I've spent too much time on this post today. But I want to get the key point posted even if the post doesn't yet have all the evidence I hope to include later. I'll be back later to work on it...
Thanks for this find, Bryan_S!
Here's a research twist, and food for thought, think about this, reprogramming somatic cells in the absence of exogenous biochemical factors. This approach is a complete 180 from the OSKM method used in the "In Vivo Amelioration of Age-Associated Hallmarks by Partial Reprogramming" project.
See: "Laterally confined growth of cells induces nuclear reprogramming in the absence of exogenous biochemical factors"
What's the significance? You don't need OSKM factors. Environmental physical constraints were used in this example, not exogenous biochemical factors. Reprogramming gene promoters were progressively acetylated, while mesenchymal promoters were deacetylated by 10 days without exogenous biochemical factors. In vivo, cells transdifferentiate into different lineages in the absence of exogenous factors, indicating that the local mechanochemical factors could be important elements and are sufficient for inducing such transitions. WHO KNEW? This opens up insight into areas of regenerative medicine. It appears somatic cells have more plasticity than previously thought given the proper environment.
What is promoting the epigenetic reprogramming? It appears the cells in contact with a designed physical substrate undergo cytoskeletal reorganization, which changes nuclear shape and facilitates nuclear orientation along the growth axis. From this the epigenetic landscape of the chromatin, particularly the levels of H3K9Ac, H3K4Me3, and H3K27Me3, changes with time. The increase in nuclear plasticity along with the reorganization of epigenetic and chromosome packing within the nucleus, with time leads to the rewiring of the nuclear architecture in a manner that primes the nucleus for reprogramming.
<SNIP>
I believe if we find the right epigenetic targets we can regress a cell without installing an OSKM polycystronic cassette in each cell of a host organism we wish to regress in age.
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The question of this post...
- A central conjecture of this thread is that Heat Shock Protein expression is implicated in epigenetic reprogramming.
- The study Bryan_S posted above highlights describes a context of mechanical stress (environmental physical constraints) and some associated gene expression changes (including in H3K4Me3, and H3K27Me3) that led to "the progressive erasure of lineage specific[/size] characteristics and incorporation of pluripotency".
Do the descriptions of the context, discovery features, and findings of the study Bryan_S posted suggest that Heat Shock Protein expression was likely implicated, even if not noted in the study?
I believe the answer to that question is Yes. I've posted study links with some explanatory text in support of that answer.
Assumption: "environmental physical constraints" constitute a kind of mechanical stress.
Is Heat Shock Protein expression implicated in contexts of mechanical stress.
2018, Heat Shock Proteins as Sensors for Mechanical Stress
Heat shock proteins (HSP) are highly responsive to stresses including temperature and oxidative stress. Some heat shock proteins bind to improperly or unfolded protein substrates and directly promote refolding in an ATP-dependent manner. Others can act as nucleotide-exchange factors while small HSP can hold unfolded proteins, prevent their aggregation, maintain them in a folding competent state, and pass them on to the ATP-dependent chaperone networks. It is now clear that HSP are also very responsive to mechanical stresses such as compression, shear, and tensile forces and new roles in modulating inflammation and cytoskeletal reorganization have been attributed to these proteins following such mechanical stress. This chapter will summarize findings within the stress protein field demonstrating HSP are sensors for mechanical forces in many tissues.
