Steven Sloan
@sloanlab.bsky.social
Neuroscientist. Glial Biologist. Astrocyte enthusiast. Neurodevelopmental lab at Emory University studying the role of glia in health and disease.
www.SloanLab.org
www.SloanLab.org
Then came one of our most astonishing observations. We exposed human progenitors to a 10-day pulse of Pb before xenografting. We left the cells for 7 weeks (!) without any more Pb in the mouse at all. THEN, we isolated these human cells and saw robust evidence of metal response genes STILL active!!
August 21, 2025 at 8:10 PM
Then came one of our most astonishing observations. We exposed human progenitors to a 10-day pulse of Pb before xenografting. We left the cells for 7 weeks (!) without any more Pb in the mouse at all. THEN, we isolated these human cells and saw robust evidence of metal response genes STILL active!!
But maybe again this is an artifact of in vitro culture conditions? So, we worked closely with our amazing collaborators Ye Zhang and @bhadurilab.bsky.social to perform xenograft experiments into the mouse cortex. Human progenitors exposed to Pb engrafted readily throughout the mouse brain.
August 21, 2025 at 8:10 PM
But maybe again this is an artifact of in vitro culture conditions? So, we worked closely with our amazing collaborators Ye Zhang and @bhadurilab.bsky.social to perform xenograft experiments into the mouse cortex. Human progenitors exposed to Pb engrafted readily throughout the mouse brain.
When we look at the composition of clone families, we again saw an increase in neuronal progenitor populations at the expense of glial progenitors.
August 21, 2025 at 8:10 PM
When we look at the composition of clone families, we again saw an increase in neuronal progenitor populations at the expense of glial progenitors.
But we wanted a more sophisticated approach for verifying this cell fate change. We used genetic lineage tracing approaches in cultured human progenitors where we could identify individual clone families as they differentiate in the presence or absence of Pb.
August 21, 2025 at 8:10 PM
But we wanted a more sophisticated approach for verifying this cell fate change. We used genetic lineage tracing approaches in cultured human progenitors where we could identify individual clone families as they differentiate in the presence or absence of Pb.
Turns out, we saw the same striking shift of cell fate away from astrocyte lineages. Sometimes by as much as a 50% decrease!
August 21, 2025 at 8:10 PM
Turns out, we saw the same striking shift of cell fate away from astrocyte lineages. Sometimes by as much as a 50% decrease!
Maybe this was some artifact of working with organoids? We optimized protocols for isolating primary human neural progenitors so we could find out.
August 21, 2025 at 8:10 PM
Maybe this was some artifact of working with organoids? We optimized protocols for isolating primary human neural progenitors so we could find out.
Once we knew Pb was getting into cells, we next wanted to know how it affected neural differentiation. One of the most striking observations we saw across multiple hiPSC lines was a shift in cell fate away from astrocytes and towards excitatory neurons.
August 21, 2025 at 8:10 PM
Once we knew Pb was getting into cells, we next wanted to know how it affected neural differentiation. One of the most striking observations we saw across multiple hiPSC lines was a shift in cell fate away from astrocytes and towards excitatory neurons.
Could we then observe Pb being actively taken up by human neural cells? Yes! A human Pb sensor (leadmium) let us literally watch Pb uptake over the course of several hours into human neurons and astrocytes.
August 21, 2025 at 8:10 PM
Could we then observe Pb being actively taken up by human neural cells? Yes! A human Pb sensor (leadmium) let us literally watch Pb uptake over the course of several hours into human neurons and astrocytes.
One of the first challenges we had was figuring out how much Pb to give to human cells to reflect true exposure levels. We dug through the literature for relevant Pb levels in brain and then empirically correlated this with exposure paradigms that resulted in similar tissue levels in human organoids
August 21, 2025 at 8:10 PM
One of the first challenges we had was figuring out how much Pb to give to human cells to reflect true exposure levels. We dug through the literature for relevant Pb levels in brain and then empirically correlated this with exposure paradigms that resulted in similar tissue levels in human organoids
Excited to share an important new pre-print from the lab led by incredibly talented postdoc @maureenbiologies.bsky.social, a neurotoxicologist who came to the lab with an ambitious goal of understanding the consequences of toxicant exposure in human neurodevelopment. www.biorxiv.org/content/10.1...
