Well, as some background, there are 2 well characterized nuclear estrogen receptors: ERα and ERβ. These function as classic nuclear steroid receptors by binding to response elements in target genes and ultimately altering transcription (genomic effects). But these receptors can also move to the plasma membrane and activate signaling cascades upon ligand binding (non-genomic rapid effects). Furthermore, there is some suggestion that a newly described g-protein coupled receptor (gpr30) also binds estrogen, again initiating signaling cascades.

Right. I guess the major misconception is that estrogen is all bad, because it is actually quite protective, at least in terms of preventing metabolic pathology. One of the things that estrogen does in humans is promote subcutaneous fat storage (versus the bad stuff - visceral), particularly butt and leg fat. While this isn’t necessarily good for physique-enhancement, it is actually the safest place to store body fat and is probably the reason that females are protected from metabolic disease compared to men.

Yes, and not only adipose tissue my friend…but my thesis work is actually aiming to get a better understanding of estrogen’s role in skeletal muscle physiology, a surprisingly understudied area.

We have found that estrogen increases LPL in muscle, while decreasing it in fat tissue. This results in a partitioning of fatty acids away from adipocytes and towards skeletal muscle where these FFA’s are likely oxidized. In support of this, we also saw that estrogen increased muscle PPARα expression (a master regulator of fat oxidation). Furthermore, we found that estrogen and a metabolite of estrogen (2-hydroxyestradiol) can rapidly activate AMPK in muscle, another mechanism for increasing fat oxidation, as well as Akt, an important signaling molecule in the insulin cascade.

So, estrogen receptors are clearly expressed in skeletal muscle, and there are obvious gender differences in terms of muscle quality and quantity. Now clearly testosterone plays a role here, and probably progesterone as well, but estrogen is quite important too.

Well, for one thing, expression of ERs in muscle is way less than say uterine tissue. Now, from the limited studies that have been done to look at ERs in muscle, there actually don’t seem to be major differences between the genders. Males definitely express estrogen receptors, and estrogen is important to male physiology in that males with rare genetic estrogen deficiencies (aromatase or ERα deficiency) have profound glucose and lipid metabolism impairments and are quite insulin resistant. Interestingly, endurance trained males have higher muscle expression of both ERα and ERβ, probably due to higher type I fiber percentage. (Muscle expression of both receptors is higher in type I oxidative fibers.) But the relative expression and importance of ERα and ERβ in muscle is still quite unclear.