Table 2.

Phenotype of MuRF1- and MAFbx-KO mice

	MuRF1-KO (Ref. Nos.)	MAFbx-KO (Ref. Nos.)
Postnatal (0–2 mo)	Normal growth (15)	Normal growth (15)
Adult (2–18 mo)	Elevated HIF-1α, increased capillary density, elevated glycolytic enzymes (GS, PFK, PDH), reduced ER Stress (62)
Aging (>18 mo)	Normal lifespan (62); normal growth response to increased loading (62)	Die at 16–18 mo of congestive heart failure (102, 192)
Atrophy models - muscle sparing	Denervation (15, 50), unloading (82), glucocorticoids (7), and acute lung injury aging (43)	Denervation (15, 50), immobilization (Bodine S, unpublished observations)
Load-induced hypertrophy	Normal growth (8, 63)	Attenuated growth (8)

KO, knockout; HIF-1α, hypoxia-inducible factor-1α; GS, glycogen synthase; PFK, phosphofructokinase; PDH, pyruvate dehydrogenase. Characteristics of skeletal muscle in MuRF1- and MAFbx-KO mice at various life stages and in response to various atrophy and hypertrophy challenges.