pathway.

FGF-2 suppresses neuronal autophagy by regulating the PI3K/Akt pathway in subarachnoid hemorrhage

The degree of early brain injury (EBI) is a significant factor that affects the prognosis of patients with subarachnoid hemorrhage (SAH). Evidence has shown that fibroblast growth factor-2 (FGF-2) may alleviate the serious consequences of EBI after SAH. The objective of the current study was to investigate the underlying mechanism that mediates the neuroprotective effects of FGF-2 in the SAH rat model. Sprague-Dawley (SD) rats that underwent different treatments were divided into various groups. FGF-2 was administered intranasally to rats in the treatment group within 30 min after modeling. Rapamycin (an autophagy activator) or LY294002 (a PI3K/Akt pathway inhibitor) was administered intracerebroventricularly (i.c.v.) 30 min before modeling. Neurological scale and brain water content were measured in the brain tissue of the rats. TUNEL staining, Western blot, and immunofluorescence staining were performed to examine and compare the diverse effects of FGF-2 treatment, activated autophagy, and inhibited the PI3K/Akt pathway. We found that FGF-2 treatment effectively reduced the number of TUNEL-positive cells, decreased the brain water content, and improved the neurological function of rats after SAH. Additionally, the expression levels of autophagy-related proteins (LC3 and Beclin-1) were obviously decreased in the FGF-2 treatment group compared with the SAH + vehicle group. The therapeutic effects of FGF-2 in the SAH + FGF-2+rapamycin group were weakened compared with that in the SAH + FGF-2+DMSO group. In the event of the PI3K/Akt pathway inhibition, the expression levels of LC3 and Beclin-1 were enhanced, and the therapeutic effects of FGF-2 were compromised. In summary, our data collectively demonstrated that FGF-2 may suppress autophagy levels to play a neuroprotective role, at least partially by activating the PI3K/Akt pathway. These results highlight FGF-2 as a promising solution to the clinical intervention of SAH.

Time Course of Metabolomic Alterations in Cerebrospinal Fluid After Aneurysmal Subarachnoid Hemorrhage

Object: The aim of this study was to investigate metabolite levels in cerebrospinal fluid (CSF) in their time-dependent course after aneurysmal subarachnoid hemorrhage (aSAH) comparing them to patients harboring unruptured intracranial aneurysms. Methods: Eighty CSF samples of 16 patients were analyzed. The study population included patients undergoing endovascular/microsurgical treatment of ruptured intracranial aneurysms (n = 8), which were assessed for 9 days after aSAH. Control samples were collected from the basal cisterns in elective aneurysm surgery (n = 8). The CSF samples were consecutively collected with extraventricular drain (EVD) placement/intraoperatively, 6 h later, and daily thereafter (day 1-9). The endogenous metabolites were analyzed with a targeted quantitative and quality controlled metabolomics approach using the AbsoluteIDQ®p180Kit. Differences inbetween timepoints and compared to the control group were evaluated. Results: Numerous alterations of amino acid (AA) levels were detected within the first hours after bleeding. The highest mean concentrations occurred 1 week after aSAH. AA levels were continuously increasing over time starting 6 h after aSAH. Taurine concentration was highest briefly after aSAH starting to decrease already after 6 h (vs. day 1-9, p = 0.02). The levels of sphingomyelins/ phosphatidylcholines/ lysophosphatidylcholines/mono-unsaturated fatty acid chain were highly elevated on day 0 (compared to other timepoints or controls, p < 0.01) and decreased over the next several days to concentrations comparable to the control group. Carnitine concentrations were decreased after SAH (vs. day 7, p < 0.01), while they recovered within the next day. The Fischer ratio of branched-chain AA to aromatic AA was lowest immediately after SAH and increased in 7 days (p < 0.001). Conclusion: AA levels in CSF increased overtime and often differ from patients without SAH. There was a peak concentration of structural AA within the first 6 h after aneurysm treatment. Time-dependent alterations of CSF metabolites and compounds may elucidate pathophysiological processes after aSAH, providing potential predictors assessed non-invasively by routine lab testing.

The Best for the Most Important: Maintaining a Pristine Proteome in Stem and Progenitor Cells

Pluripotent stem cells give rise to reproductively enabled offsprings by generating progressively lineage-restricted multipotent stem cells that would differentiate into lineage-committed stem and progenitor cells. These lineage-committed stem and progenitor cells give rise to all adult tissues and organs. Adult stem and progenitor cells are generated as part of the developmental program and play critical roles in tissue and organ maintenance and/or regeneration. The ability of pluripotent stem cells to self-renew, maintain pluripotency, and differentiate into a multicellular organism is highly dependent on sensing and integrating extracellular and extraorganismal cues. Proteins perform and integrate almost all cellular functions including signal transduction, regulation of gene expression, metabolism, and cell division and death. Therefore, maintenance of an appropriate mix of correctly folded proteins, a pristine proteome, is essential for proper stem cell function. The stem cells' proteome must be pristine because unfolded, misfolded, or otherwise damaged proteins would interfere with unlimited self-renewal, maintenance of pluripotency, differentiation into downstream lineages, and consequently with the development of properly functioning tissue and organs. Understanding how various stem cells generate and maintain a pristine proteome is therefore essential for exploiting their potential in regenerative medicine and possibly for the discovery of novel approaches for maintaining, propagating, and differentiating pluripotent, multipotent, and adult stem cells as well as induced pluripotent stem cells. In this review, we will summarize cellular networks used by various stem cells for generation and maintenance of a pristine proteome. We will also explore the coordination of these networks with one another and their integration with the gene regulatory and signaling networks.