Spaceflight-relevant microgravity triggers a sublethal Parkinson's-like dopaminergic decline in human neurons and organoids.

Key results

1. ShownSimulated microgravity (SMG) lowered mitochondrial membrane potential in both models. Organoid respiration stayed suppressed after exposure, and levels of oxidative phosphorylation (OXPHOS) complexes shifted in SH-SY5Y neurons.

   Resipher oxygen consumption was similar at baseline (~10 fmol/mm²/s). By 168 h, SMG organoids plateaued at ~0.9 vs ~12.3 fmol/mm²/s for 1G controls, which the authors report as ~92% lower. The TMRM membrane-potential signal fell in organoids (N = 3-4) and in SH-SY5Y. SH-SY5Y immunoblots: Complexes I, II and IV down, III unchanged, V up (N = 3-5). · Human DA neurons under simulated microgravity…; Real-time oxygen consumption rate measurements; Figure legends

2. ShownNeurite outgrowth and dopaminergic identity declined, and the familial-PD genes PINK1, PRKN and LRRK2 rose at the mRNA level. Dopamine in the culture medium was not depleted.

   SH-SY5Y neurite length fell while width was unchanged; organoid sprouts were shorter and thinner (n = 6-14). In SH-SY5Y, qRT-PCR showed lower TH and alpha-synuclein mRNA and higher PINK1, PRKN and LRRK2 (n = 3-8), and TH protein fell on Western blot (n = 4-8). Dopamine in SH-SY5Y medium, measured by LC-MS/MS, did not differ from 1G (n = 5-6). · Simulated microgravity reduces neurite length…; Simulated Microgravity upregulates familial…; Figure legends

3. ShownGlobal protein synthesis was repressed: the ribosomal protein RPS3 fell in both models and nascent-protein labelling dropped.

   RPS3 was significantly lower in SMG organoids than in 1G controls and was reduced on SH-SY5Y Western blots (N = 3-5). SUnSET puromycin incorporation dropped significantly vs 1G. RPS3 was also lower post-flight in skin biopsies from four astronauts, and cytosolic ribosomal gene sets in Inspiration4 PBMCs stayed down from return day +1 to 82 days after flight. · Spaceflight and PD datasets reveal convergent…; SUnSET puromycin incorporation assay; Inspiration4 PBMC transcriptomics analysis from…; Figure legends

4. ShownThe stress was sublethal: the cell-free DNA released under SMG was selectively mitochondrial, apoptotic markers did not rise, and cytotoxicity was mild.

   Cell-free DNA in conditioned medium rose in organoids (n = 3-5) and in SH-SY5Y neurons. Duplex digital PCR traced the rise to MT-ND5 (mitochondrial) rather than HPRT1 (nuclear) copies (n = 6 organoids; n = 3 SH-SY5Y). Cleaved caspase-3 and cleaved PARP in SH-SY5Y lysates did not change (n = 3-6). LDH cytotoxicity was ~9.8% (n = 5). · Post-SMG cell free DNA increase is specific to…; Digital PCR; LDH cytotoxicity assay; Figure legends

5. SuggestedThe two models' proteomes mostly moved in opposite directions. Organoids suppressed mitochondrial, ribosomal and KEGG Parkinson's disease pathways, in line with reanalysed PD neuron and blood transcriptomes. SH-SY5Y instead showed complement, inflammatory and unfolded-protein stress responses.

   Preranked gene-set enrichment on 4,602 organoid and 4,412 SH-SY5Y proteins (n = 3/group): 294 significant pathways went opposite ways, 21 concordant (FDR < 0.05). Organoids had 19 mitochondrial pathways down and all 16 splicing pathways up. In FOUNDIN-PD iPSC neurons (n = 98), ribosomal pathways were among the most reduced in idiopathic PD at days 25 and 65. · Global pathway analysis reveals fundamentally…; Bulk RNA-seq Analysis of the PPMI FOUNDIN-PD…; Spaceflight and PD datasets reveal convergent…; Proteomics data analysis