Low-intensity ultrasound increases FAK, ERK-1/2, and IRS-1 expression of intact rat bones in a noncumulative manner.
BACKGROUND
Low-intensity pulsed ultrasound stimulation (LIPUS) reportedly increases osteogenesis in fracture models but fails in intact bone, suggesting LIPUS does not act on mechanotransduction and growth factor pathways of intact bone.


OBJECTIVE
We asked whether daily 20-minute LIPUS applied to intact tibias would act on bone proteins involved in mechanotransduction (focal adhesion kinase [FAK], and extracellular signal-regulated kinase-1/2 [ERK-1/2]), and growth factor signaling (insulin receptor substrate-1 [IRS-1]) pathways at 7, 14, and 21 days of treatment.


METHODS
Immunoblotting was performed to detect FAK, ERK-1/2, and IRS-1 expression and activation from the stimulated intact tibias at 7, 14, and 21 days of daily 20-minute LIPUS.


RESULTS
LIPUS increased FAK expression (at 7 days), ERK-1/2 (at 14 days), and IRS-1 (at 7 days), but expression decreased 7 days later, indicating a noncumulative effect of LIPUS. As only FAK expression was detected at 21 days, these observations suggest LIPUS influences nuclear reactions that may be modulated by a major cellular mechanism preferentially inhibiting IRS-1 expression and not FAK expression. Increased ERK-1/2 expression at 14 days suggests the differing mechanisms for promoting ERK-1/2, FAK, and IRS-1 syntheses. IRS-1 expression behaved similarly to FAK expression; therefore, LIPUS may modulate growth factor pathways. LIPUS increased sustained FAK and ERK-1/2 activation, but not IRS-1, suggesting sustained ERK-1/2 activation is not the result of mechanically induced growth factor activation.


CONCLUSIONS
LIPUS acts on mechanotransduction and growth factor pathways in intact bone in a noncumulative manner. Clinical relevance These data suggest LIPUS applied to intact bone acts on proteins involved in osteogenesis.
de Gusmão
Carlos Vinícius Buarque
CV
Department of Orthopaedics and Traumatology, Faculty of Medical Sciences, The State University of Campinas (UNICAMP), Campinas, São Paulo, Brazil. vigusmao@yahoo.com
Pauli
José Rodrigo
JR
Saad
Mario José Abdalla
MJ
Alves
José Marcos
JM
Belangero
William Dias
WD
D000818:Animals; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000378:metabolism*; D015151:Immunoblotting; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism*; D008297:Male; D040542:Mechanotransduction, Cellular; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013977:Tibia / Q000000981:diagnostic imaging* / Q000378:metabolism; D014464:Ultrasonic Therapy; D014463:Ultrasonography
C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D051416:Focal Adhesion Protein-Tyrosine Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3