Table 4.

Single organ scRNA-seq studies (in vivo, senescence non-specific)

	Enge et al. (2017)	Hammond et al. (2019)	Yi et al. (2020)	Zheng et al. (2020)	De Micheli et al. (2020)	Zou et al. (2021)
Species	Human	Mouse	Human, primate	Human	Human	Human
Organ	Pancreas	Brain (microglia)	Retina	Peripheral blood mononuclear cells (PBMCs)	Muscle	Eyelid skin
Age	Juvenile (1 mo, 5 y, 6 y), young adult (21 y, 22 y), adult/middle aged (38 y, 44 y, 54 y)	Embryonic day 14.5 (E14.5), early postnatal day 4/5 (P4/P5), late juvenile stage (P30), adulthood (P100), old age (P540), injury (P100)	Human: infant (8 days), adult (35-87 y) Macaque: juvenile (2 y), adults (4-23 y)	Cohort-1: young healthy adults (YA) (20-45 y), aged healthy adults (AA) (≥ 60 y) Cohort-2: comprising young adults (30-45 y) (YH), aged healthy adults (AH) (≥ 60 y), young COVID-19 onset patients (30-50 y), aged COVID-19 onset patients (≥ 70 y) Cohort-3: comprising YH AH, young recovered COVID-19 patients, aged recovered COVID-19 patients	Donors (range, 41-81 y)	Young, middle aged, old*
Method	Smart-seq2	10× Genomics	10× Genomics	10× Genomics	10× Genomics	10× Genomics
Capture format	Plate	Droplets	Droplets	Droplets	Droplets	Droplets
Transcript coverage	Full length	3’ end	3’ end	5’ end	3’ end	3’ end
No. of cells	2,544	76,149	119,520	166,609	Over 22,000	35,678
Remark	An age-dependent mutational signature of endocrine cells is attributed to guanine oxidation selectively induced by reactive oxygen species.	Two microglia clusters are enriched in aging mice; one clustered has 2-4 times more microglia expressing inflammatory signals, such as Ccl4, Il1b, and Ccr5.	Human retinal aging occurs in the foveal region earlier. MYO9A− rods and the horizontal cell subtype, reduced in aging retina, are vulnerable to aging.	Age-induced immune cell polarization and expression of inflammation-related genes, such as FOS, DUSP1, IL1B, and cellular senescence-related genes, such as the CDKN family, are associated with vulnerability to COVID-19.	The muscle stem/progenitor cell (MuSC) population consists of MuSC1 and MuSC2 subpopulations. MuSC2 is enriched for inflammation markers, including CCL2, CXCL1, IL32, and TNFRSF12/FN14, that may constitute a marker set for MuSC variation in chronic muscle inflammation.	The cell-type specific downregulation of key TFs, such as KLF6 in keratinocytes and HES1 in dermal fibroblast, promote senescence phenotypes including increased SA-β-gal-positive cells and increased inflammation.

*Specific ages are not defined.