Morphogenesis and maintenance of the gastric epithelium: a role for sonic hedgehog?

Hedgehog signaling is involved in differentiation of normal colonic tissue rather than in tumor proliferation

The Hedgehog (Hh) pathway is a main regulation cascade in embryonic differentiation. It is also present in adult tissues and unusual expression has been associated with formation of benign and malignant lesions. We examined the presence of the Hedgehog pathway in normal and pathological human colon tissue. Components investigated include Sonic (Shh), Indian (Ihh), and Desert Hedgehog (Dhh), Gli1, Gli2, Gli3, and Patched (Ptch). Pathological tissue samples comprised 23 benign and 20 malignant lesions of human colon. The influence of the Hedgehog pathway on differentiation and proliferation has been investigated by analyzing the effect of the pathway inhibitor Cyclopamine on human colon cancer cell lines HT29 and CaCo2. In normal colon, we detected expression of Shh and Dhh within the lining epithelium and Patched, Gli1, and Gli2 along the whole crypts. Within all benign lesions, positive staining of Shh, Dhh, Gli1, Gli2, and Ptch was detected. Expression of Shh and Dhh was restricted to single cell aggregates. Malignant lesions also displayed focal staining pattern for Shh and Dhh but to a much lesser extent. We conclude that Hedgehog signaling is involved rather in constant differentiation and renewing of the colonic lining epithelium than in cancer formation, growth, or proliferation.

Transcription of sonic hedgehog, a potential factor for gastric morphogenesis and gastric mucosa maintenance, is up-regulated in acidic conditions

Gastric body mucosa atrophy predisposes one to gastric cancer. Disturbances in the gastric differentiation process might play a role in the evolution of gastric atrophy. Sonic hedgehog (Shh) has recently been implicated as a crucial factor in gastric organogenesis and gland differentiation. In this study we investigated the expression of key factors in the Shh pathway, namely Shh and its receptor Patched (Ptc), in normal and pathologic stomach mucosa. Furthermore, the potential role of pH for Shh dysregulation was analyzed. Ten gastric biopsy specimens each from normal gastric mucosa, chronic nonatrophic gastritis, atrophic gastritis, and gastric cancer were included. Expression of Shh and Ptc was analyzed by immunohistochemistry. In normal body mucosa and in nonatrophic body gastritis, Shh was strongly expressed in parietal cells. Ptc was also expressed in gastric chief cells. Shh expression was almost completely lost in atrophic gastritis and in gastric cancer and absent in intestinal metaplasia. Ptc was markedly reduced in atrophy and only weakly positive in intestinal metaplasia and gastric cancer. In in vitro experiments, gastric cancer cell line 23132 was found positive for Shh. In long-term culture as well as in culture conditions with low pH, transcription of Shh in 23132 was significantly increased in quantitative reverse transcription PCR analyses. We concluded that the decreased expression of the Shh pathway in atrophic gastritis and gastric cancer might reflect altered differentiation processes within the gastric unit and contributes to the development of gastric atrophy. The increase of gastric pH might play a role in the development of gastric mucosa atrophy via reduction of Shh transcription.