Cold Exposure and Cold-Shock Protein RBM3
I'm sure all of us have had the experience of forgetting the name of someone who we haven't seen (or thought of) in a few months or years. It's on the tip of your tongue, but you just can't recall it. Memory is one of those "use it or lose it" sort of deals. If the synaptic connections that encode long-term memories aren't refreshed occasionally via recall, they atrophy and disappear. Loss of synapses that encode memories is also the first indication of neurodegenerative diseases like Alzheimer's Disease (AD), happening well before the development of plaques & tangles, and well before the neuronal death that characterizes late-stage AD .
Animals that hibernate have this problem in spades - since their brains are pretty much shut down for several months during which time they aren't actively rehearsing their memories to maintain them. But when they wake up, they still need to remember where they hid their nuts the previous fall and where the neighborhood predators live.
Fortunately, it appears nature and their own biochemistry have got them covered. In response to cold and a modest (i.e. 1 °C ) drop in temperature, cells all over the body, but particularly neurons in the brain, synthesize a 'cold shock' protein called "RNA binding motif protein 3" (RBM3) . From :
In hibernating animals, RBM3 is upregulated in muscle, liver, and heart tissues of black bears [ref, ref], as well as in brain, heart, and liver tissues of squirrels at late torpor [ref].
And it's not just hibernating mammals where RBM3 is found. RBM3 or it's analogs are prevalent across both the plant and animal kingdom, present in plants, fish, amphibians, birds and mammals, including mice, rats and importantly, humans . Interestingly, this cold-induced synthesis of RBM3 is boosted by the presence of either melatonin and life-extending, cold-induced FGF-21 . In addition to cold, RBM3 also induced by UV radiation and hypoxia .
What does RBM3 do, particularly in neurons? It appears to play a role in neuronal stem cell maintenance and proliferation :
In mammals, RBM3 level peaks during the early postnatal period and then decreases to very low levels in youth and adulthood in most regions of the brain, except for areas where proliferation remains active, such as the subventricular zone (SVZ) and the hippocampal subgranular zone (SGZ) [ref, ref], indicating a pivotal role of RBM3 in the maintenance of stemness and proliferation in neural stem/progenitor cells. Regardless to this dynamic temporal expression of CIRP and RBM3 with high abundance in early developmental stages and low in mature organisms, many mature cells maintain their ability to overexpress CIRP and RBM3 in response to stressful conditions, such as cold.
So right off the bat we see cold-induced RBM3 plays a role in neurogenesis, particularly in the brain's memory formation hub, the hippocampus. So that's nice to see. But it gets even better. Again from :
RBM3 expression ... correlates with good [cancer] prognosis and reduced risk of disease progression and recurrence...
A large variety of immunohistochemical studies, including many tumor types, have shown consistently that loss of RBM3 expression is associated with clinically more aggressive tumors and an independent factor of poor prognosis.
In particular, high expression of RBM3 is associated with good prognosis in breast, epithelial, ovarian, prostate, testicular, bladder, esophageal, stomach, colorectal, and skin cancer .
RBM3 even appears to be beneficial for preventing sarcopenia and bone loss :
RBM3 is involved in the regulation of skeletal muscle size and the prevention of muscle loss, indicating a novel vital function of RBM3 in muscle disease [ref]. A subsequent study has further revealed that RBM3 inhibits both necrosis and apoptosis in muscle myoblasts, consistent with a general cytoprotective function of RBM3 [ref]. Moreover, RBM3 is suggested to mediate hypothermia-induced overexpression of bone protein alkaline phosphatase and osteocalcin [ref].
The above combination of effects is interesting and pretty unusual. Usually anabolic agents that help preserve muscles and bones (i.e. IGF-1) are associated with increased cancer proliferation. But here, we see the best of both worlds - muscle & bone preservation and lower cancer risk associated with expression of RBM3.
In summary, RBM3 appears to be a) induced by mild cold exposure / reduced body temperature, and b) have many beneficial effects all over the body, including preventing cancer proliferation, preventing muscle and bone loss, and boosting growth of new neurons, especially in the hippocampus.
