tara
Phoenix, don't leave us hanging! More scientific banter requested... 4/23/2003 12:02PM Reply | Return to Index | Report Post

Phoenix wrote:Recently, some of the signaling that causes mitochondrial biogenesis has been unraveled with a major study coming out of the lab I work in. I tell about that some other time if anybody cares. You won't find it out from runningart or anybody else on this board for that matter.


If you tell, I promise to limit my dumb questions... to less than 20.
Phoenix
AMPK 4/23/2003 4:50PM - in reply to tara Reply | Return to Index | Report Post
The AMP activated protein kinase is the "fuel-guage" of the mammalian cell and has homologues in the yeast SNF group of stress proteins.

As the name implies the AMPK is activated by AMP. During exercise, ATP is hydrolyzed to ADP. 2 ADPs are split into 1 AMP and 1 ATP by the enzyme adenylate kinase (sometimes called myokinase). AMPK is phoshorylated by putative AMPKK(s) in addition to the allosteric activation by AMP. AMPK activation signals for mitochondrial biogenesis. Additionally AMPK phosphorylates and thereby inactivates acetyl coa carboxylase (acc). When ACC is phophorylated it stops converting acetyl coa to malonyl coa. Malonyl coa inhibits carnitine palmitoyl transferase which shuttles fatty acids into the mitochondria for oxidation. Following that chain of events means that AMPK activation stimulates fatty acid oxidation. AMPK activation also stimulates glucose transport by insulin independent mechanisms. AMPK is inhibited by glycogen; this is possibly one of the reason long runs are so valuable--they deplete glycogen more and therefore allow greater AMPK activation and therefore greater mitochondrial biogenesis. AMPK is activated equally by a 1 minute sprint and a 30 min run of moderate intensity, however, the activation quickly dies off after a sprint but if prolonged after the 30 minute run. AMPK has been shown to directly phosphorylate nuclear proteins thereby having a direct effect on gene transcription. Its activity is inhibited by creatine phosphate. At least one anti-diabetic drug, metformin, has been shown to work via the AMPK. AMPK is also essential for the transcription of certain Calcium-calmodulin kinases that also play a role in mitochondrial biogenesis.
Sciolistic Smokescreen
RE: AMPK 4/23/2003 5:08PM - in reply to Phoenix Reply | Return to Index | Report Post
...and your point?
tara
RE: AMPK 4/23/2003 11:40PM - in reply to Sciolistic Smokescreen Reply | Return to Index | Report Post
For those who know as little of "mitochondrial biogenesis" as I do....

"Mitochondrial biogenesis, the process of how mitochondria are formed and maintained, generally includes two main aspects. Firstly, during cell division the organelle and its genome have to be replicated and their accurate distribution to the daughter cells has to be guaranteed. Secondly, the continuous synthesis, transport and assembly of mitochondrial macromolecules is essential for the proper function of mitochondria."
http://zoosun00.unifr.ch/Trypanos/MITBIO.html


Why as runners we might (but still probably don't) care about this...
http://research.medicine.wustl.edu/ocfr/research.nsf/Abstracts/9B0B4E02A7C18ECF8625677D00592C13?OpenDocument&VW=Metabolism

"Endurance exercise induces an increase in skeletal muscle respiratory capacity that is mediated by an increase in mitochondria. The goal of this research is to discover the mechanisms by which exercise induces an increase in muscle mitochondria...As a next step, we will test the hypothesis that an increase in NRF-1 induces an increase in mitochondrial biogenesis by overexpression of NRF-1 in muscle."


Something interesting... Benefits of exercise without actually exercising!?

