Science · Human skeletal evolutionHuman joint evolution: Study finds roughly threefold less GAG in human cartilageAired November 15, 2026 at 6:53 AM UTCWatchTranscript0:00Human joint evolution.0:01Study finds roughly threefold less gag in human cartilage.0:06Human cartilage holds roughly a third as much water, trapping sugar material as ape0:11cartilage.0:12Osteoarthritis affects about six hundred and seven million people worldwide, and0:15these molecules help joints withstand pressure.0:18Researchers have traced a possible genetic reason for the difference.0:21But how much does it explain our vulnerability to painful joints?0:24Across eight joint types, human samples contain two point six to four times less0:28sulfated GAG after adjustment for DNA content.0:32GAG stands for glycosaminoglycan, a family of long sugar chains that helps cartilage0:37retain water.0:37The chains carry a strong negative electrical charge that helps them attract water0:41into the material surrounding cartilage cells.0:43The resulting hydrated network contributes to elasticity and resistance to0:47compression.0:47JAGs account for fifteen to thirty percent of cartilage dry weight, second only to0:51collagen.0:52Researchers at the Wiseman Institute of Science in Israel and Kyoto University in0:55Japan combine genetic experiments with donated cartilage.0:58Their five-year project connected changes in human DNA regulation to lower activity1:02in the machinery that makes these water-holding molecules.1:05The study was published September23,2026 .1:09A November interview brought it renewed attention.1:11The experiments began with a broad search through genomes, looking for changes1:15shared by humans rather than starting with one suspected arthritis gene.1:18David Gukma and Fumitaka Inoue co-led the collaborating laboratories.1:22Nadev Michel led analyses and manuscript work, while Yuzi Yan performed the1:26large-scale sequence experiments.1:28Together, their teams tested how human and ancestral versions of regulatory DNA1:33behave in cartilage cells.1:34The genome comparison included178 modern humans and1309 great apes.1:40Those apes included bonabos, chimpanzees, gorillas, and orangutans.1:44Three Neanderthal genomes and one Denisovan genome helped identify changes shared1:48across modern and ancient human lineages.1:50From an initial catalog of about five point seven million single-letter differences,1:54the team selected five hundred and sixty, one four hundred ten substitutions in1:58candidate regulatory regions.2:00These regions act like controls, influencing when and where genes work and how2:04strongly they operate.2:05The researchers built three hundred sixty six four hundred two sequence pairs2:08comparing human and ancestral versions.2:11Of those, sixty, five, five hundred and seventy, six pairs showed activity.2:16Within that active group, fifteen seventy seven regulatory elements behaved2:20differently between versions, or twenty three percent of the active elements.2:24Each sequence was two hundred and seventy DNA letters long.2:27Nearby substitutions could share one sequence, so the sequence count differs from2:31the substitution count.2:32Genetic barcodes let researchers measure the activity of many sequences together.2:36They tested the library in human cartilage cells, repeating the experiment three2:40times.2:40Most human and ancestral versions behaved similarly, and this experiment tested2:44their activity in cartilage cells.2:46A sequence that appeared quiet there could still have a role in another tissue or at2:50another stage of development.2:51The team also fused cultured human cells with chimpanzee or gorilla cells.2:55They guided these laboratory hybrid cells toward an early stage capable of forming2:59bone and cartilage.3:00Human and ape chromosomes could then operate inside the same cellular environment.3:04That shared environment helped researchers separate the effects of nearby regulatory3:08DNA from differences between separate cultures.3:10It also captured changes beyond single letter substitutions, including inserted or3:15deleted DNA.3:16Both approaches pointed toward the network that builds and maintains the material3:19around cartilage cells.3:21Seventeen of twenty one gag related genes with different activity were less active3:25on the human side.3:26The average decreases were also larger than the increases.3:29The pattern points toward coordinated changes across a production pathway, rather3:33than one mutation shutting cartilage production off.3:36The sequence experiment supported that pattern.3:38Genes involved in gag metabolism appeared among relevant regulatory targets at two3:43point two times the expected rate.3:44One particularly clear example involved a gene that helps assemble chondrate and3:48sulfate, one of cartilage important sugar chains.3:51Seven of nine changed