But a closer look at the effects of RBM3 on the brain is warranted. A certain molecular variant of RBM3 (i.e. RBM3 which is 'absent a single arginine residue in the RGG domain' - whatever that means...) is found in heavy concentrations in neural dendrites  - which anyone familiar with neuroanatomy will know are the post-synaptic (i.e. the receiving side) of synapses.
What's it doing there? In general, from :
[RBM3] is known to increase local protein synthesis at dendrites [ref] and global protein synthesis through ribosomal subunit binding and/or microRNA biogenesis [ref].
That sounds good, but what exactly does it mean in terms of brain health? That is what this study  from Nature last year (popular press account, another one, and a detailed review on an Alzheimer's forum), aimed to find out. Here is where things get really interesting. What prompted the researchers from  was the question we started with - how do mammals pull off the previously-observed  trick of preserving memories & synapses during hibernation and/or reconstruct them upon awakening? By now you won't be surprised to hear that it appears to be RBM3 that mediates this synaptic preservation/reconstruction.
In particular, study  investigated the effects of cold exposure and RBM3 on the synapses in both normal mice, and in mice models of two neurodegenerative disease, Alzheimer's Disease (AD) via genetically-mutant 5XFAD mice1 and a mad-cow-like prion disease, which I'll abbreviate as MCD for "mad cow disease" although it isn't exactly, simply to avoid using PD as an abbreviation for "prion disease". PD would be more accurate, but it is too easily confused with another neurodegenerative disease, Parkinson's Disease.
Basically what they found was that in wild-type mice (w/o the AD or MCD), a short but deep bout of hypothermia (17 °C body temperature for 45 minutes) resulted in the loss of synapses, but upon rewarming the synapses were restored, at least in number, through a process dubbed structural plasticity. I'll talk about whether memory performance was also preserved/restored shortly (preview - it was). This sort of cold-induced structural plasticity is exactly what appears to happen during and after hibernation in mammals.
Mice with the AD and MCD models, in the first few weeks after exposure, i.e. before their diseases had time to take hold, showed the same structural plasticity - they lost synapse with cooling but then the synapses were restored after rewarming. And in these mice, they did test memory, via a clever object recognition task you can read about in the full text. The memories that the infected (and wild-type) mice had formed prior to cooling was preserved upon rewarming. Just like in the case of hibernation (now where did I hide those nuts?).
But a few weeks/months later, when the diseases had progressed more in the AD and MCD mice, if they cooled these messed up mice their synapses were not restored after rewarming, and memory performance was impaired after cooling and then rewarming. Importantly, as time (and the diseases) progressed, the AD and MCD mice produced less and less RBM3 in response to cooling, and this drop paralleled their drop in synapse recovery and memory performance upon rewarming - suggesting RBM3 was causal in the synapse and memory preserving process (more on that below).
By now you should be thinking to yourself - so what Dean? So you can cool normal or (early) neurodegenerative mice and rewarm them without trashing their synapses or their memory performance and this may happen as a result of upregulation of RBM3 - what good it that?
Here are three possibilities:
- It might bode well for Zeta's hope (I miss Zeta. Wonder where he's at?) that someday we'll develop technology for suspended animation. Brian points out in this post that one of the challenges of suspended animation is preserving the delicate structures of the brain (particularly synapses) during cryo-suspension. RBM3 might play a role in such preservation. BTW, I came across , titled "Is Human Hibernation Possible?", which is a good review of the feasibility of this approach to both life extension, and short-term suspended animation (see next point).
- Understanding / leveraging how RBM3 preserves the brain during hypothermia / hypoxia may be useful in clinical practice, where temporary cooling of the body is done to given doctors more time, with the hope (and fortunately, the observation) that patients can be temporarily cooled and then rewarmed without significant deleterious effects, particularly on brain function. This clinical application of cooling is discussed in this recent popular press article on a pilot study being done here in Pittsburgh with gunshot victims who come into the hospital in critical condition. The goal is to put them into "suspended animation" for a few hours or days to give doctors more time to stabilize them and treat their injuries. Understanding and leveraging RBM3 could make this sort of short-term, medically-induced cryo-suspension safer and more effective.
- These results might help explain the amazing mammalian diving reflex (MDR),which I mentioned back in my CE Albatross post two months ago, and which I promised to discuss someday. The MDR enables animals (and people!) to recover from being submerged in cold water without oxygen for up to two hours without brain damage. It would not be at all surprising to me if scientists discover that RBM3 plays an important role protecting the brain in the MDR, although I looked and couldn't find any papers that addressed this possibility.
