Exosomes in the Diagnosis of Neuropsychiatric Diseases: A Review

Simple Summary The diagnostic value of exosomes has been well recognized by researchers. The use of exosomal biomarkers as an adjunct diagnosis method not only improves diagnostic accuracy but can also be used for early diagnosis and disease progression differentiation, thus supporting personalized clinical treatment strategies for patients with neuropsychiatric disorders. In this paper, we summarize potential exosomal biomarkers in the diagnosis of neuropsychiatric diseases. Abstract Exosomes are 30–150 nm small extracellular vesicles (sEVs) which are highly stable and encapsulated by a phospholipid bilayer. Exosomes contain proteins, lipids, RNAs (mRNAs, microRNAs/miRNAs, long non-coding RNAs/lncRNAs), and DNA of their parent cell. In pathological conditions, the composition of exosomes is altered, making exosomes a potential source of biomarkers for disease diagnosis. Exosomes can cross the blood–brain barrier (BBB), which is an advantage for using exosomes in the diagnosis of central nervous system (CNS) diseases. Neuropsychiatric diseases belong to the CNS diseases, and many potential diagnostic markers have been identified for neuropsychiatric diseases. Here, we review the potential diagnostic markers of exosomes in neuropsychiatric diseases and discuss the potential application of exosomal biomarkers in the early and accurate diagnosis of these diseases. Additionally, we outline the limitations and future directions of exosomes in the diagnosis of neuropsychiatric diseases.


Introduction
Extracellular vehicles (EVs) are granules that are naturally released from cells.EVs are categorized as small extracellular vesicles (sEVs, size < 200 nm) and large extracellular vesicles (lEVs, size > 200 nm) based on their size [1].Exosomes are 30-150 nm sEVs secreted by almost all cells [2].The process of exosome formation includes these steps: extracellular components enter the cell through a vesicle formed by membrane invagination, the vesicle exchanges materials within the cell.the membrane invaginates again to form a multivesicular body (MVB), finally, the cell releases the exosome from the MVB to the outer cytosol via an in vivo degradation pathway or a cytoplasmic fusion pathway [2][3][4].The blood-brain barrier (BBB) is a defensive structure of endothelial cells, astrocytes and microglia, neurons, and the extracellular matrix that can prevent harmful substances entering the brain by selectively impeding the exchange of certain substances between microglia, neurons, and the extracellular matrix that can prevent harmful substances entering the brain by selectively impeding the exchange of certain substances between blood and brain [5].The unique phospholipid bilayer structure and nanoscale particle size of exosomes allow exosomes to cross the BBB [6].Brain-derived exosomes can be isolated in peripheral body fluids, such as plasma, serum, urine, and saliva [7][8][9][10].Exosomes can efficiently cross the BBB, and, therefore, exosomes from peripheral body fluids can be used to detect central nervous system (CNS) diseases [11,12].
Neuropsychiatric diseases, such as cognitive deficit, memory deficit, emotional deficit, volitional deficit, and behavioral deficit are deficits of the CNS caused by a variety of biological, psychological, and socio-environmental factors.Neuropsychiatric diseases are characterized by a high degree of symptom overlap with complex diagnostic procedures.Clinical diagnosis of neuropsychiatric diseases is mainly based on the assessment of the patient s behavior, with the use of genetic, metabolic, and neuroimaging data as adjunctive diagnostic methods.Certainly, their diagnosis still needs to be improved, especially for early diagnosis, subtype differentiation, and prognostic testing.Exosomes are involved in the regulation of neuroinflammation, synaptic plasticity, the immune system, redox, and cellular communication, and are related to the pathogenesis of neuropsychiatric diseases.This review summarizes exosomal biomarkers identified from patients with neuropsychiatric diseases, including neurodevelopmental diseases, mind and will disorders, mood disorders, demyelinating diseases, and neurodegenerative diseases (Table S1).It discusses the potential of using exosomal biomarkers for the diagnosis of neuropsychiatric diseases and provides an outlook on limitations and future research directions.

