Medicine & Health

IF a tripartite nuclear-recoded MT-CYB construct — comprising (a) the SOD2 mitochondrial targeting sequence (MTS) N-terminal fusion, (b) the SOD2 3′UTR for mRNA surface localization, and (c) targeted hydrophobicity-reduction mutagenesis of the two most GRAVY-scored transmembrane helices (predicted TM-IV and TM-V) limited to conservative Ile→Val and Leu→Ala substitutions at non-heme-coordinating, non-ubiquinone-contacting residue positions — is delivered first as pseudouridine/5-methylcytosine (Ψ/5mC) modified mRNA and subsequently via AAV9 to MT-CYB-null cybrid cells generated by DdCBE-mediated introduction of a premature stop codon in the endogenous MT-CYB locus,

THEN the allotopically expressed CYB protein will (i) localize to the mitochondrial inner membrane as confirmed by immunogold electron microscopy, (ii) assemble into the dimeric bc1 complex detectable by Blue Native PAGE, (iii) restore Complex III enzymatic activity (cytochrome c reductase assay) to ≥25% of isogenic wild-type levels, and (iv) confer rescue of OXPHOS-dependent proliferation on glucose-free galactose medium within 14 days post-transfection,

BECAUSE the causal chain proceeds as follows:

1. The SOD2 3′UTR directs the recoded MT-CYB mRNA to the mitochondrial outer membrane surface prior to translation, achieving ≥80% mitochondrial mRNA enrichment as demonstrated for ATP6 mRNA by the Corral-Debrinski strategy (ATP6 mRNA localized at 84.6% mitochondrial surface enrichment, enabling full NARP cybrid rescue), thereby co-localizing the ribosome-mRNA-nascent-chain complex with the TOM

IF a single intravenous dose of AAV9 encoding a human-codon-optimized OsDJ-1C transgene under a constitutive CAG promoter (1×10¹¹ vg/mouse) is administered to 18-month-old male and female C57BL/6J mice carrying established dicarbonyl damage (elevated tissue MG-H1, CEdG DNA adducts, and a depleted GSH/GSSG ratio consistent with aged tissue),

THEN quantitative LC-MS/MS measurement at 6 months post-injection will reveal ≥40% reduction in hepatic and renal tissue-free MGO concentrations, ≥30% reduction in MG-H1 adduct density on short-to-medium turnover proteins (assessed by targeted proteomics), a measurable decrease in CEdG DNA adduct burden in liver (assessed by immunoslot-blot and LC-MS), and partial restoration of endogenous PARK7/DJ-1 deglycase activity on long-lived glycated protein substrates, compared with age-matched AAV9-GFP controls,

BECAUSE the following causal chain operates in aged mammalian tissue:

1. Aged tissue suffers a "double-hit" collapse of the canonical glyoxalase system: GLO1 activity declines transcriptionally in liver, kidney, and brain with advancing age, and simultaneously the cellular GSH pool is depleted and the GSH/GSSG ratio falls, creating a kinetic bottleneck wherein even residual GLO1 protein cannot convert MGO to S-D-lactoylglutathione at physiological rates. Free reactive MGO therefore accumulates above the nanomolar steady-state, driving accelerating AGE formation and direct DNA mutagenesis (as reviewed in the Evidence Set: "the 'double hit' of reduced enzyme availability and insufficient cofactor supply leads to a supraphysiologi

IF systemic SkQ1 (5 nmol/kg/day via drinking water, 12 weeks) is administered to 22–24-month-old C57BL/6J mice of both sexes carrying the mito-QC mitophagy reporter transgene,

THEN a measurable reduction (≥20% decrease) in the fractional burden of large-scale mtDNA deletions across cardiac and skeletal muscle tissue will be observed at endpoint (week 12), accompanied by a ≥30% increase in basal mitophagic flux (mito-QC lysosomal:mitochondrial red-to-green puncta ratio) in the same tissues and normalization of lysosomal cathepsin B/D activity to levels observed in 6-month-old controls,

BECAUSE the following causal chain operates sequentially:

1. In aged mice (24 months), chronic mitochondrial ROS production generates lipid peroxidation products and protein carbonyls that accumulate as lipofuscin within lysosomes, physically and chemically inactivating cathepsins B, D, and L — the proteases required to degrade mitochondrial cargo delivered by completed mitophagosomes. This lysosomal blockade creates a downstream bottleneck that traps ubiquitinated, PINK1/Parkin-tagged damaged mitochondria in autolysosomes without degrading them, causing stalled mitophagic flux despite intact upstream recognition machinery. (Evidence: SkQ1 prevents lipofuscin formation and age-dependent autophagy decline by mitigating lipid peroxidation — Skulachev et al., Aging, 2017, cited in Evidence Set.)

