EUROPEAN  TISSUE  REPAIR  SOCIETY

THE UNIVERSITY OF MINNESOTA, USA, DEPARTMENT OF SURGERY
Wound Healing and Repairative Medicine
Website address:  http://www.surg.umn.edu/surgsci/wound/vasmuscle.htm

Surgical Sciences

Limb and Muscle Regeneration
This laboratory’s primary interest is the process of regeneration. We perceive regeneration as both a phenomenon of development and an adaptive physiologic response to injury.

We focus our research on three areas:

1. understanding what can promote regeneration, rather than repair, as the adaptive response to injury,
2. characterizing adjustments in systemic regulatory input (neural, endocrine, and immunologic) to the wound area that predispose to and promote regeneration, and
3. defining local dialogs and interactions that orchestrate the expression and culmination of regeneration.

The research models we use are the adult newt forelimb, adult rat skeletal muscle, and the polyvinyl alcohol (PVA) sponge wound healing model.

Amphibian Forelimb Regeneration
Amphibians can faithfully regenerate appendages after amputation, through epimorphic regeneration. This process requires formation of a mass of dedifferentiated cells, which then recapitulate events of limb embryogenesis. What enables this process and how it is regulated remains unknown.

One focus of our efforts is to characterization of parallels between regenerating newt limbs, regenerating mammalian skeletal muscle, and the granulation tissue of PVA sponges. Which growth factors modulate events of each process? Are certain of these factors ‘regeneration-specific’? What events of regeneration do they promote? Recent experiments suggest that bFGF, IGF-I, and TGFb5 play similar, overlapping roles in amphibian limb regeneration, seemingly parallel to their proposed roles in mammalian skeletal muscle regeneration.

We are also studying the influence of the immune system on amphibian limb regeneration. Initial data are consistent with a potential role for the immune system in regeneration of amphibian limbs. Interestingly, extrapolations from these data predict changing immunologic status during mammalian wound healing.

Mammalian wound repair and skeletal muscle regeneration
Regeneration occurs when parenchymal mass is restored, through contributions from parenchymal cells (or their precursor stem cells) or through transdifferentiation of fibroblasts or other components of the inflammatory infiltrate. We are exploring the hypothesis that either parenchymal cells or fibroblasts are selectively activated and mobilized after injury, thus determining the outcome. If fibroblasts are activated, connective tissue matrix forms and repair occurs. If parenchymal cells (e.g., muscle satellite cells) are activated, regeneration occurs and paren-chymal tissue is restored.

Studies in progress seek to:

1. ascertain differences in growth factor expression, production, and action between regeneration and repair,
2. define interactions within the injury environment that favor regeneration over repair, and
3. determine how inflammatory cells affect the mode of response at the injury site. We believe that the signal molecules used by cells differ between regeneration and repair. however, the potential perception of these signal neeecules by responder cells is a more critical determinant of the response to injury.

To date, we have documented interactions between rennerating muscle and accumulating granulation tissue that change the quantity and quality of that tissue. We have demonstrated that the early wound environments (one through five days after injury) are similar for both repair and regeneration. In particular, fluids from these environments can promote proliferation of both myoblasts and fibroblasts. However, the late wound environment does not permit skeletal muscle regeneration to be completed, since it does not support myogenesis either in vitro or in vivo. Furthermore, the late wound environment (ten and fifteen days after injury) appears to induce apoptosis of myoblasts in vitro.

Representative recent publications
Muscle regeneration:

• Sicard, RE, Menezes, J, and Nquyen, L: Apoptosis of rat fetal myoblasts is induced in vitro by late wound fluids. Wound Rep Regen 2: 92 (1994).
• Sicard, RE, Nguyen, L, and Witzke, J: Differential fates of fetal rat myoblasts in repair and regeneration environments. Wound Rep Regen 2: 92 (1994).
• Sicard, RE, and Nguyen, LMP: Interstitial fluids associated with wound repair support proliferation but not differentiation of neonatal rat myoblasts in vitro. Wound Rep Regen 2: 306–313 (1994).
• Sicard, RE, Mendez, TI, and Nguyen, LMP: Mitogenic properties of interstitial fluids from repair and muscle regeneration microenvironments. Wound Rep Regen 4: A175 (1996).
• Sicard, RE, Nguyen, L, Mendez, T, Mand, W, and Jacobs, R: Effects of regenerating muscle on a wound repair model. J. Minn Acad Science 60: 8 (1996).
• Sicard, RE and Nguyen, L: An in vivo model for evaluating wound repair and regeneration microenvironments. In Vivo 10: (in press) (1996).
• Sicard, RE, Mand W, Hwang, E, and Nguyen, L: Interactions between tissues engaged in wound repair and skeletal muscle regeneration. In Vivo 10: (in press) (1996).

Limb regeneration:

• Sicard, RE, and Lombard, ME: Epimorphic regeneration and the immune system. In: Recent Trends in Regeneration Research, V Kiortsis, S Koussoulakos, and H Wallace (eds.) NATO ASI Proceedings. Vol. 172, 107-119. Plenum Publishing Co., NY (1989).
• Sicard, RE: Phosphoprotein phosphatase activity in regenerating forelimbs of adult newts, Notophthalmus viridescens. In: Limb Development and Regeneration, Part A. I Fallon, P Goetinck, R Kelley, and D Stocum (eds), Wiley-Liss, Inc., New York, 223–231 (1993).
• Johnson, L, Fahmy, G, and Sicard, RE. Growth factor influences on forelimb regeneration of adult newts. J Minn Acad Science 60: 30 (1996).