Exosomes in the Diagnosis of Neurodevelopmental Diseases
Neurodevelopmental diseases occur when the brain or CNS encounters barriers to growth or development.The onset of these disorders is in childhood for most patients.Neurodevelopmental diseases include autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), intellectual disability (ID), etc.These diseases show a high co-occurrence rate, with overlapping symptoms, such as movement disorders, learning disabilities, and communication disorders [13].Currently, only exosomal biomarkers for ASD have been reported in patients among these neurodevelopmental diseases (Figure 1).

Neurotransmitter Transmission
Neurons release neurotransmitters from synaptic vesicles to the next neuron to complete the basic function of signal transmission in the nervous system.Synaptic vesicle glycoprotein 2C (SV2C) and synaptophysin (SYP) are synaptic vesicle-associated proteins, and their lncRNAs and mRNAs are significantly reduced [14][15][16].Synaptotagmin 15 (SYT15) and synaptotagmin 9 (SYT9) are involved in the transport and secretion of synaptic vesicles, and their lncRNAs and mRNAs are increased [14,17].Syntaxin-8 (STX8) is a fusion protein of synaptic vesicles, and solute carrier protein 18 A2 (SLC18A2) is a vesicular monoamine transporter protein that transports amine neurotransmitters to synaptic vesicles [14,18,19], their lncRNAs are significantly increased [14].

MtDNA-Mediated Neuroinflammation
Mitochondrial DNA (mtDNA) increases in both serum and serum exosomes of ASD patients [20,21].MtDNA contributes to neuroimmune dysregulation in ASD by inducing immune cells to secrete pro-inflammatory factors and activating autoimmune responses [20].Stimulation of cultured microglia with mtDNA-enriched exosomes from the serum of ASD patients results in a significant increase in the pro-inflammatory cytokine IL-1β [21], as well as occurring in the brains of children with ASD and in mouse models of ASD [22][23][24][25].MtDNA can enter exosomes, which has been reported by different studies [26][27][28].One way that mtDNA enters into exosomes is as follows: pathogenic and damage-associated molecular patterns enhance the permeability of the mitochondrial outer membrane leading to leakage of mtDNA into the cytosol, and the material exchange process in early exosomes takes place in the cytosol [29].

Exosomes in the Diagnosis of Mind and Volition Disorders
Schizophrenia (SCZ) is the most common mental disorder.The onset time of SCZ is usually from the ages of 12 to 20, and it is characterized by delusions, hallucinations, and thought and affective disorders.Exosome biomarkers in different pathways have been identified in SCZ (Figure 2).

Neurotransmitter Transmission
Neurons release neurotransmitters from synaptic vesicles to the next neuron to complete the basic function of signal transmission in the nervous system.Synaptic vesicle glycoprotein 2C (SV2C) and synaptophysin (SYP) are synaptic vesicle-associated proteins, and their lncRNAs and mRNAs are significantly reduced [14][15][16].Synaptotagmin 15 (SYT15) and synaptotagmin 9 (SYT9) are involved in the transport and secretion of synaptic vesicles, and their lncRNAs and mRNAs are increased [14,17].Syntaxin-8 (STX8) is a fusion protein of synaptic vesicles, and solute carrier protein 18 A2 (SLC18A2) is a vesicular monoamine transporter protein that transports amine neurotransmitters to synaptic vesicles [14,18,19], their lncRNAs are significantly increased [14].

MtDNA-Mediated Neuroinflammation
Mitochondrial DNA (mtDNA) increases in both serum and serum exosomes of ASD patients [20,21].MtDNA contributes to neuroimmune dysregulation in ASD by inducing immune cells to secrete pro-inflammatory factors and activating autoimmune responses [20].Stimulation of cultured microglia with mtDNA-enriched exosomes from the serum of ASD patients results in a significant increase in the pro-inflammatory cytokine IL-1β [21], as well as occurring in the brains of children with ASD and in mouse models of ASD [22][23][24][25].MtDNA can enter exosomes, which has been reported by different studies [26][27][28].One way that mtDNA enters into exosomes is as follows: pathogenic and damageassociated molecular patterns enhance the permeability of the mitochondrial outer membrane leading to leakage of mtDNA into the cytosol, and the material exchange process in early exosomes takes place in the cytosol [29].

