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RNA transcript expression of IGF-I/PI3K pathway components in regenerating skeletal muscle is sensitive to initial
Ronald W Matheny1, Christopher T Carrigan1, Mary N Abdalla1
1Military Performance Division, US Army Research Institute of Environmental Medicine, 10 General Greene Ave., Building 42, Natick, MA 01760, USA.
Objective:
Skeletal muscle regeneration is a complex process involving the coordinated input from multiple stimuli. Of these processes, actions of the insulin-like growth factor-I (IGF-I) and phosphoinositide 3-kinase (PI3K) pathways are vital; however, whether IGF-I or PI3K expression is modified during regeneration relative to initial damage intensity is unknown. The objective of this study was to determine whether mRNA expression of IGF-I/PI3K pathway components was differentially regulated during muscle regeneration in mice in response to traumatic injury induced by freezing of two different durations.
Design:
Traumatic injury was imposed by applying a 6-mm diameter cylindrical steel probe, cooled to the temperature of dry ice (-79°C), to the belly of the left tibialis anterior muscle of 12-week-old C57BL/6J mice for either 5s (5s) or 10s (10s). The right leg served as the uninjured control. RNA was obtained from injured and control muscles following 3, 7, and 21days recovery and examined by real-time PCR. Expression of transcripts within the IGF, PI3K, and Akt families, as well as for myogenic regulatory factors and micro-RNAs were studied.
Results:
Three days following injury, there was significantly increased expression of Igf1, Igf2, Igf1r, Igf2r, Pik3cb, Pik3cd, Pik3cg, Pik3r1, Pik3r5, Akt1, and Akt3 in response to either 5s or 10s injury compared to uninjured control muscle. There was a significantly greater expression of Pik3cb, Pik3cd, Pik3cg, Pik3r5, Akt1, and Akt3 in 10s injured muscle compared to 5s injured muscle. Seven days following injury, we observed significantly increased expression of Igf1, Igf2, Pik3cd, and Pik3cg in injured muscle compared to control muscle in response to 10s freeze injury. We also observed significantly reduced expression of Igf1r and miR-133a in response to 5s freeze injury compared to control muscle, and significantly reduced expression of Ckm, miR-1 and miR-133a in response to 10s freeze injury as compared to control. Twenty-one days following injury, 5s freeze-injured muscle exhibited significantly increased expression of Igf2, Igf2r, Pik3cg, Akt3, Myod1, Myog, Myf5, and miR-206 compared to control muscle, while 10s freeze-injured muscles showed significantly increased expression of Igf2, Igf2r, Pik3cb, Pik3cd, Pik3r5, Akt1, Akt3, and Myog compared to control. Expression of miR-1 was significantly reduced in 10s freeze-injured muscle compared to control muscle at this time. There were no significant differences in RNA expression between 5s and 10s injury at either 7d or 21d recovery in any transcript examined.
Conclusions:
During early skeletal muscle regeneration in mice, transcript expressions for some components of the IGF-I/PI3K pathway are sensitive to initial injury intensity induced by freeze damage.
Insights
Skeletal muscle regeneration involves the insulin-like growth factor-I (IGF-I) and phosphoinositide 3-kinase (PI3K) pathways. This study found that the expression of these pathway components in mice is sensitive to the intensity of freeze-induced muscle injury.
Area of Science:
- Muscle physiology
- Molecular biology
- Regenerative medicine
Background:
- Skeletal muscle regeneration is a complex process influenced by multiple stimuli.
- The insulin-like growth factor-I (IGF-I) and phosphoinositide 3-kinase (PI3K) pathways play crucial roles in muscle repair.
- The relationship between injury intensity and the expression of IGF-I/PI3K pathway components during regeneration remains unclear.
Purpose of the Study:
- To investigate whether mRNA expression of IGF-I/PI3K pathway components is differentially regulated during muscle regeneration in mice.
- To determine the impact of varying traumatic injury intensities (5s vs. 10s freeze duration) on gene expression during skeletal muscle recovery.
Main Methods:
- Mice (C57BL/6J, 12 weeks old) sustained traumatic injury to the tibialis anterior muscle via a freeze probe (-79°C) for either 5 or 10 seconds.
- RNA was extracted from injured and control muscles at 3, 7, and 21 days post-injury.
- Real-time PCR was used to analyze the expression of transcripts related to the IGF, PI3K, Akt families, myogenic regulatory factors, and micro-RNAs.
Main Results:
- Early in regeneration (3 days), increased expression of IGF-I/PI3K pathway components was observed in response to both injury durations, with greater expression in the 10s injury group.
- At 7 days, some components remained elevated in the 10s group, while others showed reduced expression in both groups compared to controls.
- By 21 days, specific IGF, PI3K, Akt, and myogenic factor genes were upregulated in injured muscles, with some micro-RNAs showing reduced expression, particularly in the 10s group.
Conclusions:
- Transcript expression of certain IGF-I/PI3K pathway components is sensitive to the initial intensity of freeze-induced skeletal muscle injury during early regeneration in mice.
- The findings highlight a potential dose-dependent response of molecular pathways involved in muscle repair to the severity of trauma.
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