2. Aged cardiac and hippocampal tissue show a precipitous decline in mitophagic flux relative to young controls, quantified using mito-QC and mt-Keima reporter systems; this decline is not attributa

IF aged human hematopoietic stem cells (HSCs; donors >65 years, purified Lin⁻CD34⁺CD38⁻CD90⁺ fraction) are subjected to a sequential ex vivo lysosomal reset protocol — first a 16-hour exposure to trehalose (100 mM) to activate TFEB-mediated lysosomal biogenesis and clear accumulated intracellular substrate, followed immediately by a 16-hour exposure to bafilomycin A1 (BafA1; 3 nM) to suppress v-ATPase hyperactivation rebound — prior to xenotransplantation into sub-lethally irradiated NSG mice,

THEN recipients will demonstrate ≥6-fold improvement in long-term human CD45⁺ chimerism at 16 weeks post-transplant relative to untreated aged HSC controls, with balanced myeloid/lymphoid output (CD33⁺:CD19⁺ ratio <2, matching young donor reference), and successful secondary engraftment in ≥60% of serially transplanted hosts,

BECAUSE the following mechanistic chain operates:

1. Aged HSCs accumulate undegraded intracellular substrates (protein aggregates, damaged organelles, lipofuscin-like material) due to insufficient lysosomal biogenesis relative to the rate of damage accrual — this substrate overload drives compensatory v-ATPase upregulation to acidify and process the backlog, producing the hyperactivated lysosomal phenotype observed in aged HSCs. SPECULATIVE link — supported indirectly by the neural stem cell evidence showing that reduced autophagic flux into acidified lysosomes characterizes aged quiescent stem cells, with accumulated GFP-LC3-positive material indicating unresolved substrate burden

2. Trehalose, acting as

IF a codon-optimized fusion protein comprising Pyrococcus furiosus RNase HII (PfuRNaseHII) C-terminally linked via a flexible (Gly₄Ser)₃ linker to a tandem dual-copy TRF2 TRFH-docking peptide (YRLSP×2) and an SV40 nuclear localization signal (NLS), packaged within an AAV2/9 hybrid capsid, is delivered by intratumoral injection at 1×10¹¹ vector genomes per mouse into established subcutaneous U2OS or Saos-2 xenografts (100–150 mm³) in male NSG mice aged 6–8 weeks,

THEN over 28 days the following will be observed: (1) ≥50% reduction in C-circle abundance by rolling-circle amplification qPCR (baseline sensitivity 0.1 attomoles circular template), (2) ≥40% reduction in ALT-associated PML body (APB) frequency per nucleus (scoring ≥200 nuclei per condition by PML/TRF2 co-immunofluorescence), and (3) ≥3-fold increase in telomere dysfunction-induced foci (TIF) measured by γH2AX/telomeric FISH co-localization, relative to AAV2/9-GFP control-injected xenografts,

BECAUSE the following causal chain operates:

1. ATRX loss elevates TERRA transcription and R-loop accumulation at telomeres. In ATRX-null U2OS and Saos-2 cells, failure to deposit histone H3.3 at telomeres abolishes heterochromatic repression, leading to pervasive TERRA upregulation and the chronic formation of telomeric RNA:DNA hybrids that are the mechanistic substrate of the ALT pathway (Arora et al., 2014, Science, as reviewed in Evidence Set).