Exosomes in the Diagnosis of Mind and Volition Disorders
Schizophrenia (SCZ) is the most common mental disorder.The onset time of SCZ is usually from the ages of 12 to 20, and it is characterized by delusions, hallucinations, and thought and affective disorders.Exosome biomarkers in different pathways have been identified in SCZ (Figure 2).B-cell lymphoma 2; bcl-w: B-cell lymphoma w; DJ-1/PARK7: human protein deglycase, encoding by the PARK7 gene; ROS: reactive oxygen species; (pS2448-mTOR)/m-TOR: the ratio of the ratio of phosphorylated mammalian target of rapamycin (pS2448-mTOR) to total mammalian target of rapamycin to total mammalian target of rapamycin.B-cell lymphoma 2; bcl-w: B-cell lymphoma w; DJ-1/PARK7: human protein deglycase, encoding by the PARK7 gene; ROS: reactive oxygen species; (pS2448-mTOR)/m-TOR: the ratio of the ratio of phosphorylated mammalian target of rapamycin (pS2448-mTOR) to total mammalian target of rapamycin to total mammalian target of rapamycin.

Oxidative Stress
Impaired antioxidant function and ROS production are potential pathogenic mechanisms in SCZ.Redox-related molecules are altered in SCZ patients [33,34].DJ-1 is an antioxidant protein that regulates the expression of antioxidant defence genes, protecting cells from oxidative stress damage [35,36].DJ-1 is significantly increased in serum exosomes of SCZ patients, and miR-203a-3, which targets the mRNA of DJ-1, is significantly decreased in serum exosomes of SCZ patients [37].

Exosomes in the Diagnosis of Mood Disorders
Mood disorders include persistent excessive sadness and happiness, usually beginning between the ages of 15 and 30.Mood disorders include depression, bipolar affective disorder (BD), mania, and anxiety [42].These disorders show a high co-occurrence rate, lack clear diagnostic criteria, and are usually associated with other serious comorbidities.To date, biomarkers for depression and BD have been investigated (Figure 3).

Oxidative Stress
Impaired antioxidant function and ROS production are potential pathogenic mechanisms in SCZ.Redox-related molecules are altered in SCZ patients [33,34].DJ-1 is an antioxidant protein that regulates the expression of antioxidant defence genes, protecting cells from oxidative stress damage [35,36].DJ-1 is significantly increased in serum exosomes of SCZ patients, and miR-203a-3, which targets the mRNA of DJ-1, is significantly decreased in serum exosomes of SCZ patients [37].

Exosomes in the Diagnosis of Mood Disorders
Mood disorders include persistent excessive sadness and happiness, usually beginning between the ages of 15 and 30.Mood disorders include depression, bipolar affective disorder (BD), mania, and anxiety [42].These disorders show a high co-occurrence rate, lack clear diagnostic criteria, and are usually associated with other serious comorbidities.To date, biomarkers for depression and BD have been investigated (Figure 3).

Exosomes in the Diagnosis of Demyelinating Diseases
Demyelinating diseases, which are caused by the loss of myelin sheaths on the axonal surfaces of nerve cells, are associated with the immune system, with onset between the ages of 15 and 60.Multiple sclerosis (MS) is a T-cell mediated inflammatory autoimmune disease characterized by scattered demyelinating foci in the brain and spinal cord and damage to the CNS [53][54][55].Exosome diagnostic biomarkers in different pathways have been identified in MS (Figure 4).

Exosomes in the Diagnosis of Demyelinating Diseases
Demyelinating diseases, which are caused by the loss of myelin sheaths on the axonal surfaces of nerve cells, are associated with the immune system, with onset between the ages of 15 and 60.Multiple sclerosis (MS) is a T-cell mediated inflammatory autoimmune disease characterized by scattered demyelinating foci in the brain and spinal cord and damage to the CNS [53][54][55].Exosome diagnostic biomarkers in different pathways have been identified in MS (Figure 4).

