Genetic Elimination of Connective Tissue Growth Factor in the Forebrain Affects Subplate Neurons in the Cortex and Oligodendrocytes in the Underlying White Matter

Abstract

Connective tissue growth factor (CTGF) is a secreted extracellular matrix-associated protein, which play a role in regulating various cellular functions. Although the expression of CTGF has been reported in the cortical subplate, its function is still not clear. Thus, to explore the significance of CTGF in the brain, we created a forebrain-specific Ctgf knockout (Fb Ctgf KO) mouse model. By crossing Ctgf fl/fl mice with Emx1-Cre transgenic mice, in which the expression of Cre is prenatally initiated, the full length Ctgf is removed in the forebrain structures. In young adult (2–3 months old) Fb Ctgf KO mice, subplate markers such as Nurr1 and Cplx3 are still expressed in the cortical layer VIb; however, the density of the subplate neurons is increased. Interestingly, in these mutants, we found a reduced structural complexity in the subplate neurons. The distribution patterns of neurons and glial cells, examined by immunohistochemistry, are comparable between genotypes in the somatosensory cortex. However, increased densities of mature oligodendrocytes, but not immature ones, were noticed in the external capsule underneath the cortical layer VIb in young adult Fb Ctgf KO mice. The features of myelinated axons in the external capsule were then examined using electron microscopy. Unexpectedly, the thickness of the myelin sheath was reduced in middle-aged (>12 months old), but not young adult Fb Ctgf KO mice. Our results suggest a secretory function of the subplate neurons, through the release of CTGF, which regulates the density and dendritic branching of subplate neurons as well as the maturation and function of nearby oligodendrocytes in the white matter.

Mice Lacking Connective Tissue Growth Factor in the Forebrain Exhibit Delayed Seizure Response, Reduced C-Fos Expression and Different Microglial Phenotype Following Acute PTZ Injection

“…CTGF is normally expressed in the nervous system including the olfactory bulb, cortical layer VIb and DEPN. However, the function of CTGF in the brain is not well understood [9,17,[42][43][44][45][46]. Based on the previous studies, CTGF may support critical function or even play beneficial role in the brain.…”

“…Intriguingly, on the other hand, CTGF has been shown to account for the negative regulation of oligodendrocyte maturation in the developing brain [45]. In fact, CTGF may modulate the proliferation and differentiation of oligodendrocytes and control the growth and maturation of myelin sheath in a paracrine manner [17,42,45]. In addition, CTGF is involved in certain pathogenic conditions in the nervous system, such as the glial scar formation after traumatic brain or spinal cord injury [47].…”

“…Animals were bred and kept in the Laboratory Animal Center of the College of Medicine, National Taiwan University, under a 12-h light/dark cycle (lights on at 08:00) with free access to food and water. Genotypes of the mice were examined using PCR-based protocol [17] and animals were weaned at postnatal day 28. All animal procedures were approved by the Institutional Animal Care and Use Committee of the College of Medicine, National Taiwan University (approval code: 20170291, approved on 23 September 2019).…”

“…To decipher the role of CTGF in the nervous system, we generated a forebrain-specific Ctgf knockout ( Emx1-Cre ; Ctgf flox/flox , Fb Ctgf KO) mouse line. In these mutant mice, the Ctgf gene is eliminated from the excitatory neurons in the forebrain structures [ 17 ]. The thickness of myelin sheath in the external capsule underneath the cortical layer VIb was reduced in Fb Ctgf KO mice, indicating a paracrine function of CTGF [ 17 ].…”

“…In these mutant mice, the Ctgf gene is eliminated from the excitatory neurons in the forebrain structures [ 17 ]. The thickness of myelin sheath in the external capsule underneath the cortical layer VIb was reduced in Fb Ctgf KO mice, indicating a paracrine function of CTGF [ 17 ]. Nevertheless, the role of Ctgf in the DEPN, a proposed epileptogenic site, has not been examined.…”