regulatory elements linked to that gene acted downward.3:56One human sequence produced thirty, four percent less activity in hybrid cells.4:00The human gene's expression was forty two percent below the chimpanzee version and4:05thirty four percent below the gorilla version.4:07Another result pulled in the opposite direction.4:09The human ACAN gene, which makes the Agrikin scaffold had expanded.4:13That scaffold carries many GI genes.4:16Human versions average six extra repeats, creating twelve additional potential4:19attachment sites for those chains.4:21The scaffold comparison used three hundred and sixteen human DNA versions and twenty4:26six great APR versions.4:27More attachment sites might compensate for lower gauge production.4:30The researchers suggest, but those opposing changes made direct measurements of4:34cartilage essential to learn the overall result.4:36Subscribe to this channel as researchers investigate what this cartilage difference4:40means for joint disease.4:42The tissue measurements used one hundred and eleven samples from forty two human4:45donors compared with twenty eight samples from seven great apes.4:48Some donors supplied several samples.4:50For the overall comparison, the researchers averaged those repeated measurements4:54down to one value per individual.4:56Human levels were lower in the hip, knee, shoulder, elbow, and wrist.5:00They were also lower at the knuckles and in two categories of finger joints.5:04The researchers used a dye binding test to measure sulfated GG and adjusted the5:09measurements for DNA content.5:10All eight joint categories pointed in the same direction, but some finger5:14comparisons included tissue from only one ape, limiting how precisely those results5:18represent the wider population.5:20Repeated laboratory readings improved measurement precision without adding more5:23individual donors.5:24The difference persisted after adjustments for age and sex.5:27Two methods of matching ages across species also left ape samples higher.5:31The pattern crossed joints that experience different loading in humans, making a5:35simple explanation based only on a joint's immediate workload less persuasive.5:39Every tissue sample was collected after death, and no animals were killed for the5:43study.5:43Consenting human body donors supplied tissue through the technion.5:47Zoological collaborations supplied ape material, including a chimpanzee hand from a5:51female that died naturally at sixty.5:53The human specimens were chemically preserved while that chimpanzee hand had been5:57frozen, and the comparison captured tissue at one point after death.6:00It couldn't follow how each individual's cartilage changed over a lifetime.6:04Lower gag levels are already associated with osteoarthritis and degenerating spinal6:08discs.6:09The researchers proposed that humans' lower production could leave a smaller6:12biochemical reserve, with further losses contributing to degeneration through life.6:16Great apes can develop joint disease too.6:18The paper discusses an evolutionary GJ reduction of about sixty-two percent.6:22Earlier studies found reductions of twenty five to thirty, eight percent in diseased6:26versus healthy human tissue.6:27Those separate comparisons don't identify a universal failure point.6:31This experiment didn't measure the extra disease risk.6:34The genetic experiments and tissue chemistry now fit together as a plausible6:37mechanism for vulnerability.6:39Why the change persisted during evolution is less certain.6:42Researchers suggest that it could have accompanied advantages elsewhere, or that6:46evolutionary constraints against lower production simply weakened.6:49Gags also help stabilize connections in the nervous system.6:52Lower levels might have prolonged the brain's ability to change and learn.6:55Another proposal links lower production to a more slender skeleton.6:59Compatible with endurance running.7:01Both explanations remain hypotheses.7:04The researchers didn't test learning or running performance.7:06Their findings therefore leave the particular evolutionary advantage unresolved.7:10For patients, the immediate use is to give researchers more specific biological7:14mechanisms and potential treatment targets to investigate.7:17Injections involving gauges are already used in osteoarthritis care, but this7:21experiment didn't test whether earlier injections prevent disability.7:24The atlas covers about forty percent of candidate human enhancers, regions that help7:29control genes and could guide further work in cartilage and other tissues.7:32Safely changing that regulatory machinery would require further research.7:36The study offers no new treatment patients can receive today.7:39David Gaukman put the distance to one possible application plainly.7:43He said, But we are far from using it for gene therapy.Story timelineHeyDex