Myelin Demyelination
Myelin demyelination is a pathogenic mechanism in MS.Myelin is produced by oligodendrocytes, and myelin oligodendrocyte glycoprotein (MOG) is a target of cellular and humoral immune responses in MS.MS has three subtypes: relapsing-remitting multiple sclerosis (RRMS), secondary progressive multiple sclerosis (SPMS), and primary progressive multiple sclerosis (PPMS) [56][57][58].MOG is the most immunogenic myelin phospholipid protein, and anti-MOG antibodies can lead to myelin destruction [59,60]; MOG is significantly increased in serum exosomes from patients with relapsing-remitting RRMS and patients with SPMS [61].Fibroblast growth factor-2 (FGF-2) has been implicated in myelin destruction and regeneration, and FGF-2 in cerebrospinal fluid (CSF) can be used as a diagnostic biomarker for MS [62,63].MiR-15-5p, which targets FGF-2 [64,65], is significantly increased in plasma exosomes from patients with multiple sclerosis or SPMS [66].MiR-23a-3p, which is involved in the regulation of oligodendrocyte differentiation [67], is significantly increased in the cerebral white matter of MS patients [68].

Immune System
The balance of inflammatory T-cells and regulatory T-cells is dysregulated in MS patients, and regulatory T cells inhibit the proliferation and function of inflammatory T cells [69].Let-7i is an miRNA and targets the insulin-like growth factor 1 receptor (IGF1R) and transforming growth factor β receptor 1 (TGFBR1), thereby inhibiting the induced differentiation of regulatory T cells (Treg).In MS plasma exosomes, let-7i is significantly increased [70].miR-301a-3p, a developmental regulator of inflammatory CD4 helper T cells 17 (Th17) [71], is decreased in serum exosomes with RRMS [72].

Other Pathways
miR-196b-5p, which is associated with hematopoietic processes in the bone marrow, is decreased in serum exosomes of patients with RRMS [72].The oxidative stress regulator miR-451a is significantly increased in RRMS plasma exosomes [66].The signal transducer and activator of transcription 5 (STAT5) is an inflammatory regulator and transcription factor involved in the oxidative phosphorylation process associated with ROS production [73].miR-223-3p, which targets STAT5, is increased in plasma exosomes of SPMS patients [74][75][76].

Exosomes in the Diagnosis of Neurodegenerative Diseases
Neurodegenerative diseases are caused by the loss of neurons and/or myelin sheaths, and the dysfunction worsens over time.The most common neurodegenerative diseases are Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), dementia with Lewy bodies, frontotemporal lobe dementia, and Huntington's disease.The major pathologic change in AD is neurofibrillary tangles caused by deposition of amyloid β-protein (Aβ) and Tau proteins [77], and clinical diagnosis is made by imaging of Aβ protein deposition with positron emission tomography (PET) and/or detection of Aβ and Tau protein concentrations in CSF [78,79].PD is a progressive disorder characterized by resting tremor, muscle hypertonia, bradykinesia, and, eventually, gait and postural instability; the main pathogenic mechanisms of PD are neurotoxicity caused by protein misfolding and Lewy body formation [80,81], progressive lesions of dopamine (DA) neurons caused by oxidative stress [82], and impaired glutamatergic transmission in the brain [83].ALS is caused by protein folding, oxidative stress, axonal injury, and neuroinflammation leading to degeneration of muscle motor neurons [84,85].Pathogenesis-related and other biomarkers are identified in exosomes from neurodegenerative patients (Figure 5).