"Many people who would benefit are unwilling or unable to exercise. Information obtained from this research may make it possible to mimic some of the beneficial effects of exercise through pharmacological or gene therapy intervention "
old guy II
RE: AMPK 4/24/2003 3:39AM - in reply to tara Reply | Return to Index | Report Post
Thank you Phoenix and Tara for the good info. Some of us are definitely interested in trying to understand the biochemical basis for improvements in aerobic and anaerobic capacity. The statement that creatine phosphate inhibits AMPK activity was interesting. Does this imply that taking a creatine supplement may actually inhibit mitochondrial biogenisis?
FASTERTHANU
RE: AMPK 4/24/2003 4:07AM - in reply to old guy II Reply | Return to Index | Report Post
Or, maybe you could just train a little more and run faster. Just a thought.
old guy II
RE: AMPK 4/24/2003 4:29AM - in reply to FASTERTHANU Reply | Return to Index | Report Post
Or maybe we could learn something and train a little smarter and race faster. Just a thought.
FASTERTHANU
RE: AMPK 4/24/2003 4:34AM - in reply to old guy II Reply | Return to Index | Report Post
Just seems to me that Phoenix is just rehashing some bio-chem lecture notes. For me I would read through the writings of Lydiard or Coe/Martin. I believe(correct me if I'm wrong) but these guys have actually trained runners of the highest caliber. hmmmm,
Phoenix
RE: AMPK 4/24/2003 4:51AM - in reply to old guy II Reply | Return to Index | Report Post
Great question old guy. I've wondered that myself. The biochemical "opposite" of creatine is a substance called Beta-guanidino proprionic acid, or simply B-GPA. B-GPA is a creatine analogue that jams up the enzyme creatine kinase and causes a depletion of high energy phosphates in the cell. Oral administration of B-GPA to rats induces increases in mitochondria, so one might speculate that creatine could have an inhibitory effect on increases in mitochondria.
tara
RE: AMPK 4/24/2003 6:13AM - in reply to Phoenix Reply | Return to Index | Report Post
Another good article on how MB research may lead to a drug that mimics exercise. Pretty cool...

http://dukemednews.duke.edu/news/article.php?id=5445
tara
RE: AMPK 4/24/2003 7:02AM - in reply to tara Reply | Return to Index | Report Post
Phoenix- Just a general MB question... Calmodulin-dependent protein kinase (CaMK) is another protein enzymes that signals/controls production of mitochondria in mammalian muscle tissue. So is it likely many protein enzymes along with AMPK and CaMK, many not discovered yet, play a part in siginaling MB?

I have 19, silly, tyro questions remaining... ;)

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"Endurance exercise training promotes mitochondrial biogenesis in skeletal muscle and enhances muscle oxidative capacity, but the signaling mechanisms involved are poorly understood. To investigate this adaptive process, we generated transgenic mice that selectively express in skeletal muscle a constitutively active form of calcium/calmodulin-dependent protein kinase IV (CaMKIV*). Skeletal muscles from these mice showed augmented mitochondrial DNA replication and mitochondrial biogenesis, up-regulation of mitochondrial enzymes involved in fatty acid metabolism and electron transport, and reduced susceptibility to fatigue during repetitive contractions. CaMK induced expression of peroxisome proliferator-activated receptor gamma coactivator 1 (PGC-1), a master regulator of mitochondrial biogenesis in vivo, and activated the PGC-1 gene promoter in cultured myocytes. Thus, a calcium-regulated signaling pathway controls mitochondrial biogenesis in mammalian cells.


Wu et al, Regulation of mitochondrial biogenesis in skeletal muscle by CaMK. Science 2002 Apr 12;296(5566):349-52.

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Phoenix
RE: AMPK 4/24/2003 8:50AM - in reply to tara Reply | Return to Index | Report Post
Absolutely.

That why with current technology and exercise pill is impossible. Its a LONG ways away if it every happens.

Interestingly the AMPK dominant negative mice don't express normal levels of CAMKIV.
-----------------------------------------------------------
Proc Natl Acad Sci U S A 2002 Dec 10;99(25):15983-7

AMP kinase is required for mitochondrial biogenesis in skeletal muscle in
response to chronic energy deprivation.

Zong H, Ren JM, Young LH, Pypaert M, Mu J, Birnbaum MJ, Shulman GI.

Howard Hughes Medical Institute and the Departments of Internal Medicine, Cell
Biology, and Cellular and Molecular Physiology, Yale University School of
Medicine, New Haven, CT 06510, USA.
-----------------------------------------------------------
Mitochondrial biogenesis is a critical adaptation to chronic energy deprivation,
yet the signaling mechanisms responsible for this response are poorly
understood. To examine the role of AMP-activated protein kinase (AMPK), an
evolutionarily conserved fuel sensor, in mitochondrial biogenesis we studied
transgenic mice expressing a dominant-negative mutant of AMPK in muscle
(DN-AMPK). Both DN-AMPK and WT mice were treated with beta-guanidinopropionic
acid (GPA), a creatine analog, which led to similar reductions in the
intramuscular ATPAMP ratio and phosphocreatine concentrations. In WT mice, GPA
treatment resulted in activation of muscle AMPK and mitochondrial biogenesis.
However, the same GPA treatment in DN-AMPK mice had no effect on AMPK activity
or mitochondrial content. Furthermore, AMPK inactivation abrogated GPA-induced
increases in the expression of peroxisome proliferator-activated receptor gamma
coactivator 1alpha and calciumcalmodulin-dependent protein kinase IV (both
master regulators of mitochondrial biogenesis). These data demonstrate that by
sensing the energy status of the muscle cell, AMPK is a critical regulator
involved in initiating mitochondrial biogenesis.
tara
RE: AMPK 4/24/2003 9:13AM - in reply to Phoenix Reply | Return to Index | Report Post