But the original question is a good one - If I don't think I'll be shot, fall into a frozen lake, or undergo cryo-suspension for life extension anytime soon, what use is all this RBM3 synapse preservation stuff for me now?
That's where the rest of  comes in. It turns out that cold exposure, and specifically boosting RMB3, acts as a hormetic agent - providing long-lasting protection against loss of synapses, and preserving memories.
Specifically, as we saw above, cooling and rewarming the AD and MCD mice once their disease had progressed was worse than useless - i.e. they lost synapses (and memories) during the cooling process which weren't restored upon rewarming. In contrast, cooling and rewarming early in the progress of the disease (i.e. just a couple weeks after the mice had been treated to induced AD or MCD) not only kept their memories from before the cooling intact immediately after rewarming - it also served as a hormetic stressor, which helped preserve their synapses for many weeks to come. Specifically, long after control mice with the AD or MCD conditions had lost their synapses and their ability to form new memories, the AD and MCD mice who had been cooled and rewarmed early on in their diseases were protected - their synapses and memory abilities were preserved much longer. In addition, they lived longer than the control mice who had either the AD or MCD treatment, but no cooling and rewarming. Don't get too excited. Their lives were still greatly shortened relative to wild-type mice who weren't messed up by the AD or MCD treatments.
Further, they found that this preservation of synapses and memory performance was mediated by upregulation of RBM3. In particular, a single episode of cooling raised RBM3 levels in wild-type mice for three days, and in the AD and MCD mice, a single cooling episode "resulted in sustained several-fold increase in RBM3 expression up to 6 weeks later" . When they knocked out the ability of the mice to produce RBM3 in response to cooling, it erased all the benefits - without elevated RBM3, the AD and MCD mice lost synapses and memories after cooling/rewarming at the same rate as control AD and MCD mice who hadn't been cooled/rewarmed, and they didn't live any longer either. In short, RBM3 was critical for cold-induced preservation of synapses and memories.
Finally, to get the real smoking gun, they skipped the cooling/rewarming and simply injected the AD and MCD mice with a virus that expresses RBM3. Yup - sure enough. Injecting this RBM3-expressing virus into the hippocampi of the AD and MCD increased hippocampal RBM3 by a factor of 3 and in the MCD mice, this boost to RBM3 preserved synapses, neurons, memories and extended survival relative MCD mice who got placebo virus injection into their hippocampi. The AD mice injected with the RBM3-expressing virus showed similar (although not identical) benefits. Finally, to cap it off:
RBM3 knockdown [in the absence of cooling] also reduced synapse number and
novel object memory in wild-type mice (Extended Data Fig. 10b), thus it is
likely to be involved in synaptic maintenance under normal physiological conditions.
Here is that figure 10b they mentioned, showing the number of synapses (left graph) and memory performance (right graph) of wild-type mice with normal levels of RBM3 (white bars) and suppressed levels of RBM3 (yellowish bars):
In short, when RBM3 was cut to 70% below its usual level, normal mice kept in normal conditions (i.e. no cooling) were 50% worse at retaining memories!
Here is the paper's optimistic final paragraph:
In conclusion, we have shown that early synapse loss in mouse models
of neurodegenerative disease results, at least in part, from defective
synaptic repair processes associated with failure to induce the cold-shock
RNA-binding protein, RBM3. This results in impaired synaptic
reassembly after cooling, but also appears to be important in the context
of protecting against ongoing synaptic toxicity during disease, and
in synaptic maintenance in wild-type mice. Our data suggest that further
understanding the mechanisms of action of cold-shock proteins
such as RBM3 may yield insights into endogenous repair processes and
bring new therapeutic targets for neuroprotection in neurodegenerative
In short, it appears that the cold-shock protein RBM3 can be induced by cold exposure in mice and humans. It helps to prevent cancer proliferation, sarcopenia and bone loss, boosts growth of new (hippocampal) neurons, preserves synapses and memories, and perhaps can even help prevent the onset and/or slow the progression of neurodegenerative diseases, including Alzheimer's disease.
Yet another pathway by which cold exposure appears good for your health!