2000, Mechanical Stress–Induced Heat Shock Protein 70 Expression in Vascular Smooth Muscle Cells Is Regulated by Rac and Ras Small G Proteins but Not Mitogen-Activated Protein Kinases
Previous studies have documented that acute elevation in blood pressure results in heat shock protein (hsp) 70-mRNA expression followed by hsp70-protein production in rat aortas. In this article, we provide evidence that mechanical forces evoke rapid activation of heat shock transcription factor (HSF) and hsp70 accumulation. In our study, Western blot analysis demonstrated that hsp70-protein induction peaked between 6 and 12 hours after treatment with cyclic stain stress (60 cycles/minute, up to 30% elongation). Elevated protein levels were preceded by hsp70-mRNA transcription, which was associated with HSF1 phosphorylation and activation stimulated by mechanical forces, suggesting that the response was regulated at the transcriptional level. Conditioned medium from cyclic strain-stressed vascular smooth muscle cells (VSMCs) did not result in HSF-DNA-binding activation. Furthermore, mitogen-activated protein kinases (MAPKs), including extracellular signal-regulated kinases, c-Jun NH(2)-terminal protein kinases or stress-activated protein kinases, and p38 MAPKs, were also highly activated in response to cyclic strain stress. Inhibition of extracellular signal-regulated kinase and p38-MAPK activation by their specific inhibitors (PD 98059 and SB 202190) did not influence HSF1 activation. Interestingly, VSMC lines stably expressing dominant-negative rac (rac N17) abolished hsp-protein production and HSF1 activation induced by cyclic strain stress, whereas a significant reduction of hsp70 expression was seen in ras N17-transfected VSMC lines. Thus, our findings demonstrate that cyclic strain stress-induced hsp70 expression is mediated by HSF1 activation and regulated by rac and ras GTP-binding proteins. Induction of hsp70 could be important in maintaining VSMC homeostasis during vascular remodeling in response to hemodynamic stimulation.
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In the study, Bryan_S posted, expression levels of two genes underwent change and were related to the transformation toward pluripotency.
Do the H3K4Me3 and H3K27Me3 genes have anything to do with Heat Shock Protein expression?
H3K27Me3...
From the opening post of this thread, a study from 2015...
- Richard Morimoto’s team at Northwestern found that a heat shock protein-related aging switch got flipped in c elegans around the time of sexual maturity.
Repression of the heat shock response is a programmed event at the onset of reproduction
The abstract
The heat shock response (HSR) is essential for proteostasis and cellular health. In metazoans, aging is associated with a decline in quality control, thus increasing the risk for protein conformational disease. Here, we show that in C. elegans, the HSR declines precipitously over a four hour period in early adulthood coincident with the onset of reproductive maturity. Repression of the HSR occurs due to an increase in H3K27me3 marks at stress gene loci, the timing of which is determined by reduced expression of the H3K27 demethylase jmjd-3.1. This results in a repressed chromatin state that interferes with HSF-1 binding and suppresses transcription initiation in response to stress. The removal of germ line stem cells preserves jmjd-3.1 expression, suppresses the accumulation of H3K27me3 at stress gene loci and maintains the HSR. These findings suggest that competing requirements of the germ line and soma dictate organismal stress resistance as animals begin reproduction.
And from the same year as the study above, 2015, there is this...
2015, Shockingly Early: Chromatin-Mediated Loss of the Heat Shock Response
H3K4Me3 is implicated also...
2018, Distinct heat shock factors and chromatin modifications mediate the organ‐autonomous transcriptional memory of heat stress
Plants can be primed by a stress cue to mount a faster or stronger activation of defense mechanisms upon subsequent stress. A crucial component of such stress priming is the modified reactivation of genes upon recurring stress; however, the underlying mechanisms of this are poorly understood. Here, we report that dozens of Arabidopsis thaliana genes display transcriptional memory, i.e. stronger upregulation after a recurring heat stress, that lasts for at least 3 days. We define a set of transcription factors involved in this memory response and show that the transcriptional memory results in enhanced transcriptional activation within minutes of the onset of a heat stress cue. Further, we show that the transcriptional memory is active in all tissues. It may last for up to a week, and is associated during this time with histone H3 lysine 4 hypermethylation. This transcriptional memory is cis‐encoded, as we identify a promoter fragment that confers memory onto a heterologous gene. In summary, heat‐induced transcriptional memory is a widespread and sustained response, and our study provides a framework for future mechanistic studies of somatic stress memory in higher plants.
Histone H3 lysine 4 trimethylation regulates cotranscriptional H2A variant exchange by Tip60 complexes to maximize gene expression
Edited by HighDesertWizard, 19 January 2019 - 08:21 PM.