title: Low intensity laser therapy accelerates muscle regeneration in aged rats.
abstract: Elderly people suffer from skeletal muscle disorders that undermine their daily activity and quality of life; some of these problems can be listed as but not limited to: sarcopenia, changes in central and peripheral nervous system, blood hypoperfusion, regenerative changes contributing to atrophy, and muscle weakness. Determination, proliferation and differentiation of satellite cells in the regenerative process are regulated by specific transcription factors, known as myogenic regulatory factors (MRFs). In the elderly, the activation of MRFs is inefficient which hampers the regenerative process. Recent studies found that low intensity laser therapy (LILT) has a stimulatory effect in the muscle regeneration process. However, the effects of this therapy when associated with aging are still unknown.
  
  
  
  This study aimed to evaluate the effects of LILT (λ=830 nm) on the tibialis anterior (TA) muscle of aged rats.
  
  
  
  The total of 56 male Wistar rats formed two population sets: old and young, with 28 animals in each set. Each of these sets were randomly divided into four groups of young rats (3 months of age) with n=7 per group and four groups of aged rats (10 months of age) with n=7 per group. These groups were submitted to cryoinjury + laser irradiation, cryoinjury only, laser irradiation only and the control group (no cryoinjury/no laser irradiation). The laser treatment was performed for 5 consecutive days. The first laser application was done 24 h after the injury (on day 2) and on the seventh day, the TA muscle was dissected and removed under anesthesia. After this the animals were euthanized. Histological analyses with toluidine blue as well as hematoxylin-eosin staining (for counting the blood capillaries) were performed for the lesion areas. In addition, MyoD and VEGF mRNA was assessed by quantitative polymerase chain reaction.
  
  
  
  The results showed significant elevation (p<0.05) in MyoD and VEGF genes expression levels. Moreover, capillary blood count was more prominent in elderly rats in laser irradiated groups when compared to young animals.
  
  
  
  In conclusion, LILT increased the maturation of satellite cells into myoblasts and myotubes, enhancing the regenerative process of aged rats irradiated with laser.
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, USA; and Department of Dermatology, Harvard Medical School, Boston, MA, USA.
authors.forename: Fatma
authors.initials: F
authors.lastname: Vatansever
authors.forename: Natalia C
authors.initials: NC
authors.lastname: Rodrigues
authors.forename: Livia L
authors.initials: LL
authors.lastname: Assis
authors.forename: Sabrina S
authors.initials: SS
authors.lastname: Peviani
authors.forename: Joao L
authors.initials: JL
authors.lastname: Durigan
authors.forename: Fernando M A
authors.initials: FM
authors.lastname: Moreira
authors.forename: Michael R
authors.initials: MR
authors.lastname: Hamblin
authors.forename: Nivaldo A
authors.initials: NA
authors.lastname: Parizotto
keywords: MyoD; VEGF; aged rats; low intensity laser therapy; muscle regeneration; phototherapy