1The 5XFAD mice model of Alzheimer's disease involved genetically messed up mice who express 5 human genes associated with familial, early-onset AD, which causes them to rapidly develop amyloid-beta plaques. They lose synapses and memories first, then neurons and eventually die, just like in human AD.
 Neuroscience. 2015 Oct 1;305:268-78. doi: 10.1016/j.neuroscience.2015.08.012.
Epub 2015 Aug 8.
Cold stress protein RBM3 responds to temperature change in an ultra-sensitive
manner in young neurons.
Jackson TC(1), Manole MD(2), Kotermanski SE(3), Jackson EK(3), Clark RS(4),
Extremely mild hypothermia to 36.0 °C is not thought to appreciably differ
clinically from 37.0 °C. However, it is possible that 36.0 °C stimulates highly
sensitive hypothermic signaling mechanism(s) and alters biochemistry. To the best
of our knowledge, no such ultra-sensitive pathway/mechanisms have been described.
Here we show that cold stress protein RNA binding motif 3 (RBM3) increases in
neuron and astrocyte cultures maintained at 33 °C or 36 °C for 24 or 48 h,
compared to 37 °C controls. Neurons cultured at 36 °C also had increased global
protein synthesis (GPS). Finally, we found that melatonin or fibroblast growth
factor 21 (FGF21) augmented RBM3 upregulation in young neurons cooled to 36 °C.
Our results show that a 1 °C reduction in temperature can induce pleiotropic
biochemical changes by upregulating GPS in neurons which may be mediated by RBM3
and that this process can be pharmacologically mimicked and enhanced with
melatonin or FGF21.
Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.
PMCID: PMC4570027 [Available on 2016-10-01]
 Williams DR, Epperson LE, Li W, Hughes MA, Taylor R, Rogers J, Martin SL, Cossins AR, Gracey AY (2005) Seasonally hibernating phenotype assessed through transcript screening. Physiol Genomics 24(1):13–22. doi:10.1152/physiolgenomics.00301.2004 PubMedCrossRef
 Nature. 2015 Feb 12;518(7538):236-9. doi: 10.1038/nature14142. Epub 2015 Jan 14.
RBM3 mediates structural plasticity and protective effects of cooling in
Peretti D(1), Bastide A(1), Radford H(1), Verity N(1), Molloy C(1), Martin MG(1),
Moreno JA(1), Steinert JR(1), Smith T(1), Dinsdale D(1), Willis AE(1), Mallucci
Nat Rev Neurosci. 2015 Mar;16(3):124.
Nature. 2015 Feb 12;518(7538):177-8.
Nat Rev Neurol. 2015 Mar;11(3):124.
In the healthy adult brain synapses are continuously remodelled through a process
of elimination and formation known as structural plasticity. Reduction in synapse
number is a consistent early feature of neurodegenerative diseases, suggesting
deficient compensatory mechanisms. Although much is known about toxic processes
leading to synaptic dysfunction and loss in these disorders, how synaptic
regeneration is affected is unknown. In hibernating mammals, cooling induces loss
of synaptic contacts, which are reformed on rewarming, a form of structural
plasticity. We have found that similar changes occur in artificially cooled
laboratory rodents. Cooling and hibernation also induce a number of cold-shock
proteins in the brain, including the RNA binding protein, RBM3 (ref. 6). The
relationship of such proteins to structural plasticity is unknown. Here we show
that synapse regeneration is impaired in mouse models of neurodegenerative
disease, in association with the failure to induce RBM3. In both prion-infected
and 5XFAD (Alzheimer-type) mice, the capacity to regenerate synapses after
cooling declined in parallel with the loss of induction of RBM3. Enhanced
expression of RBM3 in the hippocampus prevented this deficit and restored the
capacity for synapse reassembly after cooling. RBM3 overexpression, achieved
either by boosting endogenous levels through hypothermia before the loss of the
RBM3 response or by lentiviral delivery, resulted in sustained synaptic
protection in 5XFAD mice and throughout the course of prion disease, preventing
behavioural deficits and neuronal loss and significantly prolonging survival. In
contrast, knockdown of RBM3 exacerbated synapse loss in both models and
accelerated disease and prevented the neuroprotective effects of cooling. Thus,
deficient synapse regeneration, mediated at least in part by failure of the RBM3
stress response, contributes to synapse loss throughout the course of
neurodegenerative disease. The data support enhancing cold-shock pathways as
potential protective therapies in neurodegenerative disorders.
