Electron microscopy of human fascia lata: focus on telocytes

Abstract

From the histological point of view, fascia lata is a dense connective tissue. Although extracellular matrix is certainly the most predominant fascia's feature, there are also several cell populations encountered within this structure. The aim of this study was to describe the existence and characteristics of fascia lata cell populations viewed through a transmission electron microscope. Special emphasis was placed on telocytes as a particular interstitial cell type, recently discovered in a wide variety of tissues and organs such as the heart, skeletal muscles, skin, gastrointestinal tract, uterus and urinary system. The conducted study confirmed the existence of a telocyte population in fascia lata samples. Those cells fulfil main morphological criteria of telocytes, namely, the presence of very long, thin cell processes (telopodes) extending from a relatively small cell body. Aside from telocytes, we have found fibroblasts, mast cells and cells with features of myofibroblastic differentiation. This is the first time it has been shown that telocytes exist in human fascia. Currently, the exact role of those cells within the fascia is unknown and definitely deserves further attention. One can speculate that fascia lata telocytes likewise telocytes in other organs may be involved in regeneration, homeostasis and intracellular signalling.

Keywords: fibroblasts; human fascia lata; mast cells; myofibroblasts; telocytes; transmission electron microscopy.

Figure 1

Electron micrograph of human fascia lata. (A) Fibroblast at lower magnification; not spindle-shaped cell situated within densely packed collagen fibres (transsections), abundant mitochondria (m) and cisterns of the Golgi apparatus (G); scale bar = 1 μm. (B) Mast cell filled with numerous secretory granules of different electron densities, sizes and shapes; note nucleus (N) with peripherally condensed chromatin; scale bar = 1 μm. (C) Section of cell showing the features of myofibroblastic differentiation; note the presence of myofilaments bundles at the cell periphery (b₁) and also near the cell centre (b₂), abundant rough endoplasmic reticulum (ER) and focally surface attachment plaques (p); scale bar = 0.5 μm. CF: collagen fibres.

Figure 2

Digitally coloured transmission electron microscope (TEM) image (blue) of telocyte of human fascia lata; note relatively small cell body and 4 long characteristic processes - telopodes (Tp_1-4); scale bar = 5 μm.

Figure 3

Digitally coloured (blue) electron micrograph of section of telocyte in human fascia lata; note the small part of the cell body (cb) and the very long telopode situated between collagen fibres (CF); scale bar = 5 μm. Red inset shows higher magnification of the part of telopode neighbouring collagen fibres (longitudinal sections); scale bar = 0.5 μm.

Figure 4

Transmission electron microscopy of telocytes within fascia lata; note large telopode extending from the cell body of telocyte with podomers alternating much thicker podoms containing abundant mitochondria (m); scale bar = 2 μm. Red inset shows a part of telocyte with telopode forming a circular, convoluted appearance; scale bar = 0.5 μm.

Figure 5

Electron micrograph of another telocyte in human fascia lata; note the telopode forming dichotomous branching (db) and focal accumulations of mitochondria (m) within podoms; scale bar = 2 μm.

Figure 6

Electron micrograph of human fascia lata telocyte. Section of telopode with semi-circular arrangement and focal accumulations of mitochondria (m) and endoplasmic reticulum elements (ER); scale bar = 1 μm.