Protein-Misfolding-Induced Neurotoxicity
In patients with Alzheimer's disease, Aβ (amyloid β-protein) is increased in exosomes from several sources [86][87][88][89].Aβ is produced by hydrolysis of the transmembrane amyloid precursor protein (APP).APP is cleaved by β-secretase on the early endosome membrane; this early endosome undergoes maturation to form MVB [90].Aβ 1-42 , the long isoform of Aβ protein, is more prone to aggregation.Aβ 1-42 from plasma neuron exosomes can be used to differentiate pathogenic stages of AD [89].Aβ processing and synthesisassociated proteins are also potential markers for the diagnosis of AD.A disintegrin and metalloproteinase (ADAM10) is the major α-secretase in APP processing and prevents the accumulation of Aβ in neurons [91]; gelsolin (GSN) is an Aβ-binding that prevents Aβ aggregation [92]; insulin-like growth factor 1 (IGF-1) induces the release of neuron-bound Aβ oligomers and inhibits Tau phosphorylation [93,94].These proteins are significantly reduced in exosomes from different sources of AD patients [89,95,96].Fibulin-1 (FBLN1), which binds to APP to regulate neuronal activity and prevent Aβ production [97][98][99], is increased in serum-derived exosomes from AD patients [100].Complement C9 (CO9), a key subcomponent of the membrane attack complex (MAC), co-localizes with Aβ and Tau proteins in the brains of AD patients [101] and is increased in plasma exosomes [102].Exosomal miRNAs associated with Aβ proteins are also potential diagnostic markers for AD.Plasma and salivary exosomal miR-485-3p and serum exosomal miR-22-3p, which are involved in inhibiting Aβ aggregation, are increased in AD patients [103][104][105].Serum and plasma exosomal miR-185-5p and plasma and CSF exosomal miR-451a, which are involved in the regulation of APP hydrolysis processes, are decreased [106,107]; serum and plasma exosomal miR-384 are increased [108,109].However, in the case of miR-193b, which targets APP, trends in CSF and serum exosomes are inconsistent [110].Serum exosome-derived miR-135a increases in both mild cognitive impairment (MCI) [111] and AD patients [109], whereas it decreases in amnestic mild cognitive impairment (aMCI) [111].MiR-16-5p, which targets APP, and the CSF-derived exosome miR-16-5p decrease in early-onset AD compared to healthy controls, while the difference is not significant in late-onset AD compared with healthy controls [107], and the authors suggested that it could be used to differentiate between early-and late-onset AD. β-secretase 1 (BACE1) is the secretase of APP; the expression level of lncRNA of BACE1-AS (BACE1 Antisense RNA), which is associated with Aβ processing, is increased in AD patients [112].BACE1-AS RNA is also increased in the brain of AD patients [113,114].The differences in the expression of the above proteins, miRNAs, and lncRNAs and their application in the diagnosis of AD need to be further investigated.
In AD patients, hyperphosphorylation of Tau leading to neurofibrillary tangles and, ultimately, neuronal apoptosis is one of the major pathological causes [77,115].The Tau expression level in CSF is an important indicator for the diagnosis of AD patients.Exosomal Tau of neuronal origin in plasma is significantly increased in AD patients [87][88][89], and exosomal Tau proteins of metabolic origin from neuronal Tau proteins in plasma have the same diagnostic properties as Tau in CSF for AD.miR-138-5p is involved in the regulation of Tau protein phosphorylation, whereas miR-138-5p is decreased in the blood exosomes of AD patients [116].
In PD patients, aberrant protein aggregation is the main pathogenic mechanism [80].Mutations in leucine-rich repeat kinase 2 (LRRK2) lead to abnormal protein aggregation to form Lewy bodies [117,118], and the protein ratio of urinary exosome-phosphorylated LRRK2 (Ser(P)-129 LRRK2) to total LRRK2 is significantly increased in PD patients [119].Plasma exosomal α-synuclein is increased in PD patients compared with healthy controls [8]; serum neuronal exosomal α-synuclein is significantly higher than in the APS group [9], and serum and plasma neuronal exosomal α-synuclein are significantly lower than in the multiple system atrophy (MSA) group [8].The expression of miR-223-3p and miR-7-1-5p, which target and regulate α-synuclein, are increased [120].In PD patients, Tau levels in serum neuron-derived exosomes correlate with disease progression and are significantly lower in PD than in APS patients [9].
In PD patients, glutamatergic neurotransmission in the brain is dysregulated [131,132].The main pathogenic mechanism of PD is oxidative stress caused by impaired DA signaling.Both iron metabolism disorders and DJ-1 mutations contribute to oxidative stress and induce progressive lesions in nigrostriatal DA neurons [133,134].In PD patients, ferritin and total ferritin receptor (TFR) and DJ-1 are increased in exosomes from different sources [109,135].The oxidative stress-related proteins ATP synthase F1 subunit alpha (ATP5A), NDUFS3, and SDHB are decreased in serum exosomes [111], and miR-136-3p, miR-433, and miR-4639-5, which are associated with the dopaminergic synaptic pathway, are increased in exosomes from different sources [124,136].In the brain of PD patients, glutamatergic neurotransmission is dysregulated [83], and the activity of the glutamatergic system is associated with PD progression [137].Vesicular glutamate transporter-1 (VGLUT-1), an intermediate in glutamate-synaptic interactions, is significantly reduced in plasma neuron-derived exosomes from PD patients.However, excitatory amino acid transporter-2 (EAAT-2), also an intermediate in glutamate-synaptic interactions, is upregulated [137].Acetylcholinesterase (AChE) is significantly reduced in plasma exosomes of PD patients; acetylcholinesterase is a key enzyme in biological nerve conduction that breaks down acetylcholine, terminating the excitatory effect of neurotransmitters on synaptic membranes and ensuring the normal transmission of nerve signals throughout the organism [138].In PD patients, miR-1 and miR-19b-3p, which are associated with the neurotrophic signaling pathway, are downregulated in CSF exosomes, whereas miR-153, miR-409-3p, miR-10a-5p, and let-7g-3p are upregulated [136]; miR-128, which is specifically enriched in the brain and neurons [139,140], is upregulated in PD patients [136].In addition, there are many miRNAs with unknown functions that also show significant changes in PD.