Phoenix wrote:"AMPK is also essential for the transcription of certain Calcium-calmodulin kinases that also play a role in mitochondrial biogenesis.


Oh, I missed this upon first reading... interesting link.

Annoying how you have to subscribe to view full texts. But, neat, thanks for the reference.
mph
RE: AMPK 4/24/2003 11:15AM - in reply to Phoenix Reply | Return to Index | Report Post
CaMKIV doesn't naturally exist in skeletal muscle. Any activity of CaMK is muscle appears to be coming from CaMKI.
There is no clear cut way to differentiate the effects of specific CaMK isoforms without transcripts as there are no isoform specific inhibitors. Plus it appears that the CaMK effects on upregulation of mito. biogenesis likely work synergestically with calcinuerin in vivo. Mito biogenesis is definately the hot topic b/c the press got ahold of it and everyone has their take on its regulator be it PGC, CaMK or AMPK. The problem is the majority of these studies measure their chosen pathway or transcription factor independent of all other cellular processes. My point being that in the physiology of performance, the biochemical alterations permitting adaptations are the culmination of changes in gene expression of numerous proteins/trans. factors/etc. and to label one specific molecule the 'master regulator' is irresponsible.

While work with cell lines and transgenic models are very important in delineating mechanisms they are at best poorly applicable to human or animal physiology.

Regarding the use of GPA--it is used to 'mimic endurance exercise' by depleting the cell of ATP. This obviously drastically disrupts the energy charge of the cell as the absence of ATP triggers a cascade of apoptotic events. My question is: How applicable is GPA as ATP stores are esstentially impossible to deplete in vivo, particularly with endurance type activity?
Phoenix
RE: AMPK 4/24/2003 1:49PM - in reply to mph Reply | Return to Index | Report Post
See work by Pette on depletion of high energy phosphates during fiber type transitions. CLFS triggers a change from fast to slow muscle fibers. Fast muscle fiber have more ATP and CP than to slow at rest. So, in vivo ATP can be depleted.

AICAR, an intermediate in purine synthesis, is converted to the AMP analogue ZMP and then taken into the cell when taken in orally or intravenously.

Administration of AICAR causes mitochondrial biogenesis. AMPK is the key intermediate between a number of metabolic signaling pathways and is A master regulator rather than THE master regulator of metabolism. It has been repeatedly shown that activation of AMPK triggers translocation of glut-4 transporters through insulin independent mechanisms. Wortmannin is a potent PI3 kinase inhibitor that block the effects of insulin but not AICAR.

B-GPA would be a terrible supplement because it causes severe muscle atrophy in addition to MB. However in the AMPK-DN no such effect was observed.

MB is probably triggered by several stimuli, likely the big three are:

1) A reduced ATP/AMP ratio = AMPK
2) Calcium = CAMKs/Calcineurin
3) Peroxides = PGC-1, PPAR etc.

Can a single fiber remain viable long enough to incubate it in AICAR and observe MB?
catman
RE: AMPK 4/24/2003 2:17PM - in reply to Phoenix Reply | Return to Index | Report Post
I kept this link that was on letsrun a while back:
http://www.philly.com/mld/inquirer/3797336.htm
since we are into what may amount to nothing more than science fiction
*
RE: AMPK 4/24/2003 7:40PM - in reply to catman Reply | Return to Index | Report Post
*
mph
RE: AMPK 4/25/2003 12:52AM - in reply to catman Reply | Return to Index | Report Post
To follow up on the article regarding genetic manipulation, a group of researchers have bred a line of rats for several generations that have an intrinsically higher running capacity have recently started to publish some of these results. I saw the VO2 data at a conference last year and the difference b/w the rat lines in remarkable and the gap widens with each generation.

JAP 94: 1682-1688, 2003.

Further proof that the easiest (and perhaps only) way to be a 'great' athlete is to pick your parents better.