Biology subjects

Shantaraman, A.

Publications and source records attributed to Shantaraman, A..

4 recordsLinked to original sources

bioRxiv2024

Network Proteomics of the Lewy Body Dementia Brain Reveals Presynaptic Signatures Distinct from Alzheimer's Disease

Lewy body dementia (LBD), a class of disorders comprising Parkinsons disease dementia (PDD) and dementia with Lewy bodies (DLB), features substantial clinical and pathological overlap with Alzheimers disease (AD). The identification of biomarkers unique to LBD pathophysiology could meaningfully advance its diagnosis, monitoring, and treatment. Using quantitative mass spectrometry (MS), we measured over 9,000 proteins across 138 dorsolateral prefrontal cortex (DLPFC) tissues from a University of Pennsylvania autopsy collection comprising control, Parkinsons disease (PD), PDD, and DLB diagnoses. We then analyzed co-expression network protein alterations in those with LBD, validated these disease signatures in two independent LBD datasets, and compared these findings to those observed in network analyses of AD cases. The LBD network revealed numerous groups or "modules" of co-expressed proteins significantly altered in PDD and DLB, representing synaptic, metabolic, and inflammatory pathophysiology. A comparison of validated LBD signatures to those of AD identified distinct differences between the two diseases. Notably, synuclein-associated presynaptic modules were elevated in LBD but decreased in AD relative to controls. We also found that glial-associated matrisome signatures consistently elevated in AD were more variably altered in LBD, ultimately stratifying those LBD cases with low versus high burdens of concurrent beta-amyloid deposition. In conclusion, unbiased network proteomic analysis revealed diverse pathophysiological changes in the LBD frontal cortex distinct from alterations in AD. These results highlight the LBD brain network proteome as a promising source of biomarkers that could enhance clinical recognition and management.

systems biology↗

bioRxiv2023

Global analysis of the heparin-enriched plasma proteome captures matrisome-associated proteins in Alzheimer's disease

Matrisome-associated heparin binding proteins (HBPs) with roles in extracellular matrix assembly are strongly correlated to {beta}-amyloid (A{beta}) and tau pathology in Alzheimers disease (AD) brain and cerebrospinal fluid (CSF). However, it remains challenging to detect these proteins in plasma using standard mass spectrometry (MS)-based proteomic approaches. Here we utilized heparin affinity chromatography for the capture and enrichment of HBPs in plasma from healthy control and individuals with AD. This method was highly reproducible and effectively enriched well-known HBPs like APOE and thrombin, while also efficiently depleting high-abundance proteins such as albumin. To increase the depth of our analysis of the heparin-enriched plasma proteome and compare differences in disease we applied off-line fractionation and tandem mass tag mass spectrometry (TMT-MS) to compare the proteomic profiles between AD and control individuals across two datasets (n = 121 total samples). This led to the identification of 2865 proteins, spanning 10 orders of magnitude in protein abundance within the plasma. Notably, HBPs were some of the most increased proteins in AD plasma compared to controls. This included members of the matrisome-associated module in brain, SMOC1, SMOC2, SPON1, MDK, OLFML3, FRZB, GPNMB and the {varepsilon}4 isoform of APOE. Heparin-enriched plasma proteins also exhibited strong correlations to conventional AD biomarkers including CSF A{beta}, total tau (tTau), and phosphorylated tau (pTau) as well as plasma pTau supporting their role as potential surrogate markers of underlying brain pathology. Utilizing a consensus AD brain protein co-expression network, we assessed relationship between the plasma and brain proteomes and observed that specific plasma proteins exhibited consistent direction of change in both brain and plasma, whereas others displayed divergent changes, further highlighting the complex interplay between the two compartments. In summary, these findings provide support for the integration of a heparin enrichment method with MS-based proteomics for identifying a wide spectrum of plasma biomarkers that mirror pathological changes in the AD brain.

neuroscience↗

bioRxiv2023

Using deep long-read RNAseq in Alzheimer's disease brain to assess clinical relevance of RNA isoform diversity

Due to alternative splicing, human protein-coding genes average over eight RNA isoforms, resulting in nearly four distinct protein coding sequences per gene. Long-read RNAseq (IsoSeq) enables more accurate quantification of isoforms, shedding light on their specific roles. To assess the medical relevance of measuring RNA isoform expression, we sequenced 12 aged human frontal cortices (6 Alzheimers disease cases and 6 controls; 50% female) using one Oxford Nanopore PromethION flow cell per sample. Our study uncovered 53 new high-confidence RNA isoforms in medically relevant genes, including several where the new isoform was one of the most highly expressed for that gene. Specific examples include WDR4 (61%; microcephaly), MYL3 (44%; hypertrophic cardiomyopathy), and MTHFS (25%; major depression, schizophrenia, bipolar disorder). Other notable genes with new high-confidence isoforms include CPLX2 (10%; schizophrenia, epilepsy) and MAOB (9%; targeted for Parkinsons disease treatment). We identified 1,917 medically relevant genes expressing multiple isoforms in human frontal cortex, where 1,018 had multiple isoforms with different protein coding sequences, demonstrating the need to better understand how individual isoforms from a single gene body are involved in human health and disease, if at all. Exactly 98 of the 1,917 genes are implicated in brain-related diseases, including Alzheimers disease genes such as APP (A{beta} precursor protein; five), MAPT (tau protein; four), and BIN1 (eight). As proof of concept, we also found 99 differentially expressed RNA isoforms between Alzheimers cases and controls, despite the genes themselves not exhibiting differential expression. Our findings highlight the significant knowledge gaps in RNA isoform diversity and their medical relevance. Deep long-read RNA sequencing will be necessary going forward to fully comprehend the medical relevance of individual isoforms for a "single" gene.

genomics↗

bioRxiv2023

Mis-spliced transcripts generate de novo proteins in TDP-43-related ALS/FTD

Functional loss of TDP-43, an RNA-binding protein genetically and pathologically linked to ALS and FTD, leads to inclusion of cryptic exons in hundreds of transcripts during disease. Cryptic exons can promote degradation of affected transcripts, deleteriously altering cellular function through loss-of-function mechanisms. However, the possibility of de novo protein synthesis from cryptic exon transcripts has not been explored. Here, we show that mRNA transcripts harboring cryptic exons generate de novo proteins both in TDP-43 deficient cellular models and in disease. Using coordinated transcriptomic and proteomic studies of TDP-43 depleted iPSC-derived neurons, we identified numerous peptides that mapped to cryptic exons. Cryptic exons identified in iPSC models were highly predictive of cryptic exons expressed in brains of patients with TDP-43 proteinopathy, including cryptic transcripts that generated de novo proteins. We discovered that inclusion of cryptic peptide sequences in proteins altered their interactions with other proteins, thereby likely altering their function. Finally, we showed that these de novo peptides were present in CSF from patients with ALS. The demonstration of cryptic exon translation suggests new mechanisms for ALS pathophysiology downstream of TDP-43 dysfunction and may provide a strategy for novel biomarker development. One Sentence SummaryLoss of TDP-43 function results in the expression of de novo proteins from mis-spliced mRNA transcripts.

neuroscience↗