Brain cells release and take up small extracellular vesicles (sEVs) containing bioactive nucleic acids. sEV exchange is hypothesized to contribute to stereotyped spread of neuropathological changes in the diseased brain. We assess mRNA from sEVs of postmortem brain from non-diseased (ND) individuals and those with Alzheimer's disease (AD) using short- and long-read sequencing. sEV transcriptomes are distinct from those of bulk tissue, showing enrichment for genes including mRNAs encoding ribosomal proteins and transposable elements such as human-specific LINE-1 (L1Hs). AD versus ND sEVs show enrichment of inflammation-related mRNAs and depletion of synaptic signaling mRNAs. sEV mRNAs from cultured murine primary neurons, astrocytes, or microglia show similarities to human brain sEVs and reveal cell-type-specific packaging. Approximately 80% of neural sEV transcripts sequenced using long-read sequencing are full length. Motif analyses of sEV-enriched isoforms elucidate RNA-binding proteins that may be associated with sEV loading. Collectively, we show that mRNA in brain sEVs is intact, selectively packaged, and altered in disease.
Alzheimer Disease , Brain , Extracellular Vesicles , RNA, Messenger , Extracellular Vesicles/metabolism , Humans , RNA, Messenger/metabolism , RNA, Messenger/genetics , Brain/metabolism , Animals , Mice , Alzheimer Disease/metabolism , Alzheimer Disease/genetics , Alzheimer Disease/pathology , Neurons/metabolism , Astrocytes/metabolism , Microglia/metabolism , Transcriptome/genetics , Mice, Inbred C57BL
Over the past 20 years, analyses of single brain cell genomes have revealed that the brain is composed of cells with myriad distinct genomes: the brain is a genomic mosaic, generated by a host of DNA sequence-altering processes that occur somatically and do not affect the germline. As such, these sequence changes are not heritable. Some processes appear to occur during neurogenesis, when cells are mitotic, whereas others may also function in post-mitotic cells. Here, we review multiple forms of DNA sequence alterations that have now been documented: aneuploidies and aneusomies, smaller copy number variations (CNVs), somatic repeat expansions, retrotransposons, genomic cDNAs (gencDNAs) associated with somatic gene recombination (SGR), and single nucleotide variations (SNVs). A catch-all term of DNA content variation (DCV) has also been used to describe the overall phenomenon, which can include multiple forms within a single cell's genome. A requisite step in the analyses of genomic mosaicism is ongoing technology development, which is also discussed. Genomic mosaicism alters one of the most stable biological molecules, DNA, which may have many repercussions, ranging from normal functions including effects of aging, to creating dysfunction that occurs in neurodegenerative and other brain diseases, most of which show sporadic presentation, unlinked to causal, heritable genes.
Aging/metabolism , Brain Diseases/genetics , Hybrid Cells/physiology , Aging/genetics , Aneuploidy , Animals , Brain/cytology , Brain/metabolism , Brain Diseases/metabolism , Brain Diseases/physiopathology , DNA Copy Number Variations/genetics , Genome/genetics , Genomics/methods , Humans , Hybrid Cells/cytology , Mosaicism , Mutation/genetics , Single-Cell Analysis/methods
Diabetes mellitus represents a group of metabolic diseases that are characterized by hyperglycemia caused by either lack of insulin production or a reduced ability to respond to insulin. It is estimated that there were 347 million people worldwide who suffered from diabetes in 2008 and incidence is predicted to double by 2050. Neuropathy is the most common complication of long-term diabetes and approximately 30% of these subjects develop chronic neuropathic pain. A distinct acute, severe form of neuropathic pain, called insulin neuritis or treatment-induced painful neuropathy of diabetes (TIND), may also occur shortly after initiation of intensive glycemic control, with an incidence rate of up to 10.9%. The pathological mechanisms leading to TIND, which is mostly unresponsive to analgesics, are not yet understood, impeding the development of therapies. Studies to date have been clinical and with limited cohorts of patients. In the current study, we developed chronic and acute insulin-induced neuropathic pain in mice with type 2 insulin-resistant diabetes. Furthermore, we determined that insulin-induced acute allodynia is independent of glycemia levels, can also be induced with Insulin-like Growth Factor 1 (IGF1) and be prevented by inhibition of AKT, providing evidence of an insulin/IGF1 signaling pathway-based mechanism for TIND. This mouse model is useful for the elucidation of mechanisms contributing to TIND and for the testing of new therapeutic approaches to treat TIND.
Diabetic Neuropathies/complications , Diabetic Neuropathies/therapy , Disease Models, Animal , Hypoglycemic Agents/toxicity , Insulin/toxicity , Neuralgia/complications , Neuralgia/therapy , Amines/therapeutic use , Animals , Cyclohexanecarboxylic Acids/therapeutic use , Diabetic Neuropathies/genetics , Enzyme Inhibitors/pharmacology , Excitatory Amino Acid Antagonists/therapeutic use , Female , GTPase-Activating Proteins , Gabapentin , Guanine Nucleotide Exchange Factors/genetics , Guanine Nucleotide Exchange Factors/metabolism , Hyperalgesia/etiology , Male , Mice , Mice, Inbred C57BL , Mice, Transgenic , Neural Conduction/genetics , Neural Conduction/physiology , Neuralgia/genetics , Pain Threshold/physiology , Reaction Time/physiology , Receptor, Insulin/deficiency , Receptor, Insulin/genetics , Receptors, Leptin/genetics , Receptors, Leptin/metabolism , gamma-Aminobutyric Acid/therapeutic use