 Cell Mol Life Sci. 2016 May 4. [Epub ahead of print]
Cold-inducible proteins CIRP and RBM3, a unique couple with activities far beyond
Zhu X(1), Bührer C(2), Wellmann S(3,)(4).
Cold-inducible RNA-binding protein (CIRP) and RNA-binding motif protein 3 (RBM3)
are two evolutionarily conserved RNA-binding proteins that are transcriptionally
upregulated in response to low temperature. Featuring an RNA-recognition
motif (RRM) and an arginine-glycine-rich (RGG) domain, these proteins display
many similarities and specific disparities in the regulation of numerous
molecular and cellular events. The resistance to serum withdrawal, endoplasmic
reticulum stress, or other harsh conditions conferred by RBM3 has led to its
reputation as a survival gene. Once CIRP protein is released from cells, it
appears to bolster inflammation, contributing to poor prognosis in septic
patients. A variety of human tumor specimens have been analyzed for CIRP and RBM3
expression. Surprisingly, RBM3 expression was primarily found to be positively
associated with the survival of chemotherapy-treated patients, while CIRP
expression was inversely linked to patient survival. In this comprehensive
review, we summarize the evolutionary conservation of CIRP and RBM3 across
species as well as their molecular interactions, cellular functions, and roles in
diverse physiological and pathological processes, including circadian rhythm,
inflammation, neural plasticity, stem cell properties, and cancer development.
 Wellmann S, Buhrer C, Moderegger E, Zelmer A, Kirschner R, Koehne P, Fujita J, Seeger K (2004) Oxygen-regulated expression of the RNA-binding proteins RBM3 and CIRP by a HIF-1-independent mechanism. J Cell Sci 117(Pt 9):1785–1794. doi:10.1242/jcs.01026 PubMedCrossRef
 Smart F, Aschrafi A, Atkins A, Owens GC, Pilotte J, Cunningham BA, Vanderklish PW (2007) Two isoforms of the cold-inducible mRNA-binding protein RBM3 localize to dendrites and promote translation. J Neurochem 101(5):1367–1379. doi:10.1111/j.1471-4159.2007.04521.x PubMedCrossRef
 Selkoe, D. J. Alzheimer’s disease is a synaptic failure. Science 298, 789–791 (2002).
 Mallucci, G. R. Prion neurodegeneration: starts and stops at the synapse. Prion 3, 195–201 (2009).
 Magarin˜ os, A. M., McEwen, B. S., Saboureau, M. & Pevet, P. Rapid and reversible
changes in intrahippocampal connectivity during the course of hibernation in
European hamsters. Proc. Natl Acad. Sci. USA 103, 18775–18780 (2006).
 Popov, V. I. & Bocharova, L. S. Hibernation-induced structural changes in synaptic
contacts between mossy fibres and hippocampal pyramidal neurons.
Neuroscience 48, 53–62 (1992).
 Annu Rev Med. 2008;59:177-86. doi: 10.1146/annurev.med.59.061506.110403.
Is human hibernation possible?
Full text: 10.1146/annurev.med.59.061506.110403
The induction of hypometabolism in cells and organs to reduce ischemia damage
holds enormous clinical promise in diverse fields, including treatment of stroke
and heart attack. However, the thought that humans can undergo a severe
hypometabolic state analogous to hibernation borders on science fiction. Some
mammals can enter a severe hypothermic state during hibernation in which
metabolic activity is extremely low, and yet full viability is restored when the
animal arouses from such a state. To date, the underlying mechanism for
hibernation or similar behaviors remains an enigma. The beneficial effect of
hypothermia, which reduces cellular metabolic demands, has many well-established
clinical applications. However, severe hypothermia induced by clinical drugs is
extremely difficult and is associated with dramatically increased rates of
cardiac arrest for nonhibernators. The recent discovery of a biomolecule, 5'-AMP,
which allows nonhibernating mammals to rapidly and safely enter severe
hypothermia could remove this impediment and enable the wide adoption of
hypothermia as a routine clinical tool.
There will never be peace in the world while there are animals in our bellies.