August 21, 2025 at 8:10 PM
Excited to share an important new pre-print from the lab led by incredibly talented postdoc @maureenbiologies.bsky.social, a neurotoxicologist who came to the lab with an ambitious goal of understanding the consequences of toxicant exposure in human neurodevelopment. www.biorxiv.org/content/10.1...
But we wanted a more sophisticated approach for verifying this cell fate change. We used genetic lineage tracing approaches in cultured human progenitors where we could identify individual clone families as they differentiate in the presence or absence of Pb.
August 21, 2025 at 7:02 PM
But we wanted a more sophisticated approach for verifying this cell fate change. We used genetic lineage tracing approaches in cultured human progenitors where we could identify individual clone families as they differentiate in the presence or absence of Pb.
Turns out, we saw the same striking shift of cell fate away from astrocyte lineages. Sometimes by as much as a 50% decrease!
August 21, 2025 at 7:02 PM
Turns out, we saw the same striking shift of cell fate away from astrocyte lineages. Sometimes by as much as a 50% decrease!
Maybe this was some artifact of working with organoids? We optimized protocols for isolating primary human neural progenitors so we could find out.
August 21, 2025 at 7:02 PM
Maybe this was some artifact of working with organoids? We optimized protocols for isolating primary human neural progenitors so we could find out.
Once we knew Pb was getting into cells, we next wanted to know how it affected neural differentiation. One of the most striking observations we saw across multiple hiPSC lines was a shift in cell fate away from astrocytes and towards excitatory neurons.
August 21, 2025 at 7:02 PM
Once we knew Pb was getting into cells, we next wanted to know how it affected neural differentiation. One of the most striking observations we saw across multiple hiPSC lines was a shift in cell fate away from astrocytes and towards excitatory neurons.
Could we then observe Pb being actively taken up by human neural cells? Yes! A human Pb sensor (leadmium) let us literally watch Pb uptake over the course of several hours into human neurons and astrocytes.
August 21, 2025 at 7:02 PM
Could we then observe Pb being actively taken up by human neural cells? Yes! A human Pb sensor (leadmium) let us literally watch Pb uptake over the course of several hours into human neurons and astrocytes.
One of the first challenges we had was figuring out how much Pb to give to human cells to reflect true exposure levels. We dug through the literature for relevant Pb levels in brain and then empirically correlated this with exposure paradigms that resulted in similar tissue levels in human organoids
August 21, 2025 at 7:02 PM
One of the first challenges we had was figuring out how much Pb to give to human cells to reflect true exposure levels. We dug through the literature for relevant Pb levels in brain and then empirically correlated this with exposure paradigms that resulted in similar tissue levels in human organoids
Then we tried something fancier. We isolated peptides from human neurons and co-cultured with astrocytes in the presence of cytokines. After MHCII pulldown and MS we found lots of neuronal peptides associated with MHCII (and not cleaved by trypsin, so probably processed by cellular machinery)!
June 30, 2025 at 6:26 PM
Then we tried something fancier. We isolated peptides from human neurons and co-cultured with astrocytes in the presence of cytokines. After MHCII pulldown and MS we found lots of neuronal peptides associated with MHCII (and not cleaved by trypsin, so probably processed by cellular machinery)!
What could astrocytes be presenting? This is really hard to figure out in human models, but we took a stab at it. We pulled down MHCII proteins in astrocytes and performed mass spec to see what peptide fragments came with it. We found lots of expected proteins related to MHCII processing (phew).