Isolation, Analysis, and Validation of Exosome Biomarkers
The diagnostic accuracy of exosomes is affected by a variety of factors, such as extraction methods, analysis, and detection methods.The main exosome extraction methods used in clinical research are ultracentrifugation and immunoaffinity-and precipitationbased extraction kits.Size exclusion chromatography, ultrafiltration, and precipitation and immunoaffinity capture can also be used in exosome extraction.Newly developed exosome extraction methods include label-free microfluidic platforms, immunoaffinitybased microfluidics, asymmetric flow field-flow fractionation, etc. Label-free microfluidic platforms separate extracellular vesicles of different sizes by an acoustic nanofilter system, which enables continuous rapid and non-contact separation of exosomes [147].Immunoaffinity-based microfluidics combines antigen-antibody reactions and magnetic force with microfluidic chip technology to achieve specific extraction of different subpopulations of exosomes [148].Asymmetric flow field-flow fractionation combines size, density, Brownian motion, and translational diffusion to separate extracellular vesicles down to 1 nm [149,150].These new technologies can improve the purity and efficiency of exosome separation, and separate subpopulations of exosomes, but their role in exosome diagnosis remains to be investigated.Common detection methods for exosomes include mass spectrometry, enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR), etc., as well as new quantitative analysis methods based on nanofluorescent probes, microfluidic chips, and gene chips [151][152][153][154]. Nanofluorescent probes combine with target molecules to form fluorescent complexes, and the fluorescence intensity of the complexes can be detected to quantify the target molecules [151].A microfluidic microarray is based on the control of fluid flow and scale structure in microchannels and combines fluorescence, electrochemistry, mass spectrometry, and other methods to achieve quantitative detection of target molecules [152].Gene microarrays and gene chips are based on the principles of complementary gene pairing, and can be used for gene quantify analysis [153,154].These new detection methods are high throughput, high sensitivity, low sample consumption, and rapid analysis, and may play an important role in the detection of exosome-associated markers in the future.

Exosome Biomarkers Classification
miRNAs, genes, and proteins are three major classes of diagnostic markers in neuropsychiatric diseases.miRNA nomenclature is specific.Most genes and proteins are highly conserved, and we summarize the nomenclature of these homologue gene and protein names in different species (Table 1).

Ethical Concerns
When using human samples, ethical concerns should be considered.The collection and use of human exosomal samples requires strict adherence to the principles of privacy protection and informed consent.Researchers need to manage and store sample information appropriately and ensure that the participant recruitment process is fair and equitable.

