Upekkha,
Try to see it like this. Tilakkhana starts with anicca. Any life anywhere, however enjoyable, in a human, deva or brahma realm will come to an end, will end in death. And there is no telling what will follow (unless one has set foot on the Path). And in the PS process, all the chain making for the abhisankhara that leads to that realm ends with old age and death..then bhava, jati all over again, and again, and again.
This is how ‘Tilakkhana and Paticca Samuppada are inter-related’. I sincerely hope this helps.