2. TERRA R-loops directly nucleate the BIR-based recombination events that produce C-circles and sustain APBs. R-loop formation at telomeres loads RAD52 and drives b

IF a sequential two-phase intervention consisting of (Phase A) systemically administered TFSA (trifluoromethylsulfonyl-functionalized) pH-buffering polymeric nanoparticles (10–25 mg/kg i.p., 2×/week, 4 weeks) to chemically re-acidify RPE lysosomes, followed by (Phase B) subretinal injection of a self-complementary AAV9 (scAAV9) vector encoding human ATP6V1H (V-ATPase V1 H-subunit) under the VMD2/BEST1 RPE-specific promoter with a C-terminal HA epitope tag, is administered to aged (18–22 month) male and female C57BL/6 mice with established RPE lysosomal dysfunction,

THEN LysoSensor Yellow/Blue DND-160 ratiometric imaging of RPE flat mounts will show measurable re-acidification of RPE lysosomes (pH shift from ~5.5–5.8 baseline in aged RPE toward the youthful ~4.7–5.0 range), accompanied by a ≥30% reduction in RPE lipofuscin/A2E autofluorescence, structural preservation of the photoreceptor-RPE interface on OCT, and maintained ERG b-wave amplitude relative to vehicle-treated aged controls,

BECAUSE:

1. In aged RPE, V-ATPase assembly efficiency declines, causing lysosomal alkalinization that impairs proteolytic degradation of photoreceptor outer segment (POS) material, leading to progressive accumulation of bisretinoid lipofuscin (A2E) — the defining LysoSENS damage in AMD pathogenesis. (Evidence Set: Biodistribution and BRB Crossing section; In Vivo Ratiometric Imaging section)
2. TFSA/PBFSU-class pH-buffering polymeric nanoparticles are engineered to internalize via endocytosis, buffer the luminal pH of late endosomes and lysosomes through a proton-sponge or hy

Exploring mechanisms and implications for aging biology. What evidence supports this, and how could we test it?

Exploring mechanisms and implications for aging biology. What evidence supports this, and how could we test it?

Background

Anti-CD19 chimeric antigen receptor T-cell (CAR-T) therapy has emerged as a transformative approach for refractory systemic lupus erythematosus (SLE), achieving drug-free remission in early case series (Mackensen et al., Nat Med 2022; Müller et al., NEJM 2024). However, response heterogeneity remains unexplained — some patients achieve sustained seroconversion of anti-dsDNA with durable clinical remission, while others experience incomplete B-cell depletion or early reconstitution with persistent autoantibody production. No validated biomarker currently predicts the depth or duration of CAR-T–mediated B-cell aplasia in autoimmune indications.

Hypothesis

We hypothesize that pre-treatment circulating T follicular helper (cTfh) cell frequency — specifically the ICOS+PD-1++ subset — combined with serum CXCL13 trajectory slope over the 4 weeks preceding CAR-T infusion predicts:

1. Depth of B-cell depletion (nadir CD19+ count at week 4)
2. Duration of B-cell aplasia (time to B-cell reconstitution >10 cells/µL)
3. Probability of anti-dsDNA seroconversion by week 24

Patients with high cTfh ICOS+PD-1++ frequency (>15% of CD4+ T cells) and rising CXCL13 slope (>2 pg/mL/week) harbor active germinal center reactions that generate treatment-resistant long-lived plasma cells in survival niches (bone marrow, inflamed tissue). These patients will exhibit shorter B-cell aplasia duration (<12 weeks) and lower probability of sustained serological remission despite adequate CAR-T expansion, because the underlying Tfh-driven germinal center activity rap

Exploring mechanisms and implications for aging biology. What evidence supports this, and how could we test it?

Exploring mechanisms and implications for aging biology. What evidence supports this, and how could we test it?

IF a combinatorial, asymmetrically targeted pharmacological regimen — consisting of (i) intravenous delivery of young (3-month) donor mesenchymal stem cells (MSCs) pre-conditioned with SC-79 (an Akt activator, 5 µM, 24h ex vivo), which upregulates Miro1 protein expression and loads healthy mitochondria onto the kinesin motor complex, combined with (ii) systemic low-dose rapamycin (2 mg/kg every other day) administered to aged recipient mice to suppress aberrant mTOR hyperactivation in aged tissue-resident cells — is administered to 22-month-old male C57BL/6 mice for 8 weeks,