Conclusions and Future Directions
Using exosomal biomarkers for assistant diagnosis not only improves diagnostic accuracy but can also be used for early diagnosis and differentiation of disease progression, which can help physicians to provide appropriate treatment plans for patients, thus supporting personalized clinical treatment strategies for patients with neuropsychiatric disorders.For example, the concentrations of neuronal-derived exosomal proteins GAP43, neurogranin, SNAP25, and SYT1 were significantly lower in AD patients than in controls, which can identify preclinical AD 5-7 years before cognitive impairment appears [123].Serum exosomal miR-199a-3p, miR-195-5p, miR-28-5p, miR-22-5p, and miR-151a-5p can be used to distinguish different stage of PD from the healthy population [146].
Currently, there are no diagnostic markers of exosomes that have been applied to the clinical diagnosis of neuropsychiatric disorders.An important reason for this is the specificity of neurological diagnostic markers.Some markers show the same trend in different diseases; for example, in the exosomes of AD, PD, and ALS, Aβ and Tau proteins are increased [9,[86][87][88][89]121], and SDHB and NDUFS3 are significantly reduced [111,128].It is necessary to combine multiple biomarkers in the clinical diagnosis.In addition, most identified diagnostic biomarkers have only been studied in the control group and limited disease groups, and comprehensive studies of these biomarkers in different disease systems are needed.

Figure 2 .
Figure 2. Potential exosomal diagnostic biomarkers in mind and volition disorders.Abnormal expression of miRNAs associated with apoptosis, oxidative stress, and insulin pathways was detected in patients with SCZ.Note: Light green boxes represent exosomal biomarkers; red font represents increased expression; green font represents decreased expression.miR: microRNA/miRNA; bcl-2:B-cell lymphoma 2; bcl-w: B-cell lymphoma w; DJ-1/PARK7: human protein deglycase, encoding by the PARK7 gene; ROS: reactive oxygen species; (pS2448-mTOR)/m-TOR: the ratio of the ratio of phosphorylated mammalian target of rapamycin (pS2448-mTOR) to total mammalian target of rapamycin to total mammalian target of rapamycin.

Figure 2 .
Figure 2. Potential exosomal diagnostic biomarkers in mind and volition disorders.Abnormal expression of miRNAs associated with apoptosis, oxidative stress, and insulin pathways was detected in patients with SCZ.Note: Light green boxes represent exosomal biomarkers; red font represents increased expression; green font represents decreased expression.miR: microRNA/miRNA; bcl-2:B-cell lymphoma 2; bcl-w: B-cell lymphoma w; DJ-1/PARK7: human protein deglycase, encoding by the PARK7 gene; ROS: reactive oxygen species; (pS2448-mTOR)/m-TOR: the ratio of the ratio of phosphorylated mammalian target of rapamycin (pS2448-mTOR) to total mammalian target of rapamycin to total mammalian target of rapamycin.

Figure 4 .
Figure 4.Potential exosomal diagnostic biomarkers in demyelinating diseases.MOG proteins and related miRNAs, FGF-2-related miRNAs, and immune-system-related miRNAs have been detected in exosomes of MS patients, which are directly related to myelin damage and regeneration.Abnormal expression of miRNAs related to oxidative stress and bone marrow hematopoiesis in MS patients may also be related to myelin.Note: Light green boxes represent exosomal biomarkers; red font represents increased expression; green font represents decreased expression.miR: mi-croRNA/miRNA; MOG: myelin oligodendrocyte glycoprotein; FGF-2: fibroblast growth factor-2; IGF1R: insulin-like growth factor 1 receptor; TGFBR1: transforming growth factor β receptor 1; Treg:

Figure 4 .
Figure 4. Potential exosomal diagnostic biomarkers in demyelinating diseases.MOG proteins and related miRNAs, FGF-2-related miRNAs, and immune-system-related miRNAs have been detected in exosomes of MS patients, which are directly related to myelin damage and regeneration.Abnormal expression of miRNAs related to oxidative stress and bone marrow hematopoiesis in MS patients may also be related to myelin.Note: Light green boxes represent exosomal biomarkers; red font represents increased expression; green font represents decreased expression.miR: microRNA/miRNA; MOG: myelin oligodendrocyte glycoprotein; FGF-2: fibroblast growth factor-2; IGF1R: insulin-like growth factor 1 receptor; TGFBR1: transforming growth factor β receptor 1; Treg: regulatory T cells; Th17: T cells 17; ROS: reactive oxygen species; STAT5: signal transducer and activator of transcription 5.

Table 1 .
Protein biomarkers in the diagnosis of neuropsychiatric diseases.