June 30, 2025 at 6:26 PM
What could astrocytes be presenting? This is really hard to figure out in human models, but we took a stab at it. We pulled down MHCII proteins in astrocytes and performed mass spec to see what peptide fragments came with it. We found lots of expected proteins related to MHCII processing (phew).
I know what you're thinking. It's some artifact related to organoids. But no! We see the same thing in primary human cortical slices. We see MHCII at the cell surface AND we see CD74 loaded onto MHCII only in the presence of inflammatory cytokines.
June 30, 2025 at 6:26 PM
I know what you're thinking. It's some artifact related to organoids. But no! We see the same thing in primary human cortical slices. We see MHCII at the cell surface AND we see CD74 loaded onto MHCII only in the presence of inflammatory cytokines.
ok, but surprise! Remember those time-dependent genes that only turn on with prolonged inflammatory exposure? Almost all were related to MHCII presentation. We thought this must be a mistake. Astrocytes are not canonical antigen presenting cells! But we see this also by protein staining.
June 30, 2025 at 6:26 PM
ok, but surprise! Remember those time-dependent genes that only turn on with prolonged inflammatory exposure? Almost all were related to MHCII presentation. We thought this must be a mistake. Astrocytes are not canonical antigen presenting cells! But we see this also by protein staining.
More to come on that in a sec. But FIRST! We had another question. If you make the astrocytes "reactive", can they reverse back to a "normal" state if you remove the inflammatory cue? Does it matter how long the initial inflammatory signal lasts before withdrawing it? The answer is generally, YES!
June 30, 2025 at 6:26 PM
More to come on that in a sec. But FIRST! We had another question. If you make the astrocytes "reactive", can they reverse back to a "normal" state if you remove the inflammatory cue? Does it matter how long the initial inflammatory signal lasts before withdrawing it? The answer is generally, YES!
At both transcriptomic and chromatin accessibility levels we found evidence of genes/loci that respond IMMEDIATELY to cytokine exposure (time-independent), but also a group of genes/loci who expression/accessibility was dependent on the duration of exposure (time-DEPENDENT)
June 30, 2025 at 6:26 PM
At both transcriptomic and chromatin accessibility levels we found evidence of genes/loci that respond IMMEDIATELY to cytokine exposure (time-independent), but also a group of genes/loci who expression/accessibility was dependent on the duration of exposure (time-DEPENDENT)
So then we wondered whether it mattered how long astrocytes see an inflammatory environment. After all, some neurological injuries are very short-lasting, and others chronic. So, we exposed organoids (already aged to have astrocytes) to very short (1 day) or long (3 months) inflammatory periods.
June 30, 2025 at 6:26 PM
So then we wondered whether it mattered how long astrocytes see an inflammatory environment. After all, some neurological injuries are very short-lasting, and others chronic. So, we exposed organoids (already aged to have astrocytes) to very short (1 day) or long (3 months) inflammatory periods.
We started with a simple question. We know astrocytes form in human cortical organoids (takes awhile, but they do!), but can we induce reactivity in 3D robustly? Answer is yes. See C3 induction here in the setting of inflammatory cytokines. RNAseq shows robust reactive signatures, too!
June 30, 2025 at 6:26 PM
We started with a simple question. We know astrocytes form in human cortical organoids (takes awhile, but they do!), but can we induce reactivity in 3D robustly? Answer is yes. See C3 induction here in the setting of inflammatory cytokines. RNAseq shows robust reactive signatures, too!
I've been really hoping to see more manuscript threads here on 🦋, so here comes one!!! This is brand new work from the lab that took us in very unexpected directions and to exciting findings led by the amazing @emily-hill.bsky.social. Preprint here www.biorxiv.org/content/10.1...
and 🧵below:
and 🧵below:
June 30, 2025 at 6:26 PM
I've been really hoping to see more manuscript threads here on 🦋, so here comes one!!! This is brand new work from the lab that took us in very unexpected directions and to exciting findings led by the amazing @emily-hill.bsky.social. Preprint here www.biorxiv.org/content/10.1...
and 🧵below:
and 🧵below: