Basement membrane chondroitin sulfate proteoglycan and vascularization of the developing mammalian limb bud

CSPGs inhibit axon branching by impairing mitochondria-dependent regulation of actin dynamics and axonal translation

Chondroitin sulfate proteoglycans (CSPGs) inhibit the formation of axon collateral branches. The regulation of the axonal cytoskeleton and mitochondria are important components of the mechanism of branching. Actin-dependent axonal plasticity, reflected in the dynamics of axonal actin patches and filopodia, is greatest along segments of the axon populated by mitochondria. It is reported that CSPGs partially depolarize the membrane potential of axonal mitochondria, which impairs the dynamics of the axonal actin cytoskeleton and decreases the formation and duration of axonal filopodia, the first steps in the mechanism of branching. The effects of CSPGs on actin cytoskeletal dynamics are specific to axon segments populated by mitochondria. In contrast, CSPGs do not affect the microtubule content of axons, or the localization of microtubules into axonal filopodia, a required step in the mechanism of branch formation. It is also reported that CSPGs decrease the mitochondria-dependent axonal translation of cortactin, an actin associated protein involved in branching. Finally, the inhibitory effects of CSPGs on axon branching, actin cytoskeletal dynamics and the axonal translation of cortactin are reversed by culturing neurons with acetyl-l-carnitine, which promotes mitochondrial respiration. Collectively these data indicate that CSPGs impair mitochondrial function in axons, an effect which contributes to the inhibition of axon branching. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 419-437, 2017.

Thumb trapeziometacarpal arthritis: treatment with ligament reconstruction tendon interposition arthroplasty

LEARNING OBJECTIVES

After studying this article, the participant should be able to: 1. Understand the pathomechanical and biochemical basis for thumb trapeziometacarpal joint degeneration. 2. Diagnose and grade trapeziometacarpal joint disease based on presentation, physical examination (including provocative testing), and radiographic evidence. 3. Understand the principles of ligament reconstruction and tendon arthroplasty procedures. 4. Describe the surgical technique for ligament reconstruction tendon interposition arthroplasty and its variants.

BACKGROUND

Osteoarthritis of the trapeziometacarpal joint is the second most common site of degenerative joint disease in the hand, and mostly affects postmenopausal women. Degenerative arthritis of the thumb trapeziometacarpal joint is associated with a lack of bony constraints and laxity of the supporting ligaments, particularly the anterior oblique ("beak") ligament, which is consistently implicated in disease progression. Resultant increases in joint stress loads leads eventually to metacarpal and trapezial articular destruction, thumb instability, and pain.

METHODS

In this article, the authors review the diagnosis and treatment modalities available to the surgeon in the treatment of patients with trapeziometacarpal osteoarthritis. The technique of ligament reconstruction tendon interposition arthroplasty is discussed in detail.

RESULTS

Ligament reconstruction tendon interposition arthroplasty procedures center on three common principles: (1) excision of the diseased trapezium; (2) reconstruction of the beak ligament; and (3) interposition of a tissue substance to maintain metacarpal position.

CONCLUSIONS

Both conservative and surgical management can be effective in the treatment of trapeziometacarpal arthritis, when properly selected. The success of ligament reconstruction tendon interposition arthroplasty in treating trapeziometacarpal arthritis has withstood the test of time.