THEN a net increase in directionally biased (donor-to-recipient) TNT-mediated mitochondrial transfer to aged skeletal muscle satellite cells and hepatocytes will be observed — quantified as ≥40% increase in donor-mitochondria-positive aged cells (via mito-Dendra2 photoconversion tracing), accompanied by ≥30% reduction in mtDNA heteroplasmy burden in aged tissue, restored Complex I-driven oxygen consumption rate (OCR) ≥25% above vehicle-aged controls, and ≥50% reduction in SASP cytokine panel (IL-6, IL-8, MMP3) in treated tissue — measured at 4 and 8 weeks post-initiation,

BECAUSE the following step-by-step causal chain operates:

1. Aged tissue cells exhibit aberrant, constitutive mTOR/p70S6K hyperactivation driven by chronic mitochondrial ROS accumulation, which paradoxically drives competitive TNT protrusion from aged cells toward donor MSCs — creating a retrograde transfer risk that dilutes the therapeutic benefit (Aberrant mTOR activation in senescence and aging)[https://doi.org/10.1016/j.

IF a sequential-then-concurrent pharmacological regimen of MitoQ (mitoquinone mesylate, 500 µM in drinking water, administered ad libitum) followed by bezafibrate (0.5% w/w in chow) — with MitoQ initiated two weeks prior to bezafibrate co-administration to pre-condition the mitochondrial redox environment — is administered to aged C57BL/6J male mice (22–24 months), compared to vehicle control, MitoQ monotherapy, and bezafibrate monotherapy arms,

THEN a measurable reduction in hippocampal mutant mtDNA heteroplasmy fraction (≥20% reduction in the ratio of deletion-bearing to wild-type mtDNA copies, quantified by long-range PCR and droplet digital PCR), combined with a ≥30% increase in hippocampal mtDNA copy number, ≥25% reduction in 4-hydroxynonenal (4-HNE) adducts, and statistically significant improvement in Morris Water Maze escape latency and probe trial performance relative to vehicle-treated aged controls, will be observed,

BECAUSE the following step-by-step causal chain operates:

1. In the aged brain, elevated mitochondrial ROS drives ongoing somatic mtDNA point mutations and deletions via oxidative base damage (8-oxoguanine) and strand-break-mediated rearrangements, progressively enriching the pool of deletion-bearing mtDNA molecules and worsening electron transport chain (ETC) dysfunction. (Mitochondrial DNA replication machinery contributes to mutagenesis and age-related disease accumulation)[https://doi.org/10.1016/j.arr.2016.04.006]

2. MitoQ, accumulating ~500-fold within the mitochondrial matrix via its TPP+ cation anchor, quenches superoxide and lipid peroxy

IF dual AAV-mediated chromatin restoration — intratumoral AAV9-DAXX (week 0) followed by AAV9-ATRX (week 1), both at ~1×10¹¹ vg/tumor, administered without any concurrent G-quadruplex (G4) stabilizer — is delivered to Saos-2 ALT-positive osteosarcoma xenografts in female athymic nude mice (6–8 weeks), and then supplemented at week 3 with intratumoral AAV9-RNaseH1 overexpression to resolve residual TERRA R-loops at telomeres,

THEN ≥70% reduction in APB foci (immuno-FISH, PML/telomere colocalization) and ≥70% reduction in C-circle signal (quantitative rolling-circle amplification C-circle assay) will be observed by week 6 compared to vehicle-AAV controls, with secondary reductions in telomere sister-chromatid exchange (T-SCE) frequency and telomere length heterogeneity,

BECAUSE of the following mechanistic chain:

1. Loss of ATRX is causally sufficient to activate ALT, as demonstrated by C-circle production, APB formation, fragile telomeres, and elevated T-SCEs in ATRX-null sarcoma models (ATRX loss drives ALT hallmarks in primary CAST/EiJ sarcoma)[https://doi.org/10.1101/2023.11.06.565874]. Restoring ATRX expression re-establishes G4 resolution at TERRA-rich telomeric repeats and re-deposits H3.3 into heterochromatin, directly suppressing ALT (ATRX restoration suppresses C-circles and APBs)[https://doi.org/10.1038/ncomms8538].

2. DAXX, ATRX's obligate chromatin-remodeling partner, independently and rapidly suppresses ALT in the osteosarcoma line G292 when stably re-expressed; this requires intact C-terminal SUMO-interaction motif–mediated PML body localization and act