• 作者：Benedetto Sacchetti ; Alessia Funari ; Stefano Michienzi ; Silvia Di Cesare ; Stefania Piersanti ; Isabella Saggio ; Enrico Tagliafico ; Stefano Ferrari ; Pamela Gehron Robey ; Mara Riminucci ; Paolo Bianco
• 关键词：Knee dislocation ; Popliteal artery ; Multiligament ; Knee injury
• 刊名：Cell
• 出版年：2008
• 期刊代码：50_00928674
• 类别：med
• 出版时间：30 May 2008
• 卷：133
• 期：5
• 页码：928
• 文件大小：37 K

(1) Hematopoietic microenvironment cells advance along a three stage differentiation/maturation pathway. In the first stage, they support hematopoiesis and contain no fat. In the second stage, cells accumulate fat and no longer support steady state hematopoiesis; however, under conditions of increased hematopoietic requirement, they lose fat and regain their ability to support hematopoiesis. In the last stage, hematopoietic microenvironment cells retain the appearance of yellow bone marrow and do not support hematopoiesis regardless of the state of hematopoietic requirement.

(2) Since MSCs are bound to endosteal and trabecular surfaces, in tubular bones their number is relatively small, compared to cancellous bones that have much larger areas of internal bone surface. MSCs are exposed to proliferative and differentiative pressures, leading to gradual reduction of their number. Consequently, the MSC population in tubular bones becomes exhausted rather early, and the post-maturation compartment of mesenchymal cells finally consists of unipotential bone precursors maintaining bone tissue and hematopoietic microenvironment advancing towards the last (fatty) stage of differentiation. In contrast, in cancellous bones the relatively large number of MSCs does not suffer exhaustion and continues to provide newly differentiated hematopoietic microenvironment, thus maintaining red bone marrow throughout the organism’s life.

(3) Osteogenic and hematopoietic microenvironment differentiation pathways compete with each other for their common precursor. During the organism’s growth period osteogenic stimuli prevail, while in the post-maturation period, MSC differentiation into hematopoietic microenvironment increases at the expense of differentiation into bone. This results in the reduction of bone volume and expansion of marrow cavities in hematopoietically active cancellous bones, but not in tubular bones already depleted of MSCs and not participating in hematopoiesis.

Experimental and clinical data supporting these hypotheses are discussed.